Meiotic observations of diploid perennial teosinte

Meiotic divisions in the microsporocytes of five clones of diploid perennial teosinte were examined with standard acetocarmine squash technique. At pachytene stage, it was consistently observed that there were knobs and large chromomeres on eight of the 10 chromosome pairs. Most of these knobs and chromomeres were homozygous. The knob size varied from small to medium. The knobs on the short arms of chromosomes 1 and 2 and the long arms of chromosomes 2 and 3 were small. The knobs on the short arm of chromosome 3, and on the long arms of chromosomes 4, 6, 7, 8 and 9 were medium-sized. All of these knobs were terminal. Chromosomes 5 and 10 were knobless. Several times, the knob on the long arm of chromosome 9 was found heterozygous and synaptic beyond the knob region. However, when the chromosomes were studied with Giemsa staining procedure, the knobs appeared larger than they did with the above technique.

The characteristics of the gross morphology of the pachytene chromosomes of diploid perennial teosinte are similar to those of the tetraploid perennial teosinte reported by Longley (1937), Ibrahim (1960) and Ting (1964), except for knob number and size. In addition, we have successfully crossed five different varieties of maize with this diploid perennial teosinte. All of them resulted in fertile F1 hybrids. In view of these, it seems reasonable to conclude that diploid and tetraploid perennial teosinte should be in one species instead of two separate species as proposed by Iltis et al. (Amer. J. Bot. 67:994-1004).

At diakinesis, among a total of 322 cells examined from 5 clones, it was found that 276 (85.7%) of them had 10 regular bivalents with both closed-ring and open-ring shaped configurations. Nine bivalents and two univalents were found in 41 (12.7%), eight bivalents and four univalents in 4 (1.7%), and seven bivalents and six univalents in 1 (0.3%). At anaphase I, only 61.3 percent of a total of 476 cells had normal 10 to 10 distributions of chromosomes. The other 39 percent showed irregularities in chromosome behavior:
 
Chromosome Behavior Frequency % of Total
Normal (no B or L) 292 61.3
1 B 9 1.8
1 L 7 1.4
2 L 48 10.0
4 L 120 25.2

These irregularities ranged from one bridge without fragment (B) to one or four laggards (L). This meiotic instability is probably caused by the long time accumulation of mutations due to vegetative propagation.

Y. C. Ting, M. K. Gu and Margaret Yu


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