Comparison of seed-derived lines from 'Florigraze' rhizoma perennial peanut.
Florigraze originated from a naturally occurring plant found between 1-yr-old plots of PI 118457 and PI 151982 (Prine et al., 1986). Florigraze has been reported to establish quicker and significantly out yield PI 118457, one of its assumed parents (Prine et al., 1981). It has demonstrated good overall performance in Louisiana for plant lateral growth, height, stand, and vigor (Venuto et al, 1995). Other released cultivars include Arb (PI 118457), Arbrook (Prine et al., 1990), and Arblick (PI 262839). Although these cultivars have proven valuable, it will be necessary to extend the methods of introduction, evaluation, and selection, if the full genetic potential of RPP is to be determined.
Although RPP is a poor seed producer (Simpson et al., 1993) and is propagated vegetatively (Prine et al., 1981), naturally occurring seedlings of Florigraze do occur. Observation of a field of Florigraze, established in March 1988 at Olive Branch, LA, revealed numerous natural seedlings emerging in the spring of 1990. Seedlings were verified by the presence of hypogeal cotyledons and were moved from this field to a space-planted nursery. The large number of available seedlings made it possible to evaluate the performance of seed-derived Florigraze lines for reproductive and morphological traits.
Information on the performance of seed-derived lines from this germplasm is lacking. This information is needed to help determine the feasibility of establishing a recurrent selection breeding program to improve the performance of this germplasm. The objectives of this study were to evaluate the variation within Florigraze seedling progeny for reproductive and morphological traits, and to determine if lines with superior forage characteristics could be identified.
MATERIALS AND METHODS
An area of Florigraze, 15.2 by 30.4 m, was established in 1988 at Olive Branch, LA (Caldwell et al., 1990). A severe freeze in 1990 delayed normal spring growth and led to the observation of emerging seedling plants. On 14 April 1990, 616 seedlings of Florigraze were identified visually, verified by the presence of hypogeal cotyledons, uprooted, transplanted into 10- by 10- by 10-cm pots and maintained outside in a semi-shaded location. Twenty-three ramets of Florigraze were randomly selected from the same area as the seedlings and simultaneously established by transplanting 10-cm rhizome pieces into 10- by 10- by 10-cm pots. Three hundred healthy progeny and the 23 Florigraze ramets were transplanted to a nursery at Olive Branch, LA, on 27 June 1990. Plants were spaced 1.25 m on center, fertilized annually with 19 kg [ha.sup.-1] P and 37 kg [ha.sup.-1] K, and weeds chemically controlled between plants with applications of glyphosate [N-(phosphonomethyl) glycine] at the rate of 1.0 L a.i. [ha.sup.-1]. Soil series was a Loring silty loam (Typic Fragiudalf, fine-sandy, mixed, thermic). All progeny lines and parent plants were planted in a completely randomized design.
The date that a Florigraze line first flowered was recorded for 1990, 1991, and 1992. Since Florigraze was established by rhizome, and all plants flowered before transplanting to the nursery, no flowering data were reported for Florigraze in 1990, but date of first flower was recorded in 1991 and 1992. Flower color, hypanthium color, and hypanthium length were measured. Color was rated with a Royal Horticultural Society Colour Chart (1966). Lines were also monitored for the presence of pegs and the production of seed.
Morphological characters measured in the seedling year, 1990, included main stem height, lateral growth, number of stems per square centimeter, and leaflet length and width. Height and lateral growth were measured with a meter stick from the center of each plot. The tallest stem and the farthest shoot from the center of each plant were recorded. Two lower leaflets on the leaf at the third node down from the apex of the central seedling stem of each progeny plant were measured with a digital micrometer and averaged to obtain representative leaf width and length. A similar leaflet measurement was taken from the tallest stem of each Florigraze plant. All measurements were taken on 5 and 6 Nov. 1990.
In 1991, the second year after establishment, height, lateral growth, stem density, leaflet length and width, and growth habit were recorded. Height and lateral growth were measured as in 1990. Stem density was estimated visually as a percent of ground cover. Growth habit was determined visually by using a scale of 1 to 5. A plant scoring 1 was extremely prostrate and a plant scoring 5 was erect. Measurements were taken on 26 Sept. 1991 for all characters, except leaf measurements which were taken on 30 July 1991. Leaflet measurements were taken on all leaflets of the third leaf down from the apex on four separate stems of each plant.
After 2 yr of observation, superior lines were identified based on morphological data, visual evaluation, and a onetime yield comparison. These selections (Lines 121, 192, 423, 473, 491, 585, and 614) were subsequently transplanted by rhizome into replicated tests at two locations with four replications per location. Lines 121, 192, 423, 491, 585, and 614 were established by rhizome at Olive Branch on 12 Nov. 1991. Because of inadequate rhizome production, only three replications of progeny 585 and 614, and none of 473 were established. Plots were 1.25 by 1.25 m with 0.67 m between plots and planted at a rhizome rate of 60 kg [ha.sup.-1]. Soil type was a Loring silty loam (Typic Fragiudalf, fine-sandy, mixed, thermic).
On 11 March 1993, Lines 192, 423, 473, 491, and 585 were established by rhizome at the Idlewild Research Station. Because of limited rhizome availability, Lines 121 and 614 were not included at this location. Plots at Idlewild consisted of four replications of 3-m rows spaced 2.5 m apart planted at a rhizome rate of 60 kg [ha.sup.-1]. Soil type was a Dexter loam (Ultic Hapludalf, fine-silty, mixed, thermic). Weeds were chemically controlled between plants with applications of glyphosate at the rate of 1.0 L a.i. [ha.sup.-1]. Plots were fertilized annually with 19 kg [ha.sup.-1] P and 37 kg [ha.sup.-1] K. The experimental design for both tests was a randomized complete block, with Florigraze and Arbrook established as controls.
Forage yield and quality data were collected from Arbrook, Florigraze, and Florigraze lines in 1994 and 1995 for three harvests each year at both locations. Plots at Idlewild were harvested on 5 May 1994, 22 July 1994, 27 Sept. 1994, 30 May 1995, 25 July 1995, and 13 Sept. 1995. Plots at Olive Branch were harvested on 5 May 1994, 15 July 1994, 30 Aug. 1994, 30 May 1995, 25 July 1995, and 13 Sept. 1995. Plots were cut to a height of 5 cm and an area 30 by 30 cm, located in the center of each plot, was used to calculate percentage dry matter and to obtain quality data. The forage green weight from this area was recorded and the entire sample oven dried at 60 [degrees] C for 72 h to obtain dry weight. The entire sample was then ground to pass through a 1.0-mm screen in a Thomas Wiley mill and stored in plastic vials at room temperature for further analyses. Crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and in vitro true digestibility (IVTD) were estimated by near infrared reflectance spectroscopy (NIRS). Samples were processed at the Louisiana Expt. Stn. Feed and Forage Testing Laboratory, located at the Southeast Res. Stn., Franklinton, LA, using a previously developed sample library.
Samples from this trial were "Centered" and "Selected" using NIRS 2, version 3.0 software. Selected samples were then compared with the library file to determine if samples in the library were similar to "Selected" samples from this trial at an H of 0.5 using the "Match" program. Two matches from the library for each selected sample were used if available. Samples from the library file that matched samples from this trial were taken out of the library to start a "Calibration" data set for this trial. If selected samples from this trial were not matched by two samples in the library file, traditional wet chemistry estimates were obtained for those samples and added to the "Calibration" file. This "Calibration" file was used to predict DM, CP, NDF, ADF, and IVTD.
Table 1. Percentage of Florigraze lines to flower, mean and range for day of the year of first flower, by year, compared with Florigraze. Florigraze lines Florigraze Year % Mean Range Mean Range Day of the year 1990 6 256 209-308 - - 1991 34 220 138-283 143 122-189 1992 78 191 119-273 125 113-142
Lateral growth and height were measured at each location for each harvest in 1994. Since plots were growing together at Olive Branch by 1995, only height was measured in that year. Lateral growth was also measured, in the spring following the first full summer of growth after establishment, on 12 May 1993 at Olive Branch and 18 May 1994 at Idlewild. Stand was estimated visually at the same time using a 0 to 10 scale. A rating of 0 = no coverage and a rating of 10 = 100% coverage.
Data were analyzed with the MIXED and GLM Procedures (SAS Institute, 1989). Genotypes were considered as fixed effects. Year and year x genotype were treated as random effects. Differences were considered significant at P [less than or equal to] 0.05 and highly significant at P [less than or equal to] 0.01.
RESULTS AND DISCUSSION
None of the 300 Florigraze lines flowered earlier or more profusely than Florigraze. Six percent of the lines flowered in the establishment year, 34% in the second year, and 78% in the third year (Table 1). Since the remaining 22% of non-flowering seedlings were not monitored after the third year, it is not known if they eventually flowered. The mean flowering date within the growing season decreased an average of 33 d for each subsequent year of growth. A flowering date comparison was not made in 1990, but Florigraze flowered an average of 72 d earlier than its progeny in 1991 and 1992.
Florigraze plants varied in time of flowering, but consistently flowered earlier than progeny plants. Assuming that within line variation (since we were unable to replicate progeny) was at least as great as within Florigraze variation, few of the lines would have flowered earlier than the mean of Florigraze (Table 1).
Although the number of flowers per line was not recorded, many of the lines had only one or a few flowers each year. Progeny flower color, hypanthium color, and [TABULAR DATA FOR TABLE 2 OMITTED] hypanthium length were no different from Florigraze and none of the lines were observed to produce pegs, pods, or seed. The poor reproductive performance of the Florigraze lines is difficult to explain, since both Florigraze and PI 118457 will produce seed under similar environmental conditions (Venuto and Elkins, 1995).
Analysis of height, lateral growth, stems per square centimeter, stem density, leaflet length/width ratio, and growth habit revealed differences between the Florigraze lines and Florigraze (Table 2). Mean line height was greater than Florigraze in 1990, but not in 1991. This difference is explained by the distinct seedling morphology of RPP which results in production of a large central stem in the seedling year. Florigraze was significantly taller than the line mean in 1991.
Lateral growth was quite variable among lines and within the Florigraze germplasm, but Florigraze means were significantly greater in 1990 and 1991. The number of stems per square centimeter was more than twice as great in 1990 for Florigraze compared with Florigraze lines. This difference was reflected in the 1991 percentage stand rating difference between Florigraze and its progeny. Leaflet length/width ratio comparison between Florigraze and Florigraze lines was significant in 1990, but ratios were not different by 1991. Growth habit ratings indicated a slight tendency for Florigraze lines to be more prostrate than Florigraze.
Analysis of forage DM, CP, NDF, ADF, and IVTD produced no significant entry x year interactions. Since all entries were not represented at both locations, data was combined across years but not across locations. Total forage mass was significantly greater in 1994 versus 1995. Mean yields in 1994 were 6 and 25% greater than 1995 yields for Olive Branch and Idlewild, respectively. Reduced late summer rains were the primary limitation to yield in 1995. Significant differences were detected for all variables measured at both locations with the exception of IVTD at the Idlewild site (Tables 3 and 4).
A comparison of Florigraze line performance relative to Florigraze at Olive Branch (Table 3), revealed consistent and significantly lower forage DM production for all lines. Lines 192, 491, 585, and 614 had significantly greater CP, significantly reduced NDF, and significantly reduced IVTD values. None of the lines had greater NDF or ADF values, and only line 614 had significantly greater IVTD.
Table 3. Two-year forage dry matter production (DM), and crude protein (CP), neutral-detergent fiber (NDG), acid-detergent fiber (ADF), and in vitro true digestibility (IVTD) concentrations, weighted for forage mass, of rhizhoma perennial peanut entries at Olive Branch, LA Entry DM CP NDF ADF IVTD g [m.sup.-2] g [kg.sup.-1] Arbrook 622 147 395 316 713 Florigraze 515 152 373 302 722 121 394 153 366 290 730 192 423 176 335 271 739 423 416 160 366 294 731 491 356 174 349 273 737 585 326 182 330 256 738 614 293 175 338 263 743 Mean 425 164 358 285 731 LSD (0.05) 80 12 13 15 20 CV (%) 27.3 10.5 5.2 7.7 3.9
A comparison of Florigraze line performance relative to Florigraze at Idlewild (Table 4) revealed less consistent results. Two lines, 423 and 473, had significantly higher 2-yr mean forage yields, but neither of these lines was significantly different from Florigraze for CP, NDF, or ADF. Line 192 had significantly higher 2-yr CP mean and lower NDF, but was not significantly different for any other variable. Line 491 had lower NDF and ADF values, but was not significantly different for other traits, and line 585 was significantly different only for NDF.
Two-year height means were not different between locations and averaged 22.7 cm (Table 5). Arbrook was significantly taller than all entries, but none of the Florigraze lines were significantly taller than Florigraze at either location. Lateral growth measurements taken during the 1994 harvest season demonstrated significant variation. None of the lines significantly outspread Florigraze, but all entries outspread Arbrook. One-year lateral growth and stand measurements taken in May following the first full growth season (Table 6), an indication of establishment rate, revealed that none of the lines established significantly faster than Florigraze at either location. Arbrook was significantly less than all entries in lateral growth, and mean lateral growth rate for all entries was greater at the Olive Branch site.
Table 4. Two-year forage dry matter production (DM), and crude protein (CP), neutral-detergent fiber (NDF), acid-detergent fiber (ADF), and in vitro true digestibility (IVTD) concentrations, weighted for forage mass, of rhizoma perennial peanut entries at Idlewild, LA. Entry DM CP NDF ADF IVTD g [m.sup.-2] g [kg.sup.-1] Arbrook 501 130 395 306 709 Florigraze 252 147 378 293 721 192 287 163 355 281 727 423 311 138 371 292 725 473 358 138 385 305 717 491 264 151 353 268 694 585 270 152 358 279 728 Mean 320 146 371 289 717 LSD (0.05) 51 19 19 14 NS CV (%) 27.7 10.5 8.9 8.3 8.1 Table 5. Mean plant height and mean lateral growth for Arbrook, Florigraze, and Florigraze lines grown at two locations, Olive Branch and Idlewild, LA. Olive Branch Idlewild Lateral Lateral Entry Height(*) growth(**) Height(*) growths cm Arbrook 33.2 47.8 30.6 49.7 Florigraze 27.0 158.8 23.9 94.8 121 21.8 136.0 - - 192 19.4 93.3 19.5 88.6 423 25.6 155.6 23.3 90.4 473 - - 24.5 72.4 491 18.3 124.3 17.1 89.8 585 17.5 80.2 20.2 98.6 614 15.8 128.4 - - Mean 22.7 116.3 22.7 83.5 LSD (0.05) 2.2 22.0 1.5 16.9 CV (%) 14.0 19.3 11.9 29.0 * Means for two years (1993 and 1994). ** Means for one year (1993).
The poor reproductive performance of Florigraze lines is significant and warrants further research. Progeny segregation for daylength response for floral initiation is possible, but most of the lines flowered and none produced pegs, pods, or seed. If this inability to produce advanced generations from Florigraze lines is representative of RPP, it may seriously limit selection and advancement of RPP germplasm.
The comparison of Florigraze with its progeny was hampered by the necessity of comparing seedlings with vegetatively propagated plants. Although the slower lateral growth and stand establishment in 1990, as measured by stand density, may be only partially explained by this difference, seedlings obviously establish slower than vegetatively propagated plants. The extra time needed for establishment from seed would limit the usefulness of seed propagated RPP even if seed production were not a problem.
The increased rate of spread of replicated lines evaluated at Olive Branch relative to Idlewild also needs further research. It is unlikely that the fall planting date at Olive Branch accounts for this difference and that other factors, such as soil fertility and pH, may be more important. Lower DM production and equal or superior quality characteristics, might be partially explained by maturity differences between Florigraze and the lines evaluated. The Florigraze lines remained vegetative much longer and many did not flower at all. Additional research on agronomic management of this crop, including soil fertility and the effect of maturity on quality, is being initiated.
Table 6. Mean lateral growth and stand rating for Arbrook, Florigraze, and Florigraze lines 18 and 14 mo. after establishment at two locations, Olive Branch and Idlewild, LA, respectively. Olive Branch Idlewild Lateral Lateral growth growth Entry (cm) Stand(*) (cm) Stand(*) Arbrook 52.5 7.0 39.5 9.5 Florigraze 122.5 7.8 78.5 9.3 121 85.0 6.0 - - 192 71.3 5.0 67.8 9.3 423 121.3 7.3 75.0 9.3 473 - - 61.3 9.8 491 95.0 7.8 71.0 9.3 585 91.7 6.3 86.8 9.8 614 80.0 8.3 - - Mean 90.16 6.9 68.5 9.4 LSD (0.05) 42.4 2.0 30.9 1.6 CV (%) 26.9 16.8 27.0 10.2 * A visual rating of 1 = no plants and a rating of 10 = full ground cover.
Most of the lines evaluated lacked the vigor of the original parent and segregated over an array of traits. Line performance was generally below that of Florigraze and none of the progeny outperformed Florigraze in all categories. Our research confirms the observation of Simpson et al. (1993) that RPP is highly heterozygous and seedlings from a desirable type are highly heterogeneous. Evidence that Florigraze is demonstrating heterotic vigor does not answer the question of frequency of this occurrence. Florigraze may be the result of a rare outcrossing event and attempts to generate useful hybrids may be tedious or futile. If productive hybrids can be generated, then the vegetative propagation of this crop will make hybrid maintenance practical. Further research is needed to determine the extent of outcrossing within this species.
The authors acknowledge the help of Dr. Gordon Prine, Dep. of Agronomy, Univ. of Florida, Gainesville, FL, in providing the original Florigraze rhizomes for this research. His willingness to help in this manner has been, and continues to be, appreciated. The authors also express appreciation to Dr. G.J. Cuomo and the staff of the Louisiana Expt. Stn. Feed and Forage Testing Laboratory, located at the Southeast Res. Stn., Franklinton, LA, for their help in forage quality analysis.
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Abbreviations: ADF, acid detergent fiber; CP, Crude Protein; IVTD, in vitro true digestibility; NDF, neutral detergent fiber; NIRS, near infrared reflectance spectroscopy; RPP, rhizoma perennial peanut.
B.C. Venuto and W.M. Elkins, Louisiana State Univ. Agric. Ctr., Dep. of Agronomy, Baton Rouge, LA 70803-2110; R.W. Hintz, W-L Res., Inc., Evansville, WI 53536-8752; R.L. Reed Texas A&M Univ., College Station, TX 77843-2474. Contribution from the Agronomy Dep., Louisiana State Univ. Agric. Ctr., Baton Rouge, LA 70803-2110. Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as manuscript no. 96-09-0218. Received 26 July 1996.
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|Author:||Venuto, B.C.; Elkins, W.M.; Hintz, R.W.; Reed, R.L.|
|Date:||Jul 1, 1997|
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