MAP-BASED IDENTIFICATION AND POSITIONAL CLONING OF XYLELLA FASTIDIOSA RESISTANCE GENES FROM KNOWN SOURCES OF PIERCES DISEASE RESISTANCE IN GRAPE

• Author(s): Riaz, Summaira; Walker, Andrew;
• Abstract: Development of a framework simple sequence repeats (SSR) genetic linkage map based on the 181 genotypes of 9621 family, which segregates for Pierces disease (PD) resistance is complete. The current genetic linkage map consists of 236 non-AFLP markers (SSR, EST-SSR and ESTP-RFLP) in 19 linkage groups. The PD resistance locus, PdR1, maps to linkage group 14 (LG - essentially a chromosome) of the male parent (F8909-17), which now consists of 30 markers, nine of which are localized within 10 cM (very closely) of PdR1. The 9621 mapping population was expanded from 181 to 457 genotypes. A total of 13 markers polymorphic for F8909-17 mapped to LG 14 and were added to 276 segregants (core population set is 457). We also screened an additional 400 seedlings with two markers (one on either side of PdR1) and a total of 50 unique recombinant plants were planted in the field. To avoid confounding affects of resistance inherited from D8909-15 (which is also highly resistant, but with a very different form of resistance) the 04-190 population was selected and a map of LG 14 with 220 genotypes was completed. 04-190 is a cross of V. vinifera F2-7 (Cabernet Sauvignon x Carignane) x F8909-08 (sibling of F8909-17). We have used F8909-08 extensively in PD resistant wine and table grapes, therefore it is necessary to validate that PdR1 gene segregates 1:1 in progeny from its crosses. We completed greenhouse screening of 160 genotypes from the 04-190 population to verify the molecular marker results. The PdR1 resistance locus segregates 1:1 and mapped to the same position with surrounding markers ctg1025882 and VMCNg2b7.2. We also increased the core population of 04-190 from 220 to 395 seedling plants. Leaf tissue for DNA extraction and green cuttings for greenhouse testing and ELISA screening from the additional 175 plants were collected in late summer, and results are expected in early spring 2007. Efforts to construct a bacterial artificial chromosome (BAC) library from b43-17 (the basis of the PdR1) were initiated. A total of 200 green cuttings were collected that resulted in 160 plants that are being cultivated for young etiolated shoot tips that provide an excellent source of DNA for the BAC library. This BAC library is being developed to provide markers from BAC end sequencing for LG 14, so that we can create a physical map of the PdR1 gene family, which will lead to genetic engineering efforts. We are also working to add resistance gene analogs (RGA) markers, which are generalized genetic sequences involved in a wide range of pest and disease defense responses in plants, to our genetic maps. The addition of these markers may identify common regions of disease resistance and possible functions of the PdR1 gene family. In order to understand the stability and segregation of PD resistance from different sources, work on six different mapping populations was completed. We are also continuing mapping efforts in the 0023 population, a cross of D8909-15 x V. vinifera B90-116, to identify quantitative trait loci (QTL) and then saturate linkage groups with these QTLs with more markers. This population is important because we have extensive data for cluster and berry traits, and Xylella fastidiosa (Xf) resistance data for about 200 plants. We completed the characterization of Mexico collection, the source of the exceptional resistance to Xf and collected by Dr. Olmo in 1960. We are using these unique selections in our genetic and molecular breeding to produce PD resistant table and wine grape cultivars.
• Publication Date: Nov 2006
• Journal: 2006 Pierce's Disease Research Symposium