Effects of storage conditions on sprouting of microtubers of yam (Dioscorea cayenensis-D. rotundata complex).

The control of field tuber dormancy in the yam (Dioscorea cayenensis-D. rotundata complex) is poorly understood. Although studies have examined single environmental factors and chemical treatments that might prolong tuber dormancy and storage, only a few were focused on further tuber sprouting. The present study concerns microtubers obtained by in vitro culture. When microtubers were harvested (after 9 months of culture) and directly transferred on a new medium without hormones, the tubers rapidly sprouted in in vitro conditions. No dormancy was observed in this case. Harvested microtubers were also stored dry in jars in sterile conditions during 2 to 18 weeks before in vitro sprouting. In this case, microtubers stored during 18 weeks sprouted more rapidly than those stored 8 weeks. A constant "dormancy-like period" (storage duration+sprouting delay) was observed, between 20 and 28 weeks respectively for the more rapid and the slower microtubers. The size of the tubers used for the storage had great influence on further sprouting. The larger they were, the better they sprouted. Light during storage had no effect on the sprouting delay while a temperature of 25 degrees C permit a quicker sprouting than 18 degrees C. The medium used to obtain microtubers could also have an effect on sprouting rate. Ex vitro sprouting was not a problem. There was a delay in sprouting in contrast to in vitro conditions but the rate of 100% was kept. This fact is very important for an agronomical application of this technique to the production of "seeds" directly usable in the field or after culture in the greenhouse.