ARS | Publication request: VARIATION FOR RESISTANCE TO VERTICILLIUM WILT IN LETTUCE (LACTUCA SATIVA L.).

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 2006
Publication Date: March 19, 2007
Citation: Hayes, R.J., Vallad, G., Qin, Q., Grube, R., Subbarao, K. 2007. Variation for Resistance to Verticillium Wilt in Lettuce (Lactuca Sativa L.). Plant Disease. 91(4):439-445.

Interpretive Summary: Host resistance offers the most cost-effective control method of Verticillium wilt of lettuce, caused by Verticillium. dahliae. One hundred and seven lettuce cultivars were screened in infested fields to identify resistant cultivars. Disease progress over time was also determined on resistant and susceptible cultivars. Sixteen cultivars were selected that had no disease, low levels of disease, or high levels of disease and were tested in experiments using a race 1 and a race 2 isolate. Significant differences for resistance were observed within cultivated lettuce in field and greenhouse experiments. In susceptible cultivars, disease increased through the season, while disease in resistant cultivars remained constant or decreased. Resistance in greenhouse tests was dependant upon the V. dahliae race used. Seven romaine, Batavia, Latin, and red leaf cultivars were resistant to race 1, while all cultivars were susceptible to race 2. Cultivar reactions to race 1 in greenhouse and field experiments were correlated, and indicate that the greenhouse test is useful to identify resistant lettuce cultivars. The identification of resistance in diverse lettuce types is beneficial to the process of breeding new lettuce cultivars. However, the existence of resistance breaking race 2 isolates indicates that this resistance may not be durable. Alternatively, targeted releases of cultivars with resistance to race 1 to fields with this pathogen genotype is a likely method of extending the life of these cultivars. Additional testing of Lactuca germplasm for resistance to race 2 is needed.

Technical Abstract: Host resistance offers the most cost-effective control method of Verticillium wilt of lettuce, caused by V. dahliae. One hundred and seven lettuce cultivars were screened in infested fields for resistance and disease progress on resistant and susceptible cultivars was determined. Subsequent greenhouse experiments were conducted to evaluate 16 cultivars for resistance to a race 1 and a race 2 isolate, and to determine the effectiveness of greenhouse testing. Significant differences for resistance were observed within cultivated lettuce. In susceptible cultivars, disease increased through the season, while disease in resistant cultivars remained constant or decreased. Resistance in greenhouse tests was dependant upon the V. dahliae race used. Seven diverse cultivars were resistant to race 1, while all cultivars were susceptible to race 2. Cultivar reactions to race 1 in greenhouse and field were correlated, indicating the utility of greenhouse evaluations of host resistance. The identification of resistance in diverse lettuce types is beneficial to the breeding process. However, the existence of resistance breaking race 2 isolates indicates that this resistance may not be durable. Alternatively, targeted releases of cultivars with resistance to race 1 to fields with this pathogen genotype is a likely method of extending the life of these cultivars. Additional testing of Lactuca germplasm for resistance to race 2 is needed.