FUNGICIDAL ACTIVITY OF CHITOSAN IN SYNERGY WITH Trichoderma harzianum AND Bacillus subtilis FOR THE CONTROL OF CHILI WILT DISEASE

Chili (Capsicum annuum L.) wilt disease is considered one of the main diseases of this crop. It is caused by a complex of phytopathogens such as Fusarium oxysporum, Rhizoctonia solani, and Sclerotium rolfsii. These fungi have developed resistance to fungicides, resulting in environmental contamination that harms human health. These factors motivate the search for environmentally safe and efficient products to control this disease without causing adverse effects to ecosystems. Chitosan, which is innocuous and has antagonistic activity, favors the growth of some beneficial microorganisms. In this study, the compatibility of chitosan at eight concentrations (75, 150, 300, 600, 600, 1200, 2400, 4800, and 9600 ppm) with Trichoderma harzianum and Bacillus subtilis was evaluated, as well as its combined inhibitory effect against the causal agents of chili wilt disease (F. oxysporum, R. solani, and S. rolfsii). T. harzianum and B. subtilis were found to be compatible with chitosan. However, at concentrations of 2400 ppm and above, their growth and sporulation were affected. In the inhibition tests, low concentrations (75–600 ppm) stimulated greater mycelial growth of Trichoderma and had greater inhibition of mycelial growth of the phytopathogens, while concentrations of 600–1200 ppm stimulated their parasitism against F. oxysporum and R. solani. Similarly, the presence of chitosan in the culture medium favored greater growth of B. subtilis and higher inhibition percentages (91.65, 71.04, and 68.55 %) for S. rolfsii, F. oxysporum, and R. solani, compared to the treatment with B. subtilis without chitosan. Therefore, the combination of these microorganisms with chitosan could be considered as an alternative for the control of this disease.