| Abstract: | The effectiveness of early generation testing for combining ability for grain yield in grain sorghum restorer lines was studied at College Station, Texas. Two well-known restorer lines, Tx 7078 and Tx 09, were crossed and resulting F₂, F₄, and F₆ segregates were evaluated for combining ability. In the F₂ population, 70 F₂ plants were crossed to each of four male-sterile lines, A Tx 3197 (Combine Kafir-60), A Tx 398 (Martin), A Tx 378 (Redlan), and A Tx 3048 (Redbine sel.). These "F₂ hybrids" were grown in a replicated test in 1962. Based on the mean yield of the four hybrids with each F₂, 12 high- and 12 low-combining F₂'s were selected for advancement to the F₄ generation. The F₄ lines from each of these 24 selected F₂'s were crossed to each of the same four male-steriles and the hybrids tested in 1963. Three high- and three low-combining F₂ families were chosen for further study in the F₆. The F₆ lines were crossed to each of the same four male-steriles and the hybrids tested in 1964. By comparing, within families, the yield of "F₂ hybrids" with the yield of "F₄ hybrids" and "F₆ hybrids", the effectiveness of early generation testing for combining ability was estimated. High-combining F₂'s produced F₄ lines and F₆ lines that were significantly higher in combining activity than the F₄ and F₆ lines derived from low combining F₂'s. Correlation coefficients for yield between "F₂ hybrids" and "F₄ hybrids", "F₂ hybrids" and "F₆ hybrids", and "F₄ hybrids" and "F₆ hybrids" were generally large, positive, and significant. There was a close relationship between yield of "F₂ hybrids" and hybrids with subsequent F₄ and F₆ lines. This indicated that the performance of hybrids with F₂ pollinators was reliable in predicting performance of hybrids with subsequent F₄ and F₆ lines. For the sorghum lines in this study, early generation testing for combining ability was very effective.. |
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