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United States Department of Agriculture

Agricultural Research Service

Research Project: Evaluation, Enhancement, Genetics and Breeding of Lettuce, Spinach, and Melon Title: Assessment of resistance in lettuce (Lactuca sativa L.) to mycelial and ascospore infection by S.sclerotinia minor Jagger and S. sclerotiorum (Lib.) de Bary

Authors
item Hayes, Ryan
item Wu, Bo Ming -
item Pryor, Barry -
item Subbarao, Krishna -

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 19, 2010
Publication Date: March 1, 2010
Citation: Hayes, R.J., Wu, B., Pryor, B.M., Subbarao, K.V. Assessment of resistance in lettuce (Lactuca sativa L.) to mycelial and ascospore infection by S.sclerotinia minor Jagger and S. sclerotiorum (Lib.) de Bary. HortScience 45:333-341.

Interpretive Summary: Lettuce drop is a damaging disease of lettuce (Lactuca sativa L.) that renders the heads useless. Cultivars with resistance to soil-borne infection by the fungal species Sclerotinia sclerotiorum (Lib.) de Barry and S. minor Jagger as well as to aerial infection by S. sclerotiorum ascospores are needed. Assessing resistance in field experiments can be complicated by fast bolting or small stature lettuce lines that may escape, rather than resist the fungal infection and growth. Therefore, methods to select resistant lines from populations of lettuce with different architecture and growth habits are needed. We used S. sclerotiorum and S. minor infested field experiments, regression analysis, field experiments with artificially high plant densities, and S. sclerotiorum ascospore inoculations to identify lettuce lines with resistance to both pathogens. Three replicated S. sclerotiorum field experiments were conducted in Yuma, AZ and three S. minor field experiments were conducted in Salinas, CA using diverse populations of iceberg, romaine, leaf, butterhead, latin, oilseed lettuce and wild relatives of lettuce; genetic resistance to soil-borne infection was found. In two S. minor field experiments, bolting was rated on a 1 (rosette plants) through 6 (seed set) scale, and a quadratic regression model was developed that related faster bolting with reduced lettuce drop. Regression residuals were calculated, and ‘Eruption’, ‘Little Gem’, PI167391, PI176592, PI178921, PI226641, PI229761, and PI273589 had negative residuals, indicating higher resistance than predicted by their stage of bolting. Eruption, a small statured Latin cultivar, had significantly lower disease than susceptible cultivars in experiments with high plant densities, indicating that its small size did not facilitate disease escape. Ascospore inoculations confirmed resistance in ‘Eruption’ and L. virosa SAL012, while the oilseed lettuce PI251246 may have partial resistance to infection.

Technical Abstract: Lettuce drop is an economically important disease of lettuce (Lactuca sativa L.), and cultivars with resistance to mycelial infection by Sclerotinia sclerotiorum (Lib.) de Barry and S. minor Jagger as well as to S. sclerotiorum ascospores are needed. Assessing resistance in field experiments can be complicated by fast bolting or small stature lettuce lines that may escape, rather than resist the pathogens. Therefore, methods to select resistant lines from morphologically variable populations are needed. We used S. sclerotiorum and S. minor infested field experiments, regression analysis, field experiments with artificially high plant densities, and S. sclerotiorum ascospore inoculations to identify lettuce lines with resistance to both pathogens. Three replicated S. sclerotiorum field experiments were conducted in Yuma, AZ and three S. minor field experiments were conducted in Salinas, CA using diverse populations of iceberg, romaine, leaf, butterhead, latin, oilseed lettuce and wild relatives of lettuce; genetic variation for the incidence of lettuce drop from mycelial infections was identified. In two S. minor field experiments, bolting was rated on a 1 (rosette plants) through 6 (seed set) scale, and a quadratic regression model was developed that related faster bolting with reduced lettuce drop. Regression residuals were calculated, and ‘Eruption’, ‘Little Gem’, PI167391, PI176592, PI178921, PI226641, PI229761, and PI273589 had negative residuals, indicating higher resistance than predicted by their stage of bolting. Eruption, a small statured Latin cultivar, had significantly lower disease than susceptible cultivars in experiments with high plant densities, indicating that its small size did not facilitate disease escape. Ascospore inoculations confirmed resistance in ‘Eruption’ and L. virosa SAL012, while the oilseed lettuce PI251246 may have partial resistance to infection.

Last Modified: 11/24/2014
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