Avaliação da sensibilidade de espécies de Colletotrichum obtidas do maracujazeiro a Bacillus spp.

Abstract

Originally from tropical regions, the passion fruit plant (Passiflora edulis) finds excellent growing conditions in Brazil, which is one of the main factors contributing to the country's leading global production. However, challenges such as phytosanitary problems have compromised national yields. Anthracnose, caused by species of the Colletotrichum genus, is present in all producing regions. This study aimed to evaluate in vitro the effects of Bacillus subtilis isolates (R14 and IN937b) and a commercial mixture of B. subtilis and B. licheniformis on the mycelial growth of Colletotrichum plurivorum, C. brevisporum, C. tropicale, C. theobromicola, and C. fructicola. For the pairing test, Bacillus isolates were cultured on Nutrient Yeast-Dextrose-Agar (NYDA), and Colletotrichum species were cultured on Potato-Dextrose-Agar (PDA). Colletotrichum species were inoculated at the center of Petri dishes containing synthetic PDA medium, while the antagonistic bacteria were inoculated individually on both sides of the phytopathogens. In the control treatment, plates were inoculated only with the phytopathogens. The Petri dishes were incubated for seven days at 25 ± 1 oC with a 12-hour photoperiod. To assess differences between treatments, the Mycelial Growth Rate Index (MGRI) and the Mycelial Growth Inhibition Percentage (MGIP) were estimated. For MGRI, treatments with B. subtilis and the commercial mixture of B. subtilis and B. licheniformis showed significant differences compared to the controls for all studied species. The highest MGIP values were observed in treatments with isolates R14 and IN937b. Additionally, an evaluation of the volatile metabolites produced by the B. subtilis isolates and the commercial mixture was performed to assess their effect on the mycelial growth of Colletotrichum species. After incubation in a potato-dextrose-based liquid medium for seven days, the fermented broths were centrifuged and autoclaved before application to the PDA medium. The evaluation consisted of measuring the diameter of Colletotrichum spp. colonies after seven days of incubation. The results revealed differences in MGRI and MGIP, with isolates R14 and IN937b showing greater effectiveness against specific species such as C. brevisporum and C. tropicale. B. subtilis is a promising species for reducing the mycelial growth of Colletotrichum spp. associated with anthracnose in passion fruit cultivation.