Optimization of media and appraisement of fungicides and bioagents on leaf spot of ashwagandha, Withania somnifera (L.) Dunal caused by Alternaria alternata

Abstract

Alternaria leaf spot is a major disease in ashwagandha caused by Alternaria alternata which reduces in withaferin-A and withanolides contents and exhibited significant antitumour activity. Effect of five media viz., PDA, CMA, OMA, CA and MEA were optimized at different temperature i.e. (15, 20, 25, 30 and 350C). It was found CMA at temperature 300 C was most favoured for the growth of A. alternata (28.00 mm) while lowest growth occurred in media MEA at temperature 150C i.e. (5.60 mm). Nine fungicides, in which formulation of carbendazim, mancozeb, captan, copper oxy chloride, chlorothalonil, ridomil-MZ, thiophanate methyl, propiconazole and difenoconazole at different concentrations i.e. (100, 500, 1000, 1500 and 2000 ppm) by using poisoned food technique. Propiconazole and difenoconazole showed maximum percentage inhibition of A. alternata at all concentrations while thiophanate methyl was least effective. Four bioagents namely (T. harzianum, T. viride, P. fluorescens and B. cereus) were also evaluated for their antagonistic effect against A. alternata by using dual culture technique. The bioassay showed that T. viride was most effective with (55.66%) inhibition of mycelial growth while P. fluorescens (34.91%) was least effective.