Biological Activity And Influence Factors Of Toxin Produced By Elsinoe Arachidis Casusing Peanut Scab

Peanut（Arachis hypogara）is a kind of important oil and industrial crop in China.Peant scab is a epidemic disease in peanut producing area which was caused by fungul Elsinoe arachidis Bitaucourt et Jenkins.The disease has caused losses of 10³0%in general and more than 50%in serious susceptible peanut cultivars in China.The disease has become one of the most serious diseases in peanut production,restricted the healthy and sustainable development of the industry.Many pathogenic factors are formed in the long-term interaction between host plants and pathogenic fungal,which is helpful to the infection of pathogens.The pathogenic factors include toxin,enzyme and biologically regulated substance.As a pathogenic factor,toxin plays a vital role in the occurrence and development of diseases and has become one of the hotspots in plant pathology research in recent years.Research of the disease focused mainly on disease investigation,etiology,and chemical control of the disease but no study about the production of toxin of fungul.This study systematically researched on the extraction pocess,biological activity and the influenced factors on production of toxin to provide theoretical basement for toxin investigation of peanut scab.1.Extraction process and biological activity of toxin of E.arachidisIn order to determine the extraction technology and activity analysis of the toxin produced by E.arachidis and what the toxin is,coloration reaction,UV spectrum,thin-layer chromatography of the toxin was investigated.The results showed that the color of the toxin produced by E.arachidis is orange red and it turned green when it dissolved in alkaline solution,then it recovered orange red when it dissolved acid solution.The maximum absorption peaks at 460,525 and 565 nm were observed.R_f values are 0.68,0.5,0.35,0.22and 0.08 in TLC.All of the results showed that the toxin produced by E.arachidis is elsinochrome（ESC）.The optimum extraction method is ultrasonic oscillation and the optimum solvent is acetone,fineness of hyphal is 60 meshes,ratio of liquor to material 100:1,temperature 60℃,time 60 min,power 100 w and 2 times.Toxin has strong cytotoxicity and pathogenicity and it caused necrotic lesion which was similar to the fungal.2.The physiological and biochemical activity of toxin in the pathogenicity processTo explore the mechanism of action of ESC in pathogenesis of peanut scab,in this paper,the activity of reactive oxygen species in the host and the degree of lipid peroxidation after inoculation were measured by measuring the activity of reactive oxygen species and the effect of toxin on the pathogenicity.The results showed that the content of reactive oxygen species in the host was significantly higher than that in the control group at 8 h.The activity of SOD,CAT and POD showed a peak values at 48 h and then decrease.At the same time,the MDA content increased at 72 h and electrolyte leakage.The degree of lipid peroxidation increased and cell died,finally.3.Environmental factors affecting the production of toxinThe results of the influence factors on toxin production showed that isolate LN-JH-C01was the largest amount of toxin production and isolate LN-SY-A01 was the minimum.The most suitable condition of test isolates was same.The optimum medium for toxin production of isolate LN-JH-C01 was PDA and the amount was 70.65 nmol/plug.Continuous light promoted the production of toxin while continuous darkness abolished the production of toxin.The favorable pH value was 4.The suitable temperation of toxin production were 25 and 28℃.The amount of toxin production at 15²5 d was the most.The optimum nitrogen and carbon sources of toxin production of isolate LN-JH-C01 were Ca（NO）₃ and mannitol,respectively.4.Toxin producing ability and pathogenicity of different E.arachidis isolates.Cultural characteristics,the ability of toxin production and pathogenicity of 63 isolates which came from Liaoning,Hebei,Fujian,Jiangsu,Shandong and Guangxi of China were studied.The reaults shows,the colonies of the tested isolates were varied,the color of the colony was red,green and gray,and the center of the colony was bulge or flattened.Some isolates had developed hypha.There were significance differences in the growth and they were divided into six groups by cluster analysis according to threshold values 0-5.The average colony diameters of all groups were 21.00±0.25 mm（27）,22.21±0.62 mm（4）,19.28±0.19 mm（10）,20.24±0.25 mm（18）,18.48±0.17 mm（3）and 23.15±0.02 mm（1）.The ability to produce toxin of each isolates also had significance difference and were divided into four groups.The average colony diameters of all groups were 15.06±10.16 nmol/plug（48）,53.10±4.00 nmol/plug（6）,213.12±21.95 nmol/plug（3）和116.05±23.66 nmol/plug.Among the representative isolates,isolate LN-XC-A05 had the highest pathogenicity and the disease index reached 46.7.The disease index of isolate LN-SY-A01 was the lowest and the pathogenicity was 10.The result of analysis of the correlation between the amount of toxin production and pathogenicity showed that they were significant correlation and the correlation coefficient was 0.904**.The pathogenicity of the isolates with strong toxicity was also high.The results showed that toxin is an important virulence factor of fungul.