Cryptic homoeologies in the hybrid Zea perennis x Z. mays ssp. mays (2n=30) revealed by treatment with dilute colchicine solution
--L. Poggio (1) and C. A. Naranjo
(1) Also affiliated with Depto. de Cs. Biológicas, FCEN (UBA).

Poggio et al. (Theor. Appl. Genet. 79:461-464, 1990) show the existence of cryptic homoeology in maize and Z. perennis (2n=40) using pre-zygotene colchicine (0.5 x 10-4M) pretreatment. Under this treatment maize forms 1 to 5 quadrivalents and Z. perennis increases the frequency of quadrivalents. These results support the amphiploid nature of maize proposed by Molina and Naranjo (Theor. Appl. Genet. 73:542, 1987) and suggest that the species have homoeologous genomes (Z. mays ssp. mays, AmAm BmBm; Z. perennis, ApApAp'Ap' Bp1Bp1Bp2Bp2) which fail to pair, probably due to the presence of Ph-like genes (Poggio et al., ibid.). In Z. perennis (2n=40, ApApAp'Ap' Bp1Bp1Bp2Bp2) the number of quadrivalents increased from 5 to 10, revealing some cryptic homologies within the Ap and particularly within Bp genomes. The absence of octovalents shows the lack of homology between them.

Naranjo et al. (MNL65:74-75, 1991; submitted) pretreated with colchicine several stems of Z. diploperennis (2n=20, AdAd BdBd) and found no quadrivalents. Therefore, no noticeable homologies between Ad and Bd genomes were detected. In the Z. diploperennis x Z. perennis F1 hybrids (2n=30, ApAp'Ad BdBp1Bp2; and 2n=40, ApAp'AdAd Ap1Ap2AdAd) the frequency of multivalents increased. In the 2n=30 hybrid the frequency of trivalents increased from 25% in the untreated material to 90% in the treated one. In the 2n=40 hybrid, the quadrivalent frequency increased from 46% to 70%. Hexavalents or octovalents were not observed in these hybrids. These results show greater homologies between Bp and Bd genomes than those detected in untreated materials.

To complete the analysis of genome relationships we have studied one artificial F1 hybrid Z. perennis x Z. mays ssp. mays: 2n=30 (ApAp'Am Bp1Bp2Bm). The results indicate that the frequency of six or more trivalents was increased from 25.6% in the untreated material to 90% in the treated material (over 154 cells studied). In addition, quadrivalent and hexavalent formation was observed in 43% of the cells. According to the homologies detected between Am and Bm genomes in treated maize material, the occurrence of IV and VI in this hybrid would be predicted.

The authors acknowledge Ing. E. A. Bernatené for the technical assistance in the treatment and handling of the plants. They also thank Dr. N. Jouve for the facilities offered at the Department of Cell Biology and Genetics of the Alcala de Henares University (Spain) where the slides and the cytological observations were performed. 

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