Genetics of partial resistance against Verticillium dahliae race 2 in wild and cultivated lettuce

Authors: SANDOYA, GERMAN - University Of California; TRUCO, MARIA - University Of California; BERTIER, LIEN - University Of California; SUBBARAO, KRISHNA - University Of California; Simko, Ivan; Hayes, Ryan; MICHELMORE, RICHARD - University Of California

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2020
Publication Date: 8/23/2021
Citation: Sandoya, G.V., Truco, M.J., Bertier, L.D., Subbarao, K.V., Simko, I., Hayes, R.J., Michelmore, R.W. 2021. Genetics of partial resistance against Verticillium dahliae race 2 in wild and cultivated lettuce. Phytopathology. 111(5):842-849. https://doi.org/10.1094/PHYTO-09-20-0396-R.
DOI: https://doi.org/10.1094/PHYTO-09-20-0396-R

Interpretive Summary: Verticillium wilt, a disease caused by the soil borne fungus Verticillium dahliae, imposes economic losses on a large number of host crops. The disease is especially severe on lettuce, commercially the most valuable leafy vegetable in the USA, with a revenue of ~3.5 billion dollars in 2019. Verticillium wilt often results in near-total yield loss on lettuce in the Salinas Valley of California, which produces approximately 50% of the lettuce consumed in the USA. While 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. The inheritance of resistance against race 2 is complex but several resistance loci have been detected and may be considered in breeding programs.

Technical Abstract: Lettuce (Lactuca sativa L.) is one of the most economically important vegetables in the USA 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 Kleb., poses a major threat to lettuce production in this area. While 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 Lactuca sativa × L. sativa and L. serriola × 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.