Isolation and characterization of rhizospheric microorganisms from bacterial wilt endemic areas in Kenya

Abstract

Ralstonia solanacearum is a soil-borne bacterium causing bacterial wilt, particularly in Solanaceae crops, including tomatoes. Due to pathogen’s wide host plant range, pesticide resistance, and ability to overcome cultivars utilized for innate resistance, not even a single measure is effective against the pathogen. Screening the rhizosphere of bacterial wilt tolerant tomato plants from Bomet, Kiambu, Kajiado and Kirinyaga regions of Kenya for beneficial bacterial and fungal isolates was done using nutrient agar and potato dextrose agar, respectively. Morphological, biochemical, and microscopic characterization to identify the genus of fungal and microbial isolates revealed a total of 41 bacterial and 42 fungal isolates distributed as Bomet>Kiambu>Kajiado>kirinyaga while fungal isolates were as Bomet>Kiambu>Kirinyaga>Kajiado. Methyl Red (MR) and Voges-Proskauer (VP) tests, catalase reaction, citrate reaction, starch hydrolysis, and triple iron sugar (TSI) tests showed that the predominant bacteria were Burkholderia, Bacillus and Micrococcus species. Pseudomonas, Streptomyces, Serratia, and Enterobacter species were the least. Aspergillus, Trichoderma, and Fusarium species were the most dominant fungal isolates from the four counties. Hierarchical cluster analysis was done using DARwin software V6 to reveal different dissimilarity levels among the isolates based on biochemical and morphological characteristics.   Key words: Ralstonia solanacearum, rhizosphere screening, fungal isolates, bacterial isolates, biological control.