Cytology, Fertility and Flower Colour in Hybrids between Brassica japonica and Raphanus sativus, and the Synthesis of new Brassicoraphanus

Abstract

In order to obtain new hybrids (Brassicoraphaleus) and to examine the genetic traits of matromorphs on a cytological basis, triploids of Brassica japoeeica were crossed with diploids of Raphanus sativus. Matromorphs could not be obtained, but some F1 hybrids were produced. The chromosome numbers of the F1 plants were 2n=19 (4 plants), 21 (1 plant) and 23 (2 plants). These plants showed some bivalents and trivalents in addition to univalents. They were almost completely sterile. One 2n=19 plant produced only one seed by open-pollination. An F2 plant (2n=38) was grown from this seed. The chromosome pairing of this plant was shown to be (1-0)IV+(2-O)lll+(19-16)ll+ (3-0)l. F3 plants were derived from selfed or open-pollinated seeds of the F2 plant. Some of the selfed progeny had 36, 37 or 38 chromosomes. The fertilities of the selfed and open-pollinated progenies averaged 2.50 and 2.62 seeds per silique under open-pollinated conditions, respectively. The F1 to F3 plants in the present study were similar to the already reported F1 hybrids and amphidiploids in cytological behaviour. However, the plants in the present study showed several characteristics: (1) some of the F1 and F2 plants had pale yellow flowers, (2) almost all the F3 plants had yellow flowers, and (3) the F3 plants showed a good seed fertility. The pale yellow of flowers in F1 and F2 generations was probably due to the incomplete dominance of a flower colour gene or the existence of modifying genes. The occurrence of the yellow flowers in F3 greneration was explained as the result of fertilization with a pollen grain carrying yellovr colour genes from a foreign strain. The good fertility of the F3 plants was possibly caused by a linkage relation between the flower colour gene and a fertility gene. Nevertheless, it was further surmised that there were still other genes affecting fertility. The cause of difference in fertility amongr amphidiploids (Brassicoraphanus) from different sources is now being under investigation.