SIDEROPHORE PRODUCTION IN RELATION TO N-2 FIXATION AND IRON UPTAKE INPIGEON-PEA RHIZOBIUM SYMBIOSIS

Thirty-one bradyrhizobial and rhizobial strains infecting pigeon pea w ere screened for siderophore production using Chrome Azurol S (CAS) ag ar plate as well as a CAS assay solution. Of a total of 31 strains onl y 23 showed siderophore production. Of the 23 siderophore-positive str ains, 21 strains showed the production of hydroxamate while 6 strains showed the presence of catechol type of siderophore. A large variation in the quantity of hydroxamate and catechol produced by different rhi zobial strains was observed (1.03-3.73 mu g hydroxamate N per mg prote in; 0.19-3.43 mu mol/L of catechol per mg protein). Maximum nodule bio mass was produced by strain PP-11 (CC-1020); strain G-14 formed minimu m nodule biomass. Nitrogen contents of low, moderate and high sideroph ore-producing strains were 11.4, 15.4, 20.9 mg per plant, respectively , iron contents were 1445, 1768 and 2003 ppm, respectively. Siderophor e production was related to N-2-fixing efficiency.