Biological control of anthracnosis in papaya fruits by biofilm-forming epiphytic bacteria

ABSTRACTUMO

Aiming to obtain biocontrol agents for post-harvest anthracnose control in papaya fruits, the present study sought to: i) select, from papaya fruits, epiphytic bacteria that are antagonistic to Colletotrichum brevisporum, based on the production of diffusible and volatile antimicrobial compounds, chitinase, and conidial germination inhibition; ii) quantify biofilm production by the selected strains; iii) obtain a concentration of bacteria that would provide anthracnose control in fruit discs; iv) evaluate the disease severity reduction in papaya fruits. Of 224 bacteria, 74 exhibited one mechanism of action against the pathogen, 13 isolates showed two mechanisms, four isolates had three mechanisms, and one bacterium showed all mechanisms. Verification of compatibility between antagonists, as well as biofilm quantification, led to the formation of five “Mix” composed of four bacterial isolates. In fruit discs, bacteria were evaluated at the concentrations 10⁶, 10⁷ and 10⁸ CFU mL^-1. Except Mix 2, the remaining combinations significantly reduced anthracnose in the discs when compared to control. Mix 1, 3 and 5, at the concentration 10⁸ CFU mL^-1, showed the best performance, reducing the disease severity by up to 75.0%, 89.78% and 90.8%, respectively. Mix 3 and 5, at the concentration 10⁸ CFU mL^-1, were evaluated together with the synthetic fungicide Pyraclostrobin in fruits. There was no significant difference between the Mix and the fungicide, which reached disease reduction levels superior to 97%, while combinations reached 98%, compared to the untreated control.

Keywords
Carica papaya ; Biocontrol; Colletotrichum brevisporum