Identification Of The Pathogen Causing Walnut Twig Blight And Fungicide Screening For Its Efficient Control

Walnut twig blight is a serious disease cause walnut branch decayed and dead due to pathogen invasion and other media propagation germs.In recent years,because of the accumulation of bacteria source,extensive cultivation management,pest control technology is not in place,and other reasons,walnut twig blight has become the main disease in the walnut planting area in Guangyuan County,Sichuan province,which seriously threatens the production of walnut and brings serious economic loss to the fruit growers,and has become a major restriction factor for the production of local walnut.The depth and breadth of the relevant research is insufficient.To carrying out a thorough study of the diease,a total of 30 infested branch samples at different developing stages were randomly collected.Pathogen isolation and purification were conducted from walnut twigs tissue by normal tissue isolation method.To fulfill Koch’s postulates,pathogenicity test was done with isolates.In addition,the pathogen was identified based on morphological characteristics and molecular biotechnology,and biological characteristics were determined using colony growth methods.On this basis,the single agent of 15 kinds of common fungicides and the toxicity and disease prevention of pathogens were determined.The main findings are as follows:1.The result of identification of pathogens isolated from walnut twigs tissueThe pathogenicity test showed the pathogens of walnut twig blight were mainly caused by Phompsis capsici.Its GenBank sequence login number is KY345415.This was the first case of walnut twig blight caused by Phompsis capsici and the first report on the study thereon.Pathogenic bacteria can produce two species of spore,among A-Type（α）spore,colorless single spore,not separated,oval to elliptic,two distinct oil balls,5.6–9.2×1.0–2.2μm.B-Type（β）spore,colorless single spore,not separated,curved line,one end often hook-like,no oil balls,21.6–30.4×0.2–0.4μm.2.Study on the biological characteristics of pathogen of walnut twigs tissuePDA medium was the most appropriate for mycelium growth and spore production.The mycelium could effectively utilize a variety of carbon and nitrogen sources.Among the 9 carbon and nitrogen sources tested,the appropriate carbon sources were sucrose and fructose and the optimum nitrogen sources were molybdenum acid and phenylalanine.The best mycelium growth were obtained at 25°C.The pH requirement is not strict,in pH 5.0–12.0 range the mycelium can grow.The optimum pH was obtained at 7.0.The mycelium grew fastest under dark conditions.Phompsis capsici bear spores for longer time,in the PDA medium under dark conditions to cultivate more prone to produce spores.The lethal temperature of pathogen bacteria was 55°C,10 min.3.Sieving of fungicides in laboratory of control walnut twig blightThe results showed that 15 kinds of fungicides showed certain inhibitory effects on the mycelium growth of the pathogen in the range of test concentration.The inhibition effect of different medicament on mycelium of pathogens is different.The toxicity of25%azoxystrobin was the highest,its EC₅₀0 value was 0.1569.43%tebuconazole,0.3%tetramycin,33.5%axine copier,40%prochloraz,1%shenqinmycin,75%imazalil sulfate had a significant inhibitory effect on mycelium growth,and the EC₅₀0 values were 1.0884ug/mL、3.2906 ug/mL、4.2452 ug/mL、4.3799 ug/mL、4.4015 ug/mL、8.9220 ug/mL.4.Outdoor pot experimentThe pot experiment shows that 25%azoxystrobin（500-fold dilution）was the best to prevent diseased twigs and blight ones,with the control efficacy of 86.81%7 days after three times of the spay.0.3%tetramycin（500-fold dilution）take second place,with the control efficacy of 85.68%,but not significantly compared with 25%azoxystrobin.40%prochloraz had the worst effect with the control efficacy of 45.32%.The results showed that 25%azoxystrobin is efficient chemical control of diseased twigs and blight of walnut.0.3%tetramycin can be used as alternative medicine.