Aureobasidium pullulans strain Ach1-1 a biocontrol of postharvest diseases of apples: 15 crucial years of research before starting commercial development

Losses in harvested fruits are thoroughly associated to decaying fungi. Biological control using microbial agents including yeasts, has been reported among several alternatives to the use of synthetic chemical fungicides for managing postharvest fruit decay. Aureobasidium pullulans strain Ach1-1was isolated as potential yeast antagonist form the surface of Golden Delicious apple fruit. The biocontrol agent exhibit high efficacy towards controlling blue and grey mold infection disease caused respectively by the two fungi P. expansum and Botrytis cinerea.
Competition for nutrients was evident for strain Ach1-1 against P. expansum. The results demonstrated that exogenous amino acids, applied at high concentrations on apple wounds as a mixture of specific amino acid groups or as individuals, significantly decreased strain Ach1-1 efficacy towards P. expansum. In addition molecular markers and a semi-selective medium methods were developed, in order to monitor the population dynamic of A. pullulans strain Ach1-1 on fruit surface. The random amplified polymorphic DNA (RAPD) technique was applied to 15 strains of A. pullulans, including the strain Ach1-1. Among the five specific RAPD fragments amplified for strain Ach1-1, a 528 bp fragment was selected and used to design sequence-characterized amplified region (SCAR) primers. The results showed that these specific SCAR primers can clearly identify strain Ach1-1 among different strains of A. pullulans and other yeast strains commonly present on apple fruit surface. Furthermore, a semi-selective medium based PDA and supplemented with euparen, sumico, hygromycin B, streptomycin sulphate, cycloheximide, specific for strain Ach1-1 was developed.
These outcomes in fundamental and applied research, relevant for Aureobasidium pullulans strain Ach1-1 lead to a collaboration establishment with Elephant vert group towards the commercial development of this strain as potential biocontrol agent to control apple diseases in postharvest conditions.