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United States Department of Agriculture

Agricultural Research Service

Title: Characterization of Race-Specific Interactions among Isolates of Verticillium Dahliae Pathogenic on Lettuce

Authors
item Vallad, Gary - UC, DAVIS
item Qin, Qing-Ming - UC, DAVIS
item Grube, Rebecca - UNIV. NEW HAMPSHIRE
item Hayes, Ryan
item Subbarao, Krishna - UC, DAVIS

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 25, 2006
Publication Date: December 20, 2006
Citation: Vallad, G.E., Qin, Q., Grube, R., Hayes, R.J., Subbarao, K.V. 2006. Characterization of race-specific interactions among isolates of verticillium dahliae pathogenic on lettuce. Phytopathology. 96(12):1380-1387. DOI: 10.1094/PHYTO-96-1380.

Interpretive Summary: Verticillium wilt, a soil borne fungal disease caused by Verticillium dahliae poses a major threat to lettuce (Lactuca sativa) production in California. Incorporation of host resistance into commercial lettuce cultivars offers the least expensive control method. To test resistance identified in previous field experiments, a pair of susceptible (‘Salinas’ and ‘Sniper’) and resistant (‘La Brillante’ and ‘Little Gem’) lettuce varieties were inoculated with 30 isolates of V. dahliae and two isolates of V. albo-atrum collected from several infected host species including lettuce. Disease severity was determined when the plants reached maturity. None of the V. albo-atrum isolates or V. dahliae isolates from cruciferous hosts caused disease on lettuce. Both ‘Salinas’ and ‘Sniper’ wee susceptible to many isolates of V. dahliae from non-cruciferous hosts, and the isolates varied in their overall aggressiveness. However, only 3 isolates caused significant disease on the resistant varieties ‘La Brillante’ and ‘Little Gem’. These 3 isolates were also genetically distinct from the other V. dahliae isolates based on their deoxyribonucleic acid sequence of the intergenic spacer region of the V. dahliae genome. This suggests that they form a distinct subgroup that differs in virulence towards specific lettuce genotypes. Accordingly, these isolates were designated as race 2, while those isolates virulent only on the susceptible ‘Salinas’ and ‘Sniper’ were designated as race 1. Although a range of virulence among V. dahliae isolates has been described in other plant species, this is the first description of distinct virulence phenotypes in V. dahliae since a similar race structure was described in tomato in the 1960s.

Technical Abstract: Verticillium wilt, caused by Verticillium dahliae poses a major threat to lettuce (Lactuca sativa) production in California. Incorporation of resistance into commercial lettuce cultivars offers the least expensive technique of sustaining production in infested areas. To test the breadth of the resistance identified in field, a pair of susceptible (‘Salinas’ and ‘Sniper’) and resistant (‘La Brillante’ and ‘Little Gem’) lettuce cultivars/varieties, were used as differentials and individually inoculated with 30 isolates of V. dahliae and two isolates of V. albo-atrum from several hosts including lettuce in replicated greenhouse experiments. The reactions of the four cultivars were determined based on the disease severity at maturity. None of the V. albo-atrum isolates or V. dahliae isolates from cruciferous hosts caused significant disease on lettuce. Both ‘Salinas’ and ‘Sniper’ were susceptible to many isolates of V. dahliae from non-cruciferous hosts (22 out of 24), and the isolates varied in their overall virulence. However, of these, only 3 isolates caused significant disease on the resistant varieties ‘La Brillante’ and ‘Little Gem’. These 3 isolates were also distinct from the other V. dahliae isolates based on sequence data from the intergenic spacer (IGS) region, suggesting that they form a phylogenetically distinct subgroup that differs in virulence towards specific lettuce genotypes. Accordingly, isolates of V. dahliae virulent on all tested cultivars/varieties including the resistant “La Brillante’ and ‘Little Gem’ were designated as race 1. Although a range of virulence among isolates has been described in other hosts, this is the first description of distinct virulence phenotypes in V. dahliae since a similar race structure was described in tomato in the 1960’s.

Last Modified: 8/1/2014
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