The Study On Reproduction And Cultivation Problems Releated To Variety Breeding Of The Economic Seaweed Saccharina Japonica

Saccharina japonica is one of the most important economic seaweeds in China and of great significance for farming industry.Study on crucial reproduction and cultivation problems which are involved in variety breeding of S.japonica such as sorus formation,seedling production,ability of haptera attachment and the handling of the harmful seaweed—Sargassum horneri can help us improve the breeding technology and increase the efficiency of farming process.The thesis includes four parts as follows:1)Study on sorus formation of the hybrid cultivar B013 during the large scale production of seedling period.In order to understand the relationship between the timing of crossing of the parental gametophytes and sporogenesis of their sporophyte offspring in cultivar B013,we crossed the parental gametophytes for four times in May,June,July and August in 2014 respectively and performed open-sea cultivation at Lvshun,Dalian in surface water until September of 2015.Results showed that 100% of the May group and 80% of the June group formed 6-cm wide and 50-cm long sori in the apical one-third zone of the blade for the first time in the mid of January.No sorus formed in August group until September.These results suggest that there are no clear co-relations between timing of fertilization and sporogenesis in the cultivar B013.Prolonging growth period is useless to induce timely sorus formation in B013.2)Study on the optimization of the nutrient addation during the “summer-sporeling” production.In this case study,the entire process of a commercial hatchery manipulation in 2015's production season at Lvshun,Dalian,northern China is presented,including pre-treatment of parental plants,control of spore release,control and adjustment of solar irradiance and temperature at different developmental stages of the plants as well as the nutrient supply regime over the entire course.These results suggest that emerged sporophytes on the string requires more P during the entire process and constant supply of sufficient nutrients day and night.According to the data and process in this report,we make an optimization of the “summer-sporeling” which proved useful for husbandry of seedlings.3)Study on the overhigh problem of detachment of the adult sporophytes.To elucidate the reason,hapteras of the individually farmed plants from different cultivars were checked on longline in the production season of 2016-2017.In the mean times,culture experiments were carried out in indoor flow-through tanks so as to make us understand how haptera of this species develops on substrate.It is recommended that proper plant density on rope and timely adjustment according to water transparency be implemented in farming practice.But for the long run,cultivar improvement is the essential issue that should be focused.4)Study on origin of the drifting harmful algae— Sargassum horneri on the kelp culture system.In this study,16 populations including 3 benthic ones and 13 drifting ones were collected from The Yellow Sea and East China Sea.They were investigated using SSR(Microsatellite or Simple Sequence Repeat)markers.Cluster analysis showed that in general the drifting populations from the same year rather than from the similar location were clustered together.The existence of marked admixture in six populations also implies that the same drifting population could be of different origins.These results provide evidence suggesting that the drifting populations along the nearshore waters of China,in particular the populations occurring in different years,were originated from multiple sources.