PRODUCTIVITY OF THREE MAIZE HYBRIDS UNDER DIFFERENT PROPORTIONS OF MALE STERILE AND FERTILE SEEDS

Seed production of maize hybrids requires the physical removal of the tassel on female plants in time and in an appropriate way, so as to obtain the planned crossings and thereby to attain quality and genetic identity in the corresponding hybrid (Espinosa et al., 2003; Beck and Torres, 2005). This process involves high costs because of the use of too much labor. The manual or mechanical removal of tassels is expensive, requiring from 24 to 50 wages per ha, depending on the uniformity of the female parent, presence of tillers and ease to remove the tassel (Jugenheimer, 1990; Tadeo et al., 2003; Martínez et al., 2005). As an alternative to this high investment, it could be possible to use some types and sources of gene/cytoplasmic male sterility in maize, since female parents could be used as male-sterile lines, whereupon the detasseling process is reduced, which can also facilitate this activity, allowing a lower price for the hybrid seed (Tadeo et al., 2003, 2010, 2013; Martínez et al., 2005). Male sterility in maize was no longer used during the decade of 1970, because of the susceptibility to leaf blight disease caused by the fungus Helminthosporium maydis race T, which caused an epiphyte largely distributed in the corn belt of the USA (Fleming et al., 1960; Partas, 1997; Stamp et al., 2000; Simmons et al., 2001). New sources of male sterility have been used again in various maize breeding programs of different seed companies, the most important of which usually obtain seeds with male sterile system (Liu et al., 2002; Weingartner et al., 2002; 2004). With the use of new sources of male sterility and with the purpose not to depend on only a single source of sterility, in order to avoid problems of T race, since 1992 the Facultad de Estudios Superiores Cuautitlán (FESCUNAM) in México has worked to incorporate the male sterility character into the basic inbred lines of the maize breeding program developed at UNAM (Tadeo et al., 2003, 2010). Maize inbred lines used to produce hybrids that are increased by using male sterility Puma 1 (8989kg·ha-1) had a statistically bigger yield than H-47 AE (8190kg·ha-1). The comparison of means (Tukey, 0.05) between the proportions of male sterile and fertile seed, considering the average of the three genotypes and the two planting dates, defined two groups of significance, where the two best yielding were those of 100% male sterile:0% fertile (9441kg·ha-1) and 80% male sterile:20% fertile (9390kg·ha-1) seed proportions. Since the version with only male sterile seed is not a practical feasible option, an appropriate choice is that of 80:20, which optimizes the production schema by needing less labor and requiring only a 20% fraction of fertile seed. The proportion of 100% fertile seed had the lowest yield (8116kg·ha-1) among all seed proportions tested. SUMMARY