Basic Information - Genetics, Genomics and Breeding of Crop Plants - page 26

The origins and relationships of the polyploid hybrid species in
Helianthus have long been of interest and remain largely unresolved,
particularly for perennials (Timme et al. 2007). It is currently unknown
which polyploid species are autopolyploids and which are allopolyploids.
The hexaploid H . resinosus is currently being investigated using molecular
cytogenetics and markers in order to elucidate species origin through
polyploidy (Carrera et al. 2004).
1.4.6 Aneuploidy
Aneuploids can be the result of interspecific hybridization. Leclercq et al.
(1970) obtained trisomic plants (2 n +1) in backcross progeny of H. tuberosus
x H. annuus hybrids. The progeny were resistant to downy mildew
[ Plasmopara halstedii (Farl.) Berl and deToni] and they postulated that the
extra chromosome came from the H. tuberosus genome.
Trisomic plants were obtained after backcrossing interspecific hybrids
H. petiolaris x H. annuus (Whelan 1979) and H. maximiliani x H. annuus
(Whelan and Dorrell 1980; Whelan 1982) with cultivated H . annuus .
Multivalents were frequently observed in these F 1 hybrids indicating
reciprocal translocation heterozygosity. The trisomics presumably originated
from unequal disjunction of multivalents. Most trisomics appeared normal,
but some had distinct morphological features.
Jan et al. (1988) produced tetraploids, triploids, and aneuploids using
the inbred line P21. Meiotic chromosome pairing of the autotetraploid P21
was reasonably normal with 28.16 bivalents, 0.85 univalent, and a small
number of multivalents. Triploids were obtained by crossing tetraploids
with diploid P21, and aneuploids by crossing triploids with the diploids.
The chromosome number of the 137 plants from reciprocal triploid x diploid
crosses ranged from 2 n = 34 to 2 n = 47+ t . In general, plants with a lower
chromosome number were more prevalent when triploids were used as the
pollen parent, while the frequency of plants with a higher chromosome
number increased when triploids were used as the seed-bearing parent.
These results suggest the effective transmission of extra chromosomes
through both male and female gametes, with the female gametes being better
than the male gametes. However, for rapid trisomic production and fast
chromosome reduction, triploids are often used as the pollen parent. These
results suggest that diploid sunflower tolerates extra chromosomes well
and a set of trisomic genetic stocks is possible. Pollen stainability, an
indicator of viability, was above 90% for plants with 2 n = 34 to 2n = 37. As
chromosome numbers increased from 2 n = 38 to 2 n = 45+ t , pollen stainability
decreased to about 40%, but acceptable seed set was still obtained (Jan et al.
1988).