Basic Information - Genetics, Genomics and Breeding of Crop Plants - page 30

1.5.2 Secondary and Tertiary Gene Pools
Genetic resources of a crop consist of the total pool of genetic variability that
exists in the species or within species with which the crop plant is sexually
compatible (Holden et al. 1993). Wild relatives of crop plants typically are
genetically much more diverse than related cultivated lineages. Genetic
diversity is thought to contribute to long-term preservation of species by
allowing them to adapt quickly to changes in their environment.
Although many secondary and tertiary gene pools may appear to have
no immediate use in breeding and genetic programs (Burton 1979), they
may contain unidentified genes that will protect crops against new pests in
the future. Hopefully, the present germplasm collection will contain the
necessary germplasm. Although we cannot predict with acceptable levels
of confidence the occurrence, severity, or even the nature of future stresses,
germplasms with as wide a range of genetic diversity as possible should be
developed for breeding programs (Jones 1983). Diversity in germplasm is
also critical to successful crop breeding programs, but to date it has been
rather limited (Harlan 1976). For the domesticated sunflower, this includes
most species of Helianthus . Sunflower germplasm resources can be
categorized as in situ resources (i.e., wild populations and landraces) or ex
situ resources (accessions preserved in seed banks).
1.5.3 Ex situ Helianthus Collection
The USDA-ARS National Plant Germplasm System (NPGS) sunflower
collection is maintained at the North Central Regional Plant Introduction
Station (NCRPIS) in Ames, Iowa, USA. The mission of the NCRPIS is to
conserve genetically diverse crop germplasm and associated information,
to conduct germplasm-related research, and to encourage the use of
germplasm and associated information for research, crop improvement and
product development. The collection contains 37 perennial species, 14 annual
species, and the cultivated species, Helianthus annuus (Schilling 2006). This
NPGS sunflower collection is a diverse assemblage of 3,850 accessions:
1,708 cultivated Helianthus annuus accessions (44%) from 59 countries, 932
wild Helianthus annuus accessions (25%), 437 accessions representing 11
other wild annual Helianthus species (11%), and 773 accessions representing
37 perennial Helianthus species (20%). This collection is one of the largest
and most genetically diverse ex situ sunflower collections in the world, and
it is vital to the conservation of Helianthus germplasm. Over 14,000 samples
of wild sunflower accessions from this collection have been distributed to
more than 365 researchers from 34 different countries over the last 28 years.
The distributed accessions have become the basis of wild species
genebanks and research programs in Argentina, France, Italy, Spain,