Genotype x planting date interaction and selection of early maturing soybean genotypes

Maturity group (MG) IV soybean [Glycine max (L.) Merr.] cultivars can produce acceptable yields in April through late-June plantings in the mid-south. Seed quality from early plantings is often poor, thereby requiring use of late-June-planted seed quality nurseries for seed producers and breeders. This range of planting dates may produce genotype x planting date interactions (GDI). Our objective was to characterize the extent and potential impact of GDI on MG IV cultivar development. Twenty-seven indeterminate and nine determinate MG IV genotypes were planted in mid-April, May, or late-June in 1992, 1993, and 1994 in Arkansas. Data were collected on yield, height, number of main stem nodes, and days from planting to maturity. The GDI was significant only for height, number of nodes, and days to maturity for comparison of indeterminate lines in April vs. June plantings. There were no significant and repeatable genotype rank changes between planting dates for any trait: no planting date specific adaptation was noted for any genotype or growth habit. Heritability of seed yield, plant height, and number of nodes of indeterminate genotypes was generally greater from April or May plantings than from June plantings. The genetic correlation of plant height or number of nodes with overall yield was generally also greater from early plantings than from late plantings. Yield gain from indirect selection for increased height or node number was greater when the selection was conducted from early plantings vs. late plantings. Our results indicated a selection advantage from early plantings of MG IV indeterminate genotypes.