| Potato late blight, caused by the Phytophthora infestans(Oomycete), is dominant disease in the area of potato production in the world. This disease can reduce production of potatoes about 30%-50%, and cause losses of about $ 17 billion in the worldwide annually. China is one of the most mainly potato-producing country, the cultivated area and output are first in the world, lost about $ 4 billion annually. The composition and changes of P. infestans population structure directly related to the prevalence of the disease. Therefore, effective understanding the main pathogenic of P. infestans and their distribution, genetic structure variation could monitor of the occurred and epidemic of potato late blight. And finding natural biological source products instead of chemical pesticides to prevent and control potato late blight, it not only can reduce the agricultural economic losses caused by P. infestans, but also increase food security and reduce environmental pollution caused by chemical pesticides. The ratio of plant area of potato in Hebei province and northeast of China is about 11% in China. In this area, the enviroment is similar, important for potato industry, the related studies of P. infestans was little, as well as little report about lipopeptide inhibiting P. infestans. In present study, the pathogenic, SSR genotypic and genetic diversity of P. infestans population were studied, as well as screening antagonistic microorganisms against P. infestans and purification of antifungal substances. The major results are as follows:1. A total of 678 samples of potato late blight disease collected from Hebei, Liaoning, Jilin and Heilongjiang Province during 2008-2010. And 429 strains successfully were isolated. The virulence genes of 227 strains were identified and found that they had all virulence genes, and R3, R4, R6, R7, and R11 resistance genes existed in resistant varieties could be overcome by 80% of tested strains. A total of 30 pathogenic types were identified, and dominant pathogenic type was 1.2.3.4.5.6.7.8.9.10.11 with the widespread occurrence in 4 provinces, the frequency of occurrence in 2008-2010 was 20%, 39% and 41.6%, respectively, followed by the the pathogenic type 1.2.3.4.5.6.7.9.10.11, and the frequency of its occurrence in 2008-2010 was 7.5%, 15.5%, and 22.1%, respectively.2. In 2008-2010, pathogenic type of Hebei Province was 7, 6 and 4 kinds, respectively. Heilongjiang was 7, 10 and 11. Liaoning was 1, 3 and 3. Jilin was 1, 1 and 1, respectively. The composion of pathogenic type in Heilongjiang was the most abundant, followed by Hebei, Liaoning and Jilin.3. SSR genotypes of 373 strains of P. infestans collected from Hebei, Heilongjiang, Liaoning and Jilin Provinces in 2008-2010 were analyzed using the SSR primers Pi4 B and Pi4 G. A total of 16 kinds of SSR genotypes were identified: A-03, A-09, B-01, D-03, F-01, F-04, F-05, F-06, F-07, F-08, G-02, G-03, I-01, J-01, K-01 and L-01. Among them, the dominant genotype was F-01, accounting for 67.83% in the measured strains, followed by the F-06 genotype(14.75%). The numbers of SSR genotypes in Hebei, Heilongjiang, Liaoning and Jilin were 11, 8, 4 and 3, respectively. 7 kinds of SSR genotypes, including A-09, F-07, F-08, I-01, J-01, K-01 and L-01 were the first reported in the Northeast and the Hebei Provinces in China. During 2008-2010, the numbers of P. infestans SSR genotype were increased significantly in Hebei and Heilongjiang Province, and changed slightly in Liaoning and Jilin. It is clear that dominant SSR genotype of P. infestans in northeast of China and Hebei Province is single.4. A total of 134 strains of P. infestans were isolated from different agricultural fields in Hebei, Liaoning, Jinlin and Heilongjiang provinces in north China. The genetic variation among these strains were analyzed using 15 ‘simple-sequence repeat’(SSR) markers. The results showed that forty different SSR genotypes and an average of 3.8(range 2-9) alleles per locus were found. Low genetic diversity(Shannon’s diversity index = 0.26) was found among these 134 strains from four provinces, revealing the presence of clonal populations of the pathogen in this region. The average heterozygosity was 0.162, indicating the low level of genetic variations of P. infestans populations. There was no correlation between population genetic diversity of P. infestans and geographical origin.5. Plate culture and dual-culture experiments were used to isolate and screen antagonistic Bacillus spp. from soil. Nine strains of bacteria were obtained, which had a certain antagonism. Of which, Y-1 and Y-3 strains significantly inhibited growth of P. infestans. The experimental results showed that Y-1 and Y-3 affected on the growth P. infestans, inhibition rate was more than 80%. 6. Using the method of acid precipitation, organic solvent extraction and HPLC to isolate lipopeptide from fermentation broth of Y-1 and Y-3 strain, respectively. The results showed that lipopeptide produced by Y-3 strain could significantly inhibited gowth of P. infestans, inhibition rate was 90%. Preliminary analysis of the crude lipopeptide produced by Y-3 strains had eight kinds of components. The crude lipopeptide produed by Y-1 strains consisted of six kinds of components. The antimicrobial activity of various components and relationship between different components is being analyzed.The above results could provide preliminary theoretical basis for reveal the relationship between pathogenic types, SSR genotypes and genetic diversity of P. infestans and outbreak of disease. And the results could provide practical reference for comprehensive prevention and control strategy of potato late blight in this area, especially reasonable layout of seed potato. |
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