Expressed sequence enrichment for candidate gene analysis of citrus tristeza virus resistance.
Several studies have reported markers linked to a putative resistance gene from Poncirus trifoliata ( Ctv-R) located at linkage group 4 that confers resistance against one of the most important citrus pathogens, citrus tristeza virus (CTV). To be successful in both marker-assisted selection and transformation experiments, its accurate mapping is needed. Several factors may affect its localization, among them two are considered here: the definition of resistance and the genetic background of progeny. Two progenies derived from P. trifoliata, by self-pollination and by crossing with sour orange ( Citrus aurantium), a citrus rootstock well-adapted to arid and semi-arid areas, were used for linkage group-4 marker enrichment. Two new methodologies were used to enrich this region with expressed sequences. The enrichment of group 4 resulted in the fusion of several C. aurantium linkage groups. The new one A(7+3+4) is now saturated with 48 markers including expressed sequences. Surprisingly, sour orange was as resistant to the CTV isolate tested as was P. trifoliata, and three hybrids that carry Ctv-R, as deduced from its flanking markers, are susceptible to CTV. The new linkage maps were used to map Ctv-R under the hypothesis of monogenic inheritance. Its position on linkage group 4 of P. trifoliata differs from the location previously reported in other progenies. The genetic analysis of virus-plant interaction in the family derived from C. aurantium after a CTV chronic infection showed the segregation of five types of interaction, which is not compatible with the hypothesis of a single gene controlling resistance. Two major issues are discussed: another type of genetic analysis of CTV resistance is needed to avoid the assumption of monogenic inheritance, and transferring Ctv-R from P. trifoliata to sour orange might not avoid the CTV decline of sweet orange trees.
Bernet
G P
GP
Instituto Valenciano de Investigaciones Agrarias, Apdo. Oficial, 46113 Moncada, Valencia, Spain.
Bretó
M P
MP
Asins
M J
MJ
D002874:Chromosome Mapping; D003433:Crosses, Genetic; D020224:Expressed Sequence Tags; D005819:Genetic Markers / Q000235:genetics; D006824:Hybridization, Genetic; D007113:Immunity, Innate / Q000235:genetics*; D015151:Immunoblotting; D010940:Plant Proteins / Q000235:genetics*; D032104:Poncirus / Q000235:genetics* / Q000821:virology*; D016622:Silver Staining
D005819:Genetic Markers; D010940:Plant Proteins; C474073:citrus Tristeza virus resistance protein, Poncirus trifoliata