中文摘要：

采用X射线作为诱变源,对龙须菜进行辐照诱变,验证了果孢子作为诱变材料相对于龙须菜藻尖的优越性,并确定了最佳诱变剂量-90Gy。约10-7-10-8个野生型龙须菜果孢子经过90Gy的X射线辐照,获得了约10-6-10-7株成活的龙须菜幼苗。将诱变存活幼苗平均分成2组,分别对其进行耐高温和低磷速生品系的筛选。经过幼苗期和成熟期的双重筛选,初步获得了1株耐高温突变株和3株低磷速生突变株。分别命名为WT-3和WLP-1、WLP-9、WLP-22。其中,WT-3为经历了41和35℃高温胁迫后仍存活并保持良好生长的藻株;WLP-1、WLP-9、WLP-22在10-（-2） mg/L的磷浓度水平下相对野生藻株具有显著的生长优势。本研究提供了一套可行有效的龙须菜诱变筛选技术,同时,筛选出的优良藻株为下一步遗传研究和生产应用提供了材料。

英文摘要：

Gracilariopsis lemaneiformis（Rhodophyte）is one of the most important economic macroalgae in China.Following Laminariaand porphyra,it has become the third largest cultivated seaweed in China and the cultivation scale is increasingly enlarging.However,the suitable temperature for growth of the wild population is 12-23℃.Although the thermo-tolerant cultivar 981 has been successfully cultivated in the south area,it＇s still unable to survive in summer.In addition,the phosphorus concentration is generally low in most mariculture area,sometimes even is bellow 0.01mg/L.The productivity and quality of Gp.lemaneiforsis is seriously influenced.In order to enlarge the cultivation area,to extend the cultivation period and to increase the productivity and quality,it is urgently needed to improve its heat tolerance,low-phosphorus tolerance and growth rate.Therefore,it is essential to conduct mutagenesis breeding and selection to obtain mutants with superior traits.In this paper,X-ray was used as the mutagen to conduct the mutagenesis of Gp.lemaneiformis.Carpospores were proved to be the better mutagenic material compared to stem-tips and the optimal irradiation dose was determined to be 90Gy（Gray,1Gy=1J/kg,is the absorption of one joule of energy,in the form of ionizing radiation,per kilogram of matter.）.Approximately 10-7-10-8 carpospores were mutated by X-ray irradiation out of which 10-6-10-7 seedlings survived and were divided into 2groups to be screened further under high temperature and low phosphorus stress,respectively.The thermo-tolerate screening method was set up in two phases.When carpospores developed into 2-3mm germlings（4weeks after mutagenesis）,they were subjected to heat shock at 41℃for 30 min in water bath.Following field cultivation and development of germlings into mature algae,they were exposed to heat shock of 35℃for 72 hin incubator.One mutant with heat tolerance was obtained,named WT-3,which survived after the two screening phases and displayed rapid growth.Low-phosphorus tolerant str