Evaluation of Extremophilic Bacteria from Lakes Bogoria and Magadi for Biocontrol of Fusarium Solani and Rhizoctonia Solani in Phaseolus Vulgaris L.

Abstract

Common Bean (Phaseolus vulgaris L.) is some significant vegetable crop rich in protein, carbohydrates, and Vitamin B complex, used as a source of protein or cooked as a vegetable. It is associated with improving capillary resistance, inhibiting inflammation and act as an anticancer. Common beans face a major challenge of pests and disease hence lowering production yield. Some of the diseases are root rot triggered by Rhizoctonia solani and Fusarium solani. Application of chemical products and cultural practices are not effective in managing these diseases. Therefore, a sustainable, affordable, and effective control method needs to be devised to minimize the effect of bacterial plant diseases on the quality and quantity of bean yield. The use of bio-control agents is hypothetically self-sustaining, provides a non-target approach, spreads on its own, and is environmentally friendly. This study evaluated the biocontrol potential of extromophilic bacterial isolates from Lakes Bogoria and Magadi for against Fusarium solani and Rhizoctonia solani pathogens in beans. To explore biocontrol frontiers, a total of 110 bacteria were isolated from water, sediments, and soil of both lakes. Their antifungal properties were determined by co-culturing analyzed using SAS (ANONA) were; 17 (34.7%) isolates from L. Bogoria and 25 (41%) isolates from L. Magadi had varying mycelium inhibition rate for both Fusarium solani and Rhizoctonia solani. The characterization of the bioactive isolates revealed that 84.2% were Gram-positive and 15.8% were Gram-negative. The graphical analysis of bacterial isolates grew well at pH 7.0 and 8.5 though there was recorded growth in pH 5.0 and 10.0. In terms of temperature, the optimum temperature recorded was 30-35ºC with optimum salinity of 0-0.5M NaCl. The bioactive isolates were assayed for their ability to produce secondary metabolites whereby; most of the isolates produced phosphatase, pectinase, chitinase, protease, Indole-3-acetic acid and Hydrogen Cyanide making them potential biocontrol agents. Analysis of the partial sequence using BLASTn indicated 84.2% of the isolates were affiliated to Bacillus spp and 15.8% were affiliated to members of Gammaproteobacterial. Isolates B7, B11, B20, B21, B26, B29, B30, B32, B38, B39, M9, M10, M16, M47, M50 and M60 clustered with Bacillus at 98.71-100% similarity index. Isolates B12, B17 and B19 clustered to Gammaproteobacterial with 99.59-100% similarity index. In assessment for the selected isolates in greenhouse experiment, seed bio-priming showed significant change in terms of root mortality, germination rate, plant height, plant biomass, chlorophyll content, Phenylalanine ammonia-lyase, Polyphenol oxidase, Peroxidase and phenolic content compared to pathogen inoculated controls. In conclusion, lakes Bogoria and Magadi harbors beneficial microbes that can be used as biocontrol agents against Fusarium solani and Rhizoctonia solani.