TD Phillips; JC Wynne; GH Elkan; TJ Schneeweis
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Abstract: Improving the host genotype is one method of increasing biological nitrogen fixation by Bradyrhizobium in symbiosis with peanut (Arachis hypogaea L.), but host-strain interactions also must be considered. The objectives of this study was to estimate the effect of Bradyrhizobium strains on the inheritance of traits related to nitrogen fixation. Eight parents and the F1 generation of a diallel cross were evaluated in symbiosis with two bacterial strains for combining ability in a factorial arrangement in the greenhouse. The parents represented three taxa of cultivated peanuts. The two Bradyrhizobium strains NC 92 and NC 123 produced different General and specific combining ability, maternal (reciprocal General) effects, and reciprocal specific effects for the host genotypes. With strain NC 92, the peanut cultivars NC 7 and NC Ac 2821 had the best General combining ability for all traits evaluated; while, with strain NC 123, Robut 33-1 exhibited a high General combining ability (GCA) for nitrogenase activity and specific activity. Genotype NC Ac 2821, when inoculated with strain NC 123, had a negative GCA effect for nodule number, while with strain NC 92 this cultivar had the highest GCA effect. The importance of strain selection in evaluating lines in a breeding program is discussed.