04 Pre-Breeding_ A Link Between Genetic resources and maize breeding (IV)8 第三次.docVIP

Pre-Breeding: A Link Between GeneticResources and Maize Breeding (IV) 前育种：遗传资源与玉米育种之间的联系。 Methods. There are several alternatives for incorporating useful characteristics into adapted 方法. 在前育种中，有几种方法可将有用的性状合到一个已经适应的种质材料中。 materials. The methodology depends on the heritability, gene action, number of genes involved, 这一方法论依赖于遗传力，基因作用，涉及到的基因数目，杂种优势以及基因与环境的 heterosis, and genotype x environment interactions. Whenever a superior germplasm is available 相互作用（等因素）。在持续的育种过程中，每当有优良的种质资源时，通过改善基因渗透 from ongoing breeding programs, improvement by introgression is usually the least expensive and 的方法，通常是对前育种材料进行改良，虽然花费最少但也是最快的方法。 speedy method for improving the selected pre-breeding accessions. The ideal proportion of exotics to be incorporated into adapted germplasms has been 一些研究家通过将适当比例的外来种质资源加入到优良种质资源中进行研究测验， investigated by several researchers, but so far there is no conclusive information about this 但到目前为止，关于此方式还没有确凿的结论。 question. According to Bridges Gardner (1987), it depends on the breeding goals (short or long 根据Bridges Gardner (1987)的研究，这种方法依赖于育种目标（短期或长期的），还有依 term), and also on the performance of both exotics and adapted germplasms. Wellhausen (1965) 赖于外来种质资源和优良种质资源的产量表现。 Wellhausen (1965) recommended the incorporation of about 25% of exotic germplasm into Corn Belt adapted 建议外来种质资源对（美国）玉米带适应材料的渗入以25%为宜。 materials. Crossa Gardner (1987) reported that populations with 75% and 100% of adapted Crossa Gardner (1987)称在作物产量中，外来种质资源对适应种质的75% germplasm did not differ in grain yield, being both populations superior to populations with 50% 和100%比例渗入没有区别，两者皆优于50%的渗入比例。 of adapted germplasm. Different levels of introgression (0, 25, 50, 75, and100%) were evaluated Michelini Hallauer (1993)研究了不同水平的基因渗入(0, 25, 50, 75, by Michelini Hallauer (1993), who observed that better yields were obtained in crosses with and100%)他们观察到与50%的外来种质杂交可获得较好的产量， 50% exotic germplasm, and also suggested the use of the ex