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.
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