Use of bacterial biocontrol agents for the control of Fusarium oxysporum f.sp. Lycopersici, tomato wilt in Kenya

Abstract Fusarium oxysporum f.sp Lycopersici is a serious plant pathogen responsible for over 80% yield loss in tomatoes. The disease is mainly controlled by use of synthetic chemicals which may be harmful to bothhumans and the environment. In this study, we report on the potential use of antagonistic bacteria in controlling fusarium wilt. First, we isolated and characterized fungi from tomato plants with wilt symptoms. Analysis of the ITS gene showed that they were affiliated to the genus Fusarium, Alternaria, Plectosphaerella, Aspergillus, Gibellulopsis, Trichoderma, Papiliotrema, Rhodotorula, Mucor, Ustilago, Sporothrixand Cumuliphoma. We then then screened 20 bacterial isolates recovered from soils collected around the tomato plants for antagonistic activity against F.oxysporum using soft agar overlay method. Bacterial isolates showing inhibition zone diameters >3mm and consistent in reducing mycelial growth of the pathogen were characterized further and subsequently used for field experiments which were conducted during the short rain season in 2021 and 2022. Phylogenetically, they were affiliated to Bacillus subtilis, Paenibacillus polymyxa, Brevibacillus laterosporus, Bacillus velezensis, Bacillus amyloliquefaciens and Paenibacillus poriaewhereas one of the isolates was identified as Myroides odoratimimus. The isolates grew at an optimum salt concentration of 5 - 10 % (w/v), pH range of 5 - 8 and a temperature of 30 °C. Results from the field experiments showed that all selected strains provided a significant reduction in disease incidence on average for both years from day 14 [14.4% (s.e. 3.49)], day 28 [15.9% (s.e. 3.44)] and day 42 [15.2% (2.825)] respectively. Therefore, these isolates are good candidates for the development of effective biocontrol agents against F. oxysporum f.sp Lycopersici affecting tomatoes.