Evaluation and verification of resistance in selected vegetable crops for sustainable root-knot nematode management in developing agriculture

Abstract

Root-knot nematodes, (Meloidogyne species) are a major constraint in vegetable production systems. These parasites cause high yield losses, particularly in subsistence farming systems. This study was conducted to establish * whether monospecific populations of M. incognita race 2 and M. javanica were used in these trials by means of molecular identification, * determine whether root-knot nematode-resistance is present in commercially available tomato, green bean, pumpkin and Brassica genotypes and to * verify resistance found. M. incognita race 2 and M. javanica were identified as monospecific using molecular techniques. Host suitability trials for the relevant vegetable crops were conducted in a greenhouse. Although various nematode parameters were used (the number of eggs and 52 per root system and per gram of roots, number of egg masses and egg-laying females (ELF) per root system), reproduction factors values [RF = final egg and J2 numbers (Pf)/initial egg and J2 numbers (Pi)] were used as the main criteria to select for root-knot nematode resistance. Although substantial variation existed among the relevant vegetable genotypes with regard to all parameters used, none of these genotypes were immune to either M. incognita race 2 or M. javanica since these parasites reproduced on all vegetable genotypes used in this study. However, three tomato and a range of Brassica genotypes had W-values lower than 1, indicating resistance to M. incognita race 2. With regard to the verification of M. incognita race 2-resistance in tomato genotype Rhapsody relative to the susceptible Moneymaker in a microplot trial using a range of initial inoculation levels, strong relationship existed for both genotypes for the majority of nematode variables used. These relationships were best described by non-linear equations. Significantly lower numbers of eggs and J2 in roots, as well as J2 in soil were obtained for Rhapsody compared to Moneymaker. RF-values were inversely proportional to initial population density (Pi) for Rhapsody (r = -0.3), while it increased gradually to Pi for Moneymaker (r = 0.94). A range of Brassica genotypes were also identified resistance to M. incognita race 2 and M. javanica, respectively, but none of the green bean and pumpkin screened had RF-values 5 1, indicating susceptibility to both species.