Basic Information - Genetics, Genomics and Breeding of Crop Plants - page 32

resistant sunflower hybrids could be used with these herbicides to combat
broomrape infection.
Collection of germplasm not only serves a valuable purpose in preserving
germplasm, but it also provides valuable information about the diverse
habitats occupied by wild sunflowers and associated species. This
information is particularly important for the genus Helianthus because of
the co-evolution of its species and associated native insects and pathogens.
Knowledge of a particular habitat and adaptations of a species occurring
therein can often help to identify potential sources for a desired trait. Based
on the habitat of a species and its immediate environment, selection of
potential species for a particular characteristic may become easier, more
accurate, and more efficient.
In situ preservation of genetic diversity within wild sunflower
populations in their native habitat is critical because we lack the necessary
resources to preserve locally adapted sunflower populations of all wild
species in gene banks. The primary obstacle for long-term preservation of
wild sunflower populations is human activity. Unfortunately, the long-term
outlook for survival of many sunflower species is not promising; some
species are already rare and endangered, or in the case of H. nuttallii ssp.
parishii , probably extinct. Additional potential threats to the preservation of
rare sunflower populations include their small population sizes and
subsequent loss of genetic diversity.
The genus Helianthus, besides constituting the basic genetic stock from
which cultivated sunflower originated, continues to contribute specific
characteristics for cultivated sunflower improvement. However, there is a
continued need to collect, maintain, evaluate, and enhance wild Helianthus
germplasm for future utilization in cultivated sunflower.
1.5.4 Core Collection
Frequently, researchers are uncertain about the criteria or information
required to select germplasm materials needed for their specific research
objectives. The assembly of a core subset of the cultivated sunflower collection
may provide an efficient means of identifying useful traits. This will enable
researchers to sample the diversity within the collection without testing
excessively large numbers of accessions. A core subset of the cultivated
sunflower collection was established by Brothers and Miller (1999). Twenty
descriptors were used in the construction of the core subset. The sunflower
core subset of cultivated sunflower consists of 112 accessions (approximately
7% of the 1,708 available accessions) grouped into 10 clusters. Accessions
within the same cluster should be more genetically similar than accessions
between clusters. Accessions in the core subset represent 38 of the 57
countries of origin for the total cultivated sunflower collection. The core