Diploperennial teosinte-maize hybrids: expression of pollen grain size and pollen fertility traits

--V. R. Corcuera, M. B. Aulicino and J. L. Magoja

As part of our investigations on diploperennial teosinte-maize hybrids, two pollen grain traits were evaluated in teosinte, maize (Ever Green), and F1 and F2 progenies derived from them. Pollen grain size was evaluated for the main diameter and expressed in microns (µ). Pollen grain fertility was measured considering all those grains completely stained with an I-IK solution and expressed in percent. The results obtained are given in Table 1.

As can be seen, diploperennial teosinte has smaller pollen grains than maize, and the F1 and F2 mean values are intermediate. The F1 mean does not differ from the mid-parent, but the F2 mean is higher, probably because we couldn't dispose of a greater sample of this segregating population.

Compared with data obtained when pollen grain size was studied in hybrids between perennial teosinte (Z. perennis) (see MNL 58:118) and maize, it can be noted a similar way of inheritance, where genes with additive effect prevail. In both cases, the F2 progeny mean is approximately similar to the mid-parent one. All the opposite, and as a direct consequence that perennial teosinte-maize hybrids are triploid (two doses of teosinte and one of maize) and that pollen grain size is controlled by the maternal genotype, this trait when studied in those hybrids showed that the F1 mean was very close to perennial teosinte.

As the difference in size between maize and the perennial teosintes is relatively important, and considering that the trait is quantitatively inherited, possibly this one could be used to detect wild germplasm introgression in the cultivated species (maize).

Contrary to what some authors have pointed out, the fertility of diploperennial teosinte-maize hybrids is not too high, unless for this particular case (see Table 1). Diploperennial teosinte "per se" hasn't got high pollen grain fertility, by which it can be considered that the F1 and F2 fertility cannot be explained only on the basis of normal phenomena in interspecific hybrids, as the smaller fertility of the wild parent must be considered too. In this particular case, no one of the parents has a fertility value near 100% and the values of the hybrid progenies are a little smaller than the mid-parent ones. In spite of this fact, and especially in the F2, as was expected, one can detect a wide variation of fertility values, from relatively low up to near 100% among individuals. An adequate selection of the most fertile individuals will consequently let us be successful in maize breeding programs using these wild genetic resources.

Table 1.  Pollen traits in diploperennial teosinte (Zd), Ever green maize (Eg), and its F1 and F2 progenies.

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