Abstract
Nine isolates of Aspergillus spp., isolated from soil and compost were tested in vitro and in vivo for their antifungal activity against Fusarium sambucinum and Phytophthora erythroseptica, the causal agents of the Fusarium dry rot and pink rot of potato tubers. Tested using the dual culture method, the pathogen growth of F. sambucinum and P. erythroseptica was inhibited by 27 to 68% and 16 to 25% by all Aspergillus species, respectively. The highest inhibitory activity against both pathogens was induced by the isolate CH12 of A. niger. A significant reduction of the mycelial growth of both pathogens tested using the inverse double culture method involves the presence of volatile antifungal metabolites. Their effectiveness was also evaluated as tuber treatment prior to inoculation with the pathogens. The highest effectiveness in reducing Fusarium dry rot severity was recorded on tubers treated with the isolate CH12 of A. niger. This study also revealed that the efficacy of Aspergillus spp. as biocontrol agents may be enhanced by varying the timing of their application. In fact, the lesion diameter of dry and pink rots was reduced by 54-70 and 52% with preventive application, respectively. However, this parameter decreased by 21-48 and 47% when the Aspergillus spp. were applied simultaneously with pathogens, respectively. Similarly, diseases’ severity, estimated based on average penetration of F. sambucinum and P. erythroseptica, was reduced by 57-77 and 55% with preventive treatments and by 29-68 and 44% with simultaneous application, respectively. This study reveals that Aspergillus spp., isolated from compost and soil, exhibits an interesting antifungal activity toward F. sambucinum and P. erythroseptica and may represent a potential source of biopesticide. Testing of their culture filtrates, their organic extracts and their toxicity may give additional information on their safe use as biocontrol agents.
Highlights
Potato (Solanum tuberosum L.) is one of the most important vegetable crops in the world [1,2,3]
Dry rot induced by different Fusarium species, Pythium leak caused by Pythium spp. and pink rot incited by Phytophthora erythroseptica are responsible for important tuber storage losses in the world and in Tunisia [7,8,9,10,11,12,13]
Analysis of variance showed a highly significant inhibitory effect of the antagonists tested on the average colony diameter of F. sambucinum and P. erythroseptica, recorded after 7 and 4 days of incubation, respectively
Summary
Potato (Solanum tuberosum L.) is one of the most important vegetable crops in the world [1,2,3]. Potato production is threatened by several fungal diseases resulting in considerable yield losses [5,6] These diseases can affect potato at any growth stage or even during storage, where potato tubers may exhibit diverse types of rots. Dry rot induced by different Fusarium species, Pythium leak caused by Pythium spp. and pink rot incited by Phytophthora erythroseptica are responsible for important tuber storage losses in the world and in Tunisia [7,8,9,10,11,12,13]. The oomycete, P. erythroseptica infects potato tubers through stolons or lenticels via zoospores and through cracks and cuts made during harvest and handling operations [5,16,17]. The health of seed tubers, the management practices during the growing period, the harvesting and handling practices and the environmental conditions maintained throughout storage are key factors affecting tuber infection by these pathogens [19]
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