Antifungal activity of bioagents and plant extracts against certain fungal diseases of potatoes

Résumé

Twenty-six fungal isolates were obtained from potato plants and tubers growing in different localities in Egypt. The isolates were identified as 11 Rhizoctonia solani, 8 Sclerotinia sclerotiorum and 7 Fusarium spp. The 26 isolates were screened due to their pathogenic capabilities and the most pathogenic isolate among each of the three obtained genera was selected for this study. In vitro studies included the effect of 7 bacterial isolates, 6 Trichoderma isolates, as well as 6 plant extracts at four rates of application against the three fungal pathogens, Trichoderma harzianum (T5) achieved the highest mycelial growth inhibition, followed by T. asperellum (T34) and T.  harzianum (T10) isolates. Additionally, Bacillus subtilis (BS2) recorded the best mycelial growth inhibition against the three tested fungi, followed by B. subtilis (BS1) and B.megatirum(BM2). On the subject of plant extracts, garlic extract gave the greatest reduction of the mycelial growth with all rates of application, followed by henna and ginger extracts. Field experiments were conducted during 2018/2019 and 2019/2020 growing seasons to evaluate bioagent activities as well as plant extracts in reducing disease severity caused by the three fore-mentioned pathogenic fungi. Trichoderma harzianum (T5) exhibited the highest disease reduction in vivo, followed by (T34) and Pseudomonas fluorescens (PF2), as compared with the control. Under greenhouse conditions, garlic extract decreased disease severity of both Fusarium sp and S. sclerotiorum, followed by henna and ginger extracts. On the other hand, henna extract came in the first order in reducing disease severity caused by R.solani, followed by ginger and garlic, as compared with the control. On the whole, Trichoderma harzianum (T5) and T. asperellum (T34) were the best treatments, those reduced diseases severity to the greatest extent if compared with the other treatments and the control.