Cytogenetic studies on interspecific hybrids between Zea diploperennis and Zea perennis

A hybrid between Zea diploperennis Iltis, Doebley and Guzman (2n = 20) and Zea perennis Reeves and Mangelsdorf (2n = 40) has been obtained. It has 2n = 30 chromosome number, with the exception of one plant whose chromosome number is 2n = 40.

The meiotic configuration most frequently observed at metaphase I in Zea perennis has been 5IV + 10II; in Zea diploperennis, 10II; and in the hybrid with 2n = 30, 5III + 5II + 5I. If the phenomenon of autosyndesis is discarded it can be assumed that all the chromosomes of Zea diploperennis pair totally or partially with the chromosomes of Zea perennis, leaving 5 chromosomes of Zea perennis without pairing. The average of chiasmata was 17.25 and at pachynema some translocations and inversions were observed. The fertility of the pollen varied from 37 to 83%, obtaining only 2% of viable seed.

The hybrid with 2n = 40 probably could have originated from an unreduced gamete of Zea diploperennis (female progenitor). The meiotic configurations most frequently found were 5IV + I0II; 4IV + 12II; 3IV + 14II; 6IV + 8II. Very few monovalents and trivalents were observed. The bivalents and tetravalents were open-ring. At pachynema the chromosomes paired totally or partially. The average of chiasmata was 26. The fertility of the pollen was 58.4%, obtaining 80% viable seed.

If it is considered that the chromosomes of Zea diploperennis and Zea perennis in the hybrid (2n = 30) are paired with the configuration 5III + 5II + 5I, it would be expected that the resulting configuration in the hybrid (2n = 40) would be 5IV + 5III + 5I. In spite of that assumption and as there have been very few monovalents and trivalents observed, it is supposed that some of these alternatives would take place:

It is difficult to individualize the chromosomes of Zea diploperennis (unreduced gamete) to Zea perennis ones in chromosome pairing. However, it is important to take into account that because the hybrid has 40 chromosomes, a chromosome balance would take place, obtaining regular meiotic divisions and 80% viable seed. In opposition to that already described, in the hybrid between the aforementioned species (2n = 30), the contrary took place; therefore the fertility was 2%.

Figure 1.

Maria del Carmen Molina

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