Investigations on the influence of Neotyphodium endophytes on plant growth and seed yield of Lolium perenne genotypes.
Neotyphodium endophytcs of the important fodder grasses tall rescue (Festuca arundinacea Schreb.) and perennial ryegrass are generally considered to live in mutualistic associations, where benefit derives to each participant in the symbiosis. These endophytes produce alkaloids that protect the associations from mammalian, insect, and nematode herbivores (Latch, 1993). Furthermore, endophyte infection in tall fescue may significantly improve drought-stress tolerance of host plants (West, 1994; Malinowski and Belesky, 2000). This became evident after the release of the cultivar Kentucky 31, which showed superior herbage production and recovery after drought over other F. arundinacea varieties, but only if endophyte-infected (Hill et al., 1991; Wilkinson, 1993; Bouton et al., 1993). Apparently, during the breeding process endophyte strains were selected which could significantly improve plant persistence. The practical impact of the endophytes is so immense that, at present, symbiotic plants are dominant on tall rescue pastures in the USA, and the majority of released F. arundinacea varieties are endophyte-infected (Bacon and Siegel, 1988; Bouton, 2000).
Studies on the occurrence of Neotyphodium spp. in perennial ryegrass ecotypes showed that, as in tall fescue, summer drought conditions seem to impart a selection pressure in favor of infection (Lewis et al., 1997). However, greenhouse trials with varieties and genotypes of L. perenne revealed inconsistent endophyte effects on plant growth under drought. Eerens et al. (1998) and Cheplick et al. (2000) reported no, or negative, endophyte effects on dry matter accumulation and tiller production, while Ravel et al. (1997) and Amalric et al. (1999) found these parameters to be increased when the endophyte was present. A possible explanation for this inconsistency could be the high diversity of the Neotyphodium endophytes colonizing perennial ryegrass. Lolium perenne is known to host two different taxonomic groups of Neotyphodium spp.: N. lolii (Latch, Christensen, & Samuels) Glenn, Bacon, & Haulin and LpTG-2 (Christensen et al., 1993). The species most frequently infecting perennial ryegrass in Europe, N. lolii, shows high variability in colony morphology and in its capacity to synthesize the alkaloids ergovaline, lolitrem B, and peramine (Christensen et al., 1993; Bony et al., 2001), indicating the existence of different N. lolii strains.
The objective of this study was to determine whether is it possible to select N. lolii strains which can improve plant growth and/or persistence of perennial ryegrass. It was assumed that endophytes with beneficial effects on the stress tolerance of their hosts are more likely to be found in L. perenne plants from wild populations growing in stressful environments. Therefore, perennial ryegrass plants were collected from natural grassland habitats in Saxony-Anhalt (Germany), which have not been reseeded within the last 20 yr and are exposed to seasonal flooding and/or periodic drought (Hesse, 2002). Here we report evaluation results for 13 originally Neotyphodium-infected genotypes which were tested in a field experiment for endophyte effects on plant growth, seed production, and seed quality parameters in an area with low rainfall.
MATERIALS AND METHODS
The L. perenne genotypes, evaluated in this study, were selected from an accession of plant material collected in 1997 from native grassland habitats in Saxony-Anhalt (Germany). The plants were dug out from grassland habitats and cultivated in a greenhouse until screening for presence of endophytic fungi by means of histological leaf sheath analysis (after Saha et al., 1988). The fungi were isolated on potato-dextrose-agar and taxonomically classified as Neotyphodium spp. on the basis of colony morphology and conidial characteristics as described by Latch et al. (1984). Eventually, 13 L. perenne genotypes were selected for our field experiment, which met the criteria of varying morphological characters, different geographical origin, and stressful environmental conditions at their collection sites. The varying habitat characteristics and climate conditions at the collection sites of these genotypes are shown in Table 1.
EF clonal material was produced after a modified method of Latch and Christensen (1982) by growing EI tillers from these genotypes for 2.5 wk in hydroponic culture containing a fungicide solution with 0.4% (w/v) a.i. propiconazole as Desmel (Hora, Syngenta, Maintal, Germany). Subsequently, all plants (EI and EF) were allowed to grow in the field for 1 yr. To provide uniformly sized plants for the experiment, EI and EF clones were grown for two months in the greenhouse, and reduced to plantlets with four similar-sized tillers 3 wk before being transplanted to the field. Microscopic leaf sheath analysis of the plants before the experiment and after each harvest was performed to observe the success of endophyte eradication in EF clones as well as the survival of endophytes in EI clones.
The field trial was conducted at the experimental station of the University Halle-Wittenberg in Halle (Saale), Germany. The site (51[degrees]28'N, 11[degrees]58'E, elevation 113 m) is characterized by loamy sand (sand-loess on glacial mar; FAO: Haplic Phaeozem and Luvic Phaeozem), a mean annual precipitation of 475 mm and a mean annual temperature of 10.5[degrees]C. In April 1999, the clones were transplanted into the field at 80-cm intervals. Each plot contained 15 EI and 15 EF clones of one genotype, resulting in 13 plots with 30 clonal plants, respectively. Fertilizer was applied each year at the beginning of the growing season at a rate of 70 kg N/ha. In 1999 and 2000, seed production and regrowth were investigated; in 2001, two herbage harvests were performed. As shown in Fig. 1, in 1999 high rainfalls occurred during spring and early summer, whereas precipitation in the late summer and autumn months was below average. During the growing periods 2000 and 2001 rainfall was usually at or above average.
[FIGURE I OMITTED]
For seed harvest, conducted in the summer months of 1999 and 2000, each clone was cut 5 cm above the ground when the seeds had reached late dough-stage (decimal code 85, Zadoks et al., 1974). For each clone, dry matter yield, total number of reproductive tillers (immature and ripe inflorescences), number of seeds per ripe inflorescence, and seed yield were determined. To specify seed quality, TSW and seed germination were tested according to ISTA-regulations (ISTA, 1999). For the germination test, 4 x 100 seeds were placed on a Jacobsen apparatus (ISTA, 1999) for 14 d at 20[degrees]C. For green matter harvest, clones were cut 5 cm above the ground and dry matter yield was determined separately for each clone.
Biometrical Evaluation Procedures
The tested 13 N. lolii/L. perenne associations are likely to host different fungal genotypes because (i) endophyte-plant associations were collected from isolated native habitats with different types of selection pressure, (ii) Neotyphodium endophytes, as obligate symbionts, coevolve with their host (Craven et al., 2001; Clay and Schardl, 2002), (iii) European isolates are highly variable in colony morphology and alkaloid production (Bony et al., 2001), and (iv) isolates from the tested L. perenne genotypes showed differences in morphology and spore production (data not shown). Therefore, each endophyte-plant association was considered to be a unique symbiosis with specific interactions between endophyte and host genotype. In such a hierarchical structure (endophyte within grass genotype) the effect of the endophyte cannot be separated from the interaction effect between endophyte and host plant regarding the analyzed character. Thus, the differences between EI and EF clones in green matter production, seed production and TSW were evaluated separately for each endophyte-grass association and for each year by a one-way ANOVA (PROC MIXED; SAS Institute, Cary, NC, Release 6.12, 1989-1996). Statistical evaluation was not performed as a series of experiments over years because the same characters were measured for 2 yr only.
To elucidate the differences in yield parameters between EI and EF of each genotype, the relative difference between endophyte variants (RDE) was calculated by the following formula: RDE = (El EF) x 100/EI. A binominal distribution was assumed for germination (germinated versus not germinated). The U-test (Mann and Whitney, 1947) was performed to compare the probabilities of seed germination of the EI and EF variants.
Of the 13 endophyte-plant associations evaluated in this study, nine (A-I) originated from dry sites, the genotypes J and K from sites with seasonal flooding and periodic drought, and genotypes L and M from wet sites (Table 1). The associations responded variably to endophyte presence. A positive endophyte effect was detectable for many genotypes in the first seed harvest year in 1999 (Table 2) whereas endophyte infection induced no effects or even lower yields in the second seed harvest in 2000 (Table 3) and in the herbage yields in 2001 (Table 4).
Plant Growth and Seed Production
The genotypes from dry sites showed high variation in their response to endophyte presence. In five genotypes (A, B, C, D, and E), endophyte infection significantly improved plant growth and/or seed production in 1999 (Table 2). However, endophyte effects on plant performance in these five genotypes were not consistent in the second seed harvest year in 2000 (Table 3). EI clones produced similar or even lower numbers of reproductive tillers (genotypes C and D), lower seed yield (E) and lower dry matter yields (C, and E) than EF clones. In the genotypes F, H and I, endophyte-infection significantly reduced plant growth and/or seed production, and no positive impact of the endophyte on plant performance was observed for these genotypes in both harvest years. The low seed yield found in genotype G in 1999 (Table 2) could be a result of a severe infection with brown rust (Puccinia recondita Roberge ex Desmaz.) during flowering.
Consistent negative endophyte effects on plant growth and reproduction were detected for the genotypes J and K, which originated from sites subjected to periodical flooding and seasonal drought. Only in genotypes B (from a dry site), L and M (both from wet sites) endophyte presence improved plant growth and/or seed yield in the first harvest year, and had no adverse effects on plant performance in following harvest events.
Endophyte effect on seed quality was also inconsistent. For seed harvest in 1999, five genotypes (D, E, J, K, and L) showed significantly higher, and another five genotypes (A, B, C, G, and H) significantly lower mean TSW when endophyte-infected (Table 2). In 2000, only the genotypes I and H showed significant differences in TSW between the endophyte variants (Table 3). The germination rate of seeds was significantly higher for the EI variants of five genotypes (A, E, F, J, and L) in 1999 and two genotypes (C and I) in 2000. No significant negative endophyte effect was observed for germination rate in both seed harvest years.
Dry Matter Yield 2001
In both harvests, significantly lower dry matter yields were detected for EI clones of genotypes J and K originating from habitats with periodical flooding and seasonal drought (Table 4). These results are in accordance with the lower number of reproductive tillers (both genotypes) and the higher seed yield (genotype J) of EI clones compared to EF clones in 1999 and 2000 (Tables 2 and 3). None of the tested genotypes showed significant positive endophyte effects on either green matter harvest in 2001.
Endophyte Effects on Plant Productivity
The influence of the endophyte on a harvest parameter of a genotype can be shown as the relative difference between the EI and EF clones (RDE). For the number of reproductive tillers, RDE indicate a relationship between the efficiency of a genotype, i.e., the productivity of EF clones, and the expression of endophyte effects. It was observed that genotypes where EF clones had high yields showed no or negative endophyte effects, while in those where EF variants performed poorly the influence of the endophyte was positive (Fig. 2). This was most obvious in the harvest year 1999, when most significant positive and negative endophyte effects were detectable.
[FIGURE 2 OMITTED]
Previous studies with Neotyphodium-infected clonal material of L. perenne have shown that these endophytes can influence the growth of perennial ryegrass in a nonuniform manner. Positive as well as negative endophyte effects on herbage yields, tiller production, regrowth after clipping, and dry matter of roots were detected, and found to be dependent on the endophyte genotype, the plant genotype, and environmental conditions (Lewis and Clements, 1990; Cheplick 1998; Hesse and Latch 1999; Cheplick et al., 2000; Cheplick and Cho, 2003). The results of this investigation confirm these findings, as Neotyphodium effects on plant growth, seed production, and seed quality of the different L. perenne genotypes were highly variable.
Most significant endophyte effects on plant performance (positive as well as negative) were detected during the first harvest year, while few were found in following harvests. One possible explanation could be that the clones of each genotype and endophyte status grew more or less similar during the year of planting, but differences in growth between the clones within one genotype gradually enhanced with increasing age. The higher variability within the genotypes in the second and third year has probably masked endophyte effects on plant performance. This indicates that a higher number of clones should be tested, when evaluating endophyte effects on plant growth parameters in spacedplant trials. On the other hand, planting of the clones could have resulted in stress, which may have triggered more pronounced endophyte effects on growth in some endophyte-plant associations. Furthermore, Ravel et al. (1995) and Oliveira et al. (1997) observed beneficial endophyte effects on growth of perennial ryegrass mostly when cultivated on dry sites. Although our experimental field is situated in an area with low rainfall, drought could not mainly have accounted for differences in endophyte effects between the first 2 yr because precipitation in both years was very similar.
Genotypes J and K from a site with periodical flooding and seasonal drought showed consistent negative endophyte effects. The remaining genotypes originated from wet sites and from natural habitats where dry weather conditions prevail during summer and soil characteristics indicate low water holding capacity. For these genotypes, there is a marginal significance that the initially positive endophyte effect in the first seed harvest is reversed in the second year (P - 0.1 for the relative difference between EI and EF over 2 yr). This indicates that the endophyte effect may vary over the life cycle of a grass plant and/or the extension of the endophytic fungus within the growing host. Further studies are also needed to determine whether environmental conditions can trigger beneficial endophyte effects on plant growth.
Negative endophyte effects on plant growth of L. perenne were also reported by Cheplick et al. (1989, 2000) and Eerens et al. (1998). The authors suggested that the endophyte may be a "metabolic cost" for the host under certain environmental conditions. However, reduction of shoot growth is also a mechanism to avoid drought stress, as it decreases transpiration area. In this study, root growth of the plants was not investigated. Genotypes A, B, E, F, J, L, and M were also studied in greenhouse experiments, and except in genotypes A and M, endophyte-infection was found to significantly either increase root/shoot ratio or root dry matter of plants or both (Hcsse, 2002). Reduction of shoot growth and development of a bigger root system are drought avoidance mechanisms (Levitt, 1980), which can be of vital importance for plant persistence, particularly in dry areas.
Although endophyte effects on seed production and TSW were inconsistent, several genotypes showed improved seed germination when endophyte-infected, and no adverse symbiotic effects were detected for this parameter. Beneficial endophyte effects on seed germination and drought avoidance mechanisms of plants may help explain the findings that infected perennial ryegrass plants are found more often on dry sites than on wet sites (Hesse, 2002), and that summer drought conditions appear to impart a selection pressure in favor of infection (Lewis et al., 1997).
Improved tillering and herbage production of perennial ryegrass genotypes because of endophyte infection have been reported by Latch et al. (1985). In this study, only three genotypes showed positive (but no negative) endophyte effects on plant growth and seed production. These included genotype B from a dry site and both genotypes from wet sites (L and M). However, in these genotypes the endophyte effect on plant performance was not consistent throughout the years, indicating that the endophyte strains have the potential to improve plant growth but only under certain conditions.
Interestingly, in the first year of our study, high-yielding genotypes tended to show negative endophyte effects, while the opposite was true for genotypes performing poorly. The two genotypes J and K from a periodically flooded and dry site behaved differently (Fig. 2) as they show consistent negative endophyte effects. These genotypes are obviously related to each other and may harbor the same endophyte strain because they are both collected at the same site. However, further studies are needed to address the question if the relationship between the efficiency of a genotype (i.e., the growth and seed production of EF clones) and the endophyte effects is mainly caused by the endophyte genotype, the grass genotype, and/or their compatibility. Investigations are necessary to reveal (i) how different endophyte strains respond to a range of grass genotypes, (ii) whether the effect of an endophyte varies within the life cycle of its host plant, and (iii) whether endophyte effects are stable under different environmental conditions. Furthermore, the production of alkaloids in Neotyphodium spp., which are toxic to mammals, needs to be considered for the selection of endophyte strains and their implementation in fodder grass breeding. However, several of the endophytes tested in this study, particularly those where endophyte infection was found to improve seed germination, could be of interest for turf grass breeding and grass production for erosion protection.
Abbreviations: EF, endophyte-free; EI, endophyte-infected; RDE, relative difference between the endophyte variants; TSW, 1000-seed weight.
Table 1. Habitat characteristics, geographical position, altitude, and climate for the collection sites of the tested Lolium perenne genotypes. Location Genotype of origin Habitat characteristics A Oppin sand layer (20-311 cm deep) on concrete (former airport) B Langenbogen rocky hillside (compact variegated sandstone) C Wettin sandy hill at a farm D Langenbogen rocky hillside (compact variegated sandstone) E Langenbogen rocky hillside (compact variegated sandstone) F Oppin sand layer (20-30 cm deep) on concrete (former airport) G Langenbogen rocky hillside (compact variegated sandstone) H Langenbogen rocky hillside (compact variegated sandstone) I Gohrendorf savaging wasteland at a rocky hillside (compact variegated sandstone) J Wettin concrete bank with sand layer at riverside (river Saale), subjected to yearly flooding, dry during summer K Wettin pasture close to the river Saale, subjected to yearly flooding (Loess on variegated sandstone), dry during summer L Halle (Wormlitz) riverside in the Elster-Saale floodplain (Fluvisol, water-logged) M Dromling meadow in the Nature Park Dromling (post-glacial lower moor, permanent high groundwalcr level) Water Genotype stress type Latitude Longitude A dry 51[degrees]33' 12[degrees]02' B dry 51[degrees]29' 11[degrees]47' C dry 51[degrees]35' 11[degrees]48' D dry 51[degrees]29' 11[degrees]47' E dry 51[degrees]29' 11[degrees]47' F dry 51[degrees]33' 12[degrees]02' G dry 51[degrees]29' 11[degrees]47' H dry 51[degrees]29' 11[degrees]47' I dry 51[degrees]21' 11[degrees]40' J flooding-summer 51[degrees]35' 11[degrees]48' drought K flooding-summer 51[degrees]35' 11[degrees]48' drought L wet 51[degrees]30' 12[degrees]00' M wet 52[degrees]28' 11[degrees]03' Mean annual Mean annual tem- precipitation Genotype Altitude perature ([dagger]) ([dagger]) m above sea level [degrees]C mm A 104 8.6 475 B 107 8.4 518 C 100 9.0 483 D 107 8.4 518 E 107 8.4 518 F 104 8.6 475 G 106 8.4 518 H 106 8.4 518 I 206 8.8 488 J 70 9.0 483 K 70 9.0 483 L 79 9.0 476 M 56 8.4 592 ([dagger]) Data from meteorological stations at collection sites or nearby (Anonymous, 1987). Table 2. Plant growth and seed yield for endophyte-infected (EI) and endophyte-free (EF) clones of 13 Lolium perenne genotypes harvested in 1999. Values shown are mean values of 15 clones per El and EF variant, respectively. Seed harvest August 1999 Reproductive tillers/clone ([dagger]) Site of origin Genotype EI EF Dry A 177 * 73 B 158 * 97 C 139 * 98 D 160 * 123 E 69 78 F 108 134 G 137 145 H 109 168 * I 69 169 * Flooded-dry J 61 129 * K 56 93 * Wet L 91 * 44 M 175 * 115 Seed harvest August 1999 Seeds/ripe inflorescence ([dagger]) Site of origin Genotype EI EF Dry A 43 72 * B 81 81 C 41 * 27 D 87 91 E 99 * 78 F 84 84 G 14 16 H 76 74 I 74 100 * Flooded-dry J 69 59 K 49 52 Wet L 72 * 53 M 48 * 29 Seed harvest August 1999 Seed yield ([dagger]) Site of origin Genotype EI EF g/clone Dry A 9.4 * 6.3 B 10.3 * 6.9 C 4.1 * 1.9 D 8.5 * 6.3 E 5.5 * 4.4 F 8.8 9.9 G 0.5 ([section]) 0.6 ([section]) H 8.1 12.9 * I 3.9 13.7 * Flooded-dry J 5.4 6.9 * K 4.9 4.5 Wet L 6.5 * 2.1 M 7.2 * 2.2 Seed harvest August 1999 1000-seed weight ([dagger]) Site of origin Genotype EI EF g Dry A 1.57 1.67 * B 1.43 1.50 * C 1.47 1.71 * D 1.30 * 1.20 E 1.61 * 1.42 F 1.66 1.61 G 1.05 1.16 * H 1.44 1.51 * I 1.52 1.46 Flooded-dry J 1.90 * 1.48 K 2.06 * 1.27 Wet L 1.35 * 1.06 M 1.38 1.54 Seed harvest August 1999 Germination ([double dagger]) Site of origin Genotype EI EF % Dry A 85 * 76 B 97 97 C 90 93 D 89 92 E 96 * 87 F 96 * 87 G 50 49 H 93 91 I 95 96 Flooded-dry J 95 * 91 K 81 86 Wet L 95 * 86 M 93 92 Seed harvest August 1999 Regrowth harvest October 1999 dry matter ([dagger]) Site of origin Genotype EI EF g/clone Dry A 39.6 * 22.8 B 23.1 * 14.2 C 5.8 9.9 * D 10.8 16.3 E 6.7 10.5 * F 4.9 5.7 G 2.9 6.0 * H 8.2 9.6 I 10.7 16.6 * Flooded-dry J 9.8 21.8 * K 17.7 19.6 Wet L 10.9 9.0 M 25.6 * 17.5 * Significant differences between EI and EF at [alpha] = 5%; asterisks mark the endophyte variant with higher performance. ([dagger]) F-test. ([double dagger]) U-test. ([section]) Severe infection with brown rust (Puccinia recondita). Table 3. Plant growth and seed yield for endophyte-infected (EI) and endophyte-free (EF) clones of 13 Lolium perenne genotypes harvested in 2000. Values shown are mean values of 15 clones per El and EF variant, respectively. Seed harvest August 2000 Reproductive tillers/clone ([dagger]) Site of origin Genotype EI EF Dry A 187 224 B 148 104 C 235 292 * D 204 284 * E 196 254 F 89 155 * G 206 176 H 132 147 I 86 66 Flooded-dry J 55 220 * K 99 141 * Wet L 204 246 M 183 192 Seed harvest August 2000 Seeds/ripe inflorescence ([dagger]) Site of origin Genotype EI EF Dry A 44 46 B 95 69 C 25 16 D 74 64 E 19 27 * F 36 35 G 26 49 H 41 58 I 52 56 Flooded-dry J 35 53 * K 103 * 48 Wet L 50 45 M 47 23 Seed harvest August 2000 Seed yield ([dagger]) Site of origin Genotype EI EF g/clone Dry A 7.4 8.6 B 12.5 8.1 C 6.1 6.2 D 14.1 19.3 E 3.9 7.3 * F 3.4 5.3 G 1.5 2.9 H 5.3 9.5 * I 3.1 2.2 Flooded-dry J 1.4 8.3 * K 13.8 10.0 Wet L 5.6 2.8 M 11.2 13.0 Seed harvest August 2000 1000-seed weight ([dagger]) Site of origin Genotype EI EF g Dry A 1.58 1.71 B 1.65 1.74 C 1.60 1.51 D 1.63 1.61 E 1.38 1.36 F 1.64 1.79 G 1.48 1.36 H 1.46 1.60 * I 1.66 * 1.44 Flooded-dry J 1.72 1.71 K 2.17 1.66 Wet L 1.37 1.25 M 1.98 2.10 Seed harvest August 2000 Germination ([double dagger]) Site of origin Genotype EI EF % Dry A 93 94 B 94 94 C 87 * 77 D 89 89 E 87 88 F 92 93 G 69 69 H 92 92 I 92 * 76 Flooded-dry J 91 90 K 99 97 Wet L 88 88 M 93 96 Seed harvest August 2000 Regrowth harvest August-September 2000 dry matter ([dagger]) Site of origin Genotype EI EF g/clone Dry A 50.4 53.0 B 43.9 32.5 C 61.6 76.0 * D 75.9 77.5 E 31.7 39.2 * F 31.6 41.7 G 41.6 33.1 H 35.8 45.4 I 39.1 37.5 Flooded-dry J 15.2 57.5 * K 42.2 77.5 * Wet L 41.1 48.7 M 58.3 56.8 * Significant differences between EI and EF at [alpha] = 5%; asterisks mark the endophyte variant with higher performance. ([dagger]) F-test. ([double dagger]) U-test. Table 4. Dry matter production for endophyte-infected (EI) and endophyte-free (EF) clones of 13 Lolium perenne genotypes harvested in 2001. Values shown are mean values of 15 clones per EI and EF variant, respectively. First harvest Second harvest May-June 2001 July 2001 Site of origin Genotype EI EF EI EF Dry matter g/clone Dry A 44.7 75.2 * 19.8 34.7 B 58.8 71.8 26.6 30.8 C 76.9 84.4 32.7 25.8 D 74.7 55.2 30.3 23.0 E 43.3 46.7 47.4 39.9 F 45.9 59.4 28.2 30.8 G 51.9 44.5 26.6 24.2 H 78.9 96.2 31.8 43.4 I 38.7 23.0 no regrowth Flooded-dry J 22.7 68.4 * 20.1 47.5 * K 49.2 82.1 * 28.3 51.3 * Wet L 56.3 65.7 21.2 22.0 M 59.6 49.9 23.4 20.5 * Significant differences between EI and EF at [alpha] = 5% (F-test); asterisks mark the endophyte variant with higher performance.
The authors gratefully acknowledge the technical assistance of H. Grtitzmacher, A. Habelt, D. Helfinger, M. Kozlowski and C. Ott. We thank Dr. J. Doering from the Institute of Agricultural Geography and Regional Planning, Martin-Luther-University Halle-Wittenberg, for supplying the weather data of the experimental field in Halle. The authors also wish to thank Dr. D. Smith, Dr. P. Kachroo and A. Byrd for helpful comments on the manuscript.
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U. Hesse, H. Hahn, * K. Andreeva, K. Forster, K. Warnstorff, W. Schoberlein, and W. Diepenbrock
U. Hesse, Univ. of Kentucky, Dep. of Plant Pathology, 201A Plant Science Bldg., 1045 Veterans Dr., Lexington, KY 40546-0312, USA; H. Hahn, K. Forster, W. Schoberlein, and W. Diepenbrock, Martin-Luther-Univ. Halle-Wittenberg, Institute of Agronomy and Crop Science, Ludwig-Wucherer-Str. 2, D-06108 Halle, Germany; K. Warnstorff, Martin-Luther-Univ. Halle-Wittenberg, Biometrics and Informatics in Agriculture Group, Ludwig-Wucherer Str. 82-85, D-06108 Halle, Germany; K. Andreeva, Institute of Plant Genetics and Crop Plant Research, Corrensstr. 3, D-06466 Gatersleben, Germany. Received 19 May 2003. * Corresponding author (email@example.com).
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|Title Annotation:||Seed Physiology, Production & Technology|
|Author:||Hesse, U.; Hahn, H.; Andreeva, K.; Forster, K.; Warnstorff, K.; Schoberlein, W.; Diepenbrock, W.|
|Date:||Sep 1, 2004|
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