In vitro inhibition of corynespora cassiicola in rubber using methanolic plant extracts and fungicides

Abstract

The fungal pathogen Corynespora cassiicola causes severe leaf fall disease in rubber (Hevea brasiliensis), leading to significant yield losses. This study aimed to evaluate the antifungal potential of ten methanolic plant extracts and four synthetic fungicides against C. cassiicola using the poisoned food technique under controlled conditions. Results obtained indicate that Ocimum basilicum leaf extract demonstrated superior antifungal activity (75.2% inhibition at 100% w/v), performing statistically equivalent to azoxystrobin (82.4% at 20 ppm; p > 0.05). Minimum inhibitory concentrations (MICs) for effective plant extracts ranged from 32.4% (Amaranthus viridis) to 35.2% (Ageratum conyzoides). Among synthetic fungicides, azoxystrobin was the most potent (MIC: 15 ppm), while mancozeb showed limited efficacy (14.3% inhibition), suggesting the emergence of resistance in Nigerian C. cassiicola populations. Time-course analysis revealed rapid suppression of mycelial growth by O. basilicum within 24 hours, mirroring azoxystrobin’s inhibition pattern—a novel finding for botanical fungicides against this pathogen. These results position O. basilicum as a promising, sustainable alternative for integrated disease management, particularly in resource-limited settings where synthetic fungicides are constrained by cost or regulatory limitations. The findings highlight the potential of plant-derived antifungals to complement conventional disease control strategies while mitigating the risks of resistance.