Biodiversity and biocontrol activity of grape epiphyte yeasts in control of gray mold disease

Grape gray decay disease caused by Botrytis cinerea is one of the important factors causing rotting and reducing the quantity and quality of the grapes during the stages before and after harvesting, which makes the use of chemical fungicides inevitable. Considering the environmental issues with the excessive use of chemical fungicides for humans and the environment, the use of products based on biological agents has received special attention. Among biological agents, some yeasts have been shown to possess antagonistic activity against fungi and are considered as safe and sound alternatives for chemical pesticides. The present study aimed to identify grape epiphytic yeasts and investigate their ability against the pathogenic fungus B. cinerea in the post–harvest stage. A total of 67 yeast isolates were isolated from the surface of grape fruits in the vineyards of West Azarbaijan province. Based on morphological studies and nucleotide sequence analysis of the D1/D2 domain of the large subunit 26S rDNA gene, the isolates belong to 21 species and 11 genera. Aureobasidium pullulans was recognized as the dominant species of grape flora. The ability of 67 yeast isolates to control B. cinerea growth by the dual–culture method showed that 16 isolates belonging to 7 genera succeeded in inhibiting the growth of the gray mold, which isolates Rhodotorula glutinis G54 and Metschnikowia pulcherrima G9 showed the greatest of capability against B. cinerea. A significant difference (P≤0.01) was observed between the 16 selected isolates in terms of inhibition of gray rot on grape berries, as a completely randomized design with four replications. The isolates Meyerozyma guilliermondii G30, Rh. glutinis G54 and M. pulcherrima G9 were the most effective isolates in reducing the disease on grape berries with 92.59, 91.37 and 90.15 percent rot inhibition, respectively. Studies of mechanisms involved in biological control showed that 12 isolates were able to produce protease, 6 isolates were able to produce pectinase and 12 isolates produced amylase. Also, it was found that 9 isolates can form biofilm and 8 isolates produced a siderophore. Finally, it was found that the grape flora has a high diversity of yeasts and the superior yeast isolates including G30, G54 and G9, with various biocontrol mechanisms (such as antibiosis, protease and amylase activities as well as siderophore production), have a high potential to inhibit the gray rot of grape. However, it is necessary to conduct more studies on selected isolates to creat practical formulations for biological control or integrated management of fungal diseases of fruits and vegetables..