Characterization and in vitro Management of Alternaria alternata Causing Leaf Spot Disease of Strawberry

Abstract

Leaf spot disease poses a constraint to strawberry cultivation, and preliminary characterisation of the associated pathogen and assessment of potential biological antagonists are relevant to disease-management research. This study investigated the morphological and cultural characteristics of a fungal isolate obtained from symptomatic strawberry leaves and compared its growth on six solid media. Four microbial bioagents were also evaluated using a dual-culture assay under in vitro conditions. Symptomatic leaf material was collected from strawberry fields in Dhule District, and fungal cultures were obtained by tissue isolation on Potato Dextrose Agar (PDA), followed by hyphal-tip purification. The isolate was identified morphologically as Alternaria alternata, producing dark olive to black colonies, septate, branched mycelium and brown, muriform conidia. Among the tested media, PDA supported the greatest colony diameter (90.00 mm), followed by Oat Meal Agar (88.90 mm), whereas Czapek’s Agar supported the lowest colony diameter (40.16 mm). In the bioagent assay, Trichoderma harzianum achieved 72.08% inhibition of radial growth and T. viride achieved 70.00%. The corresponding inhibition values for Bacillus subtilis and Pseudomonas fluorescens were 57.64% and 51.11%, respectively. These findings indicate that medium composition influenced fungal growth and that the two tested Trichoderma species suppressed the isolate more strongly than the bacterial bioagents under the conditions evaluated. Further confirmation of pathogen identity and testing under plant-based conditions are warranted before practical disease-control performance can be inferred.