Efficacy and cost study of green fungicide formulated from crude beta-glucosidase

Abstract

Current agricultural management strategies to control the soil-borne pathogen Macrophomina phaseolina (Tassi) Goid, which causes charcoal rot disease, are insufficiently efficacious. We hypothesized that a natural antagonist of M. phaseolina, Trichoderma harzianum Rifai, could be used to develop a greener fungicide formulation to combat the disease. T. harzianum produces an extracellular β-glucosidase that explicitly hydrolyzes the amorphic β-1, 3-glucan filling material of the chitin cell wall in M. phaseolina during hyperparasitism. Herein, we describe a highly efficient β-glucosidase isolated from T. harzianum T12 as a safer bioactive component for reducing the plant disease index in soybean plants grown in soil inoculated with M. phaseolina. A Box–Behnken design was used to investigate the effects of metal ions, surfactants, enzyme concentration and irrigation in maximizing the efficacy of the enzyme to achieve the lowest PDI under a greenhouse setting. Under optimum conditions (Zn2+, 10 mM; Tween 80, 2% [w/v]; enzyme concentration, 15 mg/L; irrigation, 2 times/week), a minimum plant disease index of 4.32% was obtained (R2 = 0.9676). The bioenzyme-based fungicide was more efficient in lowering the plant disease index as compared with conventional methods using natural antagonists or a chemical fungicide. Our formulation yielded the lowest plant disease index (4.14%; P < 0.05) as compared with the antagonist T. harzianum (26.13%) and the fungicide Carbendazim (32.45%). This formulation was also substantially less expensive, costing US$34/acre as compared with Carbendazim at US$240/acre of soybean. This formulation is eco-friendlier and combines the practicality of an on-demand in situ spraying for rapid control of M. phaseolina infestation.