To illustrate the mode of polyploid origin in Rubus, meiotic
processes of pollen mother cells and pollen viability in
sixteen wild and cultivated bramble resources with various
ploidy levels were investigated in this study. In diploids,
formation of seven bivalents was the most predominant
meiotic association at metaphase I, except for wild R.
ellipticus var. obcordatus and red raspberry cultivars (R.
idaeus) displaying a few univalents, but in black raspberry
cultivar (R. occidentalis) both univalent and multivalents
were recorded. Meiotic pairing in tetraploids R. lambertianus
var. glaber, blackberry hybrids ‘Shawnee’ and ‘Arapaho’
recorded 13.64, 7.41 and 12.33 mean bivalents per cell,
respectively. Various chromosome configurations were
observed in hexaploid blackberry ‘Ollalie’ with mean of 12.80
bivalents and 3.85 quadrivalents. Besides predominant
bivalents, univalents and multivalents were accounted in
significant proportions among heptaploid blackberry
cultivars. Abnormal chromosomal behaviours including
chromatid bridges, lagging chromosomes, unequal
segregation, micronuclei, and polyads were also frequently
observed. The frequency of meiotic irregularities
significantly increased with increasing ploidy levels, which
has influence on the percentage of sterile pollen grains.
Based on meiotic pairing and abnormalities, wild R.
lambertianus var. glaber and blackberry ‘Arapaho’ were
supposed to be well-established allotetraploids through
diploidization process; blackberry ‘Shawnee’ and ‘Ollalie’
to be segmental allopolyploids with certain variations, while
‘Black Butte’, ‘Boysen’ and ‘Kotata’ to be alloheptaploids
via intra-specific hybridization accumulating stable
chromosomal variations. In addition, structural variations
such as chromosomal inversion and translocation play an
important role in the evolutionary history of Rubus.
Keywords: Rubus L., raspberry, blackberry, chromosome pairing, meiotic abnormality, allopolyploid
Article DOI: 10.31742/IJGPB.78.4.12
Print ISSN: 0019-5200
Online ISSN: 0975-6906
Yan Wang, Qing Chen, Huaqing Fu, Jing Zhang, Tao Chen, Bo Sun, Ya Luo, Yong Zhang, Haoru Tang and Xiaorong Wang info_circle