Basic Information - Genetics, Genomics and Breeding of Crop Plants - page 43

Kane and Rieseberg (2007) reported on the evolution of weedy
populations of the common sunflower, Helianthus annuus , using
microsatellites which showed that between 1 and 6% of genes were
significant outliers with reduced variation in weedy populations, implying
that a small but insignificant fraction of the genome may be under selection
and involved in adaptation of weedy sunflowers. They concluded that
weedy populations are more closely related to nearby wild populations
than to each other, implying that weediness likely evolved multiple times
within the species, although a single origin followed by gene flow with
local populations cannot be ruled out. Together, the results point to the
relative ease which weedy forms of this species can evolve and persist despite
the potentially high levels of gene flow with nearby wild populations.
Gene flow between crops and wild relatives has occurred for many
years and contributed to the evolution and extinction of weed species.
Resistance to imidazolinone (IMI) herbicides was discovered in wild H .
annuus and introduced into domesticated sunflower (Al-Khatib et al. 1998;
Al-Khatib and Miller 2000; Miller and Al-Khatib 2002). Massinga et al. (2003)
studied the gene flow of the IMI gene from domesticated sunflower to wild
sunflower, concluding that domesticated sunflower outcrosses with common
( H . annuus ) and prairie ( H . petiolaris ) sunflower over distances typically
encountered in the major sunflower production areas, and that backcross
resistant hybrids with wild parents are successful, further increasing the
potential spread of IMI-resistant feral sunflowers.
1.6.4 Genetic Diversity
Molecular markers provide an effective means for characterizing genetic
variability and establishing phylogenetic relationships among cultivated
and wild Helianthus species. Markers linked with both qualitative and
quantitative traits and genes will facilitate marker-assisted selection (MAS),
and eventually lead to the cloning and manipulation of desirable genes.
Using RFLP markers on 17 sunflower inbred lines, Gentzbittel et al. (1994)
reported a lower available genetic variability in cultivated sunflower than
in other crops, suggesting that efforts to introgress new genes from wild
sunflower species should be increased. More recently, simple sequence repeat
(SSR) markers have been developed for sunflower, and used in one study to
characterize the genetic diversity among 16 elite inbred lines, and in another
study among 19 elite inbred lines and 28 domestic and wild germplasm
accessions, including Native American landraces (Paniego et al. 2002;
Yu et al. 2002; Tang and Knapp 2003).
Genetic variability to mid-stem infection of Sclerotinia sclerotiorum (white
mold) among interspecific sunflower hybrids using arbitrarily primed-PCR
(AP-PCR) was demonstrated by Köhler and Friedt (1999). Interspecific hybrid