Cytogenetic analysis of the hybrids Zea mays ssp. mays x Z. mays ssp. parviglumis and Z. mays ssp. mays x Z. mays ssp. mexicana

--Mar�a del Carmen Molina, Lidia Poggio and Carlos A. Naranjo

The aim of this note is to present results that support our working hypothesis of a basic chromosome number x=5 in the genus Zea. This has been done on the basis of the meiotic behavior of species and artificial hybrids (Molina and Naranjo, TAG 73:542-550, 1987; Naranjo et al., 1990) and from the presence of multivalents in material treated with diluted concentrations of colchicine (Poggio et al., TAG 79:461-464, 1990; Naranjo et al., MNL 65:74-75, 1991). In the present work the meiotic behavior of the hybrids Zea mays ssp. mays x Z. mays ssp. parviglumis and Z. mays ssp. mays x Z. mays ssp. mexicana are discussed.

Plant materials: 1) Z. mays ssp. mays x Z. mays ssp. mexicana: Z. mays ssp. mays = the "c-tester inbred line" introduced by Horowitz from the United States. Z. mays ssp. mexicana = Nobogame race, Leg. CIMMYT. 2) Zea mays ssp. mays x Z. mays ssp. parviglumis: Z. mays ssp. mays = the "Colorado Klein" population selected at the Instituto Fitot�cnico de Santa Catalina". Z. mays ssp. parviglumis = (MO24), Leg. CIMMYT.

The hybrid Z. mays ssp. mays x Z. mays ssp. mexicana (2n=20) presented, in 81 cells analysed in diakinesis, 10 bivalents, showing a mean of closed bivalents of 9.35�0.13. Secondary association was observed and a maximum of two groups of five bivalents each at diakinesis-metaphase I were formed in 70% of the observed cells.

The hybrid Zea mays ssp. mays x Z. mays ssp. parviglumis (2n=20) presented 10ii in 98% of 271 analysed cells and the mean of closed bivalents was 7.00�2.07; the rest of the cells presented 9ii+2i. The pollen stainability was 99% and seed fertility 97%. Secondary association was observed and 46% of the studied cells presented two groups of five bivalents each.

The meiotic pairing of these two hybrids agree with the results obtained in other 2n=20 hybrids, suggesting that the subspecies have genomes homologous enough to produce normal pairing. Secondary association and the presence of two groups of five bivalents each was detected in all taxa with 2n=20. This was considered a relictual diploid condition being one of the evidences for the tetraploid origin of 2n=20 taxa (Naranjo et al., 1990).

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