| Asparagus officinalis L.known as the "King of Vegetables" is one of the top 10 most popular nutrition and health care vegetables because of unique texture and taste and high nutrition.Asparagus has many health functions due to various bioactive properties such as weight loss,anti-cancer effects,anti-aging effects and lowering of blood pressure,blood fat and blood sugar.However,the research on asparagus germplasm in our country is not systematic and therefore selection in hybrid parents is blind and the development of novel germplasm is hindered.Therefore,the aim of this work was to assess the genetic diversity of asparagus germplasm in order to elucidate the genetic background based on morphological traits and ISSR markers after collecting the germplasm resources of asparagus at home and abroad.Evaluation of agronomic characters by screening elite germplasm allows the selection of parents for hybrid breeding and the creation of new genotypes by polyploid induction and transgenic technology.The results provide additional data for genetic improvement and have great significance for development of new asparagus varieties with disease resistance and high yield.The main findings are as follows:1.The results showed that the first three principal components represented 19.87,15.38%,%and 11.92%of variance respectively.Diameter of main stem,number of secondary branches,diameter of primary branches,width of scale,length of spear scale,diameter of spear and fresh weight of spear are the main indicators of asparagus morphological differentiation and the focus of morphological traits selection on asparagus breeding.Based on the morphological cluster analysis,46 asparagus accessions were clustered into A and B groups at a Euclidean distance of 135.7,Cluster A has morphological characteristics as follow:higher plant height,high Plant height to first panicle branch,less secondary branches,thick main stem,long primary branches,more scales under the lowest panicle branch,more spear scales.Cluster B vice versa.2.The ISSR analysis system of asparagus was set up and optimized and used to study the genetic diversity of asparagus germplasm.Twenty-one ISSR primers produced 227 polymorphic bands across the 46 accessions.The percentage of polymorphic loci,h and I were 82.01%,0.243 and 0.377 respectively.A cluster analysis was performed based on genetic similarity coefficients(GSC)which ranged between 0.60 and 0.97 across the 46 accessions.The GSC result shows that abundant genetic diversity exists in the 46 accessions.There are 100 genotype pairs with potentially strong heterosis.Based on the ISSR cluster analysis,46 asparagus accessions were clustered into Pacific Challenger 2,A and B.Group A consisted of Purple passion,Pacific purple and Al which form a compact group and group B comprised Jingpurple NO.2,NJ1189,Pacific 2000 and B1.Within group A1 accessions cluster due to origin:Walker Seed,Limseed,New Zealand,Canada and Jiangxi.Whereas group B1 cluster in relation to geographic origin:Jiangxi,Shandong,Beijing,Netherlands,America and Italy.However,morphological genetic diversity of asparagus germplasm was not related to molecular genetic diversity.3.The contents of nitrogen,phosphorus,potassium,calcium and magnesium in asparagus showed significant differences in different plant organs and varieties.The nutrient quality was also significantly different and the degree of variation of each nutrient quality index was different for different asparagus germplasm.The greatest degree of variation is Se(47.62%),rutin(45.39%),soluble protein(37.79%),Fe(34.24%)and free amino acids(32.46).The results showed that the germplasm with the greatest overall quality were Pacific Purple,Backlim,JK106 and Gijnlim,New century and 82with highest Fe content,Jing purple asparagus NO.2 with highest Mn content,Pacific Endeavor with highest Cu content,TC with highest Zn content,Champion with highest Se content,Jing green asparagus NO.1 with highest Vc content.The genotypes with highest soluble sugar content were Backlim,and with highest soluble protein content Gijnlim,Genotypes with highest free amino acid content were JK104;and highest rutin content JK103.However,the nutritional quality of asparagus germplasm was not related to genetic diversity.4.Ten accessions with heat resistance and high yield were screening in the comparative experiment on the quality of asparagus germplasm for four years,these were:Jersey Supreme,Jersey giant asparagus,Grande,Atlas,97,NJ1123,UC157 and JK102.Regarding asparagus regeneration characteristics,plant growth rate is fastest in the second week after transplanting,while the stem thickening rate is the fastest in the first week after transplanting.The accessions with excellent regeneration characteristics are purple passion,Jersey Knight,Backlim,JingKang Hong,JK102,JK107 and pacific purple.The yield and regenerative characteristics of asparagus germplasm were not related to genetic diversity.5.The optimal colchicine induction system was 0.15%colchicine(containing 2%DMSO)for 16 h.The induction rate was up to 31%and 65 tetraploid plants were identified.The stomatal density of tetraploid plants of asparagus was about 1/2 that of diploid plants,while the chloroplast number of tetraploid plants was about 2 times higher than diploid plants,stomatal length and breadth was slightly larger than diploid plants,Chlorophyll A content was 2 times higher than diploid plants and Chlorophyll B and total chlorophyll were 2 times higher than diploid plants.The tetraploid plants grow better,are more vigorous,have deeper color and thicker leaves.6.The optimal genetic transformation system in asparagus was as follows:pre-culture for 2d,bacterial concentration OD600=0.6,infection time 10min,co-culture time 4d,AS concentration 200?mol/L.The transformation rates were up to 21%Ten transgenic asparagus seedlings carrying the Hevein-like gene were identified by PCR. |
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