Modified Seed Maturation Rates and Seed Yield Potentials in Soybean
Seed embryos of soybean [Glycine max (L.) Men-.] genotypes can have different levels of specific dry matter accumulation rate (SDMAR) and specific seed density (SSD) under greenhouse growing conditions, but the relevance of these measures for field-grown plants is not known. The objectives of this research were to interrelate these measures as they reflect characteristics of the developing soybean seed and to determine their association with seed-yield potential. As the seed matured, SSD increased ⊄0.01 g cm−3 d−1. Differences in this rate of change were positively associated with SDMAR. Genotypes selected for increased, as compared with decreased, seed-filling duration had lower SDMAR and lower rate of change in SSD (decreased seed maturation rate) and greater seed yield under favorable field conditions. However, the yield advantage was lost under environments having drought stress during the reproductive period. Selections for high seed protein content exhibited an apparent increased seed-maturation rate and a reduced seed yield. Divergent selection for SSD produced major shifts in SSD at the 55% seed-filling stage. In contrast, the modified reproductive period selections and the seed protein selections had only secondary differences for SSD at that seed-filling stage, indicating that the low SSD selections initiated delayed seed maturation at an earlier stage of seed development. While the low SSD selections had the reduced seed-maturation rates, they did not express the expected yield advantage. Under drought stress, they exhibited lower seed number and seed yield than the modified reproductive period and high SSD selections. The stage of maturity for initiating delayed maturation appeared important. The proposed desirable genotype maintained specific dry matter accumulation rate during early seed fill but shifted to reduced seed maturation rate at a later stage of seed development.
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