Distance Statistics and Interpretation of Southern States Regional Soybean Tests
The failure of genotypes to respond similarly to different environmental conditions, genotype environment (GXE) interaction, is an important aspect of genotypic stability. The objectives of this paper were to develop distances based on concepts of genotypic stability and to interpret regional soybean [Glycine max (L.) Merr.] tests based on these distances. Distances increased in relation to differential responses among sites for two genotypes or among genotypes for two sites. They were designed to evaluate the importance of region of origin in determining genotypic responses, the similarity of selections arising from different breeding programs, and the comparability of sites in regional testing. Seed yields for the Uniform Soybean Trials, Southern States, Maturity Groups V and VI, 1981–1991, were evaluated. Region of origin for genotypes did not have a major impact upon the nature of genotypic responses; however, genotypes from all regions showed less differential responses when tested at sites in the East Coast Region. The Group V selections from the North Carolina, Maryland, and Virginia breeding programs were more similar than selections from other breeding programs. Group VI selections from the Missouri program responded differently to environments than Group VI selections from other programs. The Plymouth, NC, Clemson, SC, and Athens, GA, test sites had similar relative seed yields among genotypes. A central belt of comparable sites extended from Virginia, North Carolina, South Carolina, and northeast Georgia to the mid and upper Delta Region. A northern belt of comparable sites covered Delaware, Maryland, western Virginia, Kentucky, upper Delta, and southeastern Kansas. The Tennessee sites were intermediate to these two belts. Sites in northwestern Georgia and northern Alabama and the remaining sites in the southern tier of states gave heterogeneous genotypic responses. Comparable sites that represent areas within this region were not found. Genotypes with unique local adaptations would be required.
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