Selection And Characteristic Analysis On New Strain Of Gracilaria Lemaneiformis

Gracilaria lemaneiformis is a kind of macro algae in the genus of Gracilaria. Under the artificial culturing conditions,Gracilaria lemaneiformis is widely used because of its high growth rate and good agar quality.Therefore it is treated as a useful species for cultivation and high-value industrialization.With the continuous development of cultivation,better heat-resistant capability,faster growth rate and higher content of agar of G.lemaneiformis are need to be approved in order to expand its cultivation area and time to improve the yield and quality to a higer level. Therefore,the basic research for genetic improvement of G.lemaneiformis has important theoretical and practical significance to develop new strains for higer values.In this study,the combined method using mutagenesis by N-methyl-N'-nitro-N-nitrosoguanidine and selection with hydroxyproline was firstly used in the breeding of G.lemaneiformis.Furthermore,we also discussed the effect of breeding method combing ⁶⁰Co-γrays and high temperature selection.Through the observation and selection of mutants,we hoped to develop new stains of G. lemaneiformis having better charaters and establish the suitable selecting methods for the heat-resisting strains,then provide experimental basis for selecting stress resistant strains of economic seaweed Gracilaria lemaneiformis.The results showed that:(1) In the test,tetrasporophyte of 981 Gracilaria lemaneiformis were uesed. They were mutated by N-methyl-N'-nitro-N-nitrosoguanidine(30mg/L,30min) and followed by selection with hydroxyproline(2mmol/L),and then selected undter high temperature(31℃).Then a new stain of Gracilaria lemaneiformis named 07-2 which had more branches,uniform color and rapidly growth was obtained from the original strain 981.But the method of combining ⁶⁰Co-γrays and high-temperature did not get goood restults(2) The selected new strain 07-2 has significant advantages in growth rate.The results showed that it grew faster,and could survive longer than 981 unter high temperature.Its diameter increased about 50%and branches added to36%.Also itsα-galactosidase activity related to agar formation was increased significantly comparing to strain 981.(3) The survival rate,growth capacity,membrane permeability and the activity of antioxidative system were suggested as the indicator of assessing the heat-resistant capability of Gracilaria lemaneiformis.The results showed that under high temperature strss,07-2 has relative less electrolyte leakage(IE) and malondiadehyde(MDA),higher praline accumulation and better activity of superoxide dismutase(SOD) and peroxides(POD)comparing to 981,which indicated that the stress-resistance of 07-2 is much better than 981.(4) Cultivation experiment in open sea in Shantou and Weihai seacoast area showed that the daily average growth rate of 07-2 was higher than 981.After 42d cultivation,the weight of 07-2 was increased 43%more than 981.The agar characteristics of these two strains were compared and it showed that the agar content and gel strength of 07-2 were better than 981,and the transparency of agar of 07-2 was also increased.All the results showd that 07-2 had faster growth rate and better agar quality compared to 981.