Title : Evaluation of fungicides and organic extracts treatments used against antifungal brown leaf spot (Helminthosporium oryzae) disease for different rice genotypes varieties
Abstract:
Brown spot is one of the most devastating fungal diseases affecting rice crops. It ranks second in severity and is notorious for causing global yield losses ranging between 16% and 43% during outbreaks, or up to 90% in severe regional epidemics. This pathogen was the principal driving force behind the infamous 1943 Bengal Famine, where it destroyed 40–90% of the regional rice crop, leading to the starvation and death of up to 3 million people. Unlike some pathogens that only target leaves, brown spot attacks the rice crop at all growth stages, necessitating integrated management strategies combining host resistance, chemical fungicides, and botanical extracts. To evaluate these approaches, fourteen rice genotypes, including Basmati and IRRI lines, were screened for disease susceptibility under field conditions. Three fungicides Score, Gemstar, and Nativo were applied at multiple concentrations (low, recommended and high), while aqueous extracts from Azadirachta indica, Calotropis procera, Allium sativum, Datura stramonium, and Zingiber officinale were tested with concentration gradients ranging from 10% to 80%. Disease severity was recorded weekly over six weeks post-inoculation. Significant genotypic variation was observed, with IRRI-6 and KS-282 exhibiting the highest resistance and minimal symptoms, whereas Basmati-515 and IRRI-9 proved most susceptible. Among fungicides, Score at 8 ml demonstrated superior efficacy, reducing disease severity to 39.8% compared to 94.8% in untreated controls; Gemstar showed moderate control, while Nativo was least effective. Notably, botanical extracts exhibited pronounced dose-dependent antifungal activity, among the plant extract in food poisoning technique, all the plant extract give inhibitory effect against Bipolaris- oryzae. The best inhibitory effect was observed in ginger at1:8 dilution, achieving the highest inhibition rate (76%) relative to control, followed by neem (61.29%), garlic at 1:4 dilution (54.2%) and onion (56.14%). Based on these findings, it is recommended that resistant varieties IRRI-6 and KS-282 be deployed in disease-prone areas, complemented by Score at 8 ml as the optimal chemical treatment and ginger -based bio-fungicides at higher concentration for sustainable organic management. These integrated approaches should be validated through multi-location trials and disseminated to farmers via extension services to reduce chemical overuse and production costs while ensuring effective disease control. Plant extracts as potential antifungals were being exploited against several plant diseases. it also helps to manage environmental pollution by chemicals. The integrated approach balances effective disease control with a reduced environmental footprint.
