| Brassica napus L. is a young crop in China. It has been introduced into China for only about 70 years. It was originated in Europe, where it has been grown just for a few hundred years. Its genetic diversity is, therefore, relatively small, and it is deemed imperative to build and broaden the genetic germplasm of the crop.According to previous studies, B. napus was evolved from hybrids of B. oleracea L. and B.campestris L. of the Brassica genus through natural crosses followed by natural doubling of chromosomes. A number of scientists, home and abroad, have made studies on resynthesized B.napus, and have proved the natural origin process with experimental evidences, and have obtained some valued breeding materials.Since 1980s, a group of landraces of B. chinensis B. campestris, and B. oleracea var alboglabra, charactevstic of the indigenous conditions, from Southeastern China (SW), including a few wild or semi-wild forms of B. campestris. Interspecific hybridizations were made with species of Chinensis species and Oleracea species, and a big group of resynthesized rapeseed lines (B. napus L.) have been developed. Various genetic types have shown in these resynthesized lines. The selection process, studies on selected lines on their morphology, cytology, agronomic and economical traits, isoenzymes and DNA molecular markers were reported in the present paper, with a hope to confirm the genetic diversity and the breeding values of these materials. The main results obtained include:1. From the hybrids of reciprocal crosses a large group of resynthesized B. napus lines were obtained through the conventional selection method for hybrids of inter-variatal hybridization. These novel materials were highly diversified with genetic types. A portion of these lines possess specially significant characteristics, such as specially long siliques, large siliques, big seeds, many branches, dwarf straw, specially early maturity, white flower, yellow-color seed, forage (vegetable)types, etc. Some resynthesized (RES) lines have been used for hybrid rapeseed breeding, showing very good general combining ability, and a good breeding potential.2. Pollen viability and Pollen mother cell (PMC) miosis were investigated with a fewRES lines showing slow stabilization and low seed set. Their pollen viability were 74.4-82.4%, 15.0-23.0% lower than that of the investigated RES lines, a high frequency of multi-valent chromosome cells, 67.8-84.4%, were observed, Tn anaphase T, the frequencies of cells showing lagging chromosomes were 7.5-12.6%. These cytological abnormalities indicated that there was a cytological instability in the progeny of the RES hybrids. This might lead to segregation, decline of pollen viability and decline of seed setting. The instability of the RES lines in cotology may be related to the partial homology in the genomes of the two parental species. Whereas in an overall view most RES lines could approach to a genetic stable status at a relatively quick speed, considerably different from other wide hybrids. It is proposed that there may be a inhibiting gene present in the parental species which may restrain the pairing of the partially homologous chromosomes, so that the interspecific hybrids can get cytogeneticlly stable with the selection process.It was shown in the results of the main agronomic and economic traits of the RES lines, the genetic diversity was big. In the 16 observed characterstics, coefficients of variation range between 11.24-42.37%. Seed yield per plant showed the largest variation, followed with effective silique number, total branch number, seed set density, branch height and erucic acid content. Their C V values are all more than 30%, with a difference of 5-7 times.Fifty (50) representative RES lines and 2 normal B. napus lines were selected to conduct analyses of main components and clustering with 12 important agronomic and economic traits. When the materials were grouped according to origin, the genetic distances (GD) among most of the groups were bigger than within g...
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