Evaluation of chitosan for in vitro control of Colletotrichum tamarilloi and anthracnose on scarlet eggplant fruit

Abstract

ABSTRACT Scarlet eggplant (Solanum aethiopicum var. gilo) is a Solanaceae with an appreciated peculiar bitter taste, which plays a significant role in family farming in Brazil. Fruit anthracnose is the main pre- and postharvest disease that affects scarlet eggplant in Brazil. This study aimed to evaluate the effect of chitosan-based coating on in vitro inhibition of Colletotrichum tamarilloi and anthracnose control of scarlet eggplant fruits. Chitosan was dissolved in a 2% citric acid solution at 40°C and then homogenized with potato dextrose agar (PDA), and poured into Petri dishes, as follows: 1) PDA + 0.1% chitosan, 2) PDA + 0.2% chitosan, 3) PDA + 0.3% chitosan, 4) PDA + 0.4% chitosan, and 5) pure PDA as control. Discs of 5 mm diameter of pure fungus culture were placed on the center of the culture medium in the plates. The plates were then maintained in BOD at 25°C and 12-h photoperiod for 10 days. Colony characteristics, mycelial growth rate, and mycelial growth inhibition were evaluated. Afterward, the effect of chitosan coating was evaluated in fruit inoculated or not with C. tamarilloi. The treatments were: T1) uncoated and injured uninoculated fruits, T2) uncoated and inoculated fruit, T3) fruits coated with 0.1% chitosan and inoculated, T4) fruits coated with 0.2% chitosan and inoculated, and T5) fruits coated with chitosan at 0.3% and inoculated. For inoculation, 15 μL of a conidial suspension (2 x 105 conidia/mL) were deposited on an injury caused by a needle, and the fruits were coated by immersion into the different concentrations of chitosan gel. Fruits were placed on expanded polystyrene trays. Fresh weight loss, the mean incidence of disease, and lesion diameter were measured. All concentrations of chitosan reduced the in vitro growth of C. tamarilloi. The treatment T4 reduced the severity of anthracnose but did not prevent its incidence in scarlet eggplant fruits.