Studies on the Induced Polyploids of Horse Gram

1. Treating seeds with colchicine completely failed to induce tetraploidy in horse gram but several tetraploid plants resulted in all the apical bud treatments of young seedlings. Most of the affected plants were chimaeras, from the progenies of which pure tetraploids were obtained.

2. The tetraploid seeds germinate at about the same time as diploid ones but the germination percentage was reduced slightly in some varieties.

3. The tetraploids were slow growing in the early stages, but grew faster later, and together with prolonged growth period managed to equal or even surpass the diploids in height at the end. The number of branches was reduced in the tetraploids of all but one variety. The dry weight was more in the tetraploids at the end, but the differences were not significant. The mean basal diameter of the stem was increased due to the increase in size of the component cells and wider medullary cavity.

4. A significant increase in width and thickness of the leaf was observed in tetraploids; all the three layers—epidermis, palisade and spongy parenchyma contributed to the increase in thickness.

5. Flowering in the tetraploid was delayed, the delay being less in the late-flowering varieties. The flowering period was prolonged in all varieties by about 4–6 weeks. All the floral parts were intensified and the increase was more in width than in length. Pollen from tetraploids was highly variable, slightly larger, mostly with four germ pores and a large proportion stainable.

6. Fruit setting was fairly good compared to the autotetraploids in general, and in two varieties the number of pods per plant exceeded even those of the corresponding diploids. The pods were, however, smaller owing to the decrease in number of seeds per pod. Seeds of tetraploids were larger and the weight increased significantly. But the seed yield was reduced considerably.

7. In the tetraploids, about two-thirds of the chromosomes form quadrivalents, but subsequent meiotic irregularities are not very conspicuous.

8. Among the selfed progenies of tetraploids, a number of odd-looking plants could be detected, three of which were found to be aneuploids.