Stability of Grain Sorghum Yield Components Across Diverse Environments1

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Abstract
Yields and components of yield of stable and unstable grain sorghum [Sorghum bicolor (L.) Moench] genotypes were evaluated across diverse environments in Nebraska and Kansas in 1978 and 1979 to determine the mechanisms importan to yield stability. From 56 genotypes, three stable and three unstable F1 hybrids were chosen for detailed evaluation across 14 environments. Mean yields of the six hybrids ranged from 9,840 to 5,410 kg/ha, and measured yield components included plants/m2, heads/m2, tillers/plant, seeds/m2, seeds/ head, and seed weight. Although all six hybrids had comparable yield potential in good environments, the stable types were higher yielding in poor environments; thus, the three stable genotypes (with regression of genotype yield on environment mean yield < 1.0) showed that high yield potential in favorable environments and yield stability were not mutually exclusive. In all genotypes, heads/m2 and seeds/ head increased with improved environments, and seeds/m2 correlated closely with yield/ha. There was no correlation between heads/m2 and seeds/head, suggesting in these environments that both were important to yield but were not inversely related. The compensation ratio relating change in seed weight to change in seed number [(b of seed weight)/(b of seeds/m2)], was three to seven times higher in stable than in nonstable genotypes. The stable hybrids had 40% more seeds/ m2 than nonstable hybrids under poor environments. This only partially explained their 70% yield advantage the balance was accounted for by seed size. Sorghum hybrids differ in capacity for yield stability across environments. In this study, the most stable hybrids maintained heads/m2, seeds/head, and seed weight in poor environments. Tolerance of stable genotypes to stress conditions and the maintenance of all yield components at relatively high levels appeared more important than compensation among the components. Breeding for more seeds/head and greater seed weights would be useful according to this evidence. Consistently higher seed weights of stable types seemed to contribute to yield and to stability.

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