Quantitative trait locus analysis of fungal disease resistance factors on a molecular map of grapevine.

A full-sibling F1 population comprising 153 individuals from the cross of 'Regent' x 'Lemberger' was employed to construct a genetic map based on 429 molecular markers. The newly-bred red grapevine variety 'Regent' has multiple field-resistance to fungal diseases inherited as polygenic traits, while 'Lemberger' is a traditional fungus-susceptible cultivar. The progeny segregate quantitatively for resistances to Plasmopara viticola and Uncinula necator, fungal pathogens that threaten viticulture in temperate areas. A double pseudo-testcross strategy was employed to construct the two parental maps under high statistical stringency for linkage to obtain a robust marker frame for subsequent quantitative trait locus (QTL) analysis. In total, 185 amplified fragment length polymorphism, 137 random amplified polymorphic DNA, 85 single sequence repeat and 22 sequence characterized amplified region or cleaved amplified polymorphic sequence markers were mapped. The maps were aligned by co-dominant or doubly heterozygous dominant anchor markers. Twelve pairs of homologous linkage groups could be integrated into consensus linkage groups. Resistance phenotypes and segregating characteristics were scored as quantitative traits in three or four growing seasons. Interval mapping reproducibly localized genetic factors that correlated with fungal disease resistances to specific regions on three linkage groups of the maternal 'Regent' map. A QTL for resistance to Uncinula necator was identified on linkage group 16, and QTLs for endurance to Plasmopara viticola on linkage groups 9 and 10 of 'Regent'. Additional QTLs for the onset of berry ripening ("veraison"), berry size and axillary shoot growth were identified. Berry color segregated as a simple trait in this cross of two red varieties and was mapped as a morphological marker. Six markers derived from functional genes could be localized. This dissection of polygenic fungus disease resistance in grapevine allows the development of marker-assisted selection for breeding, the characterization of genetic resources and the isolation of the corresponding genes.

Molecular characterization of the vir regulon of Agrobacterium tumefaciens: complete nucleotide sequence and gene organization of the 28.63-kbp regulon cloned as a single unit.

The entire vir regulon of Agrobacterium tumefaciens was subcloned and the complete 28.6-kbp nucleotide sequence was determined. The regulon was cloned as a single unit into two replicons, one of which replicates at a high copy number in this bacterium, and a second which has broad-host-range features to replicate in other Gram-negative bacteria. These vir region plasmids are able to confer in trans the processing and transfer activities on a second plasmid containing the T-DNA. In the high copy number vir region plasmid pUCD2614, a moderate increase in basal vir gene expression was observed as judged by virE::cat fusion expression assays relative to the wild-type control plasmid. Furthermore, higher efficiencies of tobacco leaf disk transformation were observed than with the widely used vir helper plasmid pAL4404. The nucleotide sequence studies showed that the vir region consists of 28,631 bp comprising 24 open reading frames which encode proteins involved in tumorigenicity. Two open reading frames not previously characterized, virH and ORF5, were uncovered within the virD/virE intervening spacer region. Together these studies more completely characterize the structure and function of the vir regulon.