Use of killer yeast in the management of postharvest papaya anthracnose

• W. anomalus and M. guilliermondii efficiently controlled C. gloeosporioides in papaya.
• The yeast colonized the hyphae causing physical damage to the pathogen.
• The time between phytopathogen inoculation and treatment had a significant effect on antagonist action.
• W. anomalus and M. guilliermondii produced β-1,3-glucanase in vitro.

The efficiency of two killer yeast strains, Wickerhamomyces anomalus (strain 422) and Meyerozyma guilliermondii (strain 443), as biocontrol agents against Colletotrichum gloeosporioides, a postharvest anthracnose agent of papaya and other tropical fruit, was assessed. These strains were previously selected through in vitro assays, but in the present study, their in vivo action was assessed. In addition, the influence of phytopathogen inoculation time on the fruit in combination with the use of the biocontrol agent was also assessed. We assessed mycoparasitism as an antagonistic mechanism of action by scanning electron microscopy (SEM). In addition, two hydrolytic enzymes, chitinase and β-1,3 glucanase, were assayed. Our results indicated that W. anomalus (strain 422) and M. guilliermondii (strain 443) reduced disease incidence by 24.62% and 20.68%, respectively, for up to 6 d after inoculation, when applied 3 h before the phytopathogen and incubated in a wet chamber (95% RH) at 28 °C. The time of yeast inoculation had a significant effect on its antagonistic action. Application of the yeasts 12 or 24 h before the phytopathogen inoculation resulted in 13.75% and 30% of disease reductions for W. anomalus (strain 422) and 31.35% and 41.17% reductions for M. guilliermondii (strain 443), respectively. Electron micrographs confirmed mycoparasitism by showing the interaction of the yeasts with C. gloeosporioides hyphae, causing in some cases, a loss of turgor and yeast penetration of walls with marked concavity formation on hypha cell walls.