Abstract:

Sugar beet (Beta vulgaris L.) is one of the most important sugar crops in the world. However, the application of molecular markers in sugar beet greatly lags behind that in other field crops. In the present study SRAP and SSR markers were employed to investigate the genetic diversity and relationships of sugar beet in order to make full use of germplasm reasonably, to select parents for breeding programs accurately, to improve breeding efficiency and to identify target cultivars quickly. We analyzed 49 sugar beet accessions, including monogerm lines (including male sterilities and maintainors), polygerm tetraploids, polygerm diploids, F₁ of monogerm cross combinations, and foreign varieties introduced. All these materials are conserved at Sugar Beet Research Institute, CAAS. In a preliminary experiment, four accessions markedly distinct in phenotype were used to screen 64 pairs of SRAP primers and 11 pairs of SSR primers. Finally, 11 pairs of SRAP primers and nine pairs of SSR primers were selected and used for the present study. A total of 199 SRAP bands (including 86 polymorphic bands) were detected and one primer pair produced 18.0 bands on average (including 7.8 polymorphic bands). The ratio of polymorphic SRAP bands was from 33.3% to 62.5%, with an average of 43.7%. The selected SSR primers yielded 35 bands, with an average of 3.9 per primer pair, and the ratio of polymorphism was as high as 100%. The average genetic distance in the 49 accessions was 0.3860 and the average genetic similarity was 0.6795. About 30% of accessions were significantly different in average genetic distance or genetic similarity. The highest genetic similarity occurred between polygerm tetraploid lines (0.7264), followed by that between F₁ of monogerm cross combinations (0.7243) and that between foreign varieties introduced (0.7060), while the lowest one was found between monogerm lines (0.6837). The 49 accessions were divided into A, B, C and D groups based on cluster analysis. About 40% of accessions belonged to the D group which was divided into 4 subgroups, including diploids, tetraploids, F₁ of monogerm cross combinations and foreign varieties introduced, which also showed high genetic diversity. Thus, the combination method with SRAP and SSR markers is economic, effective and reliable to assess genetic diversity and relationships of sugar beet. The results indicate that sugar beet has a high level of heterogeneity. There are a definite difference between foreign genetic background and native genetic background, and the closer relationships and narrower genetic basis. Introducing foreign germplasm in breeding has shorted the gap between China and other countries in sugar beet genetic basis among cultivars in production. The classification based on the identification of biological and economical properties in field experiments was generally in accord with that based on SRAP and SSR molecular markers. Therefore, the application of the technology of molecular markers in sugar beet will accelerate breeding process and improve the quality, the yield and the content of sugar.

Key words:

Sugar beet, SSR marker, SRAP marker, Genetic diversity, Relationships