Cytoplasmic effect on chromosome pairing in maize-teosinte hybrids
--M. S. Ramesha and J. K. S. Sachan

Observations on chiasma frequency and chromosome configurations of the maize-teosinte hybrids involving Zea diploperennis, Z. luxurians, Z. mays ssp. parviglumis and some primitive and advanced races of maize, under different cytoplasmic backgrounds, were made to assess the degree of cytoplasmic divergence and nucleo-cytoplasmic interactions on chromosome pairing.

All the maize-Z. diploperennis hybrids showed highly significant reciprocal effects. There was a great reduction in chiasma frequency along with a significant increase in the frequency of rod bivalents and univalents. However, the frequency of ring bivalents reduced significantly in the cytoplasmic background of Z. diplo-perennis. Besides this, there was also an increase in the frequency of cells with chromosomal abnormalities. Maize-Z. luxurians hybrids showed reciprocal effects as reflected by reduction in chiasma frequency and increase in the frequency of univalents, however, their magnitude was relatively low. Maize-Z. mays ssp. parviglumis hybrids did not show any reciprocal effects.

The results indicated that the cytoplasmic divergence between maize and Z. diploperennis was maximum, followed by Z. luxurians and Z. mays ssp. parviglumis. The probable factors responsible for cytoplasmic effects could be the time imbalance in the condensation of the maternal and paternal chromosomes of a pair, maybe as a result of some nucleotypic changes brought about by primitive and divergent cytoplasm of teosinte. Further studies on the precise mechanisms of such changes could be helpful in resolving the mystery of origin and evolution of both maize and teosinte. 

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