Antifungal potential of endophytic Bacillus species isolated from tomato (Solanum lycopersicum) against Fusarium oxysporum collected from selected farms in Nigeria

Fusarium wilt, caused by F. oxysporum, is a prevalent destructive tomato (Solanum lycopersicum L.) disease in Nigeria. Development of safe, and efficient biocontrol measures is important in the management of the disease. In this study, incidence of fusarium wilt of tomato in four agricultural zones of Oyo State was established through purposive sampling, and the abundance, and in vitro-biocontrol potential of Bacillus endophytes were determined. Strains of F. oxysporum and Bacillus endophytes were isolated from tomato plants collected from 21 farms. In vitro-inhibition potential of endophytes was determined through a modified, dual-culture assay, involving six endophytes, and carbendazim (fungicide), set up in a completely randomized design. Using a rating-scale of 0-9, the highest wilt severity (6.67) and incidence (39.30%) were observed on Akinware farm in Ibadan/Ibarapa agricultural zone of Oyo State. Fusarium oxysporum IB3q caused severe wilt symptoms, including leaf chlorosis, necrosis, vascular discoloration, and wilt, on infected Alausa and Ibadan-local tomato varieties. Thirty-nine strains of Bacillus endophytes were isolated from the tissues of healthy tomato plants. Six of the isolated Bacillus endophytes inhibited F. oxysporum. Bacillus amyloliquefaciens Sa08 and B. subtilis Og04 had inhibitory zones of 15.67 and 19.43 mm, respectively, against F. oxysporum, and caused hyphal disintegration of the pathogen. They produced cell wall-degrading enzymes, with relative activities ranging from 0.87 to 5.04. Based on their in vitro-inhibition potential, B. amyloliquefaciens Sa08 and B. subtilis Og04 should be deployed, as prospective biocontrol measures against seed-borne fusarium pathogens and fusarium wilt on tomato plants.