Combining ability and heterosis studies for adaptation in newly developed male and female inbreds of sorghum, Sorghum bicolor (L.) Moench

Typescript (photocopy).New elite inbred lines derived from crosses involving genetic material from the Sorghum Conversion Program were evaluated for combining ability and agronomic performance at four diverse locations across Texas. Entries were classified as tropical adapted (TA) or temperately adapted (TE) on the basis of a laboratory test (G50). Heterosis, phenotypic correlations, grain yield stability, and the relationship between G50 and seedling emergence at two constant soil temperatures also were studied. Mean square ratios indicated a decided preponderance of GCA effects in all traits except seeds per panicle and panicle length. SCA effects also were significant in the expression of grain yield and yield components. A3, A15, A7, A14, and A5 were the most important females, while the male 76CS490 contributed most to SCA. Manifestations of heterosis for grain yield seem dependent on seeds per panicle and panicle length. As a group, the mean of TA and TE hybrids when combined over all TA and TE females, differed significantly for G50. For grain yield, this situation was reversed (0.10[less than or equal to]P[greater than or equal to]0.05) at Weslaco while at Thrall and Halfway GCA (TE females) significantly exceeded (P[less than or equal to]0.05) the GCA (TA females). Differences of 18.85 and 20.37% at Weslaco and of 14.14 and 10.32% at Halfway were observed between the highest yielding TA and TE hybrids with one female and male parent in common, respectively; indicating a relationship between G50, yield, and adaptation. GCA effects (TA females) was larger than that for GCA effects (TE females) for grain yield, panicle exsertion, and threshing percent. Relationships detected between G50 and various agronomic characters, especially for grain yield, seeds per panicle, days to 50% anthesis, threshing percent, and green leaf number, confirm the importance of base temperature as an adaptation character. The expression of traits in TA and TE genotypes indicated that they can be genetically manipulated. Tropically adapted hybrids were the most stable group in this experiment. Data indicate that the smaller the G50 value (TA) of those sorghums investigated, the greater the seedling emergence at both soil temperatures. These relationships suggest a possible link between G50, emergence, and adaptation