Biology Reference
In-Depth Information
Chapter 16
Genetics and Gene Mapping of Disease
Resistance in Brassica
GenyiLiandPeterB.E.McVetty
Abstract
The deployment of cultivars resistant to major diseases such as sclerotinia, blackleg, and clubroot
in Brassica crop production is a cost effective and environmentally friendly method to reduce losses
caused by these diseases. To develop cultivars with high levels of disease resistance, it is necessary
to understand the genetics of resistance genes in plants and avirulence genes in pathogens and the
mechanism of interactions between host and pathogens. As the technologies in plant genomics are
advanced, it becomes feasible and effective to clone and characterize both resistance genes and
avirulence genes. There are several avirulence genes of
L. maculans
that have been characterized and
the analysis of the whole genome sequence of
L. maculans
reveals more than a hundred of effectors
similar to cloned avirulence genes. Gene mapping of resistance genes to clubroot and blackleg have
been extensively performed and more than a dozen of resistance gene loci have been identified. As
the whole genome sequence of
B. rapa
is available, these mapped genes might be cloned in the
near future. Since there is no source with dominant resistance to sclerotinia, it is very challenging
to breed Brassica cultivars with high levels of resistance to sclerotinia. QTL (quantitative trait locus)
mapping for sclerotinia medium resistance or field tolerance is reported in several publications, and
this mapping would help introduce QTLs from cultivar to cultivar, if a QTL can be constantly detected.
Because of their relatively small economic impact, other diseases in Brassica crops are not as well
characterized as sclerotinia, blackleg, and clubroot. However, the situation may change if a disease
becomes severe in brassica crop production.
ship is described as the triangle of U, on the basis
of their genomes and evolution (Figure 16.1).
B. napus
canola (or double zero rapeseed) is one
of the most important oilseed crops worldwide
and, based on its fatty acid profile, it is considered
to be a healthy vegetable oil for humans. Addi-
tionally, canola oil is a feedstock for biodiesel.
Introduction
The Brassica genus consists of numerous species
that are important agricultural and horticultural
crops used as oilseeds, vegetables, and condi-
ments. There are three major diploid and three
amphidiploid Brassica species and their relation-
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