Assessment of the Antifungal Activity of Non-pathogenic Potatoassociated Fungi toward Fusarium Species Causing Tuber Dry Rot Disease

Twenty isolates of potato-associated fungi belonging to genera Aspergillus, Penicillium, Colletotrichum, and Trichoderma and recovered from healthy potato organs (stems, roots, and tubers) were screened for their antifungal potential toward Fusarium sambucinum and F. solani the major agents of dry rot disease in Tunisia. Tested using the dual culture method, all the potato-associated isolates had significantly lowered pathogen growth, noted after 7 days of incubation at 25°C as compared to the untreated control, but with a variable range depending on isolates used and targeted Fusarium species. F. sambucinum and F. solani were inhibited by 23.4 to 71.5% and by 29.2 to 62.1%, respectively, depending on antagonistic treatments tested. The percentage of Fusarium spp. inhibition ranged from 30.1 to 47.2% using Aspergillus spp. and from 30.1 to 67.3% with Penicillium spp. compared to 40.1-50.6% and 40.8% achieved using Colletotrichum sp. and Trichoderma sp., respectively. Strong hyphal lysis, formation of mycelial cords and early production of chlamydospores are the most frequent stress responses exhibited by both pathogens during their in vitro interactions with the potato-associated fungi. Tested as tuber treatment prior to pathogen challenge using a mixed inoculum composed of F. sambucinum and F. solani, 13 isolates out of the 20 tested led to a significant decrease, by 26.9 to 54.8%, in the mean diameter of dry rot lesion, as compared to the inoculated and untreated control. All tuber treatments had significantly decreased mean rot penetration, in comparison to Fusarium spp.-inoculated and untreated control, which was lowered by more than 50% using 14 out of the 20 potato-associated isolates. Thus, the present study clearly demonstrated that fungal isolates, occurring ubiquitously within potato plants, may be promising candidates for Fusarium spp. biocontrol and may be other potato diseases.