Evaluation of heterotic patterns in diverse sorghum hybrids

Abstract

In the past, sorghum hybrids have been produced largely of kafir and durra crosses, facilitated by the milo-kafir male sterility system. Exclusive reliance upon the durra-kafir hybrids fails to utilize the great diversity of sorghum varieties, perhaps overlooking hybrid combinations which produce better heterosis or other agronomic traits. Dependence upon a single cytoplasm (from milo sorghums) creates increased disease vulnerability. The creation of new male sterility systems greatly increases the diversity of sorghum varieties which can be used to produce hybrids. This experiment evaluated a large number of hybrids produced from diverse parents, and attempted to determine which combinations of "working groups" provide the greatest heterotic expression. The study utilized 12 female inbred lines from three cytoplasmic sterility groups (5 = A3, 3 = A2, 4 = Al), 9 male lines from the TAES-USDA Sorghum Conversion Program, and the 108 hybrid combinations of female x male. Three replications of this set were grown during the 1993 season in each of three locations in Texas: Corpus Chrisfi, College Station, and Halfway. Parents and hybrids were evaluated for various agronomic traits, and from these combining ability and percent heterosis were calculated. In general, hybrids were significantly taller, had longer and more exserted panicles, reached anthesis earlier, and produced greater seed test weights and yields. Although total means for grain yield of parents and hybrids were only 3368.60 kg/ha and 4958.50 kg/ha, respectively, several hybrids attained yields over 10,000kg/ha. Stands at Corpus Christi and College Station were poor for many entries. Parents producing the highest yielding hybrids were A3Tx433, A,Tx632, A2Tx636, SC175-14.E and SC330-14E. Nine of the twelve SC330-14E hybrids were in the top 21 of the 108 hybrids when ranked by yield, and an SC330-14E hvbrid had the highest yield (13,767 kg/ha). Percent heterosis ranged from-85.01 to 235.20 %. Evidence exists in combining ability and percent heterosis scores to suggest the presence of heterotic "patterns" among the hybrids. Hybrids of less closely related parents demonstrated better heterotic effects than those of related groups. The Caffrorum working group demonstrated strong heterotic effects with Zerazera, Caudatum/Kaura, Nigricans/Feteiita, and Nigricans groups, and these should be used in the production of hybrids with Al females. Nigricans/Feterita cultivars were shown to produce exceptional yields and strong heterosis with Caudatums. Females of the A2 sterility system displayed good heterosis when bred with Caudatum/Kaura, Zerazera, and Nigricans/Feterita males. Males from groups Caudatum, CaudatunVKaura, and Durra/Dochna had high heterotic effects with A3 females. The heterotic patterns discerned in this study should facilitate the utilization of hybrid vigor in producing successful hybrids. New hypotheses may be developed to further evaluate the patterns suggested by this study.