Screening Plus Training: A Strategy to Counter Germplasm Degeneration in Cultivated Kelp ( Saccharina japonica )

ABSTRACT Based on the introduced founder sporophytes, a set of S. japonica varieties and a few hybrid kelp have been bred and intensively cultivated in China. The cultivation of S. japonica has been running up against the impasse of germplasm degeneration characterized by low growth performance, degrading disease resistance, and weak stress tolerance among others. Diverse causes, mainly the deprivation of competition and stress experience among gametophytes, eggs, sperms, and young sporophytes and the absence of stress memory, may underline such degeneration. The causes also include the intermixture, narrow genetic background, deficiencies of elite alleles, favorite haplotypes and best genomic phases, high propagation and mutation rates, and various reproduction strategies. Paving the ways out of such impasse of kelp (refers exclusively to S. japonica in this review) cultivation industry will be highly appreciated. The possible causes of kelp germplasm degeneration were summarized, and the seeable, feasible, and applicable ways out were proposed in this review. Besides introducing new genetic variations during genetic improvement and breeding elite varieties, the agronomic performance of available kelp varieties can be maintained through the intensive selection of parental sporophytes with desirable measurable traits from the cultivating population for seedling raising. Their performance can also be improved by priming the parental gametophytes of hybrid kelp and young sporophyte seedlings of both normal varieties and hybrid kelp with the stresses ever met or might bump into during cultivation. Such a strategy may also be applicable for many other aquacultured species.