Identification and mapping of quantitative trait loci for resistance to Liriomyza trifolii in romaine lettuce cultivar 'Valmaine'.

Liriomyza trifolii (Diptera: Agromyzidae) is a leafminer that causes ruinous damage to many leafy vegetables including lettuce (Lactuca sativa L.) by stippling and tunneling the leaves. In this study, a population of 125 F3 families was developed from the intraspecific cross of ‘Valmaine’ (resistant) and ‘Okeechobee’ (susceptible) romaine cultivars for inheritance analysis and molecular mapping of the resistance loci controlling stippling damage. The experiments were conducted in an insectarium (controlled environment). Stippling damage proved to be heritable because the broad-sense heritability (H2) was 0.58. A segregation analysis suggested that a single dominant allele, Sd1 locus, controls resistance against L. trifolii. Furthermore, a quantitative trait loci (QTL) analysis identified one novel QTL, named Stippling on LG5 (qSTP5), flanked by two SNPs that were mapped to a 5.2 cM (8.5 Mb region) interval, explaining over 13% of the total phenotypic variance. Desirable allele for resistance to L. trifolii was derived from resistant cultivar Valmaine. Identification of SNPs closely linked to the QTL responsible for L. trifolii resistance should facilitate plant breeders to develop resistant romaine lettuce cultivars.