Study On The Branch Blight In Caragana Arborescens (Amm.) Lam.

Caragana arborescens(Amm.)Lam.branch blight is a disease found firstly on the branches of C.arborescens in Harbin,Heilongjiang province.We need to investigate the occurrence and progress of this disease,identify pathogen,and develop corresponding preventive measures.The pathogen was identified through isolation,inoculation and re-isolation by Koch’s postulates.The species of the pathogen were identified based on morphological and molecular characteristics.Subsequently,we studied the biological characteristics of the C.arborescens branch blight pathogenic and determine its optimal growth conditions;Inoculated the pathogen spores the pathogen Spores to the host plants and determined the effects of the pathogen on the main defense enzyme activity of plant tissues.The endophytic mycoflora of the branches of the 1-5 years old C.arbrescens were analyzed.Base on this Conclusion,four strains of bacteria were selected for the tablet confrontation experiment,and the optimal biocontrol bacteria were selected.Eight kinds of common low-toxic bactericides were used to determine the mycelial growth and spore germination inhibition effects and calculate the EC50.Below are the main research findings:1.Isolation and identification of pathogen of C.arborescens branch blight:The strain S1 was isolated using a single spore separation and tissue separation method,and we suspect it is the pathogenic strain.In the laboratory,three methods were used to inoculate the 3-5 years old healthily-growing hydroponics branches,including no injury,scratch and burnt inoculation.After 30 days,the burn inoculation showed typical symptoms,while the scratch and no injury inoculation were unsuccessful.So this disease is a kind of weak parasitic disease.We selected the burn inoculation to conduct field inoculation experiments and found that the incidence of field vaccination was short and the incidence rate was as high as 83.3%.After further research on morphologic properties and rDNA-ITS sequences,the pathogen was identified as(Stromatonectria caraganae(Hohn.)Jaklitsch&Voglmayr.).On the branches of the C.arborescens,we only found the anamorph of S.caraganae,which is a new record in China.2.Through the biological characteristics experiment,we found the optimum growthtemperature of the pathogen S.caraganae is 25℃,and the S.caraganae has a strong adaptability for pH,the hyphae grow fastest at pH 5.3 then the other pH.We also found that the S.caraganae grow best on the medium which use the lactosee as carbon source,while it grow fastest on the medium which use the peptone as nitrogenous source.Spore germination requires more nutrition,And in nutrient solution with PD,the germination rate of the S.caraganae is highest,Followed by bark drizzle,respectively reached 69.5%and 50.7%.In PD nutrient solution,The spore of S.caraganae can germinate at the range of 15 to 35℃,and at22℃ the germination rate of the spore is highest,it can be 64%,while as the temperature increased the germination rate was decline.The spore of S.caraganae also has a strong adaptability for pH,at pH 4.9 the germination rate of the spore is highest,it can be 70%.3.Field inoculation of healthy branches of C.arborescens by burn inoculation method.Samples of tree branches collected every 3 days.Determination of SOD,POD and CAT in cortex of treated and control groups using the corresponding kit.The contents of three defense enzymes in the cortex of each treatment group increased first and then decreased.On the 12th to 15th day after inoculation,the symptoms appeared obvious.At this point,the three enzymes have the highest activity.The enzyme activity of the control group peaked on the 9th day.Significance test by SPSS software.The results showed that the levels of defense enzyme in the treatment group and the control group at the peak reached significant levels.It shows that the three kinds of defense activity changes are caused by the invasion of pathogenic bacteria.Studies on C.arborescens branch blight’s antagonistic pathogens.The selected 4 kinds of biocontrol strains have a good inhibitory effect on the growth of pathogenic mycelium.Trichoderma strains T5M-2 is Trzichoderma harzianum.It has the best inhibitory effect,they sppress pathogens by growth rate,covering the pathogen to stop the growth.4.Based on the research of the community of C.arbrescens endophytic in 1-5 years old shoots,we concluded that the folicolous fungal species is rich,a total of 21 species of fungi was isolated.Among them,the number of Deuteromycotina species is the largest 18 species belong to Deuteromycotina.2 species belong to Ascomycetes and 1 species of Zygomycetes.The dominant species is Phorma and Chaetomium.The separation rate of them were 13.1%and 12.6%.There was no significant difference in the number of endophytic fungi of different age-grade shoots,but the composition and frequency of separation were quite different.Branches of different ages have its own endemic fungi.The number of endophytic fungi in the bark is higher than that in the xylem.5、The experimental results of 8 kinds of low-toxic fungicides were used to investigate the indoor antibacterial experiment of the C.arborescens branch blight.The best three fungicides for inhibition of spore germination are FrostUrea Manganese Zinc,zineb and Carbendazim.The diameter of the inhibition zone reached 44.8 mm,40.8 mm and 30.3 mm when diluted 100 times respectively.The best three fungicides inhibitory effect on mycelium growth are Carbendazim,Thiophanate-Methy and.Triadimefon.Their EC50 were 0.19 mg/L,0.77 mg/L and 8.90 mg/L.Carbendazim had better inhibition on pathogen spore germination and mycelium growth.It can be used as the best medicament for controlling C.arborescens branch blight.