Principles of Plant Genetics and Breeding

What plant breeders can do to address
crop vulnerability
As previously indicated, the issue of genetic vulnerability
is very complex. However, ultimately, plant breeders are
the experts who can effectively address this issue.
Reality check
First and foremost, plant breeders need to be convinced
that genetic vulnerability is a real and present danger.
Without this first step, efforts to address the issue are not
likely to be taken seriously. A study by D. N. Duvick in
1984, albeit dated, posed the question “How serious is
the problem of genetic vulnerability in your crop?” to
plant breeders. The responses by breeders of selected
crops (cotton, soybean, wheat, sorghum, maize, and
others) indicated a wide range of perception of crop vulnerability,
ranging from 0–25% thinking it was serious
to 25–60% thinking it was not a serious problem (at least
at that time). Soybean and wheat breeders expressed the
most concern about genetic vulnerability. Their fears are
most certainly founded since, in soybean, it is estimated
that only six cultivars constitute more than 50% of the
genetic base of North American germplasm. Similarly,
more than 50% of the acreage of many crops in the USA
is planted to less than 10 cultivars per crop.
PLANT GENETIC RESOURCES FOR PLANT BREEDING 95
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Use of wild germplasm
Many of the world’s major crops are grown extensively
outside their centers of origin where they coevolved
with pests and pathogens. Breeders should make deliberate
efforts to expand the genetic base of their crops by
exploiting genes from the wild progenitors of their
species that are available in various germplasm repositories
all over the world.
Paradigm shift
As D. Tanksley and S. R. McCouch of Cornell
University point out, there is a need for a paradigm
shift regarding the use of germplasm resources.
Traditionally, breeders screen accessions from exotic
germplasm banks on a phenotypic basis for clearly
defined and recognizable features of interest. Desirable
genotypes are crossed with elite cultivars to introgress
genes of interest. However, this approach is effective
only for the utilization of simply inherited traits (conditioned
by single dominant genes). The researchers
proposed a shift from the old paradigm of looking for
phenotypes to a new paradigm of looking for genes. To
accomplish this, the modern techniques of genomics
may be used to screen exotic germplasm using a genebased
approach. They propose the use of molecular