VARIABILITY AND INTERACTION IN THE Pisum sativum L. — Rhizobium leguminosarum SYMBIOSIS

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Abstract
Symbiotic N fixation was examined in 36 plant genotype-bacterial strain combinations produced by growing 6 genotypes of P. sativum L. and 6 strains of R. leguminosarum in all combinations. Both genotypes and stains had effects not only on N fixation but also on characters associated with plant growth and photosynthesis. However, relationships between characters differed markedly depending on whether genotype or strain means were use dto calculate correlation coefficients. Genotype .times. strain (G .times. S) interactions also affected the expression of several of the characters. Using N fixation as an example, statistical methods analogous to those developed for the analysis of genotype .times. environment interactions were used to study this interaction. G .times. S variability was mainly caused by differences in the magnitude of the response of plant genotypes or bacterial strains to changes in the complementary symbiont with little difference in the stability of this response. An examination of different indicators of performance, response and stability of that response suggests that both plant genotypes and bacterial strains could be selected for relatively uniform fixation over a range of symbiotic partners, or that specific combinations could be selected for maximum symbiotic effectiveness.