Independent induction of calluses and nematophytes from exfronds and their potential application for kelp cultivation and germplasm conservation

The calluses and nematophytes were induced independently from the exfronds of kelp in this study. More frequent replacement of medium facilitated the differentiation of calluses from exfronds while less frequent replacement of medium promoted the differentiation of nematophytes. The inducibility of calluses and nematophytes was species-dependent. Callus induction was defined as “successful” only when the calluses can differentiate into sporophytes. Out of Saccharina latissima, S. sculpera, S. japonica Dongfang No. 6 and S. japonica DFKH, only the induction of S. latissima calluses met success. In contrast, the induction of nematophytes met success in all materials at a percentage of inducible exfronds varying between 9.8% (S. japonica Dongfang No. 6) and 89.9% (S. latissima). The overwhelming majority of the induced nematophytes of some species were long and slender and termed as male-dominant nematophyte while the overwhelming majority of the induced nematophytes of others were short and stocky and termed as female-dominant nematophyte. The seedlings raised by crossing the induced female-dominant nematophyte of S. japonica Dongfang No. 6 with its normal male gametophyte exhibited the improved growth vigor at harvest in comparison with the variety itself, indicating that the induced nematophytes are putative diploidy. The regeneration of sporophytes from induced calluses and the induction of fertile nematophytes provided a feasible means for kelp germplasm conservation, paved the way for exploring and utilizing the triploid growth vigor, and vigorously carried forward the findings of older generations of kelp biologists and breeders.