DIFFERENTIAL SUSCEPTIBILITY OF MELOIDOGYNE INCOGNITA AND MELOIDOGYNE JAVANICA TO NEEM BASED BIOPESTICIDES

Abstract

Root-knot nematodes are major biotic constraints to rice production, necessitating sustainable management alternatives to synthetic nematicides. In this study, populations of Meloidogyne incognita and Meloidogyne javanica were isolated from rice fields in Madhepura district, Bihar, India, and their comparative susceptibility to a neem-based biopesticide was evaluated under laboratory conditions. Juvenile (J2) mortality (72 h exposure) and egg hatching inhibition (7-day exposure) were assessed across a concentration gradient (0–2000 ppm), and LC₅₀ values were estimated using probit analysis. Juvenile mortality increased in a clear concentration-dependent manner in both field-isolated populations, rising from negligible levels in untreated controls (3.2% and 2.9%, respectively) to 91.6% in M. incognita and 78.4% in M. javanica at 2000 ppm. Egg hatching inhibition followed a similar trend, reaching 86.8% in M. incognita and 71.2% in M. javanica at the highest concentration. The Madhepura M. incognita population consistently exhibited greater neem susceptibility than the co-occurring M. javanica population across all tested parameters. Probit analysis yielded LC₅₀ values of 742 ppm (95% CI: 684–803) for M. incognita and 1085 ppm (95% CI: 1012–1161) for M. javanica, both models showing excellent fit (R² > 0.98). The non-overlapping confidence intervals, along with highly significant differences in maximum mortality and hatching inhibition (p < 0.001), confirmed differential neem sensitivity between the two species. These findings, based on nematode populations native to rice-growing soils of Madhepura district, Bihar, provide region-specific baseline data supporting species-tailored, eco-friendly nematode management strategies for rice-based cropping systems in the region.