Identification of the F2:3 homozigotic lettuce families resistant to the root-knot nematode

The commercial production of lettuce, in high temperature conditions, has been affected by root-knot nematodes (Meloidogyne spp.). The use of resistant cultivars is an alternative for the cultivation in those conditions. The objective of this research was to evaluate the behavior of lettuce families with relation to the resistance to the root-knot nematode Meloidogyne spp., verifying the probable existence of homozygous families for that character. Forty-eight plants from each of 39 F-2:3 families of lettuce and the controls 'Grand Rapids' (resistant), 'Regina 71' (susceptible) and 'Ver (o) over cap nica' (susceptible) were used; 160 plants of cultivar Grand Rapids, 160 plants of cultivar Regina 71, 160 plants of cultivar Ver (o) over cap nica and 160 plants of cultivar Santa Clara (used for verification of the efficiency of the inoculum). Following the distribution of frequency of the notes for root-knot incidence, obtained through a scale of notes from I to 5, together with the c(2) test, the existence of 10 homozygous families for resistance to the root-knot nematode was evidenced. These resistant families are a useful tool to be used in future breeding programs for the development of a resistant cultivar.