不同供体及不同回交次数对玉米自交系R08的改良效应

以R08为轮回亲本，18个优良自交系为供体亲本，不同回交和自交次数，选育出遗传背景与R08相近、但相互之间又存在一定差异的BC₁F₃和BC₂F₂各18个R08改良系。通过抗病性鉴定、配合力及SSR分子标记分析，探讨不同供体及不同回交次数对R08的改良效果。结果表明，36个改良系中，29个抗或高抗大斑病，大部分改良系的多数产量性状一般配合力(GCA)与R08相比并无下降或有所提高；相同供体不同回交次数选系的比较显示，对大斑病抗性的改良，回交1次自交2次(BC₁F₃)优于回交2次自交1次(BC₂F₂)，且改良后代选系多数产量性状GCA大体相当；相同回交次数不同供体选系的比较表明，供体对回交后代的影响较大，供体不同回交后代选系大斑病抗性及多数产量性状GCA存在较大的差异；SSR分子标记研究结果在一定程度上揭示相同供体不同回交次数所创造的遗传变异无明显差异，相同回交次数不同供体选系在分子水平上存在较大差异；供体昌7-2和川321对改良R08的大斑病抗性和产量性状GCA作用较大，属优良供体亲本；w4-1和w10-1属回交改良优良选系。因此，利用回交法改良玉米自交系，在选准供体亲本的基础上，回交1次后，在自交过程中加强目标性状的鉴定选择及配合力测定，可提高回交改良的育种效率。

Effects Contributed by Different Donor Parents and Backcross Times on R08 Improvement

In this study, we used R08 as the recurrent parent and 18 excellent inbred lines as the donor parents to improve agronomic traits and resistance to maize northern leaf blight of R08. A total of 18 BC_1F_3 lines and 18 BC_2F_2 lines with diverse genetic background were obtained. The contributions from donor parents and backcross times were analyzed by investigating agronomic traits and resistance to northern blight and evaluating genetic variation with SSR markers. The results showed that 29 lines out of 36 BC-derived lines were resistant or highly resistant to northern leaf blight. The general combining ability (GCA) of major yield traits in most improved lines showed no decrease or a little increase compared with that of R08. The BC_1F_3 lines (backcross once and self-cross twice) presented better resistance to the disease than the BC_2F_2 lines (backcross twice and self-cross once) that were derived from the same donor parent. When comparing the improved lines with the same backcross times, donor background gave distinct effect on the backcross line, especially the resistance to northern leaf blight. The result of SSR markers analysis showed slight differences between the improved lines from the same donor parent and distinct variation among the improved lines with the same backcross times. Inbred lines Chang 7-2 and Chuan 321 acted as important parents in the resistance and yield trait improvements of R08. Therefore, they are regarded as excellent donor parents. As a result, w4-1 and w10-1, which were derived from Chang 7-2 and Chuan 321, respectively, are elite lines from the backcross with R08. In the backcross breeding of maize, the donor parent is suggested for consideration at priority, and backcrossing only once is acceptable on the basis of strict selection of target traits in combination with determination of GCA.