Bacillus subtilis strain BS-QS1 promotes tomato growth and induces systemic resistance against Fusarium wilt in Shaqra, Saudi Arabia

Fusarium wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici is one of the most serious diseases responsible for substantial losses in yield and quality. In this context, this research work aims to evaluate the biocontrol and growth-promoting attributes of Bacillus subtilis BS-QS1 in greenhouse and under laboratory conditions from Shaqra, Saudi Arabia. In the present study, a randomized complete block design with four treatments, i.e., Control, Fusarium, B. subtilis, and B. subtilis+Fusarium, each replicated eight times, revealed that B. subtilis exhibited strong antifungal activity in vitro reflected by inhibition zones of 15-19mm and 60-72% reduction in mycelial growth and spore germination. Moreover, B. subtilis enhanced the activities of chitinase and β-1,3-glucanase 6-7-fold and production of siderophores over 10-fold. Under greenhouse trials, Fusarium infection reduced the plant height, shoot dry weight, and total yield by 25-46%, while exogenously applied B. subtilis enhanced the above parameters by 63, 58, and 71%, respectively. Chlorophyll a and b improved by 60 and 53%, relative water content increased by 34%, while electrolyte leakage was reduced by 30%, demonstrating the enhanced stress tolerance. Antioxidant enzyme activities improved in the range of 40-96%, while the expression of defense genes improved by 185-295% in B. subtilis-pretreated plants. In addition, DNA of Fusarium in roots was suppressed by nearly 80%, while disease incidence was reduced by 58%, confirming the strong biocontrol potential of B. subtilis. Field validation of the organism is recommended.