Generally, hybrids between maize and its nearest wild relatives are very heterotic. On the basis of our investigations on hybrids between maize and perennial teosinte (Zea perennis) (see MNL 56:104, 1982 and MNL 57:66, 1983) and between maize and diploperennial teosinte (Z. diploperennis) (see MNL 61:63 and 61:66, 1987) it is clearly evident that prolificity is the most heterotic trait.
Normally, maize is a non-prolific plant, which means that it is not capable of producing several ears per plant. On the other hand, the wild relatives of maize are prolific, in different intensity depending on the species considered. In spite of that, prolificity reaches its maximum expression in hybrids between maize and its wild relatives.
We have evaluated prolificity in progenies derived from crosses between diploperennial teosinte and maize, and their respective parents through 3 different traits (see Table 1): 1) Number of productive nodes per tiller (PN); 2) Number of ears in the uppermost node (EUN); 3) Number of ears per tiller (ET).
The results obtained for these kinds of hybrids are very similar to those previously found in perennial teosinte-maize hybrids (see MNL 57:66, 1983).
As can be easily seen in Table 2, these hybrids between diploperennial teosinte and maize generally not only exceed the mid-parent prolificity values, but the most prolific parent values too, in a highly significant way. In hybrids the prolificity frequency distribution is completely displaced to the right side, relative to their parental frequency distributions. The degree of heterosis expressed through these traits is really very high, especially when the number of ears per tiller (ET) is considered (see Table 3).
According to the results we have finally obtained, it can be stated that prolificity is transgressively inherited in a positive direction (heterosis). Unlike what happens in perennial teosinte-maize hybrids, in which the real prolificity probably can be disguised by sterility problems (lack of fecundation helps the development of a great number of ears), in this case diploperennial teosinte-maize hybrids are highly fertile and the prolificity they express cannot be attributed to sterility.
This particular means of inheritance for prolificity traits has a high practical value, since through the utilization of wild germplasm we could increase in a very significant form the prolificity degree in maize populations (see MNL 61:65 and 61:66, 1987). The results obtained also let us deduce that if the combination of maize germplasm with teosinte finally increases in a very significant way the prolificity degree, this trait in the different types of teosintes, depending on their expression level, perhaps can be taken as indicative of the introgression degree they assimilated from maize.
Table 1. Number of plants (N), means and ranges for proliflcity traits in diploperennial teosinte (Zd), Ever-green maize (Eg) and F1 and F2 populations.
Table 2. Differences between means for prolificity traits of diploperennial teosinte (Zd), Ever-green maize (Eg), F1 and F2 populations and mid-parent values (MP).
Table 3. Percent of heterosis for prolificity traits.
Victor R. Corcuera and Jorge L. Magoja
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