Application of benzothiadiazole and Trichoderma harzianum to control faba bean chocolate spot disease and their effect on some physiological and biochemical traits

Chocolate spot disease is the most prevalent and important disease in the major faba bean growing regions in the world. Different concentrations of the abiotic inducer (0.3 and 0.5 mM benzothiadiazole) and the biotic inducer (1 × 10⁷ and 2 × 10⁷ spore/ml Trichoderma harzianum) were used alone or in combination to study their efficiency against faba bean chocolate spot disease caused by Botrytis fabae and Botrytis cinerea and their effect on some chemical analyses (phenylalanine ammonia lyase activity, total flavonoids and peroxidase isozymes, pectin and lignin content and total chlorophyll content). Application of the tested inducers as foliar treatment significantly reduced the severity of chocolate spot disease as compared with untreated infected plants. The reduction in disease severity was associated with a gradual increase in phenylalanine ammonia lyase activity. Maximum increase was recorded at 72 h after inoculation with B. fabae and B. cinerea. In addition, the levels of flavonoids in induced infected leaves recorded a sharp increase at 24 h after inoculation with B. fabae or B. cinerea. Also, pectin and lignin contents in the cell wall of induced infected plants were significantly increased as compared with untreated infected plants. Beside the induction of resistance, the tested inducers markedly increased total chlorophyll content in treated infected plants as compared with untreated infected plants. Isozymes analysis revealed that new peroxidase bands were induced only in treated faba bean leaves in response to infection with B. fabae or B. cinerea.