Oral: Bacterial Disease Management
Cybridization: A promising plant resistance for citrus canker control
M. MURATA (1), A. Omar (1), C. Chase (2), J. Grosser (1), J. Graham (1) (1) University of Florida, U.S.A.; (2) University of Florida, U.S.A.
Cybridization is a somatic hybridization system that enables the construction of novel nuclear and cytoplasmic genome combinations. In this work, cybridization was used to study the role of mitochondrial (mt) and chloroplast (cp) genes in resistance to Xanthomonas citri subsp. citri (Xcc), the cause of citrus canker. Putative cybrids were created through the fusion between nucellar callus cells of Meiwa kumquat (Fortunella crassifolia), a citrus canker resistant, and mesophyll cells of citrus canker susceptible grapefruit (Citrus paradisi). Six EST-SSR markers demonstrated that all clones have a grapefruit nuclear genome; however, four CAPS markers showed variation in the cytoplasmic genomes. In 123 cybrids, kumquat mt and cp were identified, and in 19 cybrids, kumquat mt and grapefruit cp were present. Eighty-two cybrid clones were evaluated by detached leaf assay (DLA), and clones that performed better in the DLA were evaluated by syringe inoculation of attached leaves. Q-PCR was carried out to quantify the Xcc population. Cybrid clones showed a range of citrus canker resistance, but all clones produced a significantly lower number of lesions and a one log unit reduction of the Xcc population compared to grapefruit. Cybrid clones with grapefruit cp were more susceptible to Xcc compared to clones with kumquat cp. In addition to citrus canker resistance, these cybrids provide a valuable model to study the role of cytoplasmic genomes in plant disease resistance.