Perennial teosinte-Gaspe hybrids: protoandrous vs. protogynous

The Maydeae species are dichogamous, the pollen and silks are not simultaneously produced. While maize is generally protoandrous (pollen is produced before the silks emerge), the wild relatives are protogynous (silks emerge before pollen production).

In maize-perennial teosinte (Zea perennis) hybrids, as well as between maize and diploperennial teosinte (Z. diploperennis), we have invariably observed that the F1 are protogynous plants. By this we have deduced that the teosinte character (protogyny) acts as dominant. Nevertheless, our attention has been attracted to the fact that in the F2 progeny of hybrids between perennial teosinte and Gaspe, the majority of the plants (80%) are protoandrous, and only 20% are protogynous.

The hybrids between perennial teosinte and Gaspe constitute a very particular case, in that Gaspe is a protogynous maize (silks appear three days before pollen production).

The character analysis protoandrous-protogynous was carried out on an F2 population derived from the cross between perennial teosinte and Gaspe. The F2 population, constituted by 567 plants, was cultivated during the 1982/1983 cycle. In each of the F2 plants, the evolutive cycle was measured in days to tassel (T), days to silking (S) and days to pollen (P).

The days to silking less the days to pollen gives a value in days: if they are of a positive sign they are protoandrous, if the sign is negative they are protogynous (see Figure 1 and Table 1). In the protoandrous plants, the pollen is produced at an average 16.7 days before the silks. In the protogynous plants, pollen is produced at an average of 12.9 days after the silks emerge. It can be deduced that the protoandrous and the protogynous plants produce the tassel at the same length of time (there are no significant differences) (see Table 2). Nevertheless, in the protoandrous plants the appearance of the silks takes place later than in the protogynous. Likewise, in the protoandrous plants the pollen is produced before that of the protogynous.

To classify plants in two qualitative categories, i.e., protoandrous vs. protogynous, constitutes a simplification of the observed character. As can be observed in Figure 1, the variation is great in protoandrous and in protogynous plants. It seems that protoandry as well as protogyny are two aspects of the same character: the maturity of sexes not being simultaneous constitutes a character which is probably controlled by numerous genes.

The most intriguing aspect of the character is the fact that in a cross between progenitors with protogyny, protoandrous appears as the dominant character. This could be attributed perhaps to the fact that the character results from a genetic interaction between different factors contributed by both species, and subject to a preferential selection in the progeny.

If the wild character (protogyny) results from a greater adaptive value, it should be naturally selected in the hybrid's progeny. We have not detected the association of the protoandrous-protogynous character to other morphological characters studied in the hybrids. Maize specific characters preferably do not associate with protoandrous, and on the other hand, teosinte specifics do not associate with protogynous.

Table 1.

Figure 1, Table 2.

Jorge Luis Magoja and Gabriela Pischedda

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