| As the primary sources of the commercially valuable hydrocolloid carrageenan, Eucheuma and Kappaphycus are important algae resource in South China Sea. K. alvarezii about 5 kilograms have been introduced to China by Institute of Oceanology, CAS since 1980s. The single strain of K. alvarezii has been propagated vegetatively for many years and no true advances have taken place in commercial eucheumatoid farming for decades. Vegetative propagation of these species is easily done by breaking off and planting individual large pieces of the thalli. However, this labour-intensive method brings a decrease in adaptability to environmental factors, particularly when cultivated plants originate from a single mother plant. Additionally the scale of eucheumatoid farm is small and the disease(ice-ice, epiphyte filamentous algae, Siganus argenteus) relating to Eucheuma and Kappaphycus is serious in China. Therefore, it is necessary to enrich the cultivated strains, breed fine strain and study mechanisms and control methods for disease. The external forms photosynthetic pigments, characters of epidermal cellsgrowth carrageenan content viscosity and gel strength in 12 strains of tropical eucheumatoid species, which including 11 strains of Kappaphycus numbered as 1, 2, 3, 4, 6, 7, 8, 9, 10, 11 and 1 strain of Eucheuma introduced from Indonesia numbered as 5 as well as 1 strain of Kappaphycus introduced from Philippines numbered as 12, were surveyed. Different strains express a great diversity on external forms and characters of epidermal cells. Among all the experimental strains, tetraspores are found mainly on the old branches of strain 3, 5, 6 11 and 12. Among all of the strains density of tetraspores in strain12 was the highest reached to 5.5 every microsopic field under 40×magnification. PE and PBP are significantly lower in the strains, which are greenish, than the strains which are reddish. Chl a/APC, Chl a/PBP and Chl a/PE are significantly higher in the strains, which are greenish, than the strains which are reddish. All strains grow fast during January and December and slow during April. Strain 3 and 5 showed higher resistance to high temperature(3带) and Strain 5 showed higher resistance to low temperature(15-18 ). The highest carrageenan content were detected in stain 4 (25.64%) and lowest in strain 7 (16.94%). The highest gel viscosity were detected in strain 3(2893 mPaS) and lowest in strain 5(47 mPaS). The highest gel strength was detected in strain 5 and lowest in strain 7(1030 g/cm2).The brown K. alvarezii, which could produce more tetraspors, was chosen to study the formation, releasing and germination of tetraspors together with the morphogenesis of gametophyte. The results showed the brown Kappaphycus alvarezii original gained from Phillippine are tetrasporophyte and the tetraspores were mainly formed and released in summer. Both tetraspore germination and embryogenesis could be induced artificially in the laboratory, and great variation of embryos in color from brown red, yellow-green, olivine green to olivine-brown cytochimera were observed. Rhizoids were formed and then disappeared during the embryogenesis period. The germination rate of tetraspores was about 87.1±7.2% and the mean specific growth rate of embryos was about 6.3±1.1% day-1. After 160 days indoor's cultivation, the germinated tetraspores developed to young gametophytes, which in turn cultured on the soften raft in the sea. The average specific growth rate measured was over 10% day-1 in the first month culture and the highest specific growth rate for young gametophytes was over 21.2% day-1. However, the specific growth rate gradually reduced accompanied with the frond increase in size in the following culture. Number of gametophytes with different morphology, density of branches and growth rate were obtained after 4 monthes open-sea culture. The vitality and resistance to ice-ice disease in some strains of the new gametophytes improved significantly comparing to their parent plants.Ice-ice burst and caused large scale of death on eucheumatoid species in China during the 2008. Based on the experimental data of recent years we investigated the environmental reason for disease. In addition we made one paleogenetic experiment to verify the conclusion. All the results display that, low salinity of seawater, which is induced by excessive rainfall, is the reason for the large scale of disease and death during the 2008. Followed the ice-ice disease, a large-scale death of K. alvarezii was caused by epiphytic filamentous algae (EFA) in China since March 2009. The dominant epiphyte on K. alvarezii was detected to be Neosiphonia savatieri. An effective chemical method to eliminate N. savatieri in K. alvarezii farming by using glyphosate was found. Further, effects of the EFA on the photosynthetic activity of K. alvarezii and effects of glyphosate on K. alvarezii and N. savatieri were studied by using continuously chlorophyll a (Chl a) fluorescence technique. The results revealed that the infection of N. savatieri damaged oxygen-evolving complex (OEC), reduced the number of active reaction centers and plastoquinone (PQ) pool and so on in K. alvarezi, which inhibited photosynthetic electron transport and decreased photochemistry efficiency. No distinct change was detected in K. alvarezi when the glyphosate treatment concentration did not exceed 4g/l and duration did not exceed 5min. The inhibitory mechanism of glyphosate in N. savatieri can be listed as a decrease in the density of reaction centers per exited cross section (RC/CSm) and plastoquinone (PQ) pool in photochemical reaction. Moreover, 2 strains showed higher adversity resistance than other strains during the outbreak period of disease. Strain 5 showed higher resistance to low salinity EFA and ice-ice disease and strain 3 showed higher resistance to herbivore (Siganus argenteus). |
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