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1、Pre-Breeding:A Link Between Genetic 前育种：遗传材料和玉米育种间的联系 Resources and Maize Breeding(III)Importance.Pre-breeding programs can generate new base populations for breeding programs 重 要 性.预 育 种 程 序 可 以 为 以 后 的 育 种 计 划 提 供 新 的 基 础 群 体，and also assist in identifying heterotic patterns for hybrid programs.Ma
2、rshall(1989)considered 并有助于确定育种中的杂优特征。马歇尔认为 that the lack of pre-breeding programs is the most limiting factor for using landrace germplasms 利用种质库中的地方品种种质资源和驯化的外来种质的最大限制因素是缺乏前育种项目。and unadapted exotic lines from collections.Pre-breeding at CIMMYTs Germplasm Bank 在国际玉米和小麦改良中心种质资源的前育种，collections,aims
3、 to provide to breeders ready utilization of materials with specific traits of interest 目的是为育种者提供特定性状的育种材料，同事也是为了扩大改良种质资源的多样性。as well as a means to broaden the diversity of improved germplasm.Caribbean collections are 前育种工作的首要任务是receiving first priority for pre-breeding efforts,based on the interest
4、 of this germplasm both by 对加勒比海地区的种质材料，主要出发点是基于带和温带的育种家对此感兴趣，而且也是基 tropical and temperate maize breeders,and the fact that,evaluations of these collections are 于对这样的种质资源的评价工作已经经在进行中这样一件事实。already under way.As a result of these pre-breeding programs,many gene pools and populations 这些前育种计划的结果是 CIMMTY
5、 已经为热带低纬度地区培育了许多基 were developed by CIMMYT for tropical lowlands,as shown in TABLE 1(omitted).因库和群体，表 1 所示。Clearly pre-breeding programs are time-consuming and tiresome.For private plant breeders,显而易见，前育种计划是费时而且繁琐的。对于私人育种家而言，generally under pressure to fulfill short term goals,exotics that underwent
6、 pre-breeding are 一般在完成短期目标的压力下，利用外来品种进行育种可能是非常有效而且更加具有新likely to be more useful and certainly more attractive.Consequently,close cooperation between 引力的。因此，公营和私营机构之间的密切合作 public and private institutions can be especially helpful in pre-breeding programs.对于前育种计划来说是非常有帮助的。Heterotic pattern is a key f
7、actor for utilizing germplasm to maximize performance of the 杂种优势模式是利用种质资源以实现杂交组合和衍生杂交种（产量）表现最大的关键因 population crosses and derived hybrids.Prebreeding can identify heterotic patterns for 素。前育种可以为以杂种为目标的育种计划判别杂种优势breeding programs where the goal is hybrid development.Although the heterotic pattern be
8、tween 模式。虽然 Lancaster Sure Crop and Reid Lancaster Sure Crop and Reid Yellow Dent has received greatest use in U.S.programs,other Yellow Dent 的杂种优势模式已经在美国育种程序中广泛使用，其他的优势模式也已被考虑 heterotic patterns have been considered as Leaming and Midland.Identification of other 如 Leaming 和 Midland 模式。其他的杂种优势模式的识别
9、heterotic patterns should contribute for a broadening of germplasms to be used commercially.应该有助于扩大种质资源的商业用途。CIMMYTs heterotic patterns are shown in TABLE 2(omitted).国际玉米和小麦改良中心的杂种优势模式如表 2 所示。Generally,hybrid programs showed good results in tropical areas,especially where the 一般来说，在热带地区已开展杂交育种结果较好，尤
10、其在那些有优良组织结构，竞争力 existence of well-structured and competitive private companies further contributed to this 强的私人公司存在于热带地区，这些公司进一步加强了这一效果。performance.In Brazil,flint by dent crosses are widely used and usually include materials 在巴西，粉质型与硬质型的杂交应用广泛，通常包括来自 Cateto 和 Tuxpeo derived from either Cateto by Tu
11、xpeo or Suwan-1 by Tuxpeo(上述划线者均为品种名).杂交或者 Suwan-1 和 Tuxpeo 杂交得到的材料。Paterniani(1990)emphasized the remarkable contribution of the race Tuxpeo to increase the 1990 年，Paterniani 强调了，在巴西 Tuxpeo 这一物种对于提高杂交种和开放授粉品种产量 yielding potential of hybrids and open-pollinated varieties in Brazil.Brazilian maize hy
12、brid 潜力的显著作用。巴西玉米杂交育种开创了 programs pioneered the commercial utilization of semi-dent types.High levels of heterosis 半齿形玉米商业用途的先河。然而，高水平的杂交优势 however,are not restricted to crosses involving contrasting endosperm types.Paterniani&并不只限于胚乳有差异的类型间的杂交。1963 年，Paterniani Lonnquist(1963)observed that expresse
13、d heterosis was as great between cultivars with 和 Lonnquist 观察到，在具有相似胚乳的栽培品种间，以及在有差异胚乳类型的栽培品 similar endosperms as well as between those with contrasting endosperm types.These results 种间，表现出的杂种优势同样明显。这些结果表明有相 indicate genetic variability among germplasms of similar endosperm types.似类型的种质之间存在遗传变异性。Th
14、e need to keep the amount of accessions in genetic banks in a manageable number is 将基因库中计入资料的数量保持在一个易控制的数目之内，这个需要变得更加明显。becoming more evident.In this way,an additional advantage of well succeeded pre-breeding 在这种方式下，前育种的一个额外好处是建立核心种质。programs is the establishment of core collections.The main goal of
15、 the core is to represent 核心种质的主要目标是以最小重复代表代表the genetic diversity of a crop species and its relatives with a minimum of repetitiveness.Brown 作物物种及其金源物种的遗传多样性。(1989a)suggested that the core should consist of about 10%of the collection,which represents Brown 建议核心种质约占材料的 10%，它所代表了约 70%的遗传变异。nearly 70%
16、of the genetic variability.Moreover,the core should not exceed 3,000 entries.The 而且核心的数量不应超过 3000 份材料，这些材料的制定。establishment of these collections does not affect the base collection strategic role that is a source 没有影响到基础材料战略作用，这种作用是替代不同物种广泛遗传变异性的来源 of replacement of the extensive genetic variability
17、 of different species.It is important to consider that a core collection is a dynamic rather than a static set of 要认为核心材料是一个动态的而非静态的额档案库是非常重要的。accessions.It is possible to introduce new accessions into the core and also replacements due 核心材料也可能引入新的材料载入，并且也会由于宇宙弄个家的需要进行改 to changes of breeders needs.CIMMYT has developed efforts to establish maize cores.变。国际玉米和小麦改良中心已经智力于制定玉米的核心种质。Results of a Tuxpeo core collection were reported by Crossa et al.(1994)and Taba et al.(1994).Tuxpeo 的核心材料的结果已经被发表在了 Crossa et al.(1994)和 Taba et al.(1994)上。