| Cauliflower, a variety of Brassica in Cruciferae, is popular with many people as a kind of vegetable. However, cauliflower production always suffers from diseases such as black rot, blackleg, club root and so on, affecting the yield and quality of cauliflower seriously.Somatic hybridization can overcome the sexual incompatibility barriers to obtain the hybrid between different species, and transfer the alien resistant genes from other species. It can enrich the diversity of pathogen resistant genes of the breeding material, and realize the innovation of crop germplasm.One object of this study was to transfer multi-resistant genes from wild species to cauliflower by using somatic hybridization technique.Matthiola incana belongs to Cruciferae family, which possesses desirable characteristics such as the rich a-linolenic acid and the high resistance to aphids. This study produced somatic hybrids between B. oleracea and M. incana for the first time by using the symmetrical somatic hybridization technique, which laid a good foundation for the utilizing of the heterogenous excellent germ plasm. The regenerated plants were investigated on morphology, RAPD or SRAP molecular marker, isozyme pattern, chromosome number and DNA content.B. nigra, one of the three Brassica species, exhibited high resistance to black rot, black leg and clubroot diseases. In our privious study, a lot of somatic hybrids between B. nigra and cauliflower were obtained. Seventy-nine hybrids were transplanted into greenhouse successfully, the biological characters of which were studied systemicly in the present research. The backcross progeny of partial somatic hybrids were obtained through embryo rescue technique, the reaiatance of which to X. campestris pv. campestris was also assessed.The other object of this study was to transfer the alien diseases resistant genes from B. nigra to Chinese cabbage. Chinese cabbage is one of the most important vegetable crops in China. In the process of cultivation, the chinese cabbage production always suffers from diseases such as black rot, blackleg, club root and so on, affecting the yield and the quality seriously. In order to transfer the alien diseases resistant genes from other species, crosses between Brassica campestris pekinensis and B. nigra were made and the F1 plants obtained were investigated on morphology, SRAP molecular marker, chromosome number and genome constitution. The backcross progeny of partial F1 hybrids were obtained through embryo rescue technique, the reaiatance of which to X. campestris pv. campestris was also assessed.All the results were described as follows:1. Two somatic hybrids between cauliflower and Matthiola incana were produced and investigated on morphology, RAPD molecular, chromosome number, isozyme pattern and nuclear DNA content. The two hybrids were both allopolyploid and had 26-48 chromosomes. Comparing the different identification method, it was thought that the morphological observation was more simple and direct, and with enough veracity in most of the cases, but the SRAP molecular marker was more exact and dependable. Both hybrids showed limit growth and neither of them can grow to mature plants in the greenhouse.2. Seventy-nine somatic hybrids were transplanted in greenhouse successfully and were investigated on morphology, SRAP molecular marker, chromosome number and genome size. Morphology of the regenerated plants varied a lot and most of the population was intermediate to that of the parents; The hybrid plants had different nuclear DNA content:higher, lower than the parental sum or equal to it. The hybrids with higher DNA content had abnormal leaf, bad growth vigour and poor fertility, which indicated that the growth vigour and fertility had relations with the nuclear DNA content. By chromosome counting, the majority of the detected hybrids were mixoploid. Among 79 hybrids,13 aimed hybrids were picked out, which all had vigorous growth and partial fertility. Therefore, it was feasible to broaden the genetic variability of cabbage though asymmetric somatic hybridization.3. The compare of the biological characters of the fertile and sterile hybrids were also studied. The PMCs meiosis behaviors were more abnormal in sterile hybrids than in fertile ones. Laggard chromosomes, chromosome bridges and unequal separation happened more frequently. The results of GISH analysis indicated that the fertile hybrids contained the whole genome of B. nigra and cauliflower with regular meiotic divisions while the sterile hybrids had the whole genome of cauliflower and partial intact chromosomes of B. nigra. Moreover, the additional B. nigra chromosomes had a high occurrence of laggards and unequal distribution. Genome study of the two kinds of hybrids showed that the DNA recombination happened in all hybrids. 4. A total of fifteen BC1 hybrids were obtained, the biological characters of which were studied. Morphology of the BC1 hybrids was intermediate to that of the parents and three ones had similar morphology to cauliflower. The nuclear DNA content and the chromosomes number were both inconsistent, which indicated the trait of aneuploid. Comparing with the somatic hybrids, the range of the BC1 hybrids became narrow, which also showed a tendensy to cauliflower. All the fifteen BC1 plants were used to self-pollination and backcrossing with cauliflower, four of which could obtain BC2 and BC1S1 seeds.5. Eight local Xcc strains and two foreign Xcc strains belonging to raceâ… and raceâ…£respectively, were used to inoculate parent plants. A Xcc strain CH5 were selected depending on severe chlorosis around the inoculation sites on cauliflower giving a disease severity rating of 9 and no symptom development on B. nigra. The selected Xcc strain CH5 was used to inoculate hybrids, and backcross plants. Some BC2 hybrids showing good disease resistance were obtained.6. Ten F1 plants were obtained between Chinese cabbage and B. nigra, six of which were characterized to be hybrids through morphology, SRAP molecular marker and cytology analysis. One of the hybrids had 26 chromosomes with ABB genomic constitution by GISH analysis showing partial fertility. The other five hybrids had 18 chromosomes in more than 50% PMCs with AB genomic constitution were entirely sterile. An increase in the chromosomes number and homologous chromosomes pairing mignt improve the hybrids fertility.7. The BC1 hybrids were more homophylic to the female parent on morphology, showing visible heterosis. Most plants had 28 chromosomes with with AAB genomic constitution by GISH analysis. The male fertility increased obviously and many BC2 seeds were obtained. The number of BC2 hybrids chromosomes was not consistent, having 22-36 chromosomes. Some BC2 hybrids showing good Xcc resistance were obtained. |
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