Effects of genotype x bradyrhizobium inoculation or x fertilizer n interactions on genetic gains while selecting in soybean

Abstract

Introduction of soybe.an (Glycine 1n/l.X (L.) Merr.) to environments where it was not previously produced sometimes occurs without successful introduction of the symbiont, Bradyrf1izobiumjapo11icum (Kirchner) Buchanan. Plant breeders working in such environments need to kno\v whether relative performance of soybean genotypes is affected by the presence or absence of B. japonicum. Tbe primary objective of these studies was to assess genotype x inoculation interactions and expected genetic gains for a soybean population grown with and without inoculation on a soil free of B. japonicum. A second objective was to determine whether the response of soybean genotypes to N depend on the source of N (fertilizer or symbiotic fixation). A set of 52 random lines from a broad-based reference population was evaluated for 2 years with and without B.japonicum inoculation in a split-plot design. Inoculation increased protein content and lodging and decreased oil content. Genotype x inoculation interaction was significant only for protein and oil content in one year. Expected genetic gains were similar with and without inoculation. A second set of 12 genotypes was evaluated for 2 years in ll similar design but with N fertilizer applied as a third N treatment. There were no significant differences among N treatments for any trait. Genotype x inoculation interaction occurred for yield, but not for other traits. Genotype x inoculation interaction for seed yield and composition may occur in some environments but is not a major constraint to genetic gain.