Distribution of three Verticillium dahliae races in coastal California and evaluation of resistance in lettuce

Authors: MANDAL, MIHIR - University Of California; KOIKE, STEVEN - Trical Inc; TSUCHIDA, CAYLA - Trical Inc; STANGHELLINI, HANANE - Trical Inc; GUERRERO, JENNIFER - Trical Inc; SANDOYA, GERMAN - University Of Florida; Klosterman, Steven; Simko, Ivan; SUBBARAO, KRISHNA - University Of California

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2024
Publication Date: 6/12/2024
Citation: Mandal, M.K., Koike, S.T., Tsuchida, C., Stanghellini, H., Guerrero, J., Sandoya, G., Klosterman, S.J., Simko, I., Subbarao, K.V. 2024. Distribution of three Verticillium dahliae races in coastal California and evaluation of resistance in lettuce. Plant Disease. 108(7):2170-2180. https://doi.org/10.1094/PDIS-01-24-0193-RE.
DOI: https://doi.org/10.1094/PDIS-01-24-0193-RE

Interpretive Summary: The fungus Verticillium dahliae causes Verticillium wilt disease on lettuce and multiple crops grown in rotation with lettuce in coastal California. Three distinct races of the V. dahliae have been characterized based upon resistance and susceptibility reactions on differential cultivars in tomato and the presence of genetic markers specific to race 1, 2 or 3. Whether or not that same race structure is present in coastal California is not known. Therefore, in this study, the different races of V. dahliae as characterized by the genetic markers and one unknown race of V. dahliae, were assessed for their ability to cause disease on 49 lettuce lines and cultivars. Some of these cultivars were determined to be resistant to race 1, and partially resistant to race 2. Race 3 caused the least disease across all cultivars. Information on the race structure of V. dahliae can may prevent future Verticillium'wilt pandemics in California by limiting the spread through identification and deployment of resistance for more effective management.

Technical Abstract: Verticillium wilt, caused by Verticillium dahliae, is one of the most devastating soilborne diseases of lettuce (Lactuca sativa L.). There are three races of V. dahliae, and each race has been characterized by markers representing race-specific effectors. Race 1 is differentiated by the presence of the functional secretory Ave1 effector. Similarly, races2 and 3 are differentiated by effectors VdR2e and VdR3e, respectively. Although the presence of race 1 in coastal California was well established, the presence of effector-based races 2 and 3 was uncertain. This study therefore focused on characterizing 727 isolates collected from142 ranches of symptomatic lettuce and other crops from coastal California. Based on this evaluation, 523 isolates were designated as race1, 20 isolates as race 2, 23 isolates as race 3, and 17 as race undefined. Isolates representing other Verticillium species totaled 110, and 34 were non-Verticillium fungal species. Because the use of resistant cultivars is a key strategy to manage this disease, we evaluated 48 lettuce germplasm lines and 1 endive (Cichorium endivia L.) line, comprising commercial cultivars and breeding lines, including the race 1–resistant heirloom cultivar La Brillante and the susceptible cultivar Salinas as controls. Resistance against races 1, 2, and 3 along with VdLs17, a virulent isolate of V. dahliae from lettuce that is currently not assigned to a race, was evaluated in replicated greenhouse experiments. Two crisphead lettuce lines, HL28 and HL29, exhibited resistance against race 1 and a partial resistance against race 2, whereas all other lines were highly susceptible to races 1 and 2 and VdLs17. The majority of lines exhibited higher resistance to race 3 relative to the other two races. This study documents the current distribution of the different races in coastal California. In addition, the sources of resistance currently being developed should be effective or partially effective against these races for targeted deployment as soon as they are available.