Bio Efficacy of Phylloplane Bacteria Isolated from Selected Medicinal Plants against Root Knot Nematode, Meloidogyne incognita

Abstract

The present study evaluated the bio-efficacy of phylloplane bacteria isolated from selected medicinal plants against the root-knot nematode, Meloidogyne incognita, under in vitro conditions. Fresh leaves of Houttuynia cordata, Bacopa monnieri and Paederia foetida were collected from different locations of Assam Agricultural University, Jorhat, and bacteria were isolated by the leaf-wash method using nutrient agar. A total of thirty bacterial isolates were obtained, comprising fifteen isolates from H. cordata, ten from B. monnieri and five from P. foetida. Gram staining indicated that five isolates were Gram-positive, while the remaining twenty-five isolates were Gram-negative. Culture filtrates of all isolates were tested against freshly hatched second-stage juveniles of M. incognita at 25, 50, 75 and 100% concentrations and at 12, 24, 48 and 72 hours of exposure. Juvenile mortality varied among isolates and generally increased with increasing filtrate concentration and exposure period. Based on treatment mean mortality, five isolates were selected as comparatively effective: M1, VA1, B8, M15 and M8, with mean mortalities of 56.10, 54.66, 52.99, 52.99 and 50.74%, respectively. At 72 hours, several isolates produced high juvenile mortality at higher concentrations. The LC50 values of the selected isolates ranged from 19.35-28.72%. Molecular characterization using 16S rRNA sequencing identified B8 as Bacillus subtilis, M15 as Bacillus megaterium, M8 as Lactiplantibacillus plantarum, M1 as Pantoea agglomerans and VA1 as Enterobacter cloacae. The findings indicate that phylloplane bacteria associated with medicinal plants possess nematicidal potential and may be further evaluated as biological agents for the management of M. incognita.