Production of New Intergeneric Hybrids between Raphanus sativus and Brassica Wild Species

Abstract

Intergeneric reciprocal crosses between Raphanus sativus and three Brassica species, such as B. fruticulosa (ssp. cossoneana strain 201 and ssp. mauritanica strain 401), B. maurorum and B. oxyrrhina, were carried out in order to analyze their crossability and to produce their F_l hybrids. Crossability was analyzed based on the pollen germination index (P. G. I.) and the development of hybrid embryos which was evaluated in vivo by conventional crossing and in vitro by ovary culture. When R. sativus was used as the pistillate parent, pollen grains of the Brassica. species germinated well on the stigmas while only a small number of pollen tubes could elongate near the ovules in a few R. sativus pistils, resulting in a low development of hybrid embryos. Using the Brassica species as the pistillate parent in the intergeneric crosses, the crossability was relatively higher than that of the reciprocal cross. When R. sativus was used as the pistillate parent, one F₁ hybrid was produced by embryo culture in the cross of R. sativus × B. fruticulosa-401. When the Brassica species were used as the pistillate parent, 200 F₁ hybrids were obtained through ovary culture followed by embryo culture from all cross combinations and 12 F₁ hybrids were obtained in the cross of B. oxyrrhina × R. sativus by conventional crossing without embryo rescue. F_l hybrids were intermediate between their parents in several characteristics except for flower color and root thickening. In the cross of the Brassica species × R. sativus, 12 amphihaploid F_l hybrids formed trivalents and a number of bivalents at metaphase I(MI)and their pollen fertility ranged from O% to 70.2%. Induced 6 amphidiploid F_l hybrids showed relatively stable chromosome associations at MI and a higher pollen fertility than that of the corresponding amphihaploid. It is suggested that these new F_l hybrids could become valuable materials in the breeding of the tribe Brassiceae.