Developing temperate inbreds using tropical maize germplasm: rationale, results, conclusions
Developing temperate inbreds using tropical maize germplasm: rationale, results, conclusions
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作者：
M. Goodman
从1984年到1996年，美国玉米（Zea mays L.）杂交品种对外来种质的利用增加了近3倍，但1996年对热带外来种质的利用仍仅为0.3%。本文的重点是热带种质资源在恢复地区的集约利用，而不是更常用的回交或渐渗程序，将一小部分热带种质资源引入温带背景。更具体地说，除了作为抗病虫害的来源外，热带种质能否导致多基因性状（如产量）的改善？产量试验数据表明，至少有一些大部分热带或完全热带的自交系可以与国内材料杂交，生产出与商业杂交种竞争的顶级杂交种。类似地，一些GEM（玉米种质改良）f2s250%热带家庭的顶交产量至少与商业杂交种相当。与传统的穗对行自交相比，适应温度的热带自交系的发展通常需要较慢的纯合方法（STRINGFIELD, 1974）。在一个可变的外来源中进行早期选择对于发展部分外来自交系是没有必要的，在发育株系之间和株系内部的皮棉方差成分分布表明，如果只有一小部分外来变异是可取的，那么在变量f1中进行选择是有帮助的。
Use of exotic germplasm in U.S. maize (Zea mays L.) hybrids increased almost 3-fold from 1984 to 1996, but use of tropical exotic germplasm still reached only 0.3% in 1996. The focus of this paper is intensive use of tropical germplasm in recuperate areas, rather than the more commonly used backcross or introgression procedure that introduces small segments of tropical germplasm into a mostly temperate background. More specifically, can largely-tropical germplasm lead to improvement in polygenic traits such as yield, in addition to being a source of disease- and insect-resistance? Yield-trial data demonstrate that at least a few largely-tropical or completely-tropical inbreds can lie crossed with domestic materials to produce topcross hybrids that are competitive with commercial hybrids. Similarly, a few GEM (Germplasm Enhancement of Maize) F 2 S 2 , 50%-tropical families have topcross yields at least equivalent to those of commercial hybrids. Development of temperate-adapted, largely-tropical inbreds usually requires a slower approach to homozygosity (STRINGFIELD, 1974) than conventional ear-to-row selfing. Early selection within a variable exotic source is not necessary lor developing partly-exotic inbreds, lint variance component distributions among and within lines under development suggest that selection within the variable F 1 would be helpful if only a small portion of the exotic variation is desirable.