Evaluation Of Effectiveness Of Rhizobia Isolates From Rwandan Soils On Common Bean (phaseolus Vulgaris)

Abstract

The overall objective of this study was to identify superior strains of native rhizobia associated with beans and establish their suitability for use as bean inoculants. Greenhouse and field experiments were conducted to identify and evaluate the effectiveness of rhizobia isolates in Rubona/Huye and Ruhunde/Burera, both located in Rwanda. The first greenhouse experiment was conducted to evaluate the potential of 174 rhizobia isolates. Accordingly, 50 rhizobial isolates were found to be promising. The 50 rhizobial isolates were tested in a second greenhouse experiment and 5 isolates were identified as the most effective. The five isolates were: NAR 265,NAR 151, NAR 139, NAR75 and NAR 206 and they compared favorably with the standard commercial strains, CIAT 899 and UMR 1597. These five best strains were then evaluated in the field using the bush and climbing beans. A complete randomized block design with three replicates was employed. The findings showed that NAR 265 is the most effective elite native strain, followed by NAR 139. The other objective of this study was to investigate the effect of inoculation on susceptibility of the legume host to disease resistance. CIAT score technique was used to score the symptoms of diseases on common bean. The results showed that the severity and incidence on bean diseases were low for anthracnose, ascochyta, angular leaf spot, rusts, root rot and CBMV. A similar result was also shown on crop bean fertilized with nitrogen and crop bean inoculated with CIAT 899, NAR 265, NAR 139 and UMR 1597. The severity and incidence was however high for bean crop without inoculation or not fertilized on bush bean. The study concluded that the improved nodulation, both in the field and green house trials was influenced by the variety of bean used.