Extension of dormancy in tubers of tropical yams (Dioscorea spp.).

In addressing the seasonal availability of yams the key is to increase yam availability by extension of the length of dormancy of the tubers. Bulbils, tubers and tuber pieces were treated post-harvest with varying concentrations of growth regulators for varying lengths of time. Exogenously applied gibberellic acid markedly extended the dormancy of bulbils of D. alata but no effect on dormancy on bulbils of D. bulbifera. Application of CCC to bulbils of both species gave no dormancy response. Kinetin, IAA, ABA and ethrel had no effect on the time to onset of sprouting in tuber slices of D. alata. Treatments with GA3 and 2,4-D increased the time spent to shoot development in slices of D. alata tubers. GA3 extended the dormancy of D. alata and D. esculenta. Extensions were of the order of 100 to 200 percent respectively in mature tubers. Greater extension in dormancy was obtained with the more immature tubers. With tubers treated after maturity the extension obtained decreased with increasing time from maturity. GA3 also re-induced dormancy in sprouting tubers of D. alata and D. esculenta for a period of 9 and 8 weeks respectively. In pre-harvest treatments the dormancy of tubers and bulbils from all treatments except those from vines of D. esculenta cv. chinese yam treated with 2, 4-D and GA3 was unaffected by foliar treatment. Both 2, 4-D and GA3 delayed the onset of sprouting in tubers from treated vines and the effect increased concentration used. Germination of tubers from all treatments except Chinese Yam tubers treated with 2, 4-D were normal. The fact that GA3 resulted in the extension of dormancy of both tuber and bulbils of tropical Yams suggested that it is either directly or indirectly involved in the dormancy mechanism of tropical Dioscorea species. The paper concludes that GA3 offers a means of markedly extending Yam tuber availability.