Heterosis, inbreeding depression and combining ability in sorghum (Sorghum bicolor (L.) Moench)

Heterosis, inbreeding depression and combining ability were studied in a 6 X 6 diallel (excluding reciprocals) from F₁ to F₄ generations for grain yield and its five components in sorghum (Sorghum bicolor (L.) Moench). Among the different characters studied, highest heterosis in F₁ over better parent (87.5%) was recorded for grain yield/plant followed by number of grains/panicle (50.1%) and number of primaries/panicle (40.5%). All the hybrids which showed higher estimates of heterosis in F₁ in general also exhibited high inbreeding depression in F₂ and other segregating generations studied. The general (gca) as well as specific combining ability (sca) variances were found significant in all the four (F₁-F₄) generations for grain yield and its components studied except for number of primaries/panicle in F₃ and F₄ and for number of whorls/panicle in F₂ and F₃ generations. The magnitude of scavariance declined in F₂ and later generations. The predictability ratio showed preponderance of nonadditive genetic variance for grainyield and additive genetic variance for 1000-grain weight in sorghum. The study of F₁ and F₂ would be sufficient to assess repeatability of gca effects in advance generations. Fourcross combinations,viz SPV 451 X SPV 474, SPV 474 X IS 508, CSV 10 X SPV 451 and CSV 10 x SPV 474 were identified as promising, which can be exploited to improve grain yield in sorghum.