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Response of stored potato seed tubers from contrasting cultivars to accumulated day-degrees.

IN POTATO, many factors determining crop yield are influenced by seed quality. Relevant seed quality characteristics include seed tuber size, other physical characteristics such as shape and presence of wounds, physiological age, and seed tuber health. The physiological status of seed potatoes has a great impact on the emergence, number of stems per plant, number of tubers per stem, tuber-size distribution, and tuber yield of the progeny crop (Van der Zaag and Van Loon, 1987; Reust, 1982; Van Ittersum, 1992 and papers therein; for an overview see Struik and Wiersema, 1999). The physiological status needs to be optimized to efficiently produce a specific crop structure that allows tuber production for specific outlets (Struik et al., 1990, 1991).

Physiological age can be defined as the stage of development of a seed tuber, which is modified progressively by increasing chronological age, depending on growth history and storage conditions (Reust, 1986; Struik and Wiersema, 1999). The definition emphasizes that physiological age also includes aspects other than chronological age. The development of a seed tuber starts with a phase of dormancy. Immediately after it is initiated, a tuber develops a certain degree of dormancy. Dormancy is the physiological state of the tuber in which autonomous sprout growth will not occur within a reasonable period of time (usually 2 wk), even when the tuber is kept in conditions ideal for sprout growth (Reust, 1986; Van Ittersum, 1992; Struik and Wiersema, 1999). During dormancy, biochemical and physiological processes occur that do not trigger immediate morphological changes but are relevant for the number of sprouts produced after breaking of the dormancy and for their growth vigor.

Krijthe (1962) and Van Ittersum (1992) already demonstrated that both mother tuber and sprout age affect the physiological age of a seed tuber. Until breaking of the dormancy, changes in the physiological status of the seed are only reflected by biochemical and physiological changes in the seed tuber itself and not by morphological changes. After dormancy breaking, the physiological age is still influenced by the age of the mother tuber but modified by the additional effects of conditions and treatments on the behavior of the sprouts (Caldiz et al., 2001). The evidence for these separate effects from experimentation is, however, still limited.

Conditions during dormancy and thereafter affect the progress of the physiological ageing and are therefore relevant for the performance of the seed tuber. An overview of the different stages of physiological age and their consequences for crop performance is provided by Ewing and Struik (1992) and Struik and Wiersema (1999). It is essential to control the conditions during storage to optimize seed tuber quality. Environmental factors during storage having an effect on physiological age include relative humidity, temperature, photoperiod, and diffuse light. The temperature effect especially is highly complex. As the metabolic processes and physiological events taking place before and after dormancy differ, the sensitivity toward environmental conditions, and especially toward temperature, during the different stages of physiological development of the seed tuber may also differ (Scholte, 1986; Struik and Wiersema, 1999). Heat shocks, cold shocks, and similar accumulated day-degrees built up in different ways may all have their specific effects, depending on cultivar (Van Ittersum, 1992; Struik and Wiersema, 1999).

It has been stressed by many authors that both for scientific and practical purpose a good indicator of dormancy and/or physiological age would be useful. Many different characteristics have been proposed as indicators, including physiological, (bio)chemical, molecular, and biophysical ones (see, e.g., Bachem et al., 2000; Caldiz et al., 2001). Such indicators are needed to quantify and explain differences in rate of ageing between seed lots as induced by differences in origin, storage conditions, cultivar and treatment, and to quantify and model the effects of seed age on crop growth and yield.

The most direct and simple way to indicate physiological age is on the basis of the accumulated day-degrees from dormancy break (O'Brien and Allen, 1981; O'Brien et al., 1983), storage temperature sum (Scholte, 1986; Struik and Wiersema, 1999), and relative growth vigor indices (Bodlaender et al., 1987; Van der Zaag and Van Loon, 1987; Van Ittersum et al., 1990; Van Ittersum, 1992). Developing a unifying concept that is applicable under all conditions of production and storage and to all cultivars, however, is difficult.

This study shows that the concept of accumulated day-degrees from dormancy break is not a good estimator for physiological age across temperature conditions during storage and across cultivars and, therefore, needs to be refined.

MATERIALS AND METHODS

General

Data sets presented in this paper are extracted from an unpublished set of large experiments containing many combinations of storage temperature treatments and cultivars and starting in four different years. These experiments included a seed storage phase (including the storage treatments), a phase in which incubation tests were performed to determine the time of dormancy breaking, and a field phase in which the effects of the different storage treatments were assessed on various crop physiological parameters throughout the growing season.

Starting Material

Experiments were performed with a set of cultivars differing in maturity type and rate of physiological ageing (Table 1). Five of the six cultivars used in this research were categorized into different classes of rate of physiological ageing by Van Ittersum et al. (1990) using different performance parameters and relative growth vigor indices. The sixth cultivar, Sirtema, was tested for its rate of ageing in comparison with many other varieties by Van Ittersum (1992) and in unpublished experiments by the Department of Agronomy, now part of the Crop and Weed Ecology Group, Wageningen University.

Seed tubers from these cultivars were produced under field conditions with known and strictly controlled agricultural practice and selected for uniformity in weight (Table 2) and absence of disorders and infections of pests or diseases.

Storage Facilities and Treatments

Seed tubers were stored in trays under darkness. Storage treatments were performed in growth cabinets of the former Department of Agronomy of Wageningen University with precise temperature and relative humidity control.

Storage treatments reported in this paper consisted of different combinations of phases of low temperature (4[degrees] C) and warm temperatures (16 or 20[degrees]C) during storage. Storage temperatures during a specific phase were constant, without diurnal cycle. Temperature sums accumulated during a specific phase can therefore be calculated by the product of the number of days of that phase and the set temperature, without considering a base temperature or a maximum temperature. Experiments 1 through 3 were similar in set up; storage treatments and their codes and temperature sums (T-sum in [degrees] C d) are illustrated in Fig. 1A. In Exp. 4, not only the timing but also the duration of the warm temperature was varied; these storage treatments and their codes and T-sums are indicated in Fig. 1B. The caption to Fig. 1 also contains an explanation of the coding of the treatments. L4 or L5 are considered control treatments as they reflect common practice in seed tuber storage.

[FIGURE 1 OMITTED]

Observations on Sprouting and Incubation Tests

Observations on sprouting during storage and special incubation tests under controlled conditions were performed for all experiments. Here, we will only report on the observations on sprouting performed on the seed lots stored for Exp. 4, as the split-up of the storage period into different phases was most refined in this experiment and as the data from these observations in Exp. 4 will be used to interpret the field data of that experiment. Thermotime needed to reach onset of sprouting (sprouts >3 mm in 80% of the seed tubers) and the thermotime from the onset of sprouting until the end of the storage phase were assessed. Detailed data on the incubation tests can be made available by the corresponding author on request.

Field Experiments

General Methodology

Storage treatments started at the end of August to end of September depending on year (Table 2). RH was high (at least 80%) to avoid any effect of RH on treatment effects. Tubers that already had produced sprouts were desprouted some time before planting (Table 2). Tubers were planted in the field to test the rate of emergence, growth vigor, and yield potential at different harvesting dates. The experimental design depended on the other treatments included in the experiments not reported here. Agronomic and experimental details are provided in Table 2.

Data Collected

Timing of early and late harvests depended on cultivar maturity type. Field data collected included number of plants emerged, number of stems [m.sup.-2], number of tubers harvested m 2 and per stem, fresh tuber yield, tuber dry matter content, and fraction of tubers >55 mm in diameter. On the basis of the analysis over time of these parameters and the statistical interaction between harvest and treatment effects, we report on the final or maximum number of stems and tubers on the basis of the data of the very early harvest or the early harvest.

Data Processing and Statistical Analysis

Standard ANOVA with a randomized complete block design was performed followed by LSD tests using GENSTAT PC version (GenStat, 2000). Although in some cases raw data were transformed before analysis to obtain normality or uniformity of standard deviations, data and LSD values in the tables and figures represent untransformed values.

Data Presentation

After presenting the data on onset of sprouting of Exp. 4, we will then show data of the Exp. 1 through 4, in which potato tubers stored at different temperature regimes were then planted out in the field. Detailed information for Exp. 4 on the relation between early yield and temperature sum after onset of sprouting will be given.

RESULTS

Observations on Onset of Sprouting in Experiment 4

Prolonged cold storage (L5) delayed the end of the dormancy period measured in day-degrees compared with prolonged warm storage (H5) in cultivars Sirtema and Astarte (Table 3; for treatment codes see explanation in Fig. 1). In cultivars Jaerla, Kennebec, Bintje and Desiree, seed tubers stored cold were still dormant after 30 wk of storage, so precise comparison between these two treatments for end of dormancy was not possible, but also for these cultivars, L5 prolonged dormancy compared with H5. When seed tubers were stored at 4[degrees]C during the first phase of storage (LH treatments), dormancy was broken at increasingly lower thermotime when warm storage was initiated earlier (and thus when warm storage lasted longer and the final temperature sum was higher), except for Desiree, the cultivar with a very low rate of physiological ageing. When seed tubers were initially stored at 16[degrees]C (HL treatments), dormancy was not affected by the timing of the low temperatures for cultivars Sirtema and Bintje, whereas for the other cultivars only a difference was recorded between H1L4 and the other three HL treatments. Cultivar differences in thermotime needed to break dormancy were larger for HL treatments than for LH treatments, but the ranking of the cultivars remained more or less consistent within the group of LH or the group of HL treatments. Ranking of cultivars was not the same for LH and HL treatments.

Field Experiments

At the early assessments of number of plants emerged, number of stems and number of tubers, and of early yields, all interactions between storage treatment and cultivar were statistically significant. For final yields and quality assessments, this was also true except for the tuber dry matter content.

Fraction of Plants Emerged and Number of Stems [m.sup.-2]

Cold storage (L4 or L5) gave 91 to 100% (usually 99 or 100%) emergence in all cultivars and experiments (Table 4). The cultivar Jaerla (ageing rapidly) proved to be sensitive to prolonged warm storage (H4 or H5): emergence rates varied between 1% (Exp. 1) and 81% (Exp. 2) and were always lowest for this cultivar. Also the emergence of cv. Bintje was often seriously reduced by H4 or H5 storage treatments, whereas the effects on Kennebec and especially Astarte were inconsistent over experiments. Treatments L2H2 or L2H3 gave low emergence rates for Astarte (1-10%) in all experiments and in Jaerla for Exp. 1 (55%) (Table 4). In all other experiments or cultivars, rates of emergence were well above 80% for these treatments. Treatments H2L2 or H3L2 gave better or similar emergence rates compared with L2H2 or L2H3 (with the same thermotime), with most values being 98 to 100%. However, emergence rates of Jaerla in Exp. 1 (75%) and Exp. 4 (68%) were significantly reduced (Table 4). So, in general, the cultivars with a high rate of physiological ageing proved to be most sensitive to high storage temperatures during the entire storage period or during the last 12 to 18 wk of the storage period and much less sensitive to warm storage during the first 12 to 18 wk of storage. Sirtema, another cultivar with a very high rate of ageing, performed relatively well.

Cold storage (L4 or L5) resulted in high stem densities (Table 4). Depending on cultivar, these densities ranged from 9.2 to 30.5 stems [m.sup.-2] (Table 4). Jaerla produced fewer stems per square meter than the other cultivars. At H5, cultivars Jaerla and Astarte produced low stem densities, except in the case of Astarte in Exp. 4 (see also fraction of plants emerged), but the effects depended on the experiment (Table 4). In some cases hardly any stems were produced at all. The same two cultivars also produced lowest stem densities after storage treatments L2H2 or L2H3, although the differences with the other cultivars were in some experiments smaller than for treatments H4 or H5. On average, stem densities were higher after storage at L2H2 or L2H3 than after H4 or H5 (Table 4). Numbers of stems per square meter were usually high for H2L2 or H3L2 (on average even higher than for the treatments L4 or L5), although again comparatively low for Jaerla.

So, for stem density, especially the temperature during the last 12 to 18 wk of the storage period was the determining factor. When the temperature during this period was warm, stem densities were low, especially when the temperature during the first 12 to 18 wk of storage had also been warm.

Number of Tubers per Square Meter and Fresh Tuber Yield on Early Observation Dates

For the crops from seed tubers stored at L4 or L5, the number of tubers per square meter at early observation dates differed considerably among experiments. These differences were mainly associated with differences in stem density (Table 4). Bintje generally had the highest number of tubers, whereas Kennebec had the lowest. In Exp. 1 through 3, early tuber densities were considerably lower for H4 or H5 than for L4 or L5 in almost all cases. Largest differences were obtained for the rapidly ageing cv. Astarte and the abundantly tuberizing Bintje; differences were smallest for Desiree. For Exp. 4, the differences in early tuber densities were much smaller, but the pattern was similar.

Tuber densities varied greatly for treatments L2H2 and L2H3. Values of particular cultivars within certain experiments could be both significantly lower (e.g., for Astarte in Exp. 4) or significantly higher (e.g., for all cultivars but Astarte in Exp. 3 and Jaerla in Exp. 4) than those for H4 or H5 and significantly lower (Exp. 1; Jaerla in Exp. 2; Astarte in Exp. 3; Bintje and Astarte in Exp. 4) or statistically not different compared with those for L4 or L5 (Bintje and Desiree in Exp. 2; all cultivars but Astarte in Exp. 3; all cultivars but Bintje and Astarte in Exp. 4).

Early numbers of tubers per square meter for H2L2 or H3L2 were usually similar with those for the control treatment L4 or L5, except in Exp. 2, where the three cultivars showed inconsistent effects and in Exp. 4, where Desiree showed more tubers at H2L2.

So, for the early number of tubers per square meter especially the temperature during the last 12 to 18 wk of storage was the determining factor. High temperature during the last 12 to 18 wk of storage usually resulted in fewer tubers, especially after warm storage during the first 12 to 18 wk of storage. Effects were not the same for all cultivars. For example, for Desiree warm storage during the last 12 to 18 wk of storage did not reduce tuber density.

Early Fresh Tuber Yields

Early fresh tuber yields varied greatly, depending on the harvest date, the earliness of the cultivar, and the physiological age of the seed tubers (Table 4). The seed tubers which were stored at warm temperatures throughout the storage phase (treatments H4 or H5) often performed poorly, especially in the cultivars Jaerla and Bintje. Desiree was much less sensitive to this treatment. Compared with the low temperature control, treatments L2H2 or L2H3 always gave much smaller yield reductions than H4 or H5 in all cultivars but Astarte, in which effects were similar or worse. Treatments H2L2 or H3L2 gave yields similar to L4 or L5. In fact, only in two cases were the yields significantly different; in Exp. 3 treatment H2L2 of Desiree yielded significantly more than L4, whereas in Exp. 4 treatment H3L2 of Bintje yielded significantly less than L5.

Differences in performance of seed lots differing in physiological age are usually visible in early tuber yields. When these early yields are plotted against the temperature sum after the onset of sprouting the differences between different types of storage treatments and cultivars become clear (Fig. 2). In general, the early tuber dry matter yield strongly declined with an increase in temperature sum after sprouting. With equal temperature sums but different sequences of cold and warm storage, the treatments with an early warm period were higher than or equal to the treatments with an early cool period. The differences between the lines for LH and HL were large for Sirtema and Astarte, two cultivars with a very high rate of physiological ageing (Table 1). At the storage temperature sum of 2856[degrees]C d, the H4L1 treatment of Sirtema gave an early tuber dry matter yield of 695 kg [ha.sup.-1] compared with 540 kg [ha.sup.-1] for L1H4. For Astarte these yields were 756 kg ha-1 for H4L1 and 56 kg [ha.sup.-1] for L1H4. The two curves were almost coinciding for Kennebec (low rate of physiological ageing) and Desiree (very low rate of physiological ageing) over the entire range of temperature sums. Jaerla and Astarte showed a drastic decline in early performance with an increase in temperature sum after onset of sprouting but for different treatment types. Jaerla seemed to be an outlier in the set of cultivars tested, which might have been associated with the fact that this cultivar showed the largest effects of storage treatments on emergence.

[FIGURE 2 OMITTED]

Final Number of Tubers per Square Meter and per Stem at Late Harvest

Effects of storage treatments on final numbers of tubers per unit area and per stem were assessed. Table 5 provides these data for Exp. 1 and 4. Numbers of tubers per square meter at late harvest were closely and linearly correlated with the tuber densities of the early harvest (Exp. 1: [R.sup.2] = 0.953;N = 20; Exp. 4: [R.sup.2] = 0.920; N = 24). In Exp. 1, about 11% of the tubers disappeared during the growing season; in Exp. 4, this figure was about 18%. In both experiments, early warm storage (treatment H2L2 or H3L2) did not affect tuber number per square meter compared with L4 or L5, except in Bintje of Exp. 4, where it increased the tuber number. Warm storage during the last 16 to 18 wk of storage (treatment L2H2 or L2H3) reduced tuber number per square meter in Sirtema, Bintje and Astarte in Exp. 1 and in Astarte in Exp. 4 compared with the control treatment (L4 or L5). Warm storage throughout the storage period (treatment H4 or H5) reduced the tuber number per square meter compared with L4 or L5 in all cases, although the effect was not significant in Kennebec and Desiree of Exp. 4. Differences between storage treatments in number of tubers per stem were usually not statistically significant within a cultivar. Only in Jaerla and Bintje low stem densities were consistently but only partly compensated by more tubers per stem. Compare for example the values for number of tubers per stem for treatments H4 or H5 with those of L4 or L5.

Final Fresh Tuber Yields

Table 6 shows the final tuber yields for all treatments in Exp. 1 and 4. In Exp. 1, the final yields for Jaerla, Bintje, and Astarte were much lower for the warm storage than for the cool storage (H4 versus L4). The seed of Desiree did not age much, resulting in similar yields for all treatments. Sirtema, Bintje, and (especially) Astarte showed significant yield reductions when seed was stored warm during the second phase of the storage period. Warm storage during the first part of the storage period did not affect yield compared with L4, although the temperature sum was the same as for warm storage during the second part of the storage period. In Exp. 4, treatments with the same accumulated temperature sum during storage gave similar yields except for Astarte. For some treatments in this cultivar, yields could drop well below the yields of the seed tubers exposed to the highest temperature sum (i.e., H5). This was the case in treatments L1H4 and L2H3.

Tuber Dry Matter Content

Table 6 also shows that storage regime affected tuber dry matter content at final harvesting. In Exp. 1, warm storage resulted in lower tuber dry matter content, but this was not observed in Exp. 4. The trends over storage temperature sum were not consistent in Exp. 4. In both experiments, largest differences between storage regimes were observed in Astarte, where dry matter contents were also highest. In this cultivar, the treatments with low tuber densities also showed much reduced tuber dry matter content.

Grading at Final Harvest

In Exp. 1, treatment effects on percentage of tubers >55 mm in diameter were significant in three cultivars (Sirtema, Jaerla, and Astarte), but inconsistent. In Exp. 4, treatments with the same storage temperature sum often showed different proportions of large tubers, especially in cultivars Desiree and Astarte. Late warm storage periods shifted tuber-size distribution toward the larger sizes.

Relations between Yield Components in Experiment 4

Figure 3 shows for all cultivars in Exp. 4 the relations between temperature sum and yield components. The stem density usually increased when seed was used that was stored warm for a short period of time (Quadrant I). But when this period was prolonged the stem density decreased again. The temperature sum at which the maximum number of stems was reached was different for different cultivars but also differed for the two types of treatments: whether a warm period was followed by a cool period or a cool period was followed by a warm period. In most cultivars, there was a close relationship between number of stems square meter and number of tubers square meter (Quadrant II). There were no consistent effects of the sequence of warm and cool periods on this relationship. The same was true for the relation between number of tubers per square meter and the late tuber dry matter yield (Quadrant III). The overall response reflected by the relationship between thermal time during storage and late tuber dry matter yield (Quadrant IV) shows that the yields were usually slightly higher when the warm periods started earlier during the storage period (HL versus LH).

[FIGURE 3 OMITTED]

DISCUSSION

The present results show that a cultivar specific response to accumulated temperature sum during storage exists. Some cultivars (e.g., Jaerla) age much more rapidly than other cultivars (such as Desiree). This difference in cultivar specific behavior was consistent over the four experiments, when L4 or L5 treatments were compared with H4 or H5 treatments, with the exception of the behavior of Desiree in Exp. 4. Moreover, cultivars differ in their response to the timing of warm periods. Late periods of high storage temperatures result in poorer performance of the seed than early periods of warmth except in cultivars Bintje (inconsistent difference) and Kennebec (no difference). The most detailed experiment, Exp. 4, showed that this effect of the timing of the warm period depends on its duration.

Seed tubers were desprouted before planting when they had sprouts at the end of the storage period (see Materials and Methods). This means that it is likely that most of the ageing effects were associated with effects on the seed tubers themselves. However, ageing treatments were given when sprouts were still attached to the tubers and therefore the storage temperature treatments might have affected the tubers partly through effects on the sprouts. Desprouting in and of itself might also have contributed to the effects observed since not all storage temperature treatments allowed sprouting before planting (see Table 4).

There were large differences between treatments with a different order of low and warm storage temperatures (the LH versus the HL treatments). When the low storage temperature lasted no longer than 6 to 16 wk and preceded the high storage temperature, the fraction of the plants emerging, the number of stems per unit area, the number of tubers per unit area, the early tuber yield, and the final tuber yield were generally lower than when warm storage preceded cool storage. These parameters usually showed lower values for L2H2 than for H2L2 (Exp. 1), for L1H4 than for H4L1 (Exp. 4) and for L2H3 than for H3L2 (Exp. 4) (Tables 4, 5, and 6). When the low storage temperature lasted longer in Exp. 4, differences were much smaller (compare fresh tuber yields for L3H2 with those of H2L3 and fresh tuber yields of L4H1 with those of H1IA [Table 6]).

With an increase in duration of the warm period (whether the storage season started or ended with a warm period) the early tuber yield and the final tuber yield declined, but this effect was dependent on cultivar. Cultivars Desiree and Astarte are representatives of two extremes: Desiree showed relatively little effect of temperature sum on crop performance and Astarte showed a large effect. The extreme behavior in Astarte was associated with a low number of stems per unit area.

The main effect of the ageing is through stem number. However, with a wide range of temperature sum, the stem number seems adequate to reach a relatively high yield. Over that same range, there usually was a close relationship between number of stems and number of tubers both per unit area and per plant (see also Fig. 3, Quadrant II). This indicates that the physiological age can be used to manipulate tuber number per unit area and average tuber weight, thus defining tuber-size distribution. Physiological age might have an additional effect on the coefficient of variation in tuber size. Such an effect is suggested by the data on proportion of tubers >55 mm (Table 6) but also by the data in lower size classes (data not shown). Also this effect was strongly dependent on cultivar. We did not record data on tuber numbers in classes with a much larger minimum grade as such tubers were rare in our research.

The large differences in behavior among cultivars calls for a separation of seed lots during storage whenever possible since each might need a special storage temperature regime dependent on when and how it will be used. Moreover, the yield reductions caused by warm storage might be drastic. Results also show that risk of early presprouting might be larger in some cultivars than in other cultivars.

CONCLUSIONS

The temperature sum before the end of dormancy has only a limited effect on the process of physiological ageing. The temperature sum after the end of dormancy is crucial for the process of ageing of seed tubers. Cultivars respond differently on the latter temperature sum and on the sequence of high or low temperatures. Cultivars with a high rate of ageing show much greater difference between the same temperature sums built up over time in different ways. In those cases, later warm storage was detrimental.

ACKNOWLEDGMENTS

The authors thank the following students who have contributed to this research as partial fulfillment of the requirements for their MSc degrees: T. Biemond, M. Calon, H. Hock, L. de Jong, EM. Koops, RL. Kooman, H. Marring, A. Nieuwhuijse, D.A.M. Risseeuw, H. Scholten, and C.J. van der Wckken. We also thank the staff of the research farm of the former Department of Agronomy, Wageningen University, and especially Ing. L. Mol and L. Haalstra, for their role in managing the experiments.

REFERENCES

Anonymous. 2002. 77th list of varieties of field crops 2002. Commissie voor de Samenstelling van de Rassenlijst voor Landbouwgewassen, Wageningen, the Netherlands.

Bachem, C.W.E.B., R.G.F. Visser, and P.C. Struik. 2000. Tuber dormancy and sprouting. Special issue of Potato Research. Potato Res. 43:297-454.

Bodlaender, K.B.A., H.M. Dekhuijzen, J. Marinus, A. van Es, K.J. Hartmans, L.J.R Kupers, C.D. van Loon, and D.E. van der Zaag. 1987. Effect of physiological age on growth vigour of seed potatoes. A study with seed tubers of two cultivars stored at two different temperatures. Rapport 555. Instituut voor Bewaring en Verwerking van Landbouwprodukten (IBVL), Wageningen, the Netherlands.

Caldiz, D.O., L.V. Fernandez, and P.C. Struik. 2001. Physiological age index: A new, simple and reliable index to assess the physiological age of seed potato tubers based on haulm killing date and length of the incubation period. Field Crops Res. 69:69-79.

Ewing, E.E., and RC. Struik. 1992. Tuber formation in potato: Induction, initiation, and growth. Hort. Rev. 14:89-198.

GenStat. 2000. GenStat for Windows. Release 4.2, 5th ed. VSN International Ltd, Oxford, England.

Krijthe, N. 1962. Observations on the sprouting of seed potatoes. Eur. Potato J. 5:316-333.

O'Brien, P.J., and E.J. Allen. 1981. The concept and measurement of physiological age. p. 64-66. In Abstracts of Conference Papers, 8th Triennial Conference EAPR, 3, Munich. 0 Aug.-4 Sept. 1981. European Association for Potato Research, Wageningen, the Netherlands.

O'Brien, P.J., E.J. Allen, J.N. Bean, R.J. Griffith, S.A. Jones, and J.L. Jones. 1983. Accumulated day degrees as a measure of physiological age and the relationships with growth and yield in early potato varieties. J. Agric. Sci. (Cambridge) 101:613-131.

Reust, W. 1982. Contribution a l'appreciation de l'age physiologique des tubercules de pomme de terre (Solanum tuberosum L.) et etude de son importance sur le rendement. Thrse no. 7046, Ecole Polytechnique Federale Zurich, Suisse.

Reust, W. 1986. EAPR Working group "Physiological age of the potato". Potato Res. 29:268-271.

Scholte, K. 1986. Relation between storage T sum and vigour of seed potatoes, p. 28-29. In Abstracts of Conference Papers, 10th Triennial Conference EAPR, Aalborg, Denmark.

Struik, RC., A.J. Haverkort, D. Vreugdenhil, C.B. Bus, and R. Dankert. 1990. Manipulation of tuber-size distribution of a potato crop. Potato Res. 33:417-432.

Struik, P.C., D. Vreugdenhil, A.J. Haverkort, C.B. Bus, and R. Dankert. 1991. Possible mechanisms of size hierarchy among tubers on one stem of a potato (Solanum tuberosum L.) plant. Potato Res. 34:187-203.

Struik, EC., and S.G. Wiersema. 1999. Seed potato technology. Wageningen Pers, Wageningen, the Netherlands.

Van der Zaag, D.E., and C.D. van Loon. 1987. Effect of physiological age on growth vigour of seed potatoes of two cultivars. 5. Review of literature and integration of some experimental results. Potato Res. 30:451-472.

Van Ittersum, M.K. 1992. Dormancy and vigour of seed potatoes. PhD Thesis, Wageningen Agricultural University, Wageningen, the Netherlands.

Van Ittersum, M.K., K. Scholte, and L.J.P. Kupers. 1990. A method to assess cultivar differences in rate of physiological ageing of seed tubers. Am. Potato J. 67:603-513.

Abbreviations: dm, dry matter; H, high; L, low.

P. C. Struik, * P. E. L. van der Putten, D. O. Caldiz, and K. Scholte

P.C. Struik, P.E.L. van der Putten, and K. Scholte, Crop and Weed Ecology (CWE) Group, Dep. of Plant Sciences, Wageningen Univ., Haarweg 333, 6709 RZ Wageningen, the Netherlands; D.O. Caldiz, McCain Argentina, Balcarce, Argentina. Received 23 Aug. 2005. * Corresponding author (paul.struik@wur.nl).
Fig. 1. Schematic presentation of storage treatments, their codes and
accumulated temperatures (T-sums) of Exp. 1 through 3 (Fig. 1A) and
Exp. 4 (Fig. 1B). The storage period of each experiment was subdivided
into different phases of 6 (Exp. 4), 7.5 (Exp. 2 and 3), or S (Exp. 1)
wk, giving four phases in the first three experiments and five phases
in Exp. 4. Different treatments were created by assigning a low or a
high temperature to the different phases. For Exp. 1 through 3, we only
selected treatments with constant temperature during the first two
phases and the last two phases. Treatments were coded by indicating the
temperature (L for low and H for high) followed by the number of phases
that such a temperature was maintained. Treatments without a
temperature switch are indicated by L4 or H4 (Exp. 1-3) or L5 or H5
(Exp. 4) for a low storage temperature throughout the storage period
and high storage temperature throughout the storage period,
respectively. In Exp. 1 through 3, the treatments with a switch in
storage temperature from low to high are indicated by L2H2, treatments
with a switch in storage temperature from high to low are indicated by
H2L2. Similarly, in Exp. 4, the letters L and H in the treatments with
temperature switches are followed by the numbers 1, 2, 3, or 4
indicating the number of phases that a specific temperature was
maintained. These codes are listed behind the schematic representation
of the treatments and followed by the temperature sum over the entire
storage period in the different experiments.

A

Code    T-sum ([degrees]C d)

        Exp. 1    Exp. 2    Exp. 3

  L4       896       840       840
  H4      4480      4200      4200
L2H2      2688      2520      2520
H2L2      2688      2520      2520

B

Code    T-sum ([degrees]C d)

  L5     840
  H5    3360
L4H1    1344
L3H2    1848
L2H3    2352
L1H4    2856
H1H4    1344
H2L3    1848
H3L2    2352
H4L1    2856

Table 1. Relative rate of physiological ageing of the cultivars used
(ranked on the basis of their maturity type) and their presence
in the four experiments.

                                         Relative
                          Maturity        of rate
                           types       physiological
Cultivar                 ([dagger])      ageing *          Exp. 1

Sirtema                  very early    very high        + ([section])
Jaerla                   early         very high        +
Kennebec                 mid-early     low              -
Bintje                   mid-early     intermediate     +
Desiree                  mid-late      very low         +
Astarte ([paragraph])    very late     very high        +

Cultivar                 Exp. 2    Exp. 3    Exp. 4

Sirtema                    -         +         +
Jaerla                     +         +         +
Kennebec                   -         +         +
Bintje                     +         +         +
Desiree                    +         +         +
Astarte ([paragraph])      -         +         +

([dagger]) Based on Anonymous (2002).

([double dagger]) Based on Van Ittersum et al. (1990) and Van Ittersum
(1992) who compared seed tuber behavior of a large set of cultivars
under different storage regimes. Ranking is based on several
performance parameters assessed after cool and warm storage.

([section]) + = present; - = not present.

([paragraph]) Starch potato cultivar, cultivars with this specific use
are usually late and have a high tuber dry matter content, but their
use or maturity type is not necessarily related to physiological
behavior of seed tubers.

Table 2. Relevant details on materials and methods of the four
experiments carried out in four different years.

                                             Experiment 1

Seed production
Harvest date of seed tubers                    23 July
Storage
Seed tuber weight (g)                          about 70
First day in controlled storage               23 August
Date of desprouting                            4 April
Agronomic details during field phase
Planting date                                  18 April
Planting arrangement (m x m)                 0.75 x 0.30
Number of seed tubers [m.sup.-2]                 4.4
N fertilizer (kg N [ha.sup.-1])                  250
Irrigation                                       Yes
Weed control                            Metobromuron/Terbutryn
Late blight control                          Maneb/Fentin
Experimental details
No of replications                                3
Dates of experimental harvests
  ([double dagger])
* Very early harvest                          20-29 June
* Early harvest                               12-27 July
* Late harvest                            9 August-5 October
Weather during field phase                       Warm

                                             Experiment 2

Seed production
Harvest date of seed tubers                  5 September
Storage
Seed tuber weight (g)                           40-50
First day in controlled storage              19 September
Date of desprouting                            17 April
Agronomic details during field phase
Planting date                                  26 April
Planting arrangement (m x m)                 0.75 x 0.33
Number of seed tubers [m.sup.-2]                 4.0
N fertilizer (kg N [ha.sup.-1])                  205
Irrigation                                        No
Weed control                                  Mechanical
Late blight control                       Maneb/Fentin/Zineb
Experimental details
No of replications                                4
Dates of experimental harvests
  ([double dagger])
* Very early harvest                        -- ([section])
* Early harvest                           25 July-11 August
* Late harvest                                    --
Weather during field phase                      Cool

                                            Experiment 3

Seed production
Harvest date of seed tubers                 3 September
Storage
Seed tuber weight (g)                          40-50
First day in controlled storage             24 September
Date of desprouting                         End of March
Agronomic details during field phase
Planting date                                 23 April
Planting arrangement (m x m)                0.75 x 0.25
Number of seed tubers [m.sup.-2]                5.3
N fertilizer (kg N [ha.sup.-1])         240 + 55 ([dagger])
Irrigation                                       No
Weed control                               Aclonifen/DNOC
Late blight control                         Maneb/Fentin
Experimental details
No of replications                                2
Dates of experimental harvests
  ([double dagger])
* Very early harvest                           25 June
* Early harvest                                   --
* Late harvest                                    --
Weather during field phase                      Normal

                                                 Experiment 4

Seed production
Harvest date of seed tubers             14-18 July ([double dagger])
Storage
Seed tuber weight (g)                               40-50
First day in controlled storage                  1 September
Date of desprouting                                30 March
Agronomic details during field phase
Planting date                                    14, 15 April
Planting arrangement (m x m)                     0.75 x 0.275
Number of seed tubers [m.sup.-2]                     4.8
N fertilizer (kg N [ha.sup.-1])              230 + 40 ([dagger])
Irrigation                                            No
Weed control                                      Aclonifen
Late blight control                           Maneb/Fentin/Zineb
Experimental details
No of replications                                    4
Dates of experimental harvests
  ([double dagger])
* Very early harvest                                  --
* Early harvest                                   13-20 July
* Late harvest                               28 August-23 October
Weather during field phase                           Cool

([dagger]) Second figure: quantity of N present in stable manure
applied in early spring.

([double dagger]) Harvest dates cultivar specific and depending on
maturity type.

([section]) -- Not present.

Table 3. Thermal time in [degrees]C d until onset of sprouting (i.e.
thermal time needed to break dormancy; see Materials and Methods; value
before slash) and during the period from onset of sprouting until the
end of the controlled storage period (value after slash) for several
cultivars differing in relative rate of physiological ageing and
different storage treatments (Exp. 4). For storage treatment codes see
Fig. 1B. Values between parentheses after the codes are temperature
sums during controlled storage (in [degrees]C d). Data based on
assessments on 5 dates starting on 13.10 and ending on 30.03.

                       Thermal time ([degrees]C d) until onset of
                      sprouting/after onset of sprouting until end
                                       of storage

Storage treatment    Cultivar    Sirtema      Jaerla      Kennebec

L5 (840)                         704/136     >840/0       >840/0
L4H1 (1344)                      736/608      800/544      800/544
L3H2 (1848)                      584/1264     696/1152     632/1216
L2H3 (2352)                      464/1888     528/1824     576/1776
LIH4 (2856)                      408/2448     408/2448     664/2192
H1L4 (1344)                      400/944      688/656     >1344/0
H2L3 (1848)                      400/1448     576/1272     800/1048
H3L2 (2352)                      400/1952     576/1776     800/1552
H4L1(2856)                       400/2456     576/2280     800/2056
H5 (3360)                        400/2960     576/2784     800/2560

                        Thermal time ([degrees]C d) until onset of
                      sprouting/after onset of sprouting until end of
                                          storage

Storage treatment           Bintje      Desiree       Astarte

L5 (840)                   >840/0       >840/0         564/276
L4H1 (1344)                 736/608      736/608       564/780
L3H2 (1848)                 632/1216     584/1264      584/1264
L2H3 (2352)                 496/1856     464/1888      464/1888
LIH4 (2856)                 472/2384     664/2192      472/2384
H1L4 (1344)                 512/832     >1344/0       1192/152
H2L3 (1848)                 512/1336     1168/680      912/936
H3L2 (2352)                 512/1840     1168/1184     912/1440
H4L1(2856)                  512/2344     1168/1688     912/1944
H5 (3360)                   512/2848     1168/2192     912/2448

Table 4. Fraction of plants emerged (maximum number of plants divided
by number of seeds planted), number of stems per [m.sup.2] and number
of tubers per [m.sup.2] at early (Exp. 1, 2, and 4) or very early (Exp.
3) harvest and tuber fresh yields (g [m.sup.-2]) at very early (Exp. 1
and 3) or early (Exp. 2 and 4) harvest. Cultivars (CV) are abbreviated
by the first four letters of their full names and are listed in the
order of their maturity type. Sirt = Sirtema; Jaer = Jaerla; Kenn =
Kennebec; Bint = Bintie; Desi = Desiree; Asta = Astarte.

Storage treatment (ST)
([dagger])                                 Experiment 1

CV                           Sirt              Jaer              Bint

Fraction of plants emerged:
L4 or L5                     0.99      0.91                      0.99
H4 or H5                     0.89      0.01                      0.52
L2H2 or L2H3                 0.98      0.55                      0.95
H2L2 or H3L2                 1.00      0.75                      0.99
LSD: ST x CV ([section])     0.09

(Very) Early number of stems [m.sup.-2] on observation dates:

                             12/7     12/7                      19/7
L4 or L5                     13.1      9.2                      15.9
H4 or H5                      7.7     -- ([double dagger])       6.2
L2H2 or L2H3                  8.5      2.7                      13.1
H2L2 or H3L2                 16.2      7.0                      17.3
LSD: ST x CV ([section])      3.0

(Very) Early number of tubers [m.sup.-2] on observation dates:

                             12/7     12/7                      19/7
L4 or L5                     57       34                        97
H4 or H5                     34        0                        37
L2H2 or L2H3                 38       17                        59
H2L2 or H3L2                 69       25                        99
LSD: ST x CV ([section])     17

(Very) Early fresh tuber yield (g [m.sup.-2]) on observation dates:

                             22/6     20/6                      27/6
L4 or L5                    692      470                      1498
H4 or H5                    317        5                       136
L2H2 or L2H3                438      177                       669
H2L2 or H3L2                788      344                      1335
LSD: ST x CV ([section])    261

Storage treatment (ST)
([dagger])                         Experiment 1

CV                            Desi                Asta

Fraction of plants emerged:
L4 or L5                       0.99        0.98
H4 or H5                       0.91        0.05
L2H2 or L2H3                   0.98        0.01
H2L2 or H3L2                   0.99        0.98
LSD: ST x CV ([section])

(Very) Early number of stems [m.sup.-2] on observation dates:

                              20/7        27/7
L4 or L5                      15.2        18.8
H4 or H5                      12.1        -- ([double dagger])
L2H2 or L2H3                  14.0        -- ([double dagger])
H2L2 or H3L2                  14.4        15.3
LSD: ST x CV ([section])

(Very) Early number of tubers [m.sup.-2] on observation dates:

                              20/7        27/7
L4 or L5                      66          82
H4 or H5                      50           4
L2H2 or L2H3                  54           0
H2L2 or H3L2                  61          82
LSD: ST x CV ([section])

(Very) Early fresh tuber yield (g [m.sup.-2]) on observation dates:

                              28/6        29/6
L4 or L5                    1079        1389
H4 or H5                     674          16
L2H2 or L2H3                1009           0
H2L2 or H3L2                1318        1203
LSD: ST x CV ([section])

Storage treatment (ST)                                       Experiment
([dagger])                             Experiment 2               3

CV                           Jaer       Bint       Desi       Sift

Fraction of plants emerged:
L4 or L5                       1.00       1.00       1.00        1.00
H4 or H5                       0.81       0.99       1.00        0.95
L2H2 or L2H3                   0.95       1.00       1.00        1.00
H2L2 or H3L2                   0.99       1.00       1.00        0.99
LSD: ST x CV ([section])       0.05                              0.05

(Very) Early number of stems [m.sup.-2] on observation dates:

                              25/7       02/8       11/8        25/6
L4 or L5                      12.7       22.1       14.3        24.1
H4 or H5                      10.0       18.0       17.4        14.5
L2H2 or L2H3                  13.4       17.2       18.0        23.6
H2L2 or H3L2                  15.4       26.4       20.8        25.3
LSD: ST x CV ([section])       1.9                               3.4

(Very) Early number of tubers [m.sup.-2] on observation dates:

                               25/7      02/8     1118          25/6
L4 or L5                       51       114         67          76
H4 or H5                       25        79         81          51
L2H2 or L2H3                   34       116         77          84
H2L2 or H3L2                   51        96         81          83
LSD: ST x CV ([section])       12                               20

(Very) Early fresh tuber yield (g [m.sup.-2]) on observation dates:

                              25/7       02/8     1118          25/6
L4 or L5                    3626       4799       9985        1742
H4 or H5                     463       2794       6970         810
L2H2 or L2H3                1162       4789       9350        1577
H2L2 or H3L2                2949       4517       9718        2009
LSD: ST x CV ([section])     696                               281

Storage treatment (ST)
([dagger])                                Experiment 3

CV                           Jaer       Kenn       Bint       Desi

Fraction of plants emerged:
L4 or L5                       0.99       1.00       1.00       1.00
H4 or H5                       0.35       0.64       0.84       0.97
L2H2 or L2H3                   0.97       1.00       1.00       0.99
H2L2 or H3L2                   1.00       0.99       0.99       1.00
LSD: ST x CV ([section])

(Very) Early number of stems [m.sup.-2] on observation dates:

                              25/6       25/6       25/6       25/6
L4 or L5                      20.6       20.6       30.5       23.4
H4 or H5                       2.9        5.6       10.3       20.5
L2H2 or L2H3                  16.9       19.7       29.1       24.5
H2L2 or H3L2                  18.5       18.7       29.3       25.4
LSD: ST x CV ([section])

(Very) Early number of tubers [m.sup.-2] on observation dates:

                              25/6       25/6       25/6       25/6
L4 or L5                      65         39        119         79
H4 or H5                      12         11         32         61
L2H2 or L2H3                  66         42        116         83
H2L2 or H3L2                  68         39        119         82
LSD: ST x CV ([section])

(Very) Early fresh tuber yield (g [m.sup.-2]) on observation dates:

                              25/6       25/6      25/6        25/6
L4 or L5                    1704        841       1187       1262
H4 or H5                     213        253        252        824
L2H2 or L2H3                1283       1036       1553       1300
H2L2 or H3L2                1574        989       1087       1584
LSD: ST x CV ([section])

Storage treatment (ST)
([dagger])                             Experiment 4

CV                                   Asta              Sift

Fraction of plants emerged:
L4 or L5                       0.99                      1.00
H4 or H5                       0.04                      0.78
L2H2 or L2H3                   0.06                      0.87
H2L2 or H3L2                   0.99                      0.97
LSD: ST x CV ([section])                                 0.06

(Very) Early number of stems [m.sup.-2] on observation dates:

                              25/6                      13/7
L4 or L5                      24.9                      17.4
H4 or H5                       0.6                       8.2
L2H2 or L2H3                  -- ([double dagger])      14.4
H2L2 or H3L2                  21.8                      21.4
LSD: ST x CV ([section])                                 3.0

(Very) Early number of tubers [m.sup.-2] on observation dates:

                              25/6                      13/7
L4 or L5                     100                        63
H4 or H5                       2                        37
L2H2 or L2H3                   3                        57
H2L2 or H3L2                  91                        74
LSD: ST x CV ([section])                               112

(Very) Early fresh tuber yield (g [m.sup.-2]) on observation dates:

                              25/6                      13/7
L4 or L5                    1243                      4504
H4 or H5                      17                      3072
L2H2 or L2H3                  50                      3822
H2L2 or H3L2                1092                      4379
LSD: ST x CV ([section])                               412

Storage treatment (ST)
([dagger])                                Experiment 4

CV                           Jaer       Kenn       Bint       Desi

Fraction of plants emerged:
L4 or L5                       0.97       1.00       1.00       1.00
H4 or H5                       0.45       0.99       0.86       0.92
L2H2 or L2H3                   0.87       1.00       0.93       0.91
H2L2 or H3L2                   0.68       1.00       1.00       1.00
LSD: ST x CV ([section])

(Very) Early number of stems [m.sup.-2] on observation dates:

                              13/7       16/7       16/7       20/7
L4 or L5                      11.8       13.5       19.5       18.5
H4 or H5                       3.7       12.7       13.0       15.0
L2H2 or L2H3                  14.3       15.1       16.0       18.8
H2L2 or H3L2                  17.4       16.7       29.3       22.9
LSD: ST x CV ([section])

(Very) Early number of tubers [m.sup.-2] on observation dates:

                              13/7       16/7       16/7       20/7
L4 or L5                      48         40         91         70
H4 or H5                      17         34         75         62
L2H2 or L2H3                  44         39         70         66
H2L2 or H3L2                  59         38         93         83
LSD: ST x CV ([section])

(Very) Early fresh tuber yield (g [m.sup.-2]) on observation dates:

                              13/7       16/7       16/7       20/7
L4 or L5                    3715       3135       4763       3652
H4 or H5                    1325       2647       3242       2373
L2H2 or L2H3                3734       2849       3994       3077
H2L2 or H3L2                3522       3201       4058       3691
LSD: ST x CV ([section])

Storage treatment (ST)
([dagger])                       Experiment 4

CV                                   Asta

Fraction of plants emerged:
L4 or L5                       1.00
H4 or H5                       0.97
L2H2 or L2H3                   0.10
H2L2 or H3L2                   1.00
LSD: ST x CV ([section])

(Very) Early number of stems [m.sup.-2] on observation dates:

                              20/7
L4 or L5                      25.2
H4 or H5                      12.1
L2H2 or L2H3                  -- ([double dagger])
H2L2 or H3L2                  18.7
LSD: ST x CV ([section])

(Very) Early number of tubers [m.sup.-2] on observation dates:

                              20/7
L4 or L5                      71
H4 or H5                      54
L2H2 or L2H3                   3
H2L2 or H3L2                  67
LSD: ST x CV ([section])

(Very) Early fresh tuber yield (g [m.sup.-2]) on observation dates:

                              20/7
L4 or L5                    3660
H4 or H5                    2970
L2H2 or L2H3                 222
H2L2 or H3L2                3634
LSD: ST x CV ([section])

([dagger]) Treatments are coded by indicating the temperature (L for
low and H for high) followed by the number of phases that such a
temperature was maintained. Treatments without a temperature switch are
indicated by L4 or H4 (Exp. 1-3) or L5 or H5 (Exp. 4) for a low storage
temperature throughout the storage period and high storage temperature
throughout the storage period, respectively. In Exp. 1-3, the
treatments with a switch in storage temperature from low to high are
indicated by L2H2, treatments with a switch in storage temperature from
high to low are indicated by H2L2. Similarly, in Exp treatments with a
switch in storage temperature are coded L2H3 or H3L2. Temperature sums
(in [degrees]C d) for the different treatments are: Exp. 1: L4 896, H4
4480, L2H2 2688, H2L2 2688; Exp. 2 and 3: H4 4200, L2H2 2520, H2L2
2520; Exp. 4: L5 840, H5 3360, L2H3 2352; H3L2 2352.

([double dagger]) Number of stems [m.sup.-2] [less than or equal to]
0.5.

([section]) LSDs for storage treatment x cultivar combinations at
P [less than or equal to] 0.05.

Table 5. Final number of tubers per [m.sup.2] or per stem at late
harvest (Exp. 1 and 4). Sirt = Sirtema; Jaer = Jaerla; Kenn =
Kennebec; Bint = Bintje; Desi = Desiree; Asta = Astarte.

Storage                                    Experiment 1:
treatment (ST) ([dagger])            No. of tubers [m.sup.-2]

CV                           Sirt    Jaer    Bint     Desi     Asta

Observation date:            22/8    22/8      9/8    21/9      5/10
L4 or L5                     68      26      104      68      100
H4 or H5                     46       4       58      47        0
L2H2 or L2H3                 43      21       74      56        0
H2L2 or H3L2                 67      34      106      65       91
LSD: ST x CV ([section])     16

Storage                                  Experiment 1:
treatment (ST) ([dagger])           No. of tubers per stem

CV                           Sirt            Jaer            Bint

Observation date:            22/8    22/8                    9/8
L4 or L5                      5.3     2.9                    6.6
H4 or H5                      6.0    -- ([double dagger])    9.3
L2H2 or L2H3                  5.1     7.9                    5.8
H2L2 or H3L2                  4.2     5.0                    6.1
LSD: ST x CV ([section])      3.2

Storage                              Experiment 1:
treatment (ST) ([dagger])       No. of tubers per stem

CV                           Desi    Asta

Observation date:            21/9     5/10
L4 or L5                      4.6     5.3
H4 or H5                      3.9    -- ([double dagger])
L2H2 or L2H3                  4.0    -- ([double dagger])
H2L2 or H3L2                  4.5     6.0
LSD: ST x CV ([section])

Storage                                Experiment 1:
treatment (ST) ([dagger])        No. of tubers [m.sup.-2]

CV                           Sirt    Jaer    Kenn    Bint    Desi

Observation date:            28/8    28/8    11/9    11/9    25/9
L4 or L5                     53      35      34      68      61
H4 or H5                     29      20      26      56      54
L2H2 or L2H3                 47      33      31      63      54
H2L2 or H3L2                 50      40      33      84      70
LSD: ST x CV ([section])     10

                             Experiment 4:
Storage                      No. of tubers         Experiment 1:
treatment (ST) ([dagger])     [m.sup.-2]      No. of tubers per stem

CV                               Asta              Sirt    Jaer

Observation date:                23/10             28/8    28/8
L4 or L5                          68                3.1     3.0
H4 or H5                          52                3.7     5.7
L2H2 or L2H3                       3                3.3     2.4
H2L2 or H3L2                      62                2.3     2.3
LSD: ST x CV ([section])                            1.0

Storage                           Experiment 1:
treatment (ST) ([dagger])    No. of tubers per stem

CV                            Kenn    Bint    Desi

Observation date:             11/9    11/9    25/9
L4 or L5                       2.6     3.5     3.3
H4 or H5                       2.1     4.2     3.8
L2H2 or L2H3                   2.1     3.9     2.8
H2L2 or H3L2                   2.0     2.9     3.0
LSD: ST x CV ([section])

Storage                           Experiment 1:
treatment (ST) ([dagger])    No. of tubers per stem

CV                           Asta

Observation date:             23/10
L4 or L5                       2.7
H4 or H5                       4.2
L2H2 or L2H3                  -- ([double dagger])
H2L2 or H3L2                   3.3
LSD: ST x CV ([section])

([dagger]) Treatments areare coded by indicating the temperature (L for
low and H for high) followed by the number of phases that such a
temperature was maintained. Treatments without a temperature switch
indicated by L4 or H4 (Exp. 1) or by L5 or H5 (Exp. 4) for a low
storage temperature throughout the storage period and high storage
temperature throughout the storage period, respectively treatments with
a switch in storage temperature from low to high are indicated by L2H2,
treatments with a switch in storage temperature from high to low are
indicated by H2L2. Similarly, in Exp. 4, the treatments with a switch
in storage temperature are coded L2H3 or H3L2. Temperature sums
(in [degrees]C d) for the different treatments are: Exp. 1: L4 896, H4
4480, L2H2 2688, H2L2 2688; Exp. 4: L5 840, H5 336 L2H3 2352; H3L2
2352.

([double dagger]) Number of stems [m.sup.-2] [less than or equal to]
0.5; therefore, ANOVA input is zero.

([section]) LSDs for storage treatment x cultivar combinations at
P [less than or equal to] 0.05.

Table 6. Tuber fresh weight (g m-Z), dry matter content in tuber (%)
and fraction of tubers > 55 mm (%), at late harvests of different
cultivars (CV) in Exp. 1 and 4. Sirt = Sirtema; Jaer = Jaerla; Kenn =
Kennebec; Bint = Bintje; Desi = Desiree; Asta = Astarte.

Storage treatment (ST)         Experiment 1: Tuber fresh weight
([dagger])                              (g [m.sup.-2])

CV                        Sirt     Jaer     Bint     Desi   Asta

Observation date:          22/8     22/8      9/8     21/9      5/10
LA                       5290     4621     5766     4787     6526
H4                       4502      367     3284     3961      192
L2H2                     4231     3934     4562     4684        0
H2L2                     5206     4523     5750     4626     6473
LSD: CV
  ST
  ST x CV
    ([double dagger])    1034

Storage treatment (ST)
([dagger])                   Experiment 1: Tuber dry matter (%)

CV                       Sirt    Jaer   Bint   Desi        Asta

Observation date:        22/8    22/8    9/8   21/9     5/10
LA                       19.4    18.7   22.2   22.1    27.5
H4                       19.7    17.1   20.9   21.5    25.2
L2H2                     19.2    18.5   22.7   21.1    * ([section])
H2L2                     19.1    18.1   22.4   21.5    27.3
LSD: CV                   0.64
  ST                      0.57
  ST x CV
    ([double dagger])

Storage treatment (ST)
([dagger])                Experiment 1: Tubers > 55 mm (%)

CV                       Sirt   Jaer   Bint    Desi   Asta

Observation date:        22/8   22/8    9/8    21/9    5/10
LA                       38     87      9      22     10
H4                       53     56     11      22     20
L2H2                     57     84      8      21      0
H2L2                     30     72      8      21     15
LSD: CV
  ST
  ST x CV
    ([double dagger])    19

Storage treatment (ST)       Experiment 4: Tuber fresh weight
([dagger])                            (g [m.sup.-2])

CV                        Sirt     Jaer     Kenn     Bint     Desi

Observation date:          22/8     28/8     11/9     11/9     25/9
L5                       6020     5402     5135     5716     6122
H5                       4031     4260     4266     4174     4622
L2H3                     5100     5336     4543     4934     4974
H3L2                     5444     5047     5041     5054     5573
L4H1-1344                5892     5421     4781     5337     5919
H1L4-1344                6181     5618     4989     5250     5577
L3H2-1848                5225     5004     4647     5209     5731
H2L3-1848                5426     5422     5134     5007     5560
L1H4-2856                4096     5319     4149     4873     4640
H4L1-2856                4728     5395     4395     5334     5051
LSD: ST x CV
  ([double dagger])       862

                           Experiment 4:
Storage treatment (ST)   Tuber fresh weight    Experiment 4: Tuber dry
([dagger])                 (g [m.sup.-2])            matter (%)

CV                              Asta          Sirt   Jaer   Kenn   Bint

Observation date:              23/10          22/8   28/8   11/9   11/9
L5                              6878          17.2   16.7   20.4   19.7
H5                              5885          17.9   17.3   20.7   20.2
L2H3                            387           18.1   16.7   21.0   19.7
H3L2                            6056          17.0   16.8   20.3   19.9
L4H1-1344                       6362          17.2   16.7   19.4   19.4
H1L4-1344                       6105          17.3   16.6   20.6   19.6
L3H2-1848                       6228          17.0   16.8   20.0   19.7
H2L3-1848                       6140          17.3   16.7   20.2   19.4
L1H4-2856                       1223          17.6   17.2   21.1   20.5
H4L1-2856                       6228          17.3   17.1   21.2   20.3
LSD: ST x CV
  ([double dagger])                            0.9

                         Experiment 4:
Storage treatment (ST)     Tuber dry     Experiment 4: Tubers > 55 mm
([dagger])                 matter (%)                 (%)

CV                        Desi   Asta         Sirt   Jaer   Kenn

Observation date:         25/9   23/10        22/8   28/8   11/9
L5                        19.5   25.2         57     72     77
H5                        20.0   26.0         78     86     78
L2H3                      19.7   22.6         53     72     72
H3L2                      19.8   24.5         48     56     77
L4H1-1344                 19.8   25.3         52     67     66
H1L4-1344                 20.0   25.8         50     66     73
L3H2-1848                 19.9   25.5         37     56     67
H2L3-1848                 19.9   25.6         38     68     74
L1H4-2856                 20.0   24.3         75     81     76
H4L1-2856                 19.6   25.6         51     75     75
LSD: ST x CV
  ([double dagger])                           10

Storage treatment (ST)
([dagger])               Experiment 4: Tubers > 55 mm (%)

CV                             Bint   Desi   Asta

Observation date:              1119   25/9   23/10
L5                               22   32     25
H5                               20   20     35
L2H3                             19   26     67
H3L2                              6   14     30
L4H1-1344                         9   38     21
H1L4-1344                        13   23     19
L3H2-1848                         7   32     40
H2L3-1848                         8   14     28
L1H4-2856                        29   35     60
H4L1-2856                         8   10     27
LSD: ST x CV
  ([double dagger])

([dagger]) Treatments are coded by indicating the temperature (L for
low and H for High) follwed by the number of phases that such a
temperature was maintained. Treatments without a temperature switch are
indicated by L4 or H4 (Exp. 1) or by L5 or H5 (Exp. 4) for a low
storage temperature throughout the storage period and high storage
temperature throughout the storage period, respectively. In Exp. 1, the
treatments with a switch in storage temperature from low to high are
indicated by L2H2, treatments with a switch in storage temperature from
high to low are indicated by H2L2. Similarly, in Exp. 4, the treatments
with a switch in storage temperature are coded L2H3 or H3L2.
Temperature sums (in [degrees]C d) for the different treatments are:
Exp. 1: L4 896, H4 4480, L2H2 2688, H2L2 2688; Exp. 4: L5 840, H5 3360,
L2H3 2352; H3L2 2352; other treatments as indicated.

([double dagger]) LSDs for cultivar, storage treatment or storage
treatment x cultivar combinations at P [less than or equal to] 0.05.

([section]) In ANOVA missing value as input.
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Author:Struik, P.C.; van der Putten, P.E.L.; Caldiz, D.O.; Scholte, K.
Publication:Crop Science
Geographic Code:1USA
Date:May 1, 2006
Words:9855
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