Cytogenetic studies on Zea diploperennis

Zea diploperennis Iltis, Doebley and Guzman is a new species of the Maydeae tribe which has 2n = 20 chromosome number. The meiotic configuration shows either 10 bivalent chromosomes or 9 bivalent + 2 monovalent chromosomes. In addition there has been found a Zea diploperennis plant with 2n = 20 + 1 chromosomes. Apparently this extra chromosome is a B chromosome and according to Mangelsdorf (personal communication) it may be a plant of Zea diploperennis with introgression of Zea mays.

The length of the chromosomes (Fig. 1) in the state of intermediate pachynema is as follows:
Chromosome Relative lengths (µ) Ratio of arms (L/S)
1 107 1.07
2 107 1.11
3 101.3 1.27
4 95 1.62
5 87 - -
6 63.6 2.78
7 67.6 2.18
8 64.9 4
9 62.2 1.41
10 50.6 5.66
Extra (possible B) chromosome 15.4  

Zea diploperennis is characterized by very small terminal knobs in chromosomes 1, 2 and 6; medium size terminal knobs in chromosomes 5, 8 and 9, a very large one in both chromosome 4 and the extra chromosome or possible B chromosome. It does not have knobs in chromosomes 3, 7 and 10.

In 3% of the cells, the nucleolus is detached from its organizer either in advanced pachynema, diplonema and diakinesis. In that case the organizer begins to form one or more additional nucleoli. This phenomenon has been previously observed by the author in Zea perennis x Zea mays hybrids.

Figure 1.

Maria del Carmen Molina

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