Symbiotic and phenotypic characterization of Rhizobium isolates of field pea (Pisum sativum L.) Fabaceae, from central and southern Ethiopia

Abstract

A total of 25 rhizobial isolates from field pea (Pisum sativum L.) were collected from Shewa, Gojam, Gondar, Wollo and Tigray, and authenticated as root nodule using the trap host. They showed significant variations in their symbiotic effectiveness in nitrogen fixation and enhancing growth of the pea cultivar Markose plants compared to the uninoculated and non-fertilized control plants on sand culture under greenhouse conditions. Although there was inter-site difference in harbouring effective and very effective isolates ranging from 86% (Tigray) and 67% (Gondar) in terms of shoot dry matter accumulation of 50-100%, on the average 76% of the pea rhizobial isolates in the soils of major growing areas in the country were effective and very effective. The inoculated plants also showed differences in total nitrogen contents in the range of 1.72% and 2.93%. These isolates were then characterized based on their cultural, physiological and ecological features in relation to their symbiotic characteristics. The isolates showed diversity in their eco-physiological tolerance (NaCl, pH and temperature) inherent resistance to antibiotics and heavy metals, and heterotrophic competence of utilization of 17 carbon sources. Consequently, isolates NSRlFP1, NSRlFP3, NSRlFP13, NSRlFP17 and NSRlFP18 were the elite rhizobia that can be selected and further tested for their genetic and symbiotic performance in field trials for future bio-inoculant formulation.

Key words/phrases: Antibiotic resistance, Eco-physiological tolerance, Heavy metal resistance, Symbiotic effectiveness.