Study On Anthracnose Of Houttuynia Cordata Thunb. Caused By Colletotrichum Gloeosporioides

Anthracnose is considered as a new and destructive disease of Houttuynia cordata Thunb. in Sichuan in recent years. The symptom and pathogen identification, biological characteristics of the pathogen, infection process and fungicides screening were studied first and systematically. The results are as follows: 1.Symptom of pathogenAnthracnose of Houttuynia cordata Thunb. mainly appears on the leaves, sometimes also on stemes. The ealy symptom is small brown spots, spots gradually expand, In the front of typical leaf,the spot is dark brown in the center and red purple in the edge,round or nearly round. In the back of leaf,the spot is dark brown. On stemes,the symptom is dark brown strip or irregular spot. 2.Identification of pathogenIt's been proved that the isolate was the pathogenic bacteria by the method of Koch's Rule.Based on morphological classification and with molecular biology technology, the pathogen of Anthracnose was identified as Colletotrichum gloeosporioides. The pathogen's acervuli was round or nearly round, at first it was brown dots then changed into black. Conidia, colourless, cylindric in shape, in size of 13.09～23.09μm×3.09～4.24μm, was monadic and usually had an oil ball in the center. Appressorium was dark brown and nearly round or irregular,in size of 6.30-7.51μm×4.56～6.04μm. 3.Biological characteristics of Colletotrichum gloeosporioidesResults showed that the temperature and pH value rage for mycelium growth and sporulation was 15～30℃,pH4～10,with the optimum at 28℃,pH 6,7. All kinds of carbon sources could be effectively used by the pathogen, and the most suitable nitrogen sources was nitrates.It could grow and sporulate well on host juice medium and dark treatment. The germination ratio of conidia was very low in sterile water and would rise with host juice. Conidia were able to germinate in 15～35℃, humidity of RH=98% and pH 4～10, the optimum rate of spore germination was in 30℃, water and pH7. The optimum rate of germ tube extended was in 25℃and PH6.The lethal temperature of conidia was 63℃.4.Infection process and conditions of Colletotrichum gloeosporioidesAfter inoculation, conidia of Colletotrichum gloeosporioides began to germinate within 6-12 hours. Then, from 24 to 48 hours, the pathogen started to penetrate into host. The pathogen was able to penetrate host through two paths such as stomata and epidermis, with the infection structure of appressorium and hypha。The infection of anthracnose caused by Colletotrichum gloeosporioides could be occurred at 15 to 30℃, and the optimum temperature was 25-30℃, the incubation period was the shortest(3-4 days). The wetness period rage for infecting leaf by the pathogen was18 to 48 hours, and the optimum time is 48h, the incubation period was the Shortest.5. The fungicides screening in laboratoryThe four fungicides were tested in laboratory to determine the effect on the hypha growth and the germination of conidia. The results showed that carbendazim inhibited the hypha growth and the germination of conidia well, Thiophanate-methyl and diniconazole were good fungicides on the inhibition of the hypha growth and the germination of conidia. Chlorothalonil almost had no inhibition on the hypha growth and the germination of conidia...