AGENTES DE BIOCONTROLE CONTRA INFECÇÃO POR Penicillium digitatum EM LARANJA ‘PERA’

Abstract

The objective of this work was to evaluate the efficiency of biocontrol agents in the occurrence of green mold (Penicillium digitatum) in Pêra orange fruits, and their effects on defense responses and post-harvest quality. For that, an in vitro experiment was carried out with an isolate of the fungus in BDA medium submitted to different systems of commercial products based on biocontrol agents: Trichoderma harzianum (0, 5, 10, 15, 20 e 25 mL L-1), Bacillus subtilis (0, 2, 4, 6, 8 e 10 mL L-1) and B. licheniformis + B. subtilis + T. longibrachiatum (0, 5, 10, 15, 20 e 25 g L-1) and as a standard the fungicide imazalil (2 mL L-1) mycelial growth and spore germination were evaluated. Based on the results of in vitro tests, in vivo tests were carried out in two stages. In the first stage, the curative and preventive effect of the application of the biocontrol agents T. harzianum on the concentrations of 0, 5, 10, 15, 20 e 25 mL L-1, B. subtilis in concentrations of 0, 2, 4, 6, 8 e 10 mL L-1 and; B. licheniformis + B. subtilis + T. longibrachiatum in concentrations of 0, 5, 10, 15, 20 e 25 g L-1, and as a standard the fungicide imazalil (2 mL L-1). These experiments were carried out on fruits inoculated with 10 µL of conidia suspension (108 conidia mL-1). In the second stage, the fruits were evaluated only for the preventive effect of applying 25 mL L -1 of T. harzianum, 10 mL L-1 of B. subtilis and 25 g L-1 of B. licheniformis + B. subtilis + T. longibrachiatum, fungicide imazalil (2 mL L-1) and control (water) with seven phytopathogen inoculation periods (0, 4, 8, 12, 16, 20 and 24 hours after treatments). In all in vivo tests, the fruits were stored at 25 °C and 80% relative humidity for up to seven days. To evaluate the preventive effect of biocontrol agents as inducers of resistance, the activity of the enzymes peroxidase, phenylalanine ammonia lyase, β-1,3-glucanase and chitinase in the peel of fruits treated with 25 mL L-1 of T. harzianum, 10 mL L-1 of B. subtilis and 25 g L-1 of B. licheniformis + B. subtilis + T. longibrachiatum, fungicide imazalil (2 mL L-1) and control (water) and stored for 24 and 48 hours (inoculated and non-inoculated). The effect of treatments on postharvest quality was verified from the analysis of pH, total soluble solids, titratable acidity, ratio, ascorbic acid, phenolic compounds and antioxidant capacity, evaluated at 0, 48, 96 and 144 hours after application of 25 mL L-1 of T. harzianum, 10 mL L-1 of B. subtilis and 25 g L-1 of B. licheniformis + B. subtilis + T. longibrachiatum. There was 100% control on mycelial growth and a linear effect to inhibit the germination of P. digitatum, for all biocontrol agents in vitro. For in vivo tests, in the first phase, all biocontrol agents showed a linear effect, both in the curative effect and in the preventive effect, significantly reducing the development of green mold in 'Pera' orange fruits. The biocontrol agents promoted an increase in the activity of the enzymes peroxidase, phenylalanine ammonia lyase, β-1,3-glucanase and chitinase. The concentrations of total soluble solids, titratable acidity, ratio, ascorbic acid, phenolic compounds and antioxidant capacity were influenced by the storage time and treatments with biocontrol agents. It was concluded that the preventive application of 25 mL L-1 of T. harzianum, 10 mL L-1 of B. subtilis and 25 g L-1 of B. licheniformis + B. subtilis + T. longibrachiatum in 'Pera' orange fruits it has the potential to control P. digitatum, in addition to inducing defense responses and increasing the antioxidant capacity of the fruits.