Morphological, cytological and fertility consequences of a spontaneous tetraploid of the diploid pear (Pyrus pyrifolia Nakai) cultivar 'Cuiguan'

- CBM was a new spontaneous tetraploid pear.
- CBM showed morphological and cytological variations.
- CBM showed a more rapid fruit growth rate and better fruit quality.
- CBM had the potential for generating polyploids.
- CBM was valuable for pear polyploid breeding.

Chromosome multiplication, polyploidy, is usually correlated with improved agronomic performance. However, the lack of knowledge regarding variation in polyploids limits their efficient use in breeding. The main objective of this study was to demonstrate variations in morphology, cytology and fertility in the spontaneous 'Cuiguan' bud mutant (CBM). Using flow cytometry, we found that CBM was a new tetraploid pear with doubled 2C-DNA. Compared with its diploid donor, the 'Cuiguan' pear (control), CBM produced bigger flowers, anthers and leaves, longer guard cells, less and low-viability pollen grains, and faster growing fruits. In CBM fruits, the malic acid content was reduced more than 9%, but the glucose and sucrose contents were significantly increased by 38.6% and 72.9% respectively, which made the CBM fruits sweeter. Cross tests revealed that CBM, used as the male parent, showed a lower male fertility rate compared to the control and produced hybrid fruits with lower seed numbers and reduced seed germination rates. Additionally, the first filial generation (F1) plants were all diploids. However, CBM had the same female fertility as the control and mainly generated triploid or tetraploid F1 plants. Based on its quick fruit growth, fine fruit quality and potential for generating polyploids, CBM is a valuable germplasm for pear polyploid breeding.