A Cytogenetic Study of Triploids and Aneuploids in Job's Tears, <i>Coix lacryma-jobi</i> L

Abstract

In Job's tears (Coix lacryma-jobi L.) autotriploids (3n=30), hypo-triploids (3n=29) and hyper-triploids (3n=31) were produced by crossing diploids and colchicine induced autotetraploids. Trisomics (2n=21), double trisomics (2n=22) and multiple trisomics (2n=27) were obtained in the progenies of triploids. In none of the trisomics or double trisomics, the nucleolar chromosome was involved in trisomy. In each of the chromosome classes, meiotic behaviour, fertility and transmission of extra chromosomes to the progenies were studied. The average frequency of trivalents for a set of 3 chromosomes in triploids and aneuploids varied between 0.62 and 0.92, which is much higher compared to the average frequency of quadrivalents for a set of 4 chromosomes in the tetraploids (including hypo- and hyper-tetraploids) which varied between 0.49 and 0.58. These apparently indicate that the frequency of multivalents tends to decrease as the number of homologues of a chromosome in the complement increases. The average chiasma frequency per cell in triploid was significantly less than one-and-half times that in diploid. Although this depression in chiasmata in triploid is difficult to explain, some probable causes were mentioned. In general, aneuploids were lower in fertility compared to diploids, and both hypo- and hyper-triploids were less fertile than triploids. Transmission of extra chromosomes to the progenies occurred more frequently through the female gametes than male gametes.