Meiotic studies in native races from northwestern Argentina
--C. A. Naranjo, A M. Chiavarino (1) and L. Poggio (1)
(1) Also affiliated with Depto. Cs. Biologicas, FCEN, UBA

Several previous studies presented cytogenetical evidence that maize and related species with 2n=20 chromosomes have an amphiploid origin, and five was postulated as the basic number of the genus Zea (Molina and Naranjo, 1987; Naranjo et al., 1990, 1991; Poggio et al., 1990). The principal evidences are: 1) Secondary association of bivalents at meiosis and a maximum of five groups of two bivalents each was frequent at diplotene-diakinesis; 2) formation of two spindles with five bivalents each at metaphase-anaphase I.

In maize most of the studies were done on several lines and improved populations cultivated in the "Instituto Fitotécnico de Santa Catalina (IFSC)". We have just begun cytological studies in six native races from northwestern Argentina. All six races showed the presence of two groups of five bivalents at diplotene-metaphase I in most of the studied cells (Fig. 1B, C, D). On the other hand, secondary association of bivalents, with a maximum of five groups of two bivalents each was frequent at diakinesis-metaphase I (Fig. 1A). These observations indicate that these phenomena are general and not restricted only to commercial lines and intraspecific hybrids of maize. In these races there is a variable frequency of B-chromosomes (see Chiavarino et al., this volume). The presence of B-chromosomes does not alter the disposition of the two groups of five bivalents each since the extra chromosome joins one of the two groups or, in a few cases, rests outside of the metaphase plate. In some cases a very slight asynchrony in the meiotic behavior between both groups of five bivalents each was detected. This asynchrony, which is very strong in alloplasmic lines of Zea (Poggio et al., 1992) supports the hypothesis that the groups of five bivalents each belong to different genomes (Poggio et al., unpubl.).

Figure 1. A-B: "Altiplano" race. A: Metaphase I, secondary association; B: Diplotene, two groups of 5II each. C: "Negro" race, diakinesis, two groups of 5II each. D: "Amarillo de ocho" race, metaphase I, two groups of 5II each. The bar=10µm.

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