Population structure of the blacklegged tick Ixodes scapularis revealed by SSCP data using the mitochondrial Cyt b and the nuclear ITS1 markers

The population genetic structure of the blacklegged tick Ixodes scapularis was analyzed using 853 individual ticks collected from 12 sites along the eastern seaboard of the United States. PCR-based DNA single strand conformation polymorphism(SSCP) was used for analysis of one haploid locus, the mitochondrial cytochrome b(Cyt b), and one diploid locus, the internal transcribed spacer 1(ITS1) of nuclear ribosomal RNA. Seven haplotypes in the Cyt b locus and 13 genotypes in the ITS1 locus were identified. Population differentiation and isolation by distance were found. Distribution of haplotype and genotype frequencies across geographic regions suggests that two distinct populations exist along the Eastern Coast of the US. However, genetic variation among individuals within regions was large. This degree of variation suggests frequent gene flow between regions. Moreover, overall genetic diversity among individuals was much higher in ticks from the southern population.

Identification of a Tobacco Disease on Flat Tray System

[ Objective] The pathogen of a new disease found in floating seedlings of tobacco was isolated and identified to provide the basis for the control of the disease. [ Method] The pathogenicity of the isolated strain was determined according to Koch＇s rules, and the pathogen was identified through Biolog system, 16S rDNA sequence analysis and physiological and biochemical methods. [ Result] Through Koch＇s test, the isolated 3 -3 strain was verified to be the pathogen causing floating seedling disease, which was consistent with the characteristics of Pectobacterium carotovo- rum subsp. Carotovorum through Biolog determination and the other physiological and biochemical methods. 16S rDNA sequence analysis showed that 3 -3 strain had the highest similarity with P. carotovorum subsp. Carotovorum strains Kun28213 （accession number GU936996）, reaching 99. 9%. [Conclusion] Base on the identification results of several methods, the pathogen causing floating seedling disease was P. carotovorum subsp. Carotovorum, and the disease was first reported in China. According to the English name of the disease, the disease was called as tobacco blackleg disease.

Genetic diversity and population structure of Leptosphaeria maculans isolates in Western Canada

Leptosphaeria maculans is a serious concern for canola production worldwide.For effective disease management,knowledge of the pathogen’s genetic variability and population structure is a prerequisite.In this study,whole-genome sequencing was performed for 162 of 1590 L.maculans isolates collected in the years 2007e2008 and 2012e2014 in Western Canada.DNA variants in genome-wide and specific regions including avirulence(Avr)genes were characterized.A total of 31,870 high-quality polymorphic DNA variants were used to study L.maculans genetic diversity and population structure.Cluster analysis showed that 150 isolates were clustered into 2 main groups and 4 subgroups by DNA variants located in either Avr or small secreted protein-encoding genes and into 2 main groups and 6 subgroups by genome-wide variants.The analysis of nucleotide diversity and differentiation also confirmed genetic variation within a population and among populations.Principal component analysis with genome-wide variants showed that the isolates collected in 2012e2014 were more genetically diverse than those collected in 2007e2008.Population structure analysis discovered three distinct sub-populations.Although isolates from Saskatchewan and Alberta were of similar genetic composition,Manitoba isolates were highly diverse.Genome-wide association study detected DNA variants in genes AvrLm4-7,Lema_T86300,and Lema_T86310 associated with the years of collection.