2011 Annual Report
Baby leaf lettuce is an important and highly valuable California crop, but the varieties used are susceptible to many pests that reduce profits of lettuce producers and packers. The purpose of this project is to reduce or eliminate grower and packing company losses on baby leaf lettuce production from the pests downy mildew, Xanthomonas campestris pv. vitians (Xcv), and leafminers. One objective is to develop resistant lettuce breeding lines and populations within three years and release these to private seed companies for distribution to growers. This will increase the number of available pest resistant baby leaf varieties, thereby reducing crop losses. Another objective is to generate critically needed information regarding the Xcv-lettuce pathosystem, this will increase the effectiveness of developing new resistant cultivars and lead to improved cultural control measures due to the identification of important inoculums sources. For the Xanthomonas campestris pv. vitians Bacteriology (XcvB) project, 93 strains were obtained either by purchasing them from culture collections or by donations from researchers. The strains included the type strain of X. campestris pv. vitians and the pathogenic reference strain for X. hortorum pv. vitians. All strains are stored at the USDA/ARS. Additional strains may be collected throughout the grant period as outbreaks are reported. For the Leafminer resistance project, we prepared and cataloged more than 100 S3-S6 green leaf, red leaf, and romaine lettuce breeding lines for further field testing. For the Xcv resistance project, a greenhouse experiment to select red leaf type plants with Bacterial Leaf Spot (BLS) resistance from a cross with Batavia Reine des Glaces and Eruption was completed. Red leaf and red romaine plants with low bacterial leaf spot severity were selected. For the Downy mildew (DM) project, our evaluation of downy mildew resistance in greenhouse trials produced inconsistent results that did not correlate well with previous field observations. Therefore, we used an alternative approach to select breeding lines for field evaluation. Using a rank-based approach to combine data from multiple trials, 20 lines with potentially very good levels of non-specific resistance were selected.