Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 59pg1
GENOMIC MAPPING AND TRANSFER OF BROAD SPECTRUM VIRUS
RESISTANCE: Capsicum AS A MODEL SYSTEM
J.R.Blauth, J.P. Prince, V.K. Lackney, and M.M. Kyle, Department
of Plant Breeding and Biometry, Cornell University, Ithaca,
NY 14853
Multiple virus resistance is considered an important
objective in crop improvement because of the anticipated impact
on yield stability, product quality, and reduced pesticide use to
control vectors. Breeding lines with the full complement of
necessary resistance have not been developed with conventional
procedures despite considerable investment through several
decades. The typical selection criterion, symptom expression,
is variable and may take weeks to be evaluated, it is difficult
to screen an individual with several viruses, to produce seed on
infected plants, and selection of recessive or multigenic
resistance requires progeny testing. These problems can be
overcome by the application of marker assisted selection using
molecular markers tightly linked to the resistance genes. We are
using framework markers from a low-density-molecular map of
pepper (from a Capsicum annuum x C. chinense cross, developed
primarily with RFLP markers from tomato) to map genes for
resistance to three of the most important viral diseases of
pepper caused by cucumber mosaic virus (CMV), tomato spotted
wilt virus (TSWV), and three closely related potyviruses.
Resistance to CMV is polygenic; resistance to the three
potyviruses is conditioned by factor(s) that segregate as a unit,
while resistance to TSWV involves the combination of genes which
singly result in a lethal necrotic reaction to the virus. A
resistant accession of C. chinense and of C. frutescens have been
crossed to each other and to a susceptible C. annuum to develop
three sets of interspecific populations for mapping and
identification of tightly linked markers. We are also using a
library of random pepper genomic clones, additional tomato
clones, and RAPD markers to fill in gaps in the existing linkage
groups and increase the density of markers. The traits in pepper
are conditioned by distinct genetic mechanisms that exemplify
major classes of gene action and interactions not limited to
disease resistance. Because the viruses involved cause major
losses in a number of important crops, these genes in pepper
could become more widely useful as map-based gene isolation
strategies and wide transfer techniques become routine.
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