Basic Information - Genetics, Genomics and Breeding of Crop Plants - page 16

varieties with oil contents of 450 to 550 g/kg were available. The discovery
of cytoplasmic male sterility (PET1 CMS) by the French scientist Leclercq in
the early 1970s laid the foundation for the development of modern day
sunflower hybrid. Hybrid sunflower, with higher yields and oil content
and more uniformity compared to open-pollinated varieties, provided the
last great impetus in establishing sunflower as a global crop.
The dispersion of wild species achenes has been by man and animals.
Wild achenes do not have any special mechanisms for effective achene
dispersal. Man, of course, has proved to be an important agent and certainly
the wide distribution of many species can be largely explained as a result of
human activity. Long-distance achene dispersal within North America was
probably facilitated by the fact that many species grow along roadsides and
railroad yards. Moreover, the perennials with tubers or rhizomes are also
spread by man as the results of his development activities. Also, some of the
species that are intentionally cultivated have often escaped and become
established. However, before man, birds and small mammals were important
agents in dispersal for sunflower achenes because they are an attractive
food for both. With the exception of being spread by man at times, it seems
likely that sunflower achene dispersal is probably highly localized and it is
unlikely that long distance dispersal has been involved in extending the
distribution of most of the species (Heiser et al. 1969).
1.4 Botanical Description
1.4.1 Taxonomic Position
The Compositae (Asteraceae) is the largest and most diverse family of
flowering plants, comprising one-tenth of all known Angiosperm species
(Heywood 1978; Funk et al. 2005). Species within this family are
characterized by a compound inflorescence that has the appearance of a
single “composite” flower. The Compositae family is divided into three major
subfamilies and one minor subfamily, with 1,100 to 2,000 genera and over
20,000 species (Cronquist 1977; Heywood 1978; Jansen et al. 1991; Funk
et al. 2005). The family has undergone extensive diversifications producing
a cosmopolitan array of taxa encompassing ephemeral herbs, vines, and
trees that thrive in some of the world's most inhospitable habitats (e.g.,
vertisols, deserts, and salt marshes). In contrast to some other large
Angiosperm families, much of the biodiversity of the Compositae is in
extreme environments rather than within the tropics. Representatives of
this family are present on every continent and in nearly all habitats except
Antarctica (Funk et al. 2005).
Helianthus belongs to the Asteraceae subfamily Asteroideae, tribe
Heliantheae, subtribe Helianthineae (Panero and Funk 2002). The