Studies On Biological Characteristics Of Causal Organism Of Pepper Anthracnose And Fungicides Selection For Disease Control

Two pathogenic fungi causing pepper anthracnose were isolated and identified. Thebiological characteristics of anthracnose pathogens and the toxicity of nine kinds offungicides and their mixed preparations to the fungi were tested. Moreover, the controleffect of the better mixtures was investigated in field experimen. The main results weresummarized as follows:1Symptoms of pepper anthracnosePepper anthracnose mainly damages fruit and leaf, especially ripe fruit and leaves.The diseased pepper leave show brown spots at the beginning, then developed into darkbrown or rusty lesion and finally the leaves shrink to fall off. The diseased fruits showsoaked, yellow and brown spots at the beginning, and then developed into sunken spotswith protuberant edges and circular black dots. The lesions shrink in dry weather whiletheir surface overflows pink sticky substance in wet condition.2Identification of the anthracnose pathogensTwo isolates CC-1and CG-1were isolated from diseased peppers of Shitai, Anhuiprovince. The acervulus of CC-1with dark brown bristles has2~4diaphragms, conidiumfalcate-shaped, monocelled, colorless and the size ranged from20~30×3~6m; Theacervulus of CG-1has no bristle, conidium cylinder-shaped, monocelled, colorless and thesize ranged from18~29×4~6m. The two isolates caused pepper anthracnose in Shitaiof Anhui province were preliminarily identified as Colletotrichum capsici andColletotrichum gloeosporioides according to the symptoms caused by the pathogens,morphological and cultureal characteristics on the basis of classification criteria ofColletotrichum edited by Sutton.3Biological characteristics of anthracnose pathogenThe effects of temperature, light, pH and nutriment of carbon and nitrogen source onthe mycelial growth, conidial production and spore germination were studied by means ofdecussating method, hemocytometer measurement method and concave slides method. Theresults showed that the optimum temperatures for the mycelial growth of C. capsici and C.gloeosporioides were25℃and28℃, respectively; the lethal temperatures were50℃and55℃, respectively; the optimum temperatures of conidial production were all28℃. Theoptimum pH values for mycelium growth of C. capsici and C. gloeosporioide were7and6severally; the optimum pH values for conidial production were all5and for sporegermination were7. The light condition had little infulence on the colony diameter of pepper anthracnose while it contributed to conidial production. The best carbon souces ofmaltose and starch were the best suitable for the mycelial growth and conidial productionof C. capsici, respectively; the best carbon souces of glucose and sorbose were suitable forthe mycelial growth and conidial production of C.gloeosporioide separately. The optimumnitrogen sources for mycelium growth of C. capsici and C.gloeosporioide were beefextract and protein peptone, respectively. The optimal nitrogen sources for sporeproduction were both yeast.4Toxicity tests of fungicides to two anthracnose pathogens,Colletotrichum capsici and C. gloeosporioideToxicity index of nine miticides pesticide to C. capsici and C. gloeosporioide hadbeen tested and the mixtures had been screened. pyraclostrobin, propiconazole anddifenoconazole had better inhibition action to C. capsici among the nine tested single agent,the EC50was0.4818μg/mL,0.0095μg/mL and0.1295μg/mL, respectively; prochloraz,difenoconazole and propiconazole had stronger inhibition to the mycelium ofC.gloeosporioide, the EC50was0.0440μg/mL,0.3638μg/mL and0.0401μg/mLrespectively while azoxystrobin had the strongest inhibition to spore germination of pepperanthracnose.Propiconazole, azoxystrobin pyrazole, prochloraz and difenoconazole with a singleagent were compounded in this study. The tested pesticides mixed with1:1and theefficiency coefficient of the effect to pepper anthracnose showed as follows: the mixture ofpropiconazole and difenoconazole, propiconazole and pyrazole azoxystrobin all hadefficiency effects and the CTC to C.campsium were210.26and201.12, respectively; theCTC to C.gloeosporioide were211.25and205.25, respectively. The mixtre of pyrazoleazoxystrobin and prochloraz had efficiency effect to C. capsici and the CTC was215.13.The mixture of pyrazole azoxystrobin and difenoconazole had efficiency effect toC.gloeosporioide and the CTC was213.03while the mixture of difenoconazole andprochloraz showed antagonism to C. capsici.5Field experiment for the control of pepper anthracnoseSeveral tests had good control effect to C. capsici. Prevention effect all reached morethan75%in experimental ethephon concentration of the three times within10days afterapplying pesticide. It showed that several of the best-performing potions were newhigh-efficiency microbicides. According to the control of pepper anthracnose, the authorsuggested several pesticides should rotate in use, and chemical control and preventionmeasures, such as implementing agricultural measurements and crop rotation, choosing disease-resistance species, establish the diseased-free orchard and breeding diseased-freeseedlings, the reasonable application, etc. Reducing the use of chemical pesticide will notonly save cost but also has an important ecological meaning.