Comparison of F 1 's and Inbreds as Female Parents for Sorghum‐Sudangrass Seed Production 1

Two field studies involving different groups of germplasm were conducted to compare sorghum-sudangrass, Sorghum bicolor (L.) Moench X S. sudanense (Piper) Stapf, hybrid seed production of male-sterile FI's with their component A·lines. The FI's yielded 45 and 82% more grain than their A·line counterparts in Study I and 2, respectively, with the increase attributable to more seeds per panicle and a greater threshing percentage. Mean values of nine traits measured on nine groups of eight FI's in Study I and seven groups of six FI's in Study 2 were compared with their respective A·lines. All groups of FI's significantly outyielded their A·line counterparts in both studies except for A·line N35 in Study 1. Phenotypic correlations of yield and seeds per panicle were high in both A·lines and FI's in both studies, as were the correlations of yield and threshing percentage except for the FI's in Study 1. Application of these findings should facilitate the production of higher yields of sorghum-sudangrass hybrid seed at reduced cost per unit of seed. The best FI's to use and the magnitude of their superiority over A·lines will be influenced by the location in which seed is produced. Additional indexwords:Sorghum bicolor (L.) Moench, Sorghum sudanense (Piper) Stapf, Single-cross hybrids, Three-way hybrids. SORGHUM-SUDANGRASS, Sorghum bicolor (L.) Moench X S. sudanense (Piper) Stapf, hybrids are grown extensively to provide supplementary forage for animals as pasture, silage, or greenchop. These hybrids play an important role in the management plans of many livestock producers, particularly in drouth-prone regions such as the Great Plains. In a 1977 survey by Harvey (I), 81.5% of the commercially produced sorghum-sudangrass hybrids in the United States were F I 's, with 'Redlan' grain sorghum being the preferred male-sterile and 'Greenleaf sudangrass the most often used pollinator. Also, three-way cross hybrids made up I I% of the total seed production of sorghums and sudangrasses used for forage compared with less than 2% in grain sorghum (I). Despite this rather extensive use of three-way crosses in forage and sudangrass hybrids, only two preliminary reports were found in which the seed production of three-way and single cross hybrids was compared. In a I-year study of seed production of sorghum-sudangrass hybrids in Hungary (3), seed yields of F I male steriles were greater and production was more dependable than for Alines because the F1's matured earlier, but comparative seed yields of three-way and single cross hybrids were not presented. In Japan (6), four grain sorghum A-lines, six grain-sorghum male-sterile F I 's and six sorgo male-sterile F I 's were used in a comparative I Contribution of USDA-ARS and the NebraskaAgric. Exp. Stn. Published asPaper no. 7415, Journal Series, Nebraska Agric. Exp, Stn., Lincoln. Research was conducted under Nebraska Project no. 12-114. Received 29 Feb. 1984. 2 Supervisory research geneticist, USDA-ARS; research technologist inagronomy;George Holmes professorof agronomy; and research geneticist, USDA-ARS, Lincoln, NE68583, respectively. study of seed production of forage sorghum hybrids. Seed weight per head on the grain-sorghum malesterile F I 's was slightly lower than for the A-lines, while seed weight per head on the sorgo male-sterile F I 's was substantially greater than on either of the other two female types. Seed yield per land area was not given. The A-lines used differed in each of the three groups of material, and seed weights of F I 's could not be compared with those of their component A-lines. Although published information on comparisons of three-way with single cross forage-type hybrids is limited, more extensive literature is available for grain sorghums as indicated in a recent report (2). The objectives of this study were to I) compare seed yield and other agronomIC traits between malesterile F I seed parents and their component A-line seed parents in the production of sorghum-sudangrass hybrids in two different groups of germplasm, 2) determine phenotypic correlations among traits within parental groups, and 3) relate the findings to hybrid seed production. Evaluation of the hybrid seed produced in terms of forage production will be reported in a subsequent paper. MA TERIALS AND METHODS The seed parents used in Study 1 were nine combineheight cytoplasmic male-sterile A-lines and their 36 malesterile AX B-line crosses (FI'S) that were identical to those used in a similar study with grain sorghum hybrids (2). The A-lines included KS4, KS23, 'Martin', N30, N35, N36, N38, WD4, and 'Wheatland'. In Study 2, the seed parents were seven A-lines and their 21 male-sterile F t's. The A-lines were KS5 and KS9, described by Ross et al. (4); N38 and N48, described by Ross et al. (5); N4692, described by Webster et al. (7); N50I3, an experimental line; and the cultivar Redlan. The pollen source was produced from a composite of equal seed weights of the sudangrass cultivars Greenleaf and 'Piper', Nebraska 7035, and experimentallow-dhurrin strains of Greenleaf and Piper. This heterogeneous pollen source assured continuous and adequate pollen dispersal to the female parents over the range of their stigma receptivity. The sudangrass composite was seeded in double rows, with six rows of male-sterile sorghums being grouped between each pair of sudangrass rows. The outside rows of each group of six male-steriles were seeded to cytoplasmic male-sterile 'Combine Kafir-60', which served as unharvested border rows to minimize any effect of the taller sudangrass rows on the four randomly assigned male-sterile lines and F I hybrids that were harvested in each group. The experiments were planted 29 May 1979 and 27 May 1980 at the University of Nebraska Field Laboratory, Mead, in a medium textured Sharpsburg silty clay loam soil (fine, montmorillonitic, mesic Typic Argiudoll) to which 112 kg haI of N had been applied. Four replications of singlerow plots 7.6 m long and 0.76 m apart in a randomized complete block design were used each year. All plots were overseeded and thinned to 15 em between plants, giving a plant population of about 87 000 plants ha1• The exper1134 Published in Crop Science (November-December 1984) v.24, no. 6