Pathogen Identification And Fungicides Screening Of Curcuma Phaeocaulis Leaf Blight

Curcuma phaeocaulis Valeton is a perennial herbaceous plant of the Zingiberaceae Curcuma,which has a very high medicinal value in traditional Chinese medicinal material In the last few years,its demand has increased year by year in the market,and many places have began to develop artificial planting.However,as the planting area continues to expand and various diseases show an increasing trend year by year,which seriously affects the yield and quality.In the early stage of the disease,a nearly round lesion appeared at the tip or edge of the leaf,which was faded green and pale yellow.As the further enlargement of the disease spot,the surface color of the disease spot gradually deepened.The center of the lesion is brown and its outer edge was light yellow.This disease shows a meteor-like shape and spreads to the whole leaf in the later stage.The outer edge to the inner edge of the lesion darkens in turn from dark yellow to light brown to dark brown.In 2017,a new disease was discovered in the C.phaeocaulis planting base in Nanxiong District,Guangxi Zhuang Autonomous Region.The pathogen,mainly occurs in the upper and middle leaves of the plant.It usually starts from the top and edge of the leaves.The leaves appeared chlorotic light yellow spots in the early stage of disease.With the further development of the disease,the leaves gradually turned serious.The center of the disease spot color is brown and the outer edge is yellow.This disease shows a meteor-like shape,which spreads to the whole leaf in the later stage.From the outer edge to the inner edge of the lesion,it gradually deepened from dark yellow to light brown,then deepened to dark brown.In severe cases,the whole plant dies.According to the symptoms,the disease is named C.phaeocaulis leaf blight.At present,there are few studies on the disease,and scientific and reasonable countermeasures are lacking when the disease appears in the field.Therefore,in order to clarify the pathogen of the disease and biological characteristics of the pathogen,my research carried out the identification of the pathogen,biological characteristics of the pathogen and fungicides screening,to grasp the occurrence of the disease,effective prevention and control measures,and provide theoretical basis for the C.phaeocaulis planting industry.The results are as follows:1.Pathogen identification.Three strains（CP1,CP2 and CP3）were isolated with typical symptoms leaves.All strains were identified as the pathogen causing C.phaeocaulis leaf blight based on Koch‘s postulates.The CP1 strain with the fastest disease and strongest pathogenicity was selected as the representative strain for follow-up experiments.Firstly,according to CP1 strain,the colony size,characteristics,conidia,attachment filaments,acervulus and other characteristics of the strains identified on PDA medium are described.Secondly,a phylogenetic tree was constructed by combining the ITS,TUB and TEF gene sequences of the pathogenic genomic DNA.Finally,the CP1 strain was identified as an approximate species of Neopetalotiopsis asiatica,with a support rate of 100%.2.Biological characteristics.The results showed that CP1 strain can grow at temperatures ranging from 5 to 35℃.CP1 strain grows suitable temperature is 20～25℃and 25℃is the best growth temperature.The spores can be produced in the temperature range of 10～35℃,and 25℃is best temperature for spores production.CP1 strain has a strong ability to adapt to light,and can grow under five different light conditions.Among them,18h light+6h darkness has a significant promotion effect on the growth of mycelia,and the maximum spore production is under 24h light conditions.The optimum p H for growth of conidia is between 5.0～5.5.The lethal temperature of the pathogenic mycelia is 55℃,10 min.CP1 strain was selected to use Biolog phenotypic analysis technique to determine the utilization about 190 kinds of carbon sources,95 nitrogen source,59phosphorus sources and 35 sulfur sources.The results showed that the utilization rates of the CP1strain for carbon source,nitrogen source,phosphorus source and sulfur source were 52.63%、33.68%、18.64%and 37.14%respectively;Among 94 substances in different biosynthetic pathways,only2’-deoxyadenosine can promote the growth of pathogens,and the rest can not be effectively used;Under different ion concentrations,4%sodium lactate,5.5%Na Cl,and 3%potassium chloride can be metabolized by pathogens,but increasing the concentration causes the osmotic pressure to increase,and the growth of pathogens is inhibited.3.Toxicity fungicides.All 12 fungicides tested had certain virulence to the growth of mycelia,with the EC₅₀ ranging from 0.0786 to 13.4117μg/m L.Among them,97.3%carbendazim technical material（TC）and 96%prochloraz-manganese chloride complex technical material（TC）had strong antibacterial ability.The EC₅₀ values were 0.0786μg/m L and 0.1189μg/m L.In the virulence test,97%azoxystrobin technical material（TC）and 96%prochloraz-manganese chloride complex technical material（TC）have a strong inhibitory effect on the germination of conidia,and the EC₅₀ values were0.0277μg/m L and 0.0448μg/mL.