--M. B. Aulicino and J. L. Magoja
A maize inbred (OU) used as female parent was crossed by two of the wild taxa of the genus Zea: Balsas teosinte (Z. mays ssp. parviglumis var. parviglumis) and Guatemala teosinte (Z. luxurians). The parents and the F1 hybrids were cultivated during the growing season 87/88 as part of a complete randomized block design with three replicates.
The following traits were evaluated: (A) prolificity traits: (1) number of productive nodes per tiller (PN), (2) number of female spikes in the uppermost node (EUN), (3) number of female spikes per tiller (ET) and (4) number of female spikes per plant (EP); (B) plant traits: (5) number of tillers with female spikes (TE), (6) plant height (cm) (PH), (7) leaf width in the uppermost productive node (cm) (ULW), (8) leaf width in the 10th node (cm) (LLW), (9) leaf length in the uppermost productive node (cm) (ULL), (10) leaf length in the 10th node (cm) (LLL) (11) sheath length (cm) in the uppermost productive node (USL), (12) sheath length (cm) in the 10th node (LSL), (13) stalk diameter (cm) in the uppermost productive node (USD) and (14) stalk diameter (cm) in the 10th node (LSD).
The results obtained (see Table 1 and 2) show in the first place that the teosintes clearly distinguish themselves from the maize line for all the traits. The teosintes are much more prolific, with taller and thinner tillers than maize and also a greater number of them than in the cultivated species. In the second place our attention is called to the considerable (sometimes enormous) phenotypical variation that the teosintes show for most of the traits.
Bearing in mind that one of the parents of these hybrids is an inbred (OU), the great variation shown by the F1 can be attributed to the diversity of the resulting genotypes as a consequence of the heterogeneity expressed by the teosintes.
This fact has a great practical meaning, as we could verify through teosinte introgressed populations of maize, that the most primitive taxa constitute the most valuable genetic resources to be used in maize breeding.
When comparing the values obtained for the traits studied in the hybrid progeny with respect to those calculated for the mid-parent (see Tables 1 and 2), it can be deduced that for most of the traits the F1 plants are higher than the estimated mean values. This fact is reflected in the percents of heterosis shown in Table 3, in which it can be noted that in most of the cases heterotic expression exists especially when prolificity traits are considered, though not always significant.
As was previously pointed out in preliminary studies using another kind of interspecific hybrids of maize, prolificity traits exhibit the greater heterotic expression. From this fact it can be deduced that the OU-Guatemala teosinte hybrids are much more heterotic than the OU-Balsas. This is what we expected, considering that Guatemala teosinte is phylogenetically much farther away from maize than Balsas teosinte.
The results shown in this work arise from a project whose objective was hybridizing all the wild taxa of Zea by the same tester (maize). Unfortunately, it was difficult to cross the maize line (OU) with the perennial teosintes, and when it was crossed by Z. mays ssp. mexicana only a few seeds were obtained. This fact prevented us from doing a rigorous evaluation of the differential heterosis which could be generated in comparable crossings, as was planned.
While we have the results obtained from hybrids between maize and the perennial teosintes (Z. perennis and Z. diploperennis), the maizes used then were different, by which comparing the heterosis values estimated in those cases with the present ones would not be of great strength. Nevertheless, the experience we've accumulated through the last years lets us affirm that the heterosis degree expressed by teosinte-maize hybrids increases as the wild taxa used in the crossing phylogenetically separate more and more from the cultivated species.
The results we have obtained suggest that the hybrids using teosintes belonging to Section Zea are much less heterotic than those obtained when using the ones of Section Luxuriantes. Inside this last Section of the genus Zea, we have verified that Z. luxurians-maize hybrids are the less heterotic ones and that Z. perennis-maize hybrids are the most heterotic ones.
Table 1. Prolificity and plant traits in OU maize inbred, Balsas teosinte (Zmpp) and its hybrids.
Table 2. Prolificity and plant traits in OU maize inbred, Guatemala teosinte (Z1) and its hybrids (OUxZ1).
3. Heterosis for prolificity and plant traits.
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