With 3 figures and 5 tables Abstract To develop alloplasmic lines of Allium cepa, cytoplasmic substitution by continuous backcrossing was performed using Allium roylei as a cytoplasm donor. The chromosomes of a single F1 plant between A. roylei (♀) and shallot were doubled, and then backcrossing with shallot was performed to produce BC1 as allotriploids. One allotriploid plant was used for backcrossing with bulb onion to produce BC2 with 2n = 16, 17, 23 and 24. The BC2 plants possessing 16 chromosomes were checked for pollen fertility in Yamaguchi, Japan (N34°11′), and then backcrossed with bulb onion again to evaluate their seed‐setting characteristics. The pollen fertility of BC2 ranged from 0% to more than 10%. A large number of plants showed no pollen fertility (0%). In Kagawa and Hokkaido, most of the plants were completely pollen sterile, while the percentages of seed sets in BC2 were high enough to reproduce BC3 seeds. The results of this study revealed that an exploitation of A. roylei cytoplasm would be useful for the development of a novel cytoplasmic male sterility line in Allium.

No abstract