Kelp species such as Saccharina japonica and Undaria pinnatifida serve as critical global economic resources. However, global warming, marked by rising seawater temperatures, is severely impacting kelp cultivation. This reality has made the development of new, heat-resistant kelp cultivars with broader adaptability an urgent priority to mitigate climate-related threats. While triploid breeding is a common practice in terrestrial crops, it has rarely been applied to seaweeds.
To address this challenge, a research team led by Prof. SHAN Tifeng from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) has developed a new method for breeding triploid cultivars in kelp species.
The study was published in Journal of Phycology on Nov. 15.
Prior research efforts obtained diploid gametophytes from heterozygous sporophytes via apospory, but the sex of these gametophytes was variable and unpredictable. This inconsistency made it difficult to conduct precise crosses for the development of triploid lines. "This issue has become the primary technical bottleneck limiting triploid breeding in kelp," noted Prof. SHAN, the corresponding author of the study.
Building on doubled haploid (DH) population construction technology and using Undaria pinnatifida as the target species, the researchers proposed a new approach: generating homozygous diploid gametophytes by inducing apospory in DH sporophytes, then crossing these homozygous diploid gametophytes with haploid gametophytes to produce triploid sporophytes. This method effectively resolves the aforementioned technical bottleneck.
Specifically, the researchers first obtained DH sporophytes through the selfing of a monoicous gametophyte. They then derived single-sex (male) diploid gametophytes via apospory. These male diploid gametophytes were crossed with three female haploid gametophyte clonal lines, resulting in the successful development of three triploid hybrid lines.
Cultivation trials conducted at a seaweed farm revealed that, compared to conventional diploid cultivars, the triploid hybrids exhibited superior traits: a faster growth rate, longer blades, enhanced resistance to high temperatures and aging, and a notable sterility characteristic.
"The triploid breeding method established in this study may also be applicable to other kelp species, as they share a similar life cycle," Prof. SHAN added.
This study provides a practical polyploid breeding tool for kelp, helping develop hardier, more adaptable cultivars to support the stable development of the seaweed farming industry.
Triploid sporophytes of Undaria pinnatifida (a,b,c) and their sporophylls (e,f,g) and their diploid counterparts (d, h). (Image by IOCAS)
