Demand-Driven Technologies for Sustainable Maize ... - IITA

The larger GCA than SCA mean squares implies that, althoughnon-additive gene action, especially dominance, plays an important partin the inheritance of the traits evaluated in this study, additive geneaction is by far more important. However, estimates of additive effectswould be greatly infl uenced by the environmental conditions of theevaluation trials. Therefore, recurrent selection could be used to improvethe performance of the population developed from the lines while thelines per se or their derivatives could be used to develop Striga-resistantsingle-cross hybrids that would be released to farmers.In the present study, greater attention was focused on Striga hostdamage score and number of emerged Striga plants 10 weeks afterplanting because of the use of Z. diploperennis as the donor parentfor Striga resistance genes. The grain-yield performance of the lines inhybrid combinations was also considered to be important. Estimates ofthe GCA effect for each line, which is the average performance of theline in hybrid combination with other lines in the study, are presentedfor the three traits in Tables 5, 6 and 7. For Striga host damage scoreand number of emerged Striga plants at 10 weeks after planting,signifi cant negative GCA effect indicates tolerance/resistance while forgrain yield, signifi cant positive GCA value is desirable. Judging by thereaction of the lines to S. hermonthica as presented in Table 1, all theZd lines and TZL TC87 were expected to have negative GCA valuesfor Striga host damage score and number of emerged Striga plants,and positive values for grain yield. On the other hand, the standardinbreds would have positive values for the fi rst two traits and negativevalues for grain yield.Proportions of signifi cant positive and negative GCA values for thethree traits are summarized in Table 8 for the three groups of lines inthe study (that is, Zd lines, TZL TC87 and the standard inbreds) andin Table 9 for the individual lines. Of the 40 possible values for the Zdlines, 17 and 18 (42.5 and 45%) were negative for emerged Strigaplants and Striga host damage score. Corresponding values for TZLTC87 were 3 and 2 (37.5 and 25%) for the two traits. The two groupsof inbreds had few or no positive values for the two traits. On thecontrary, 53% of the values for the four standard inbreds were positivefor Striga host damage score and 12.5% for emerged Striga plants.For grain yield, 55 and 50% of the GCA values for Zd linesand TZL TC87 were positive (Table 8). The four standard inbredshad only 6.3% positive values compared with 50% negative values.These results indicated that, indeed, the Zd lines and TZL TC87 weretolerant/resistant to S. hermonthica while the standard inbreds weresusceptible.In this study as in previous ones (Efron 1993; Efron et al. 1989;Kim 1991; 1994; 1996; Kim et al. 1997; Kim and Adetimirin 1997),71