Inheritance of resistance of ‘Salinas 88’ lettuce to the root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood

Abstract

This study looked into the inheritance mode of resistance of ‘Salinas 88’ lettuce to the root-knot nematode Meloidogyne incognita race 1 (Kofoid & White) Chitwood. The treatments involved the parental lines ‘Regina 71’ (P2, nematode susceptible) and ‘Salinas 88’ (P1, nematode resistant), as well as the F1(P1xP2) and F2(P1xP2) generations. The experiment had a randomized complete block design with five replications. Altogether, 37 plants from ‘Regina 71’, 40 from ‘Salinas 88’, 40 from the F1 generation and 181 from the F2 generation were evaluated. Individual plants were evaluated with a score grades from 1(=resistant) to 5(=susceptible), 45 days after infestation with the pathogen, for gall number scores (GNS), eggmass number scores(ENS), and overall gall incidence (OGI) on the root system. Broad-sense heritabilities for GNS, ENS and OGI were estimated at 16.3%, 57.4% and 21.5%, respectively. The estimates of the mean degrees of dominance indicated partial dominance in the direction of a higher resistance. The monogenic hipothesis of inheritance was not rejected (at the limit of c2 test significance) for OGI and GNS, indicating that that resistance may be under control of a single gene locus. Divergent c2 tests performed for ENS rejected the hipothesis of monogenic inheritance, indicating that, if a major gene for nematode resistance is present in 'Salinas-88', its action may be influenced by the action of additional modifier genes. The test of maximum likelihood provided evidence both for the presence of one major gene with with partial dominance (in the direction of higher levels of resistance) and for the action of modifier polygenes.