In vitro Efficacy of Bio-agents and Plant Extracts against Alternaria alternata Causing Leaf Blight of Yardlong Bean

Abstract

Yardlong bean (Vigna unguiculata subsp. sesquipedalis) is an important vegetable crop affected by fungal diseases, including leaf blight caused by Alternaria alternata. This study evaluated the in vitro efficacy of selected bio-agents and aqueous plant extracts against A. alternata under controlled laboratory conditions. Six bio-agents were assessed using the dual culture technique, while five plant extracts were evaluated using the poisoned food technique; untreated cultures served as controls. Among the bio-agents, Trichoderma harzianum produced the greatest inhibition of mycelial growth (68.18%), followed by T. viride (67.48%) and Pseudomonas fluorescens (65.04%). Bacillus subtilis showed the lowest inhibition among the tested bio-agents (35.48%). Among the plant extracts, garlic clove extract was the most effective, resulting in 71.84% inhibition and a mean colony diameter of 25.34 mm. Datura leaf extract ranked next, with 69.64% inhibition and a mean colony diameter of 27.32 mm, whereas Karanj leaf extract showed the lowest inhibition among the tested botanicals (30.81%). The findings demonstrate differential in vitro activity among the tested treatments. Under the conditions of this study, T. harzianum and garlic clove extract were the most effective bio-agent and botanical treatment, respectively. Their efficacy should be evaluated further under field conditions before practical disease-management recommendations are made.