Survey of root knot nematodes and RMi resistance to Meloidogyne incognita in soybean from Khyber Pakhtunkhwa, Pakistan

Abstract

The root knot nematode (RKN), Meloidogyne spp. is one of the most significant pests limiting the agricultural productivity. The RKN constitute the most widely distributed group among the plant parasitic nematodes. This study was carried out to find the pathogenicity of Meloidogyne incognita in soybean. Occurrence and prevalence of Meloidogyne species in soybean fields along with categorization of soybean varieties on the basis of resistance to M. incognita was also studied. An extensive survey for RKN was carried out from Khyber Pakhtunkhwa (KPK) province of Pakistan. The most prevalent specie in all studied hot spots was M. incognita, followed by M. javanica that was observed in Akbar Pura, Bari Kot, and Dargai. In this study, fifteen soybean varieties were generously provided by agricultural field’s farmers and National Agriculture Research Centre of Pakistan. These selected varieties were assessed against M. incognita in experimental area of National Nematological Research Center, University of Karachi in three separate trials from 2014 to 2016. Internationally known susceptible (Bossier and Lee) and resistant (Gregg and Forrest) soybean varieties were checked as positive controls. The reproduction factor (RF) and damage index (DI) were employed to sort out the varieties as resistant or susceptible. Statistically significant differences (P < 0.01) were noticed amongst the studied varieties for RKN reproduction factors such as egg mass index (EMI), gall index (GI) and Juveniles/250 g soil. Moreover, thirty SSR markers were used for the identification of RMi gene, amongst them only three diagnostic markers exhibited the presence of RMi gene in resistant varieties. The resistant genotypes are potential materials against M. incognita. In the present investigation, molecular results confirmed locus of RMi gene in resistant genotypes and their functional presence in nematode management programs for choosing resistant varieties in the field. For the confirmation of resistance in soybean against RKN different biochemical indicators, which play active role in resistance mechanism, were also studied. Resistant varieties exhibited maximum amount of phenol, salicylic acid, chlorogenic acid and ascorbic acid as compared to susceptible plants.