Cytogenetic study of diploid and triploid F1 hybrids of Zea mays ssp. mays x Zea parviglumis
--Molina, M del C; García, MD

Diploid and triploid hybrids were obtained from crosses between diploid or tetraploid Z. mays ssp mays (2n=20 and 2n=40, respectively) and Z. parviglumis (2n = 20). The maize tetraploid lines used in these experiments were N103A and N107B, obtained from the Maize Genetics Cooperation Stock Centre. Z. parviglumis seeds were kindly supplied by Dr. Bird (CIMMYT, Mexico).

Diploid hybrid plants were fertile with a chromosome number of 2n = 20; their meiotic analysis is shown in Table 1. Chromosomes of both species were paired in 73.45 % of the cells in pachytene and a small reciprocal translocation was observed between 2 chromosomes of both species. 10% of the cells in anaphase showed chromatid bridges. The pollen fertility ranged from 80 to 94% and 80% of seeds were fertile.

Triploid hybrids were obtained by embryo rescue because of the endosperm failure, about 14 days after pollination. The meiotic configurations of triploid hybrids are shown in Table 2. Pollen fertility ranged between 46 and 86% and the seed set was very low.

The results from the cytogenetic studies of diploid and triploid F1 hybrids of Z. mays ssp. mays x Z. parviglumis suggest the following conclusions:

-Chromosomes of both species were paired in 73% of the diploid hybrid cells, which indicates that maize and Z. parviglumis chromosomes are homologous or homoeologous.
-The meiotic configuration 5I (Zp) + 5II (2 Zm) + 5III (2 Zm +1Zp) found in 30% of the triploid hybrid cells confirmed that 5 chromosomes of both species are homologous or highly homoeologous and the other 5 are partially homoeologous.

Table 1. Meiotic configurations of F1 diploid hybrids of Z. mays ssp. mays x Z. parviglumis.
 
No. of cells I II III IV %
130 10 73.45
26 8 1 14.69
16 2 9 9.04
2 2 7 1 2 1.13
2 4 8 1.13
1 1 6 1 1 0.56
T = 177

Table 2. Meiotic configurations of F1 triploid hybrids of Z. mays ssp. mays x Z. parviglumis.
 
No. of cells I II III %
38 5 5 5 31.66
26 6 6 4 21.66
20 7 7 3 16.66
15 8 8 2 12.50
10 4 4 6 8.33
5 9 9 1 4.16
2 10 10 1.66
2 8 5 4 1.66
1 2 2 8 0.83
1 7 10 1 0.83
T = 120

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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