GENETIC VARIABILITY AMONG DIFFERENT POPULATIONS OF ROOT KNOT NEMATODES ASSOCIATED WITH VEGETABLES AND THEIR VULNERABILITY TO PASTEURIA PENETRANS

Abstract

Plant-parasitic nematodes particularly root knot nematodes (RKNs), Meloidogyne spp., are a severe constraint to vegetable production. They cause heavy economic damages in Pakistan and also worldwide. Determination of genetic diversity among root knot nematodes is critical to investigate their host range so as to devise consequent disease management plan. Therefore present study investigated genetic variability among RKNs and their response to Pasteuria (hyperparasite/biocontrol of RKNs). Different fields in major vegetable production areas in Punjab (Faisalabad, Jhang, Khanewal, Multan and Rawalpindi) was randomly surveyed for reliable estimation of different RKN populations and Pasteuria penetrans associated with tomato and cucumber crops. 700 soil and roots samples (6-9cm depth) were collected. Out of which 340 (48.57%) were infested with RKN. Maximum disease incidence 54.28% was reported in Faisalabad followed by 50, 44.28, 42.85 and 31.42% in Jhang, Multan, Rawalpindi and Khanewal respectively. In vitro, different isolates of P. penetrans (PP-3 and PP-J) at different temperatures and concentrations were evaluated against 116 RKN populations. The results revealed that with the increase in temperature and spore concentration the mean encumbrance level of Pasteuria with J2 cuticle increased. A population of RKN giving best attachment with Pasteuria was studied for their genetic variability using PCR-RFLP. The sizes of PCR products were 1.7 kb for M. incognita and M. javanica populations while populations of M. arenaria produced 1.1 kb fragment. The digestion with Hinf I of 1.7 kb product of M. javanica yielded two fragments of 1.0 and 0.7 kb, while an additional enzyme digestion site on M. incognita product cleavage the 0.7 kb fragment to generate two more fragments of about 0.4 and 0.3 kb. M. arenaria had no enzyme digestion site by Hinf I digestion. Developments of PP-3 and PP-J on different populations of Meliodogyne spp. were not varied significantly when tomato and cucumber growth responses were compared. However nematode reproduction parameters were variable. In microplat, increase in plant growth responses of tomato in i.e., fresh and dry weight of shoot, shoot length and yield of tomato plants was observed when nematodes were treated with spores of P. penetrans. Nematode reproduction parameters i.e., galls/plant, galls with egg masses, J2/100 ml3 and reproduction factor were variable between plants inoculated with nematodes and nematode + Pasteuria treated plants. The influence of five levels of endospore attachment (1-2 spores/J2, 3-5 spores/J2, 7-10 spores/J2, >15spores/J2 and control) decreased root invasion by J2, galling index, egg masses/plant and females/plant while infected females and their percentage increased with increase in level of endospores. In different soil textures viz., sandy soil, silt, clay soil, loam soil, sandy loam, loamy sand, sandy clay and clay loam, the rate of encumbrance of J2 and P. penetrans development parameters were maximum in light textured soil than heavier ones. The results of this project provided updated status of RKN infestation level in Punjab, genetic diversity among different populations of RKN and efficacy of P. penetrans for sustainable crop protection against RKN.