In 1980, a population of Zea mays "Colorado Klein" was successfully crossed with Zea diploperennis. Both species hybridize readily, and the F1 hybrid is not only fertile and vigorous but also preferably annual or biannual, except for 12% of the plants which are perennial. The cytological analysis of the hybrid indicated that the chromosomes of such species paired totally, while occasionally partial pairing and some deficiencies were observed.
In the counting of 121 cells in diakinesis, the meiotic configurations most frequently found were: 10II in 71.9% of the cells, 9II + 2I in 23.14%; 8II + 4I in 4.13% and 7II + 6I in 0.83%. The average of chiasmata was 15% per cell. At anaphase, 10 chromosomes migrated towards each pole, but occasionally 11 chromosomes to one pole and 9 of them to the other, and in rare cases, lagging chromosomes. The percentage of fertile pollen was 92%.
The size of the knobs exceeded considerably their parents, especially in the 4 chromosomes with terminal knobs provided by Zea diploperennis. In the hybrid, some of the chromosomes given by the parental species could be differentiated due to the position of knobs (subterminal in Zea mays and terminal in Zea diploperennis). However, it is not possible to determine the origin of the chromosomes without knobs.
It can be concluded that Zea mays markedly differs from Zea diploperennis in its morphology but not in its chromosome set, since their chromosomes pair totally, getting a fertile offspring. Thus, the chromosomes of such species are considered to be homologous or homeologous.
Teresa Pilar Rosales and Maria del Carmen Molina
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