Location: Crop Improvement and Protection ResearchTitle: Resistance to bacterial leaf spot in baby leaf lettuce
Submitted to: American Society of Horticulture Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2020
Publication Date: 8/12/2020
Citation: Sthapit Kandel, J., Sandoya, G.V., Mou, B., Simko, I. 2020. Resistance to bacterial leaf spot in baby leaf lettuce. American Society of Horticulture Science Annual Conference, August 9-13, 2020, Orlando, Florida.
Technical Abstract: Spring mix is a popular type of packaged salad and baby leaf lettuce (BLL; Lactuca sativa L.) is one of its main ingredients. BLL is sown at very high densities, which enhances occurrence of bacterial leaf spot (BLS), caused by Xanthomonas campestris pv. vitians (Xcv), a disease that can make the crop unmarketable. The market demands disease-free, high-quality BLL all year round. Growing highly BLS-resistant cultivars will reduce yield/quality losses and minimize economic harm to lettuce and spring mix growers. Our objectives were to identify lettuce varieties resistant to BLS and associated quantitative trait loci (QTL) conferring BLS resistance. Nearly 500 lettuce accessions were screened with three BLS isolates (BS0347, BS2861, BS3127) at USDA-ARS, Crop Improvement and Protection Research Unit, Salinas, CA and three isolates (L7, L44, and Sc8B) at Everglades Research and Education Center, University of Florida, Belle Glade, FL. The plants were inoculated with a single BLS isolate in each test at around the 3-week stage of growth and incubated with water misters to ensure constant leaf wetness for optimal disease development, with at least one experiment for each isolate. Disease severity was scored on a 0-5 visual scale (0, no disease; 5, > 50 % of the leaves diseased). Accessions showing high level resistance to one or more BLS strains include ARM09-161-10-1-4 (wild lettuce, Lactuca serriola), ‘Bunte Forellen’, ‘Grenadier’, ‘La Brillante’, PI 176592, PI 226514, PI 358004, PI 491056 0-COS- WP 070, SalVal-321, and ‘Tango’. Approximately 4,615 high-quality, polymorphic, single-nucleotide polymorphism markers were used for genome-wide association studies (GWAS) of BLS resistance by mixed linear model analyses; the genetic relationships among the individuals were incorporated into statistical models using principal component analysis and kinship matrix. A significant QTL was detected on Linkage Group 2 (LG2) for isolate BS0347 (P-value 5.54E-6) and for combined results of Florida isolates (P-value 4.00E-6). A major QTL for resistance to BLS in LG2 was previously reported in recombinant inbred line (RIL) populations. Molecular markers closely linked with the QTL can be applied for marker-assisted selection of BLS-resistant lettuce germplasm and development of new lettuce cultivars with multiple disease resistance.