Breeding And Application Of Hybrid Laminaria

Laminaria is a group of brown macroalgae living in cold seawater and distributing in northern seashore of Pacific and Atlantic naturally. China is the biggest country of Laminaria cultivation. The species cultivated in China on large scale is Laminaria japonica northward to Liaoning and Shandong and southward to Jiangsu,Zhejiang and Fujian.Genetic improvement played a crucial role in the development of Laminaria cultivation of China. Genetic improvement of Laminaria began in 1950s and more than 20 varieties have been bred and used. Their popularization promoted the development of Laminaria cultivation industry drastically. Because the restriction of traditional methods, the problems such as degeneration, heterozygosis and weak stress resistance have become severe and severe. Moreover, with rapid development of the relative industries depending on Laminaria, diverse varieties are appreciated. Laminaria varieties available currently can not satisfy the development of Laminaria depending industry. Fortunately, Laminaria hybrids can be cultivated directly, and the breeding of Laminaria hybrids is relatively fast. However, the selection of Laminaria hybrids is still labor intensive and fortune dependent.This thesis reported our results obtained in breeding and application of hybrid Laminaria. Dongfang No. 2 hybrid Laminaria was developed by interspecific hybridization of gametophyte clones. And Dongfang No. 3 hybrid Laminaria was bred through hybridization of gametophyte clones with a more than intraspecific but less than interspecific relationship. In addition, a method of predicting the heterosis of Laminaria hybrids with the genetic distance between their parental gametophyte clones was established and validated.The following are our major findings:A male gametophyte clone from L. longissima and a female one from L. japonica were hybridized with the filial generation, Dongfang No. 2 hybrid Laminaria, used directly in trial cultivation. This initiated the direct use of Laminaria heterosis in production. The agronomic traits of Dongfang No. 2 hybrid, the source sporophytes from which its parental gametophyte clones were isolated and two commercial varieties widely used currently were compared in Zhifu Bay. Dongfang No. 2 showed 56.5% heterozygous vigor (heterosis) in yield, increasing the yield by 40.8% and 76.3% over that of L. longissima and L. japonica, and by 35.4% and 52.2% over that of commercial Variety 1 and Variety 2. In combination with gametophyte clone based seedling raising method, Dongfang No. 2 was cultivated in large area at different places and in different years. On average, the yield of Dongfang No. 2 was significantly higher than those of two commercial varieties, boosting up the yield by 25.6% in average over that of commercial Variety 1 and by 61.9% over that of another. Dongfang No. 2 hybrid Laminaria is the first hybrid Laminaria which was used in large-scale cultivation in China. It has a robust holdfast and a wide, long and deep brown uniform blade with a very clear groove in blade. In addition, Dongfang No. 2 also holds heterosis in other traits including the tolerance to strong irradiance. The vegetative maturation date of Dongfang No. 2 is moderate. Dongfang No. 2 hybrid Laminaria adapts well to a wide range of culturing environments.Dongfang No. 3, a Laminaria hybrid, was bred by hybridizing a female gametophyte clone isolated from Line 7 of L. japonica with a male one isolated from Line LZZ developed through hybridizing female gametophyte clones of L. longissima and male gametophyte clones of L. japonica followed by continuous self-crossing and tolerances of strong irradiance and high seawater temperature targeted selection. The parental gametophyte clones of Dongfang No. 3 have a more than intraspecific but less than interspecific relationship. The dark brown hybrid has a wide, uniform, ripple-less and very tough blade and a very robust holdfast. A deep vertical groove, a half-round joint between stipe and blade and thick blade edges distinguished the hybrid from other varieties of L. japonica. The hybrid grows faster than other control varieties. It tolerates high irradiance and seawater temperature and resists the tissue rottenness of blade tip and edges. The hybrid matured later than the varieties of L. japonica widely used currently. As were observed in continuous three years in Chudao Bay, Dongfang No. 3 hybrid Laminaria increased the yield by 54.1% and 62.3% in average over that of Control I and Control II, respectively, and by 60.7% and 74.1% over that of Line LZZ and Line 7. Across 10 sites on the coast of north China and in different years, it boosted up the yield by 32.0% and 56.9% in average over that of Control I and II, respectively.Microsatellite DNA markers were used to determine the genetic distances between 27 parental gametophyte clones, which were then regressed to the heterosis (heterozygous vigor) of economic traits including blade length, blade width, mean blade thickness, mean blade fresh weight, mean blade dry weight and yield. Significant regression was established between the genetic distance (x) and the heterosis (y) of blade length ( y = 76. 31x?59.911,R2 =0.6498,P<0.0001), mean blade fresh weight ( y = 85. 016x?66.497,R2 =0.6603,P<0.0001), mean blade dry weight ( y = 90. 984x?70.625,R2 =0.6423,P<0.0001) and yield ( y = 90. 984x? 70 .625,R 2 = 0.6423,P<0.0001). Based on the regression equations established and the complementary hypothesis of non-quantitative characteristics such as stress resistance, a few combinations were predicted to perform high yield and stress tolerance. Such prediction was proved to be true in the trait evaluation of these hybrids conducted subsequently. Our findings have indicated that the method is effective for predicting the heterosis of yield and yield related traits. The method will facilitate the selection of elite Laminaria hybrids by avoiding the time-consuming and labor-intensive field trait evaluation of a large number of hybridization combinations.