Possibility of earlyseason culture of water yam (Dioscorea alata L.) in Yaku island

Early-season culture of water yam was required in Yaku Island, because of the long growing period, the concentrating work at the harvesting time, the lack of storehouse and so on. Thus we tried to search the early-maturing strains and use a plant growth regulator that promote the tuber enlargement. Then we found out the extremely early maturing strains introduced from high altitude area in the Kingdom of Nepal. On the other hand, foliar applications of gibberellins promoted the tuber enlargement. These results suggest the possibility of early season culture of water yam. Further research would be required to use the new strains and the plant growth regulator

Distinction of mixed yam strains (Dioscorea alata L.) cultivated in Yaku Island

This study clarified we could effectively distinguish mixed water yam strains by observing the differences of morphology of the leaves and tubers in Yaku Island. However, there are considerable variations in morphology, so we may be able to more confidently distinguish strains by also employing the electrophoresis method using acetone powder

Induction of sprouting in dormant yam (Dioscorea spp.) tubers with inhibitors of gibberellins

A reliable means to induce sprouting in dormant seed tubers of yams (Dioscorea species) is required to enhance flexibility in planting date and rate of propagation of the crop. Experiments were conducted to assess the potential of two gibberellin inhibitors, Uniconazole-P and Prohexadione-calcium, to induce sprouting in tubers from three varieties of D. rotundata and four of D. alata.Uniconazole-P and Prohexadione-calcium shortened the period of dormancy in tubers of some varieties. In others, they either had no effect or extended dormancy. The varietal responses were also influenced by whether the tubers were treated at harvest (before shoot senescence) or four weeks after harvest by which time shoots had senesced fully. Tubers stored in darkness at a constant temperature of 30◦ C sprouted earlier but lost weight faster than did those stored under natural daylight and ambient temperature. The apparent slow action of Uniconazole-P and Prohexadione-calcium, and their variable effectiveness in relation to variety, would limit their usefulness in seed or breeding programmes, or in determining treatment timing and the best storage environment for the tubers after treatment

Relationship between dormancy and its release and external factors in tubers of water yam (Dioscorea alata L.)

To analyze the mechanism of dormancy in tubers of water yam (Dioscorea alata L.), we studied the relationship between external factors and dormancy and its release in tubers. Several strains of water yam that have been introduced into Japan from Southeast Asia and Oceania were grown in Kagoshima, Japan. Dormancy period ranging from 2 to 4 months in length (from harvest to sprouting), has been observed in 48 strains that were tested at 25 ℃. It was found that the duration of the dormancy period differed among the strains. The moisture content of the tubers decreased with storage time. Although the mean of the ratio of decreasing fresh weight found in 48 strains that were stored for 90 days was 20.5%, each strain differed in the tuber moisture content after the 90-day storage period. However, comparison of the group of strains with long dormancy with the group of strains with short dormancy showed that the ratio of decreasing fresh weight of the tubers did not differ between two groups. Thus the ratio did not appear to be related to the dormancy of water yam tubers. The duration of the dormancy period of 4 early maturing, 37 medium maturing, and 7 late maturing strains was determined and found to be 65, 66, and 61 days, respectively

Influence of exogenous gibberellins inhibitors on tuber sprouting in yam

To induce sprouting two gibberellin inhibitors, uniconazole-P (UP) and prohexadione-calcium (PC), were applied to foliage of white Guinea yam (Dioscorea rotundata) and water yam (D. alata) 30 days before harvest or to tubers at harvest. The tuber sprouting period was shortened by about 35 days in D. alata TDa 95/00328 in response to UP and PC, and TDa 92-2 in response to PC, but not in others through foliage treatment. Sprouting of tubers was promoted in D. rotundata TDr 99-12 and D. alata TDa 99/00049 and TDa 291 when they were soaked in UP or PC, but the others had a limited response at harvest. Sprouting of TDa 99/00049 tubers started 70 days earlier and the periods of sprouting were 35 to 42 days shorter in response to the UP and PC. Foliar application was more effective in promoting tuber sprouting than tuber soaking at harvest in TDa 92-2 and TDr 93-31, and the reverse was true for TDr 99-12 and TDa 291. The responses of yam varieties to UP and PC seem to vary depending on the stage of dormancy in their tubers