玉米抗丝黑穗病的基因效应

利用2个抗玉米丝黑穗病自交系（齐319和Mo17）与2个感病系（E28和黄早四），组配4个抗感杂交组合。2004年，对4个组合的亲本、F₁、F₂、BCR（F₁与抗病亲本回交1代）和BCS（F₁与感病亲本回交1代）6个世代群体分别在北京和黑龙江进行丝黑穗病的人工接种鉴定，采用世代平均值分析玉米抗丝黑穗病的遗传特点。研究表明，各杂交组合的抗病性均含有显著的加性效应，其中3个组合有显著的显性效应。不同杂交组合的抗病遗传模式表现不同，用感病亲本E28组配的2个组合（齐319×E28）和（Mo17×E28）的抗病性基本符合加性-显性遗传模型；而用另一个感病亲本黄早四组配的组合（齐319×黄早四）和（Mo17×黄早四）的抗病性存在明显的上位性效应。这说明玉米对丝黑穗病的抗性呈现较复杂的遗传模式。因此，在抗玉米丝黑穗病育种中既要重视对自交系抗病水平的鉴定，也要加强杂种F₁的合理组配及抗病性评估。

Gene Effects of Resistance to Head Smut in Maize

Head smut of maize is a kind of worldwide disease. Development of resistant varieties is an effective choice to control the disease, which depends on the knowledge of the resistance resources and genetic mechanism. In order to select and breed resistant varieties, some resistant resources of head smut have been selected. The resistance to head smut of maize is quantitative character controlled by numerous genes, and additive effect of resistant gene plays the leading role, while the dominant effect and the epitasis effect are much weaken. In this study, two resistant inbred lines (Qi 319 and Mo17) and two susceptible lines (Huangzao 4 and E28) were used to produce four cross populations. The parental lines, F₁, F₂, BCR (F₁ backcrossed to the resistant parents) and BCS (F₁ backcrossed to the susceptible parents) were evaluated by artificial inoculation in Beijing and Heilongjiang province in 2004. The randomized complete block design in the filed was used with 2 repetitions. The parental lines and F₁ were grown in 1-row lots, BCR and BCS backcross generations in 4-row pots, F₂ in 8-row plots, and the rows were 5 m long each and spaced 0.7 m apart with 17 holes per row and 2 seedlings per hole. In soft ripe stage, the total number of the seedlings and the number of the diseased seedlings and the diseased seedling rate of various generations by taking the plot as a unit was calculated. The gene effects of resistance to head smut in maize was evaluated through generation means for the four cross combinations. The additive-dominant genetic model used was Y=m+αa+βd; the additive-dominance-epistasis genetic model used was Y=m+αa+βd+α²aa+αβad+β²dd. The variances among means of generations in the four cross combinations were analyzed to find the models for a, d, aa, ad and dd gene effects using least squares regression analysis. Point estimated of m, a, d, aa, ad and dd were obtained by solving the system of equations. For the former model, the genetic effects were evaluated by the least squares regression analysis, and the latter that was analyzed by the same method, but the effects with no-significant should be omitted firstly, after that the χ² test was involved to judge the significance of the models. The results showed that the additive effects were significant in 4 cross combinations, and dominant effects were significant in 3 cross combinations. The inheritance of resistance in Qi 319×E28 and Mo17×E28 fitted additive-dominant model, whereas the inheritance of Qi 319×Huangzao4 and Mo17×Huangzaov4 was in accordance with additive-dominant-epistasis model. The results indicated that the mode of resistance to head smut varied under different genetic background of maize. Therefore, not only the level of resistance to head smut is important, but also that of parental combination and F₁ should be emphasized.