Poster: Plant-pathogen interactions

Abs # 574: Positional cloning of the Citrus tristeza virus resistance gene.

Presenter:	Rai, M , mrai@agprg.tamu.edu
Authors	Mirkov, TE  (A)   Rai,  M  (A)   Yang, ZN  (A)   Molina, J  (A)   Gonzales, JR  (A)   Ye, XR  (B)   Roose, ML  (B)
Affiliations:	(A): Texas A&M Experimental Station (B): University of California, Riverside

Citrus tristeza virus (CTV) causes a devastating disease of citrus, leading to economic losses by killing trees or reducing fruit size. Aphids transmit the virus, making control difficult. All commercially grown Citrus is susceptible to CTV, but the severity of damage is cultivar and virus strain specific. Development and use of resistant Citrus varieties will aim at minimizing damage to new plantings. We have used positional cloning in Poncirus trifoliata, which is resistant to almost all CTV strains, to demarcate a 300 kb region that must contain the single dominant resistance gene, Ctv. 22 genes were identified in this region. Genetic mapping with new microsatellite markers facilitated narrowing of this region to 121 kb, that contains only 10 genes. Transgenic plants are being developed using each of these candidate genes in three citrus cultivars: Ruby Red, Rio Red and Duncan Grapefruit. A total of 24 independent transgenic plants, representing 8 of the 10 candidate genes have been obtained to date. Progress to evaluate the effect of CTV on these transgenic plants will be presented.