Biological control and molecular differences among some isolates of Alternaria solani, the causative agent of early blight in potatoes

In this study, some isolates of Alternariasolani; the causative agent of potato early blight disease were isolated and identified from different Egyptian governorates. The pathogenicity of these isolates was examined on the potato cultivar (Lady-Rosetta). The genetic variation among these isolates were identified using the RAPD and SDS-PAGE techniques. Also, the antifungal activity of some biological agents against the highest aggressive isolate of El-Minia governorate (El-Borgia No.1) was evaluated in the laboratory, the greenhouse and the field. Five isolates were isolated from leaves and tubers of naturally infected potato plants, collected from fields planted with the varieties (Kara, Lady-Rosetta and Spunta) representing different localities of some governorates. The fungal isolates were symbolized from 1 to 5 according to their regions. Data showed that all tested isolates proved to be pathogenic to the tested potato (cv. Lady-Rosetta) causing symptoms of early blight comparing with the control. The fungal isolate No. 1 which was obtained from (El-Borgia, Minia governorate) was the most aggressive isolate with the highest significant values of disease severity (44.30 and 56.19%) of the two successive seasons, respectively. Regarding to, RAPD-PCR, SDS-PAGE protein patterns and phylogenetic analysis data showed that isolates 1, 2 and 3 that have the high pathogenicity were similar to each other and share the same cluster while the other fungal isolates 4 and 5 with the low pathogenicity were phylogenetically close to each other. Moreover, there were no relationship between the pathogenicity and the geographic distribution of all tested A. solani isolates. Finally, in vitro antagonistic test declared that Trichodermaharzianum was the best bioagent that gave the highest inhibition zone (67.33cm) against the most aggressive A. solani isolates as compared with all other bioagents. Spraying the sensitive potato plants (cv. Lady Rosetta) in the greenhouse and field antagonistic with T. harzianum suspension showed the best results and gave the lowest values of early blight disease severity during the two seasons (19.77, 11.25%) and (25.32 and 10.66%, respectively) as compared with the control and other treatments.