Association analysis of bacterial leaf spot resistance and SNP markers derived from expressed sequence tags (ESTs) in lettuce (Lactuca sativa L.)

摘要

Bacterial leaf spot of lettuce, caused by Xanthomonas campestris pv. vitians, is a devastating disease of lettuce worldwide. Since there are no chemicals available for effective control of the disease, host-plant resistance is highly desirable to protect lettuce production. A total of 179 lettuce genotypes consisting of 29 leaf, 15 crisphead, one stem, 21 romaine, and 113 butterhead types were evaluated for response to X. c. vitians. One source of high resistance and five sources of moderate resistance were identified with four being butterhead lettuce and two leaf lettuce. The population genetic structure based on 350 expressed-sequence-tag-derived single nucleotide polymorphism generated two clades: Clade I and Clade II. The butterhead type was genetically distinct from romaine and crisphead types, while the leaf type was found to frequently exchange genes with other types through the history of breeding. Association mapping identified one single nucleotide polymorphism (QGB19C20.yg-1-OP5) associated with disease severity in Q general linear model and Q + K mixed linear model. Two SNP markers (Contig15389-1-OP1 and Contig6039-19-OP1) were associated with the resistance in the leaf lettuce PI 358000-1 which had no disease symptoms. The marker QGB19C20.yg-1-OP5 is in linkage group 2, while both of Contig15389-1-OP1 and Contig6039-19-OP1 are in linkage group 4. The resistant lines and the associated SNPs should be useful to develop resistant cultivars to battle against the devastating disease in lettuce