Plant Genome II Conference
Town & Country Conference Center, San Diego, CA, January, 1994.
PG-II: MAPPING DISEASE-RESISTANCE GENES IN CITRUS: CURRENT STATUS
MAPPING DISEASE-RESISTANCE GENES IN CITRUS: CURRENT STATUS.
F. G. Gmitter, Jr., S. Y. Xiao, S. Huang, X. L. Hu, and P. Ling,
Citrus Research and Education Center, University of Florida, Lake
Alfred, FL 33850.
Citrus is the number one fruit crop worldwide, but projected
production levels will be jeopardized as exotic pathogens and
vectors are introduced to and cause new disease problems in
previously unaffected citrus growing areas. It is difficult for
breeders to develop urgently needed, disease resistant cuttivars,
partly because of the lack of cost-effective, and validated
selection methods. Marker assisted, indirect of hybrids with
multiple disease resistance is an attractive solution, especially
a for long lived perennial crop like citrus. One focus of our
work is the identification of markers tightly linked with genes
conferring resistance to citrus tristeza virus (CTV) or citrus
nematode (Tylenchulus semipenetrans). Individuals from six
different intergeneric families (F1 and BC1) were tested for
their reaction to CTV inoculation, resistance is controlled by a
single dominant gene inherited from a closely related genus,
Poncirus. Bulked segregant analysis (BSA) was used, first in two
BC families, to screen random 10-mer primers for potentially
useful marker fragments. Many cis-dominant markers were found to
be family specific, as were several linked with susceptibility.
All unambiguously phenotyped individuals have been tested for the
presence of markers linked with the resistance allele, to
estimate genetic distances. The first goal of this project soon
will be realized; i.e. the identification of universal markers
useful for selecting CTV-resistant hybrids from genetically
diverse families. The inheritance of citrus nematode resistance,
another trait transmitted by hybridization with Poncirus, is not
clearly understood. A study of inheritance, using an
intergeneric BC family has been undertaken, and preliminary
analysis of the results suggests polygenic control. BSA, using
DNA bulks of individuals from extremes of the mean distribution
curve, is in progress. Markers found to be associated with
nematode resistance in this family will need to be evaluated in
other genetic backgrounds to determine the range of applicability
to marker assisted selection.
Return to Previous Page or Intl-PAG Homepage