Molecular Breeding - Genetics, Genomics and Breeding of Crop Plants - page 230

provide accurate and detailed information which complements phenotypic
evaluation. Molecular characterization of cultivated sunflower was initially
carried out using biochemical methods. Studies by Torres (1983) resolved
enzymatic systems such as alcohol dehydrogenase and acid phosphatase
and concluded that they could be used for evaluation of genetic similarity of
sunflower cultivars. Quillet et al. (1992) described the discrimination of 52
distantly related inbred lines from different origins using eight polymorphic
isozyme loci, whereas Tersac et al. (1994) were able to group 39 cultivated
sunflower populations according to their geographical origin using nine
polymorphic isozymes. Finally, Carrera et al. (2002) reported that eight
polymorphic isozyme loci were capable of separating the majority of
maintainer lines (B) from restorer lines (R) in a survey of 25 elite inbred
lines.
Enzymatic systems have also been used to assess genetic variation in
both domesticated and wild sunflower populations. Rieseberg and Seiler
(1990) used this technique, in addition to RFLP analysis of chloroplast
DNA, for an evolutionary study of cultivated sunflower in relation to wild
Helianthus annuus . They found extensive isozyme and chloroplast DNA
polymorphism in the wild accessions and a virtual monomorphism in
cultivated lines, concluding that domesticated sunflower must have evolved
from a very limited gene pool. Cronn et al. (1997) undertook a larger survey
of 146 germplasm accessions from the US National Plant Germplasm System
(NPGS) sunflower collection using 20 allozyme loci and demonstrated that
domesticated sunflowers (ranging from Native American landraces to elite
cultivars of both confectionary and oilseed types) and wild sunflowers
formed two nearly independent groups. Again, the wild H. annuus group
was genetically more diverse than the domesticated group and this diversity
was geographically structured.
Despite their value in these initial studies, biochemical markers have
not been used extensively to characterize sunflower germplasm due to their
poor genome coverage and low levels of polymorphism. For example, the
previously mentioned study of Cronn et al. (1997) revealed only 53 alleles at
20 allozyme loci, with an average of 1.39 alleles per locus, in a large survey
of over 700 achenes, representing 114 domesticated accessions. Pizarro et
al. (2000) and Popov et al. (2002) compared isozyme and RAPD markers to
assess genetic diversity in 21 and 30 sunflower inbred lines, respectively,
and demonstrated the greater discriminatory power of the DNA-based
marker systems.
The characterization of genetic structures in cultivated sunflower was
one of the first aims of genetic fingerprinting using DNA-based markers.
Initial studies using RFLPs consistently separated sunflower inbred lines
into sterility maintainer (B-line) and fertility restorer (R-line) groups (Berry
et al. 1994; Gentzbittel et al. 1994; Zhang et al. 1995), reflecting the breeding