Efficacy of Trichoderma Harzianum and Bacillus Subtilis in the Management of Brown Spot Disease in Rice (oryza Sativa)

Alternaria brown spot, brought on by Alternaria alternata, poses a significant threat to the adequate production of rice, a staple crop vital for global food security, particularly in Nigeria. Two biocontrol agents, Trichoderma harzianum (TH) and Bacillus subtillis (BS) (alone and in combination), Standard check (SC), Positive control (PC), Negative control (NC) were investigated using a completely randomized design (CRD) with three replications in a laboratory experiment on the germination, growth, and disease severity in rice. Rice was cultivated under controlled conditions in plastic pots. Selected seeds were artificially inoculated with Alternaria alternata spore (106 ) suspension. The biocontrol agents were evaluated prophylactically through seed priming. Primed seeds were inoculated with Alternaria alternata. The standard check was seed dressing with seed plus fungicide. The treated seeds were placed in a medium infested with A. alternata and allowed to germinate and thrive for three weeks. Brown spot disease early symptoms were monitored in growing seedlings. Germination percentage, root length (cm), shoot length (cm), number of leaves, root volume (cm³), fresh root weight (g), disease incidence (%), and disease severity (%) were all recorded. Minitab Statistical software was used for the data analysis while the collected data were subjected to two-way ANOVA to assess for significance among treatments. The findings revealed that TH only had the highest germination percentage, plant height and number of leaves while TH + BS recorded the highest root length, root volume and fresh root weight. Both sole and combined TH and BS improved plant health and growth relative to other treatments including NC while NC had the highest disease incidence and severity. TH + BS is recommended as a sustainable substitute for chemical fungicide in the control of rice brown spot disease caused by Alternaria alternata.