Study Of The Economic Alga Undaria Pinnatifida: On Its Breeding And Cultivation Of Cultivar Related Issues

In the western Pacific,Undaria pinnatifida(Harv.)Suringar is extensively cultivated as an export-orientated edible sea vegetable in Liaoning Province,the prime seaweed farming ground for this species in China.The present study focuses on several crucial breeding and cultivation problems includingalgal pests,morphological and genetic analyses of the current major cultivars and transcriptome and metabolome profiling in different forms of sporohpyll.The results can help us improve the breeding technology and increase the efficiency of farming process.The thesis includes three parts as follows:1.In late October 2019,insect pests caused serious damage to seedlings of U.pinnatifida in this region.We performed field investigation excursions and analyzed pest samples through the sequencing of the mitochondrial COI gene.The results showed that explosive growth of Caprella danilevskii was the major cause.Caprella spp.are considered common biofouling organisms that usually inhabit the surface of maricultural algae and maricultural facilities,such as cultural rope and oyster nets.Steadily increased seawater temperature and the drifting brown alga Sargassum horneri biomass also played a role in the explosion of the pests.To the best of our knowledge,this is the first description of the morphological characteristics of different Caprella spp.collected in the same area in China.Caprella spp.are commonly found on the surface of cultured seaweed and marine aquaculture facilities,which has caused enormous losses to the Sargassum fusiforme farming industry in Fujian Province and Gracilaria lemaneaformis farming industry in Shandong Province in the past few years.We recommend the use of ammonium bicarbonate fertilizer for dispersing or killing Caprella species.Sequence analysis revealed that the COI gene fragments were 479 bp in length and showed an obvious AT-skewness.The transition/transversion bias(1.130)was much higher than the critical value(0.4),which could offer effective phylogenetic information.There was no insertion or deletion that occurred in each fragment.The average inter-species genetic distance was 0.231(0.210-0.279)and the average intra-species genetic distance was 0.014(0-0.030).The phylogenetic relationships among Caprella species were represented.The results proved that the cloned COI gene contains rich information on gene variations.This gene is conserved in intra-species and is different among species.It is a suitable DNA barcode for identifying species in the genus Caprella.2.Morphological and genetic analyses of the current major cultivars of U.pinnatifida at the principal farming region in North China.To clarify the agronomic characters and genetic differences of currently farmed U.pinnatifida,we investigated three major farmed cultivars in combination with other traditional ones focusing specially on sporophylls,one of the principal end products in a typical farm at Lvshun,Dalian city.Results showed that these cultivars differ in timing of maturation and are arranged to be harvested in sequence in the farm to diversify the periods of harvesting and processing.Sporophyll fresh weight and the stipe width are positively correlated with the growth of the plant.Ten neutral microsatellite markers were used to assess relationships among major farmed cultivars.Both genetic distance and Bayesian modelbased analyses showed that there was genetic differentiation among C1,C2,and other traditional cultivars.C3 showed the highest genetic variations in major farmed cultivars,with three private alleles and a mean expected heterozygosity of 0.817.In general,prominent genetic divergences were found among different cultivars confirming the effect of consecutive selection,while weak relationships were observed between sporophyll forms and genotypes.3.Transcriptomics and untargeted metabolomics profilings for carbon metabolism in different forms of sporophylls.The carbon meatabolism pathway in U.pinnatifida had been reconstructed including mannitol pathway,alginate patheway,threalose pathway and fucoidan pathway.Differentially expressed metabolites of monosaccharides were identified by LC-MS.The content of L-fucose was detected by high performance liquid chromatography with pre-column derivatization.MYB and b HLH are potential key transcription factors in the regulation of the carbon metabolism.The key genes were screened by WGCNA.GMD-3,PMM-1,and MC5E(-5,-31)may play key roles in the regulation of alginate pathway.ST-3 may play a key role in the regulation of fucoidan pathway in S-formed sporphylls.M1 Pase and M1PDH-1 are the key genes associated with mannitol pathway.The regulation mechanisms remain to be elucidated.TPS/TPP-2 and TPS/TPP-4 may play an essential role in trehalose pathway.