Extrinsic factors governing the spore encumbrance of an indigenous population of Pasteuria hyperparasitizing root-knot nematodes, Meloidogyne species.

Abstract

Isolates of indigenous populations of gram-positive endospore-forming bacterial hyperparasite Pasteuria spp. infecting root-knot nematodes were made from arid, semi-arid, humid and sub humid ecosystems of India. A semi-arid population was successfully multiplied on cowpea (Vigna unguiculata), cv Pusa Komal under soil-less conditions in growth pouches maintained at 250C for 32±2 days. The recovery of Pasteuria infected females varied from 38.4 to 91.3% per plant. A nematode inoculum of 15 J2 per root tip with 15 spores per J2 resulted in significantly higher number of infected females than inoculum levels of 5 or 10 J2 per root tip with 10 spores/J2. Host-specificity assays with four species of root-knot showed a greater affinity of endospore attachment to M. incognita (6.25 spores per J2), followed by M. javanica (3.90), M. hapla (1.10) and M. graminicola (0.90) at a spore density of 6.9 x 105 spores per mL. Endospore attachment was not observed on infective juveniles of Heterodera cajani, H. avenae or Rotylenchulus reniformis, nor to the developmental stages of M. incognita (J3, J4 and males). A pre-exposure of spores to high temperatures (40, 45 and 500C) resulted in a progressive decline in spore attachment on M. incognita J2s with an increase in exposure period; resulting in 81.5 per cent decline on exposure at 500C, 10 minutes. Preincubation of the Pasteuria endospores with Bacillus cereus, B. subtilis and B. pumilus, followed by spore attachment assays with M. incognita J2, exhibited a per cent decline in attachment of 97.23, 94.60 and 96.5, respectively, over the untreated controls.