Adaptation of chickpea to desiccation stress is enhanced by symbiotic rhizobia

This study examined the influence of three inoculant strains of Bradyrhizobium japonicum (Thal-8, Tal 620, Dulawala) on the ability of chickpea (Cicer arietinum (L.) to adapt to drought-stress. Strain Thal-8 was most effective in the root-nodule symbiosis and also partially alleviated decreased growth and yield imposed by drought stress. Strain Thal-8, in pure culture, also produced higher amounts of gibberellic acid (GA) and indole-3-acetic acid (IAA) and lower amounts of abscisic acid (ABA) than the other two test strains. Thal-8 increased the root biomass, GA and IAA contents of leaves of chickpea plants, including ICC 4948NN, a non-nodulating line. These results are consistent with the hypothesis that GA and IAA is produced by the Thal-8 strain and/or elevates levels of these phytohormones in chickpeas. This contributes to its high performance as a nitrogen-fixing microsymbiont. The growth-promoting response evoked by different strains of Bradyrhizobium correlated with higher ratios of GA and IAA relative to ABA phytohormones in the plants.