Inheritance of the resistance to tropical rust caused by Physopella zeae in maize

Four inbred lines of maize (Zea mays L.) were selected from a previous evaluation for resistance to tropical rust caused by Physopella zeae. Lines L426 and L82 were selected as resistant and the lines L47 and L37 as susceptible ones. Lines were crossed in a diallel scheme and six sets were obtained. Each set comprised the two parents (P 1 and P 2 ) and derived generations, F 1 , F 2 and backcrosses (B 1 and B 2 ) to both parents, and two hybrid checks, AG 951 (resistant) and P 3210 (susceptible). The experimental design was in randomized complete blocks, in a split-plot arrangement with three replications. The sets were allocated in the whole plots and generations within sets (including checks) in the subplots. The severity of the disease was evaluated by a discrete scale of I to 9, representing the percentage of the whole-infected area of the plant. Generation mean analysis indicated that additive effects are the most important and significant source of variation in contrasting crosses The dominance effects were less expressive and significant in only one instance in this study; they tended to he positive (dominance for susceptibility) in contrasting crosses. Deviations from the model were significant (P<0.05) in only one instance. General results lead to conclude that crosses between contrasting lines tend to be nearly intermediate between parents, but dominance deviation also may occur.