Department of Agronomy, USDA, Agricultural Research Service, USA.
Theor Appl Genet. 1990 Oct;80(4):488-96. doi: 10.1007/BF00226750.
Changes that may have occurred over the past 50 years of hybrid breeding in maize (Zea maize L.) with respect to heterosis for yield and heterozygosity at the molecular level are of interest to both maize breeders and quantitative geneticists. The objectives of this study were twofold: The first, to compare two diallels produced from six older maize inbreds released in the 1950's and earlier and six newer inbreds released during the 1970's with respect to (a) genetic variation for restriction fragment length polymorphisms (RFLPs) and (b) the size of heterosis and epistatic effects, and the second, to evaluate the usefulness of RFLP-based genetic distance measures in predicting heterosis and performance of single-cross hybrids. Five generations (parents, F1; F2, and backcrosses) from the 15 crosses in each diallel were evaluated for grain yield and yield components in four Iowa environments. Genetic effects were estimated from generation means by ordinary diallel analyses and by the Eberhart-Gardner model. Newer lines showed significantly greater yield for inbred generations than did older lines but smaller heterosis estimates. In most cases, estimates of additive x additive epistatic effects for yield and yield components were significantly positive for both groups of lines. RFLP analyses of inbred lines included two restriction enzymes and 82 genomic DNA clones distributed over the maize genome. Eighty-one clones revealed polymorphisms with at least one enzyme. In each set, about three different RFLP variants were typically found per RFLP locus. Genetic distances between inbred lines were estimated from RFLP data as Rogers' distance (RD), which was subdivided into general (GRD) and specific (SRD) Rogers' distances within each diallel. The mean and range of RDs were similar for the older and newer lines, suggesting that the level of heterozygosity at the molecular level had not changed. GRD explained about 50% of the variation among RD values in both sets. Cluster analyses, based on modified Rogers' distances, revealed associations among lines that were generally consistent with expectations based on known pedigree and on previous research. Correlations of RD and SRD with f1 performance, specific combining ability, and heterosis for yield and yield components, were generally positive, but too small to be of predictive value. In agreement with previous studies, our results suggest that RFLPs can be used to investigate relationships among maize inbreds, but that they are of limited usefulness for predicting the heterotic performance of single crosses between unrelated lines.
过去 50 年来，玉米（Zea mays L.）的杂种优势在产量和分子水平的杂合性方面发生了变化，这引起了玉米育种家和数量遗传学家的兴趣。本研究的目的有两个：第一，比较来自 20 世纪 50 年代和更早的 6 个旧玉米自交系和 20 世纪 70 年代的 6 个新自交系的两个双列杂交，比较（a）限制片段长度多态性（RFLP）的遗传变异和（b）杂种优势和上位性效应的大小；第二，评估基于 RFLP 的遗传距离度量在预测单交杂种杂种优势和表现中的有用性。在每个双列中，从 15 个杂交的 5 个世代（亲本、F1；F2 和回交）在爱荷华州的 4 个环境中评估了籽粒产量和产量构成。通过普通双列分析和 Eberhart-Gardner 模型从世代均值估计遗传效应。与旧系相比，新系的自交世代产量显著增加，但杂种优势估计值较小。在大多数情况下，两组系的产量和产量构成的加性 x 加性上位性效应估计值均为正。对自交系的 RFLP 分析包括两种限制酶和 82 个基因组 DNA 克隆，分布在玉米基因组上。81 个克隆与至少一种酶显示出多态性。在每个集合中，每个 RFLP 基因座通常发现 3 种不同的 RFLP 变体。从 RFLP 数据估计自交系之间的遗传距离为 Rogers 距离（RD），RD 可分为每个双列内的一般（GRD）和特殊（SRD）Rogers 距离。旧系和新系的平均和范围的 RD 相似，表明分子水平的杂合度没有改变。GRD 解释了两组 RD 值之间 50%的变异。基于改良的 Rogers 距离的聚类分析揭示了系之间的关联，这些关联通常与已知的系谱和先前的研究一致。RD 和 SRD 与 f1 表现、特殊配合力和产量及产量构成的杂种优势的相关性通常为正，但太小而没有预测价值。与以前的研究一致，我们的结果表明，RFLP 可用于研究玉米自交系之间的关系，但它们对预测无关系之间单交杂种的杂种优势表现的用途有限。
