Evidencias de un número básico X=5 en el género Zea y su importancia en estudios del origen del maíz.

C.A. NARANJO,M. C. MOLINA Y L. POGGIO

Anales de la Academia Nacional de Ciencias Exactas, Físicas y Naturales de Buenos Aires

ACADEMIA NACIONAL DE CIENCIAS EXACTAS FÍSICAS Y NATURALES

Lugar: Buenos Aires; Año: 1990 vol. 5 p. 43 - 53

0365-1185

The aim of this paper is to present results that support the working hypothesis of a basic chromosome number x = 5 in the genus Zea. These results has been obtained as a consequence of our analysis of meiotic configurations of Z. mays ssp. mays, Z. diplopcrennis, Z. perennis and in six Fl artificial interspecific hybrids. The following are the cytological evidences presented and discussed: 1. In the 2n = 30 hybrids the most frequent meiotic configuration was 5III +5II + 5I, and in Z. perennis and hybrids with 2n = 40 was 5IV + 10II. 2. In the 2n = 30 hybrids, there is a clear tendency of A, C and B genome separation through the respectively grouped trivalents, bivalents and univalents. 3. In all species and hybrids with 2n = 20, secondary association was observed, and a maximun of five groups of two bivalents each was frequent at diploleno-diakinesia. 4. In all taxa with 2n = 20 formation of two spindles with five bivalents each was detected in metaphase-anaphase I. This would be a relictual condition. 5. In Z. mays ssp. mays, colchicine (0.5 x 10-4M) was applied 36 hs prior to the onset of meiosis, during 12 hs. The control material formed bivalents only. In the treated material was observed the formation of 0-5 quadrivalents. Colchicine treatment probably disrupts a bivalent promoting mechanism, revealing cryptic genome homologies. In view of the posiblc tetraploid nature of maize and other 2n = 20 species, a reconsideration of the"amphiploid theory" on the origen of maize is proposed.