Genetic Study of Serpentine Leafminer Resistance in Valmaine Romaine Lettuce

Serpentine leafminer (Liriomyza trifolii) is an economically important pest of lettuce in the U.S. Control of the insect historically relies on use of pesticides but this increases crop production costs and causes environmental concerns. The insect has also developed resistance to many pesticides, rendering chemicals useless in protection of the lettuce crop. Host plant resistance is an environmentally friendly method that can be readily integrated into IPM to control the insect. The edible romaine lettuce cultivar Valmaine is known to be resistant to serpentine leafminer and three other insect species. In this study, a population consisting of 126 F_2:3 families derived from a cross of Valmaine and Okeechobee was developed for genetic study of the serpentine leafminer resistance. Plants of each family and the parents are being screened for response to stippling by the serpentine leafminer using a clip cage method. A damage score, based on the amount of stippling, is being measured on each plant on a scale of 0-4. The data will be subjected to statistical analysis to determine inheritance of the resistance in Valmaine. A preliminary result from 20 families suggests that the resistance to serpentine leafminer may be controlled by the same gene Bcb1 for resistance to banded cucumber beetle. Genotyping the F₂ individual to identify closely linked molecular markers is underway.