Water stress and insect defoliation promote the colonization of Quercus cerris by the fungus Biscogniauxia mediterranea

The effects of water stress and defoliation by Lymantria dispar on the successful infection of the fungal pathogen Biscogniauxia mediterranea in seedlings of the Turkey oak (Quercus cerris) were studied under controlled conditions. Seedlings were inoculated by spraying with a spore suspension of Biscogniauxia mediterranea and were subjected to different levels of water stress, insect defoliation, and combinations of the two factors. The leaf water potential was periodically assessed throughout the experiment. The fungus was isolated exclusively from seedlings deprived of water, and insect defoliation increased significantly the proportion of fungus isolation when the water stress was moderate. Thus insect defoliation seems to promote fungal colonization in case of moderate water stress.