Basic Information - Genetics, Genomics and Breeding of Crop Plants - page 25

(1981) reported smaller chromosome sizes, chromosome types equally
distributed among m, sm and st, and only 1 or 2 satellited chromosomes.
The large variation in chromosome condensation among studies of different
authors was probably due to differences in chromosome preparation.
Perhaps the use of common cultivated H. annuus as a check would have
helped to resolve some of the problems when comparing the total
chromosome length of different genomes.
According to Georgieva-Todorova and Lakova (1978), closely related
tetraploid species H. decapetalus and H. hirsutus had remarkable similarity
regarding most features of their karyotypes. The 2 n = 30 H. mollis studied by
Kulshreshtha and Gupta (1981) was much lower than the basic set of 2 n =
34 and was presumably from roots of a nonviable plant. Also, H. californicus
is expected to be hexaploid with 2 n = 102. The H. californicus with 2n = 34
may have been a misidentified species. Speciation of Helianthus was shown
to have involved chromosome exchanges such as translocation and
inversion (Chandler et al. 1986), as well as the obvious polyploidization for
the tetraploid and hexaploid species. One would expect a continuous
variation in DNA and total chromosome length in diploid species, and
multiples of single or combinations of the diploids for tetraploids and
hexaploids.
The karyotype of Helianthus annuus was analyzed using Giemsa banding
and fluorescence in situ hybridization (FISH) and computer-aided image
processing with respect to the chromosome length, arm ratio, occurrence
and chromosomal position of intercalary heterochromatin and the position
of 18S/25S and 5S ribosomal RNA genes were located using Giemsa banding
and fluorescence in situ hybridization (Schrader et al. 1997). In situ
hybridization techniques involving GISH, FISH, and BAC-FISH are being
optimized for diversity and evolutionary studies between species of the
genus Helianthus and development of a physical sunflower map allowing a
cross reference to the genetic map (Paniego et al. 2007). Measurements of
chromosomes in combination with Giemsa banding and FISH should allow
for the discrimination of most chromosome pairs of the sunflower.
1.4.5 Polyploidy
The genus Helianthus has a basic chromosome number of n = 17 and contains
diploid (2 n = 2 x = 34), tetraploid (2 n = 4 x = 68), and hexaploid (2 n = 6 x =
102) species ( Tables 1-2 and 1-3 ) . The 14 annual species are all diploid, and
the 37 perennial species include 27 diploid, 4 tetraploid, 6 hexaploid, and 4
mixi-ploid species. Helianthus ciliaris and H. strumosus have both tetraploid
and hexaploid forms, while H. decapetalus and H. smithii contain diploid
and tetraploid forms.