The Effects Of Yellow Stunt And Root Rot Of Astragalus Adsurgens On Swainsonine Content In Plants And Evaluation On New Disease Resistant Germplasms

Standing milkvetch(Astragalus adsurgens)is a domestic forage plant of China.Yellow stunt and root rot of the plant is the most serious disease caused by Alternaria gansuense.Diseased plants may contain poisonous compound resulted from a feeding study with mice and diseased plants.However,this hypothesize until did not proved with more evidence,so we do not clear if livestock is safe when consume diseased plants.Additionally,it is urgent requirement for no resistant varieties to this disease since there is no available so far.The object of this thesis is to determine the toxicity of diseased plants,and to evaluate the resistant characteristics of selected germplasms of A.adsurgens.The main results are as follows:1.All the diseased plants(100%)and healthy plants(40%)collected from field contained KS gene for swainsonine synthesis,detected with a pair of specific primers designed according to the gene,but no in plants cultured in greenhouse.2.Swainsonine content in diseased plants is significantly higher than in healthy plants assayed with HPLC-MS,73.93 mg/kg and 15.11 mg/kg in plants collected in 2017,increased 3.89 times,and 89.11 mg/kg and 9.16 mg/kg in plants collected in 2018,increased 8.72 times.Swainsonine content in pure culture of Alternaria gansuense(561.61 mg/kg)is lower than endophyte of Oxytropis ochrocephala,Alternaria sect.undifium oxytropis(703.99 mg/kg).Swainsonine in O.ochrocephala plants with endophytic fungi(703.99mg/kg)were significantly higher than those without endophytic fungi(21.11mg/kg),in Sphaerophysa salsula plants was 51.53 mg/kg.Swainsonine in diseased plants is close to in the locoweed(O.ochrocephala)with endophyte.3.The infected seeds from inflorescence with brown base was 31.05%,while no seeds from inflorescence with white or green base were infected.Two healthy seed germplasms were collected in field from variety pengyang and Shaanxi yulin according to no symptoms of the disease and no color change on inflorescence base.Resistance test indicated the 2 germplasm were higher resistant to the disease than control varieties after inoculated with A.gansuense with the method of dipping conidial suspension of the pathogen for 14 wk.They can be used in further breeding.The incidence of germplasm 1,germplasm 2,and Neimengzaoshu,Liaoningfuxin were 15.20%,9.60%,23.20% and 20.80%,mortality were 8.80%,3.20%,11.20% and 8.80%,and the loss of dry weight per plant were 49.66%,30.60%,89.01% and 57.16%,respectively.