NATURAL CROSS-POLLINATION OF 12 SOYBEAN CULTIVARS IN ARKANSAS

Previous experiments have shown that some cross-pollination (usually <1%) occurs in soybean [Glycine mar (L.) Merr.] under field conditions. Information is needed on a broader spectrum of germplasm to determine if genotypes differ significantly for this trait and should be managed differently to produce genetically pure seed in small plots bordered by other genotypes. Twelve soybean cultivars differing in maturity were evaluated during two growing seasons to determine the extent of cross-pollination under field conditions where both honey bees (Apis mellifera L.) and indigenous insect populations were present. Flower color, pubescence color, and quintafoliolate leaves were used as genetic markers to measure extent of cross-pollination when plants were grown in adjacent rows 102 cm apart. In maturity group (MG) IV, cultivars did not differ significantly (P > 0.05) for percent cross-pollination in 1990, but were different in 1991 and when the 2 yr were combined. 'Competitor' was significantly higher for percent cross-pollination (1.22%) than the other cultivars within this MG. Cultivars within MG V and VI differed significantly in 1990 but were not different in 1991. Based on a 2-yr average, cross-pollination varied from a low of 0.09% for 'Walters' to a high of 1.63% for 'Brim'. Results show that cultivars differ significantly (P > 0.05) in the extent of cross-pollination and as much as 2.5% outcrossing may occur in MG IV, V, and VI cultivars in some environments where adequate pollinators are present and other conditions are favorable. Based on these results, soybean breeders should use greater isolation of initial progeny rows and breeder seed of a new cultivar than has commonly been used in the past because of the increased potential for outcrossing of some cultivars.