Identification,Biological Characteristics And Laboratory Fungicides Screening Of Pitaya Two Kinds Of Pathogens

This thesis focuses on the recent pitaya diseases,study of filed investigation,filed symptoms description,pathogen isolation and purification,pathogenicity test,observation and photography of pathogen morphological characteristics,molecular biological identific-ation,biological characteristics,and laboratory screening of fungicides.In order to provide theoretical basis for the effective control of pitaya diseases.The main contents and conclus-ions of the paper are as follows:Field investigation of pitaya cultivation was conducted in Hainan,Guangdong,Guang xi and Guizhou province.The Pitaya region have a large area of canker and Fusicoccum sp.stem spot disease,the incidence rate was as high as 99%?100%.The pathogen of pitaya canker maindamaged stems and fruits.At the early stage of the disease,the disease stems and fruits appeared slightly concave,round and white faded green,a severe lesion occurred.Then lesion extended slightly protruding red to purple red,round or oval spots and the lesion gradually hardened.With the further expansion of the lesion,central depression,around suberification slightly uplift,lesion showed grayish brown or grayish white,black dots were produced on the spot,then the whole of stems and fruits dead.The pathogen of pitaya Fusicoccum sp.stem spot main damaged stems.At the early stage of the disease,it produced water shape round or irregular spots.With the further expansion of the lesion,it showed purple or yellow-brown,with the edge slightly raised.Later period,the central of the lesion become pale,and the lesion healed into lager plaques,with a lager number of small black spots.The pathogen of pitaya diseases was identified by isolation and purification of fungus,pathogenicity test,morphological characteristics,and analysis of rDNA-ITS sequences.The results turned out that the rDNA-ITS sequences of pitaya canker strain showed 100%of identity with Neoscytalidium dimidiatum,indicating that,the strain was the pathogen cau-sing pitaya canker when combine with morphological analysis.The rDNA-ITS sequences of pitaya Fusicoccum sp.stem spotstrain showed 99%of identity with Botryosphaeria dothidea,the strain was the pathogen causing pitaya Fusicoccum sp.stem spot when comb-ine with morphological analysis.Its anamorph was Fusicoccum sp..Biological characteristics of pitaya canker and stem rot were studied.The results sho-wed that PSA culture medium,32 ?,pH 5,Sucrose of carbon source and Potassium nitra-te of nitrogen source was the optimum growth condition of Neoscytalidium dimidiatum.Light had little effect on the growth of mycelium.PSA culture medium,28 ?,full illumin-ation,pH 5,Sucrose of carbon source and Aodium nitrate of nitrogen source was the optim-um growth condition of Fusicoccum sp..The virulence of different fungicides on pitaya canker and Fusicoccum sp.stem spot was determined by growth rate method in the laboratory.Test result indicated that in the 12 kinds of single agent,40%Flusilazole EC,10%Difenoconazole WG,50%Carbendazim WP and 12.5%Diniconazole EC had strong activites against the pathogen of pitaya canker,with EC50 all less than 0.1731mg/L.In the 6 kinds of formulated agent,the ratio of 50%Carbendazim WP and 12.5%Diniconazole EC with 1:1 had best inhibitory for pitaya canker,EC50 was 0.0241 mg/L.In the 12 kinds of single agent,50%Carbendazim WP and 12.5%Diniconazole EC had strong activites against the pathogen of pitaya stem spot,EC50 respectively were 0.0986 mg/L and 0.2547 mg/L.Therefore,the above results could provide a theoretical basis for the effective control of pitaya diseases.