Genetics of Partial Resistance Against Verticillium dahliae Race 2 in Wild and Cultivated Lettuce

Lettuce (Lactuca sativa) is one of the most economically important vegetables in the United States, with approximately 50% of the domestic production concentrated in the Salinas Valley of California. Verticillium wilt, caused by races 1 and 2 of the fungal pathogen Verticillium dahliae, poses a major threat to lettuce production in this area. Although resistance governed by a single dominant gene against race 1 has previously been identified and is currently being incorporated into commercial cultivars, identification of resistance against race 2 has been challenging and no lines with complete resistance have been identified. In this study, we screened germplasm for resistance and investigated the genetics of partial resistance against race 2 using three mapping populations derived from crosses involving L. sativa x L. sativa and L. serriola x L. sativa. The inheritance of resistance in Lactuca species against race 2 is complex but a common quantitative trait locus (QTL) on linkage group 6, designated qVERT6.1 (quantitative Verticillium dahliae resistance on LG 6, first QTL), was detected in multiple populations. Additional race 2 resistance QTLs located in several linkage groups were detected in individual populations and environments. Because resistance in lettuce against race 2 is polygenic with a large genotype by environment interaction, breeding programs to incorporate these resistance genes should be aware of this complexity as they implement strategies to control race 2.

Automated summary

Lettuce is an economically important vegetable in the United States, with a majority of production in the Salinas Valley of California. While resistance genes against race 1 have been identified, resistance against race 2 remains challenging. Research reveals that resistance in lettuce against race 2 is polygenic with a significant genotype by environment interaction.