Use of Rhizobia in the Integrated Control of Root Rot disease of Crop Plants

Abstract

Root rot disease caused by Macrophomina phaseolina, Rhizoctonia solani and Fusarium spp, produce losses to crop plants and adversely affect the agricultural economy of a country. Among the various soil macroorganisms rhizobia the nodule producing bacteria which fix atmospheric nitrogen in association with leguminous plants was found to inhibit the growth of many root infecting fungi both in vitro and in vivo. In a previous study 32, rhizobial strains either isolated from root nodules of leguminous plants or obtained from different culture collection when tested in vitro showed growth inhibition of root infecting fungi. Selected rhizobial strains used alone or with fungicides, fertilizers, organic amendment and plant growth promoting bacteria showed promising results in the control of root rot pathogens in vivo. In the present study, 7 more rhizobial strains were isolated from Melilotus alba, M. indica, Medicago sative, Sesbania aegyptiaca, Phaseoulus lunatus and Trifolium alexandrinum and identified. In dual culture plate assay, one strain of R. meliloti inhibited the growth of Macrophomina phaseolina, Rhizoctonia solani and Sclerotinia sclerotiorum and produced zone of inhibition. Other strains showed variation in their antagonistic activity towards different pathogens. Cultures of R. Trifolli (KUCC 842 & KUCC 843 Trifolium isolate), R. meliloti (KUCC 845 Melilotus isolate) and Bradyrhizobium sp. (KUCC 840 Sesbania isolate) used as seed dressing and or as soil drench significantly (p˂0.05) reduced F. solani and R. solani infection on sunflower, mungbean and mashbean and showed an increase in plant height and fresh weight of shoot. Use of Bradyrhizobium isolates KUCC 811, KUCC 818, KUCC 819, KUCC 821, KUCC 823, KUCC 824, KUCC 839 and R. meliloti (KUCC 139 and KUCC 815) as seed dressing and or soil drench significantly (p˂0.05) reduced M. phaseolina, and R. Solani infection on okra and chickpea. Some rhizobial strains also enhanced plant height and fresh weight of shoot. In field trials R. phaseoli, R. trifolli and Bradyrhizobium sp. significantly (p˂0.05) reduced M. phaseolina, F. solani and R. solani infection when used as seed dressing and or as soil drench. Rhizobial strain also enhanced plant growth. Use pf rhizobia with Pseudomonas aeruginosa plant growth promoting bacteria showed better control of M. phaseolina and F. solani infection on mash bean than either used alone. Rhizobia used with other biocontrol agents viz, paecilomyces lilacinus, Memnoneilla echinate, Trichoderma harzianum and Stachybotrys atra showed significant control of M. phaseolina, R. solani and F. solani infection on chickpea. Use of rhizobia with P. lilacinus and S. atra produced greater plant height in mash bean. Rhizobia with P. lilacinus showed better control of F. solani infection on sunflower. Similarly, R. solani infection was reduced where rhizobia were used with T. harzianum, M. echinate and S. atra with maximum fresh weight of shott produced with P. lilacinus. Use of rhizobia with Stoechospermum marginatum, seaweed @ 20 g/ 1 meter row showed better control of M. phaseolina and R. solani infection in 90 days mungbean plant and produced greater plant height and fresh weight of shoot in 45-day old plant with greater number nodule per plant. Rhizobia with S. marginatum @ 20 g/ 1 meter row showed better control of M. phaseolina infection in 45-day old cotton plants. Use of seaweed alone or with rhizobia also significantly enhanced growth of cotton plant. Another seaweed Sargassum tenerrimum was more effective @ 60 g/ 1 meter row against M. phaeolina and @ 20 g/ 1 meter row with rhizobia against F. solani. Rhizobia used alone or with S. tenerrimum also significantly enhanced growth of mungbean and cotton plant. Use of rhizobia with organic amendment seems promising.