Selection of antagonists of postharvest apple parasites: Penicillium expansum and Botrytis cinerea

The objectives of this study were to constitute a collection of pathogenic agents of economic importance which cause losses of apple fruits after harvest namely Botrytis cinerea and Penicillium expansum and to select in vivo efficient antagonistic strains able to protect fruits against both pathogens at 5 degrees C (P. expansum) and 25 degrees C (P. expansum & B. cinerea). Twenty strains of P. expansum and ten strains of B. cinerea have been isolated from infected apple fruits. Potential antagonistic micro-organisms (thirty three isolates) belonging to yeast, bacteria and fungi have been isolated from apple surface. Six of them (strains Ach1-1, Ach2-1, Ach2-2 belonging to Aureobasidium pullulans (De Bary) Arnaud, and strains 1112-3, 1113-10 and 1113-5 belonging to Aureobasidium pullulans (de Bary) Am. v. pullulans) showed a high level of protection (more than 80%) at 25 degrees C. once inoculated with P. expansum or B. cinerea for 5 days. The highest level of protection against P. expansum (96%) was observed with the application of Ach 2-1. Six days after inoculation of B. cinerea, strains Ach 2-2 and Ach 2-1 insured 100% and 96% of protection, respectively. At lower temperature (5 degrees C), first symptoms of P. expansum appeared 13 days after its inoculation. Percentages of protection observed after apple treatment with one of the six antagonistic strains were ranged from 78% to 94% 20 days after P. expansum inoculation. Strains labelled Ach showed a protective level higher than 90% against this pathogen, followed by strain 1113-10 (90%), strain 1113-5 (89%) and strain 1112-3 (82%). At 26 days post-inoculation, levels of protection decreased but remained higher than 60% (more than 80% with strain Ach2-2 and strain 1113-5, 75% with strain Ach2-1 and 1113-10, 72% with ach1-1, 61% for the other strains). Strain Ach2-2 and 1113-10 were retained as the best antagonists for the subsequent studies.