A New Type of Tetraploid (2n=40) Derived by Aneuploidy Breeding of Brassica crops

Aneuploidy breeding was utilized as a method to develop a new type of diploid Brassica crop. Novel combinations of the A genome of Chinese cabbage and C genome of cabbage were established by crossing to produce a sesquidiploid and successive backcrossing with B. campestris to produce aneuploids. Successive selfing resulted in aneuploids with chromosome complement ranging from 2n=21 to 2n=40. Among progenies in the BC₂F₃ and BC₂F₄ generations, plants with 2n=40 were selected and characterized. These plants were found to be stable cytogenetically but fertility was very low. A reciprocal cross was made but the resulting progenies with 2n=40 in the BC₂F₅ generation, although stable cytogenetically, were also sterile. The two lines from the reciprocal crosses, one derived from an initial cross with B. campestris as female parent and the other with B. oleracea as the female parent, were crossed and the resulting progenies were found to be stable in terms of chromosome number and fertility. Successive selfing for almost 10 generations yielded progenies with 2n=40 only. Cytological and morphological analyses indicate distinct characteristics of a new type of Brassica tetraploid. Now widely known in Korea as Ssamchoo, it is well suited to the eating culture of the Korean people.