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strategies that maximize heterosis. These results were later confirmed using
AFLPs and SSRs (Hongtrakul et al. 1997; Paniego et al. 2002; Yu et al. 2002).
Tang and Knapp (2003) performed phylogenetic analyses on 19 elite inbred
lines and 28 domesticated (Native American landraces and open-pollinated
cultivars, including oilseed, confectionary and ornamental types) and wild
( H. annuus ) germplasm accessions using 122 SSRs distributed throughout
the sunflower genome. The authors found an extraordinary allelic diversity
in the Native American landraces and wild populations, and progressively
less allelic diversity in germplasm produced by successive cycles of
domestication and breeding. These findings suggest that the contemporary
oilseed sunflower pool could profit from an infusion of novel alleles from
the reservoir of latent genetic diversity present in both wild populations
and Native American landraces. DNA-based markers have also been used
to characterize specific sunflower collections. For example, Dong et al. (2007)
evaluated a confectionary sunflower collection of 70 accessions from China
with AFLP markers. They found an absence of duplicated entries and a lack
of a consistent classification of the material according to their geographical
origin.
Zhang et al. (1995) used RFLPs to screen four inbred lines for intra-line
polymorphisms, and found RFLPs within them. However, these four lines
presented a good uniformity for morphological characters in the field, which
led the authors to conclude that the polymorphisms stemmed from residual
heterozygosity or outcrossing. Zhang (1995) proposed using RFLPs for
distinctness, uniformity, and stability (DUS) testing in sunflower, taking
into account inter-line variability for distinctness, and intraline variability
for uniformity and stability. Later on, Zhang et al. (2005) also demonstrated
the usefulness of SSRs for diversity assessment of sunflower inbred lines,
and suggested that a set of mapped SSR markers with a high PIC
(polymorphism information content) value could be very useful for varietal
description, purity testing, hybrid formula verification, and varietal
identification in the process of seed certification. These molecular markers
could also play an important role in protecting plant breeders' rights in
sunflower and in assessing whether or not an inbred line was essentially
derived [UPOV (International Union for the Protection of New Varieties of
Plants) Convention revised in 1991].
Molecular markers have also been employed to characterize different
sources of cytoplasmic male sterility (CMS). The development of new
CMS systems and their respective fertility restoration genes is an important
breeding objective in sunflower. Commercial hybrid production is currently
based on a single source of CMS, cmsPET1 from H. petiolaris , which narrows
the genetic base of the crop and increases its vulnerability to pests and
environmental stresses. Understanding the molecular biology of the various
CMS systems helps to classify different types and to identify novel
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