Study On Toxic Substance Of Astragalus Adsurgens Infected By Alternaria Gansuense

Standing milkvetch(Astragalus adsurgens)which has been widely planted in North China,is a very important legume forage and also used as sand fixation plant.Yellow stunt and root rot(YSRR)of standing milkvetch is a systematic fungal disease,and one of major factor of standing milkvetch pasture decline.The pathogen,Alternaria gansuense,is closed to locoweed endophyte Alternaria sect.Undifilum spp.(Embellisia spp.,Undifilum spp.)that produce poisonious swainsonine and caused livestock locoism.Livers of white mice fed with diseased milkvetch fodder were larger,and the content of glutamate-pyruvate transaminase in serum was increased,compared with white mice fed with healthy plants.However,what is the toxic substance was not determined yet.Therefore,the object of this study is to assay if swainsonine exist in diseased plants with healthy plants and diseased plants collected from 4 year old of the plant field by the method of.enzyme-linked immunosorbent assay(ELISA).Selenium content was assayed with the method of inductively coupled plasma-mass spectrometry(ICP-MS).Mineral elements was assayed with the method of atomic absorption spectrometry,AAS).The main results are as follows:1.Swainsonine was detected from both healthy plants and diseased plants cuased by A.gansuense.The content of swainsonine respectively was 22.13-27.91 mg/kg and 81.86-128 mg/kg,which increased by 193% in variety of Zhongsha No.1.and 329% in variety of Henan.Additionally,swainsonine was also detected from pure culture of the fungal pathogen at the level of 55.02 mg/kg.This is the first discovery that swainsonine has existed in healthy and diseased plants,and in pure culture of the pathogen.2.Selenium was detected from healthy plants and diseased plants,at the level of 0.192~0.367 mg/kg and 0.748~1.109 mg/kg.The content in diseased plants increased significantly(P<0.05).However,selenium content varied in different varieties.3.The content of Fe,Zn,Na and Mg in diseased plants lower than in healthy plants(P<0.05).The contents of Mn and Ca in disesed plants was not significant varied compared with healthy plants(P<0.05).4.The genome of the fungus was 73.62 Mb after whole sequenced,with 37.24% GC,and 7600 protein-coding genes.There were 170 genes associatedd with the biosynthesis pathway of swainsonine including the genes of enzymes of saccharopine dehydrogenase,saccharopine oxidase,pyrroline-5-carboxylate reductase and cytochrome P450.This study confirmed that the poisonous substance damaged white mice in the priovious study was swainsonine.The healthy plants of standing milkvetch contain swainsonine,while,once it infected by A.gansuense,the content of swainsonine increased.Therefore,it is should be careful to fed the diseased standing milkvetch to livestock.