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Characterizing sources of resistance in tomato in response to Xanthomonas spp.
Abstract: Bacterial Spot of tomato is a detrimental disease caused by four species of Xanthomonas. Wild species, S. pimpinellifolium and S. lycopersicum var. cerasiforme, provide quantitative trait loci (QTL) for partial resistance when introgressed into cultivated tomato. Three independent sources of resistance have been identified with QTL on chromosome 11. The objectives of this project are (1) to determine which QTL provides the best resistance to multiple species of Xanthomonas and (2) to develop assays to measure the response of plants infected by X. gardneri. To determine which QTL provides the greatest resistance to multiple species, I will develop near isogenic lines using marker-assisted backcrossing. QTL-11 (H7998; S. lycopersicum), QTL-11b (PI11490; S.lycopersicum var. cerasiforme) and QTL-11c (LA2533; S. pimpinellifolium), will be introduced into a uniform genetic background (OH88119). Lines will then be evaluated for resistance to the major species causing bacterial spot. Quantitatively measuring plant response will determine whether the resistance observed in LA2533 against X. gardneri is a classic hypersensitive response (HR). HR is characterized by cell death around a site of infiltration within 24 to 48 hours. However, the HR-like symptoms in LA2533 in response to X. gardneri are delayed until 72 hrs. Additionally, there is a poor correlation between HR and resistance measured in field evaluations. These results suggest that studies aimed at better understanding the plant response to X. gardneri are warranted. Successful completion of these objectives will result in characterization of resistance to X. gardneri and a better understanding of quantitative resistance to multiple species of Xanthomonas.