Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 85pg1
MAPPING GENETIC FACTORS CONTROLLING HOST-BACTERIUM INTERACTIONS
IN COMMON BEAN.
R.O. Nodari*, S.M. Tsai*, P. Guzman', R.L. Gilbertson', and P.
Gepts*, *Department of Agronomy and Tange Science, and
'Department of Plant Pathology, University of California, Davis,
CA 95616-8515.
We have performed a quantitative trait locus (QTL) analysis
for two tratis in common bean (Phaseolus vulgaris L.), involving
interactions between the plant host and bacteria, namely
Rhizobium nodule number (NN) and resistance to common bacterial
blight (CBB) caused by Xanthomonas campestris pv. phaseoli.
Analyses were conducted in the progeny of a cross between BAT93
(fewer nodules; moderately resistant to CBB) and Jalo EEP558
(more nodules; susceptible to CBB). An RFLP-based linkage map
for common bean based on 152 markers had previously been derived
in the F2 of this cross. Seventy F2-derived F3 families were
innoculated in separate greenhouse experiments with Rhizobium
tropici strain UMR1899 or Xanthomonas campestris pv. phaseoli
isolate W18. Regression and interval mapping analyses were used
to identify genomic regions involved in the genetic control of
these traits. The two methods identified the same genomic
regions for each trait, with a few exceptions. For each trait,
at least 4 putative QTLs were identified, which accounted for
approximately 50% and 75% of the phenotypic variation in NN and
CBB resistance, respectively. A chromosome region on linkage
group D7 carried factor(s) influencing both traits. In all other
cases, the putative QTLs affecting NN and DBB were located in
different linkage groups or in the smae linkage group, but far
apart (more than 50 cM). Both BAT93 and Jalo EEP558 contributed
alleles associated with higher NN, whereas CBB resistance was
always associated with BAT93 alleles. Additive gene action was
the main component of genetic variation for both traits, but
significant dominance deviations were also observed. In less
that 5% of the cases, digenic epistasis had a significant effect.
Subsequently, a more detailed analysis involving additional
markers was conducted of the region on linkage group D7 to
further analyze the location of the QTLs for CBB and NN.
Identification of these QTLs raises the possibility of initiating
map-based cloning and markers-assisted selection for these
traits.
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