Effect of fungicides on Colletotrichum species associated with anthracnose in passion fruit

Brazil is the world's largest producer of passion fruit (Passiflora spp.), with the Northeast region accounting for 70% of national production. In this scenario, fungal diseases such as anthracnose, caused by species of the Colletotrichum genus, are among the main factors reducing yield and affecting fruit quality. From this perspective, this study aimed to evaluate in vitro the effects of the fungicides difenoconazole, pyraclostrobin, flutriafol, and azoxystrobin + difenoconazole (Amistar Top®) on the mycelial growth of Colletotrichum plurivorum, C. brevisporum, C. theobromicola, C. tropicale, and C. fructicola, and to analyze the behavior of these species in passion fruit seedlings treated with pyraclostrobin. In the in vitro evaluation of Colletotrichum spp. sensitivity to fungicides, a 5-mm disk of synthetic Potato Dextrose Agar (PDA – Kasvi) medium containing fungal structures was placed onto PDA medium supplemented with the fungicides, using both a higher and a lower concentration based on the manufacturer’s recommended dose for anthracnose control. The plates were incubated at 25 ± 1°C in the dark and measured daily for seven days. To compare treatments, the Mycelial Growth Rate Index (MGRI) and Mycelial Growth Inhibition Percentage (PIC) were calculated. Asymptomatic seedlings of the Cerrado passion fruit variety were used for the in vivo evaluation. Pyraclostrobin was applied at a concentration of 100 µg L⁻¹. In the preventive treatment, the fungicide was sprayed on the seedlings and, after 48 hours, fungal discs containing Colletotrichum structures were inoculated. In the curative treatment, the seedlings were first inoculated with the pathogen, and after four days, the fungicide was applied. The control group consisted of seedlings inoculated only with Colletotrichum spp. Both treatments were assessed on the tenth day by measuring lesion diameters. In the in vitro tests, the manufacturer-recommended doses of flutriafol, pyraclostrobin, and Amistar Top® were the most effective; however, for difenoconazole, the best results were obtained with the highest concentration. The preventive treatment resulted in the smallest lesion sizes for all species except C. plurivorum, which was less aggressive in the curative treatment. Overall, pyraclostrobin was the most effective fungicide both in vitro and in vivo for Colletotrichum spp.