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2013 ASHS Annual Conference

14820:
QTL Analysis for Early Blight Resistance in Tomato

Tuesday, July 23, 2013: 4:15 PM
Desert Salon 13-14 (Desert Springs J.W Marriott Resort )
Dilip Panthee, North Carolina State University, Mills River, NC
Allen van Deynze, University of California, Davis, Davis, CA
Sung-Chur Sim, Horticulture and Crop Science, Sejong University, Seol, South Korea
David Francis, Department of Horticulture and Crop Science, The Ohio State University, Wooster, OH
Early blight (EB), caused by Alternaria solani and related fungi is a potentially devastating disease of tomato grown under humid conditions.  Although it is controlled by fungicides, resistance can effectively lengthen spray intervals and reduce the amount of pesticides applied. Some quantitative trait loci (QTL) associated with resistance to EB have been reported but the location of those QTL on the tomato genome is still not precise. The objective of this study was to map the QTL associated with EB resistance within culitvated tomato genetic backgrounds. A mapping population (F2:3) was derived from a cross of NC 1CELBR x Fla 7775. NC 1CELBR is resistant and Fla 7775 is susceptible to EB. A population of 250 F2-derived lines with six plants per line were planted at the Mountain Research Station, Waynesville, NC, with two replicates. Natural inoculum provided disease pressure. Disease rating was performed at the scale of 0 to 5, where 0 = no disease symptom at all on the leaf surface, 1 = symptoms spread over about 20% of the leaf surface area, 2 = symptoms spread over 21% to 40% of the leaf surface area, 3 = symptoms spread over about 41% to 60% of the leaf surface area, 4 = symptoms spread over 61% to 80% of the leaf surface area, and 5 = symptoms spread over 100% of the leaf surface area. The population was genotyped with 384 single nucleotide polymorphic (SNP) molecular markers optimized for polymorphism rate in fresh-market tomato germplasm and assayed using the KASPAR platform, of which 183 were found to be polymorphic in this population. Composite interval mapping (CIM) using QTL Cartographer (version 2.5) revealed that there are three QTL on chromosome 2 located at 10cM (R2=4.6%), 13cM (R2=5.3%) and 35cM (R2=5.9%) positions, and one on each of chromosome 4 located at 55cM (R2=6.2%) and 12 located at 47cM (R2=41.3%) positions, respectively. Chromosome 6 may have an important genomic region which was detected by single factor analysis of variance (ANOVA) but not by CIM. Additional work on these chromosomes may provide precise mapping of QTL conferring resistance to EB in tomato.
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