Tuber induction and initiation during production and early field growth of transplants from in vitro-derived potato plants

In transplants from in vitro-derived plantlets from very early potato (Solanum tuberosum) cultivars, a lower degree of tuber induction at the time of field planting is thought to increase tuber production. Leaf-bud cuttings were used to assess the progress to tuber induction in in vitro-derived potato plantlets during the transplant production phase and after subsequent transplanting into the field. Induction and initiation of tubers on the same plants were assessed to study the effects of the duration of transplant production and conditions during transplant production for cv. Gloria (very early) and cv. Bintje (mid-early). In vitro-produced plantlets were not induced by the time of planting but rapidly progressed to the induced state thereafter. The progress in induction with time and the change in percentage of plants showing tubers fitted typical sigmoid curves. Plantlets achieved 50% induction ca 15 days after planting into in vivo conditions, and 50% tuber initiation usually occurred 10 days later. Shorter transplant production periods reduced the degree of induction of the transplants at field planting. Transplant production for more than 2 weeks was required to allow conditions during that period to affect induction or initiation. Long-term non-inducing conditions delayed the progress to tuber induction in cv. Gloria and delayed tuber initiation in both cultivars. Cv. Gloria showed no faster progress to induction than cv. Bintje but initiated tubers earlier. The results suggest that the relation between progress to induction and tuber initiation is cultivar dependent and that leaf-bud cuttings can be used successfully in very young in vitro-derived plants for assessing the progress to tuber induction.