Plant & Animal Genomes XI Conference Plant & Animal Genomes XI ConferenceJanuary 11-15, 2003
Town & Country Convention Center
San Diego, CA
Workshop: Citrus
Poncirus trifoliata (a close relative of citrus) carries a single dominant allele, Ctv, that confers resistance to Citrus tristeza virus (CTV). CTV is one of the most important pathogens detrimentally affecting citrus production worldwide.Poncirus also carries resistance genes to other important citrus pathogens and pests and genes for tolerance to abiotic stresses such as cold. Because Poncirus contains many important genes that could be used in transgenic approaches for citrus improvement, a bacterial artificial chromosome (BAC) library has been constructed. The library was constructed in pBeloBAC11 from an individual homozygous for Ctv, and over 100,000 clones were obtained with an average insert size of 80 kb. Forty five thousand clones have been stored in triplicate in 384 well microtiter plates, and 18,000 unique clones per filter has been spotted in duplicate onto hybridization filters using advanced robotics. Screening two filters (36,000 clones) represents 7X coverage of the Poncirus genome. A 1.2 megabase walk across the Ctv region has been completed, and further fine mapping and genomic shotgun sequencing has delimited the region that must contain Ctv to a 172 kb region that contains eleven candidate genes. We are transforming susceptible citrus genotypes with BACs that carry three or four genes and genomic fragments that carry one each of the eleven candidate genes. Other resources include a cDNA library constructed from the same individual plant homozygous for Ctv, and methods for routine transformation of Citrus and Poncirus species. Progress in identification of Ctv, and improvements in citrus transformation will be presented.