At Least Three Loci Encode the Leaf-Curl Phenotype in Rhizobium Strain IC3342

Abstract

Pigeonpea, an important grain legume crop in the semi-arid tropics, is nodulated by cowpea group rhizobia. Nodulation by the fast-growing Rhizobium strains, IC3342 and IC3324, causes pronounced curling and deformation of leaves (Kumar Rao et al., 1984). The symptoms appear first on the third developing trifoliate leaf bud which bends outwards, followed by hypernasty, reduced leaf expansion, suppression of apical dominance, sprouting of axial buds, and generally stunted growth. These strains also effectively nodulate siratro (Macroptilium atropurpureum) and Desmodium causing leaf-deformation, and ineffectively nodulate Lathyrus sativus, Phaseolus vulgaris and Arachis hypogaea without symptoms. Grafting and sap feeding studies indicate the production of curl-inducing principle in nodules or roots and translocation through the sap to the leaves (Upadhyaya et al., 1985). We report on genetic analyses of strain IC3342 aimed at identifying the genes involved in curl induction and their relationship to nodulation and nitrogen-fixation.