2012 Annual Report 1a.Objectives (from AD-416): Objective 1. Provide phenotypic data for breeding lines essential to the development of BLS resistant germplasm. Objective 2. Determine if resistant, susceptible and important parental cultivars differ in their influence on Xcv populations. Objective 3. Develop a reliable and sensitive scheme for detecting and quantifying bacteria from potential inoculum sources. Objective 4. Evaluate the effect of pathogen diversity on severity of disease on susceptible and resistant cultivars. 1b.Approach (from AD-416): We will conduct laboratory and greenhouse experiments of lettuce to advance disease resistance breeding, understanding of mechanisms involved in resistance and to understand how pathogen diversity influences disease. 3.Progress Report: This project relates to objective C: Identify emerging diseases and their etiology and evaluate resistant germplasm for diseases of strawberry, lettuce, and vegetables. Bacterial leaf spot (BLS) of lettuce caused by the pathogen Xanthomonas campestris pv. vitians (Xcv) results in significant losses throughout California. Among the cultivars evaluated, the resistant cultivar was the only one on which Xcv elicited an HR within 24 hours. In plant tissue from these cultivars, bacterial populations levels did not increase at the same rate or to the same level as those on susceptible cultivars. We demonstrated differences in virulence among strain mixtures used to evaluate resistance here and abroad. A mixture of strains from Quebec, Canada, was more virulent than the mixture of strains from California. Preliminary data indicate that this is because two of the three strains are more virulent than strains from California. Only one strain from California appears to be as virulent as the strains from Quebec. Two of the three strains from Quebec belonged to a different genetic group than the third strain and the strains from California. According to analyses with three genes sequenced from 120 Xcv strains, there are three different genetic groups of Xcv. The Quebec strains belong to a group with few representatives and to which new pathogens from radicchio belong. Sequences from these three genes and an additional three genes are being used to design new specific primers for detection and quantification, because the PCR primers and protocols currently available are not specific for Xcv strains.