| Valsa canker is the most important disease of the pear. When infected by the disease, the bark of the trunk and bough of the pear will decay and the growth status become retarded, even the tree will be destroyed. In this study, we screened out fungicides against pathogen caused pear valsa canker, and made a comparison of the cultural characteristics and cross infection of valsa canker pathogens from four kinds of forest-fruit trees which included pear, apple, poplar and peach. The results were as follows:1. Isolation and identification of the pathogens caused poplar valsa canker. In this study, the isolates of poplar valsa canker which originated from korla were purified. Then, through pathogenicity test, we confirmed that the strains YF-XJ-1 and YF-XJ-2 were the pathogens caused the valsa canker. In addition, the sequence alignment of r DNA-ITS gene and phylogenetic analysis of the 2 strains and the other valsa canker pathogens were completed. The results showed that the strain YF-XJ-1 gathered in the same clade with the representative isolates of valsa nivea, and the strain YF-XJ-2 gathered in another clade with the representative isolates of V. sordida.2. Biological characteristics of the pathogens from different host plants caused canker. In this test, biological characteristics of the tested strains which included 2 strains(LF-HN-6, LF-HN-2a-1) from pear, 2 strains(PF-SX-A6、PF-SD-a) from apple, 2 strains(YF-XJ-1、YF-XJ-2) from poplar and 1 strain(TF-LN-1) from peach were compared. The results showed that the growth temperature was different for these tested strains, which the optimum growth temperature of the strains LF-HN-6, LF-HN-2a-1, YF-XJ-1, TF-LN-1 was 25℃, but for the other strains, the temperature was 28℃. There were significant differences in the optimum media inducing conidia for the tested strains. For the strains LF-HN-6, YF-XJ-1 and YF-XJ-2, the medium was PDA, for the strains PF-SD-a and TF-LN-1, the medium was oatmeal, and for the strains LF-HN-2a-1 and PF-SX-A6, the medium were changed to barleycorn. The test of the inoculation on the ‘huangguan’ pear showed that all of the tested strains could infect the ‘Huangguan’ pear, but YF-XJ-2 had a low pathogenicity which exist significant difference with the other strains. There were 21 kinds of inoculation treatments could be successfully inoculated in all of the inoculation treatments of the 7 kinds of Valsa canker pathogens with 4 kinds of detached shoots except for the 7 kinds of inoculation treatments included the YF-XJ-1 with all of the 4 kinds of detached shoots, LF-HN-2a-1 and TF-LN-1 with the shoots of poplar and YF-XJ-2 with the shoots of peach. The test showed that the pathogens from different host plants caused canker exist cross infection on different hosts, but the pathogens showed stronger pathogenicity on their original hosts.3. Screening fungicides against pear valsa canker. In this study, we measured the growth rate, spore germination rate and incidence degree after inoculation on the detached and in vivo shoots for 12 kinds of fungicides. In the growth rate test, the result showed that the tested strain were very sensitive to 4 kinds of fungicides including coumoxystrobin, propiconazole, tebuconazole and difenoconazole which the EC50 was all less than 0.10μg/ml. In the inhibition of spore germination test, the result showed that the spores of the tested strain were very sensitive to 6 kinds of fungicides included imazalil, amobam, coumoxystrobin, propiconazole, tebuconazole and difenoconazole that the EC50 was all less than 0.1μg/ml. In the test of incidence degree after inoculation on the detached and in vivo shoots, the result showed that 3 fungicides revealed optimal impact on the protection and treatment effects against the tested strain, and the lesions were only respectively 2.88 mm, 2.08 mm and 0.71 mm on the in vivo shoots in the test of treatment effects. |
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