Guarding the ridge gourd: Characterization and in vitro management of Phytophthora nicotianae causing fruit rot of Luffa acutangula in North Kerala

Abstract

Fruit rot disease, a significant threat to ridge gourd cultivation, was prevalent in the North Zone of Kerala in 2019 from May to August. The prevalence of the disease was attributed to warm and humid climatic conditions, resulting in an incidence of 47 percent. This led to a devastating economic loss, accounting for 43.75 percent of the produce. Extensive studies encompassing symptomatology, cultural, morphological, and molecular characterisation were conducted to identify the causative pathogen, which was identified as Phytophthora nicotianae (Gen Bank Accession No. MK789292.1). In a bid to manage the disease, the efficacy of various fungicides, including mancozeb 75WP, carbendazim (12%) + mancozeb (63%) (Saaf), cymoxanil (8%) + mancozeb (64%) (Curzate M-8), and tebuconazole 250EC (Folicur), was assessed through in vitro experimentation. Remarkably, cent percent pathogen inhibition was achieved across different concentrations, demonstrating their promising potential. Furthermore, botanicals such as garlic extract, azadirachtin 0.1 percent (Neemazal), and ready-to-use neem oil garlic soap (Raksha) were evaluated. These botanicals exhibited varying levels of inhibition, with garlic extract displaying the highest efficacy at 77.77 percent, followed by azadirachtin at 22.22 percent and ready-touse neem oil garlic soap at 16.66 percent across different concentration ranges. Trichoderma viride and PGPM have emerged as strong contenders in investigating potential biological control agents, demonstrating complete inhibition against Phytophthora nicotianae. Additionally, Pseudomonas fluorescens and Bacillus subtilis exhibited 61.1 percent and 50 percent inhibition rates, while PGPR Mix-II exhibited an inhibition rate of 16.66 percent.