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mostly about hybrid F 1 achene (seed) set, pollen fertility, meiosis
abnormalities, and further crosses (Jan 1997). Using classical breeding
methods, this research provided more taxonomic information for
evolutionary studies than information about agronomic potential. Successful
interspecific crosses among the wild species of Helianthus have been reviewed
by Whelan (1978) and Miller et al. (1992). The development of a two-step
embryo procedure by Chandler and Beard (1983) greatly facilitated
interspecific hybridization in sunflower. They successfully produced 53
interspecific cross combinations without the exhaustive effort of endless
pollination, with 21 of these combinations not previously produced. Using
this method, Kräuter et al. (1991) obtained 33 interspecific hybrids with an
overall success rate of 41%. This procedure allowed for the production of
interspecific combinations not previously available and has facilitated
additional studies of species relationships not previously possible.
In recent years, there has been greater interest in interspecific
hybridization for transferring desired genes from wild species into cultivated
lines to develop pre-breeding germplasm for sunflower improvement.
Characteristics such as disease and insect resistance, salt tolerance, drought
tolerance, fatty acid variation, CMS, and fertility-restoration diversity have
been emphasized. Whelan (1980, 1981) and Whelan and Dorrell (1980)
used interspecific hybridization to obtain cytoplasmic male sterility
conditioned by the cytoplasm of three species, H. petiolaris , H. giganteus , and
H. maximiliani . Sunflower has served as a model crop for the transfer of
genes from the wild species into the cultivated crop.
1.6.3 Gene Flow
The sunflower crop is unique in being one of the few crops native to North
America. This has facilitated the collection and preservation of the
germplasm. Since wild sunflower species are native to the major sunflower
production areas of North America, there is a concern about the flow of
genes from the cultivated crop to the wild species. A widely acknowledged
risk associated with transgenic crops is the possibility that hybridization
with wild relatives will transfer fitness-related transgenes to persist in wild
populations (Armstrong et al. 2005). If wild populations acquire transgenes
for resistance to diseases, herbivory, environmental stress, and/or commonly
used herbicides, they could become more abundant in their natural habits,
or invade previously unsuitable habitats. Hybrids between cultivated and
wild annual sunflower ( H . annuus ) are frequent. As high as 42% of progeny
from wild plants near cultivated fields are hybrids with cultivar genes persist
in the wild populations for at least five generations, and in certain areas up
to 40 years (Linder et al. 1998). Moreover, there was morphological evidence
of hybridization in 10-33% of the populations surveyed within a given
 
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