Hybrid progenies of the cross, Brassica campestris × B. oleracea. IV. Crossability of F₂, B₁ and hybrid plants, and their progenies

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Crossability was examined in the F₂, B₁ and hybrid plants, and the somatic chromosomes of their progenies were investigated. The F₂ and B₁ plants were obtained in the self- and open pollinations, and in the F₁ hybrids backcrossed to both parents, respectively. The hybrid plants were obtained in the cross between F₁ hybrids and diploid Brassica oleracea, and between F₁ hybrids and B. napus. All F₁ hybrids were produced by ovary culture in vitro in the cross between B. campestris and B. oleracea, and between B. campestris and autotetraploid B. oleracea. The plants examined were classified into three types. The first type had 29 chromosomes in root tip cells, and the second had 38 chromosomes. The third type of plants was the plants having chromosomes other than 29 or 38 chromosomes. Many different types of aneuploids were obtained in open pollination of the F₂, B₁ and hybrid plants, in the progenies of the F₂, B₁ and hybrid plants crossed to B. campestris, and B. napus. It was suggested that the different types of normal egg cell with one by one or little by little chromosome addition might be produced, and that some specific chromosome or chromosome group might increase or decrease the crossability in aneuploid production. It might be considered that there were genes related to fertility. It might be possible that the genes of B. campestris and B. oleracea could exchange reciprocally. Further selection had to be done for the production of a new type crop of B. napus which had been reported in a previous paper.