抄録
During the study of the somatic chromosomes, it was noted that two good table varieties, viz., Safet-velchi and Met-halal were having the chromosome number 2n=22 and thus were sterile diploids. The cytological studies of these varieties are presented.
There were as many as 6 types of chromosomes in Safet-velchi and 5 types in Met-balai. Karyotypic formulae for these varieties were E4I1K6L4M2N5 and E4K6L4M2N6, respectively. Karyotypic variation and doubling of chromosomes in the somatic cells were also observed in Safet-velchi.
During diakinesis, besides bivalents, univalents in varying numbers were noted. A maximum of one trivalent in Safet-velchi and two in Met-balai, per nucleus were found. Metaphase plates with typical bipolar spindles were rarely met with. The range of bivalent formation was between 6 and 7 out of the expected 11 bivalents. But the frequency of univalent formation was very high up to 56 percent with a range of 7 to 22 univalents per nucleus. Occassionally, PMCs containing a chromatid bridge and fragment at anaphase I was seen in both the varieties, indicating inversion and structural alteration of chromosomes. The chromosome movement during anaphase was irregular. In many cases, one of the divisions failed, with the result that the second division metaphase plates were rather rare. In cells where the second division took place, the chromosome distribution was highly irregular. Apart from this, lagging chromosomes formed micronuclei in the cytoplasm, leading to the formation of more than 4 microcytes. The pollen grains degenerated. The pollen was 95-98 percent sterile.
These observations lead to the inference that Safet-velchi and Met-balai are probably one and the same variety; the minor differences found between them are attributable to the changes brought about by change in the environmental conditions. It might also be probable that these two varieties might have evolved from the same parental types by hybrid origin. The few bivalents found during meiosis in these two varieties may be said to be due to non-homology of many of the chromosomes brought about by structural alterations or by interspecific crossing.
Isolation of these sterile diploids, induction of tetraploidy by colchicine technique and further crossing these with parthenocarpic diploids, have been suggested to be good method for the production of edible triploid bananas.
