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Characterization of resistance to Sclerotinia, and its association with plant architecture and composition in lettuce

Bullo Erena Mamo: University of California at Davis, c/o U.S. Agricultural Research Station

<div>Cultivated lettuce (<em>Lactuca sativa </em>L.) is an economically important vegetable crop. Lettuce drop, caused by the fungal pathogens <em>Sclerotinia minor</em> and <em>S</em>. <em>sclerotiorum</em>, causes significant yield loss in all lettuce types. Development of resistant cultivars has been impeded by the lack of resistance in lettuce germplasm. The resistance identified to the disease in lettuce landraces and non-adapted accessions cultivated for seed (oil consumption) is often linked with plant architecture mainly associated with premature bolting. Resistance to crown degradation due to Sclerotinia infection increases with plant age in non-leafy lettuce accessions. Research is underway to understand the relationship between plant architecture and crown degradation, and identify possible mechanisms underlying resistance. Preliminary results indicate that resistance to crown degradation is associated with stem strength and composition. Comprehensive analysis of plant tissue compositions implicated in differentiating susceptible vs. resistant accessions will be presented. For genetic analysis, a recombinant inbred lines (RILs) population derived from a cross between a susceptible cultivar and a resistant accession, and genotyped with molecular markers has been identified. This population is being evaluated for lettuce drop incidence, disease severity and rate of bolting in a field infested with <em>S. minor</em>. The RILs will also be evaluated for stem firmness and composition. QTL analyses of these traits will unravel the genetic mechanism of Sclerotinia resistance, its association with development-related traits and tissue composition in lettuce.</div>