Characterization of selected rhizobia as potential inoculants for crop legumes in South Africa

Abstract

Rhizobia are Gram negative bacteria that facilitate biological nitrogen fixation in association with plant hosts. These organisms have two main lifestyles, they can be either endophytic (associated with plants) or free living (non-symbiotic). There are several factors that mediate the legume-rhizobium symbiosis such as flavonoids excreted by the host legume, Nod factors produced by the rhizobia, and host immunity. These factors play a significant role in determining host specificity and whether nodulation by the rhizobia will occur. Whereas a number of legumes only interact with a few selected rhizobial species. There are legumes such as cowpea, common bean and siratro that are labelled as promiscuous hosts. These legumes can interact with diverse rhizobial species belonging to several genera and in some instances even from the two different classes, the Alpha- and Beta-proteobacteria. The objective of this study was to investigate interactions of different economically important agricultural legumes with diverse native, naturalized, or non-native rhizobia under glasshouse conditions.