Population Genetic Structure Of Potato Early Blight In China

knowledge on the spatiotemporal population dynamics distribution and the evolutionary mechanisms of plant pathogens is important in breeding durable resistance and sustainable diseases management.Potato early blight disease caused by pathogenic fungi in Alternaria genus is prevalent in major potato cropping regions in the world.Considerable economic losses caused by this disease is second only to potato late blight,especially in developing countries.China is the largest country in the planting area and consumption of potato and occurrence and severity of the disease has increased inrecnt years duo to both increased planting acreage and lack of roation,particularly in the Northern China.Although studies on the population genetic structure of the pathogens increased in the world,the majority of these studies have focused the descriptions of within-population variation using virulence,vegetative compatibility or genetic markers with less reliability and resolution such as RAPD.Population genetic analysis on the spatiotemporal dynamics of genetic variation and the evolutionary mechanisms driving the dynamics are scarce,particularly for A.alternata and A.solani from potato.In this paper,a set of polymorphic SSR was developled and used to analyze spatiotemporatal dynamics and infer ther evolutionary mechanisms such as gene flow and recombination in the pathogens collected from 17 field populations in 10 provinces(Heilongjiang,Inner Mongolia,Hebei,Shanxi,Shandong,Henan,Hubei,Hunan,Fujian and Yunnan)in four potato cropping regions(NSR,CDR,SWR and SMR)of China between 2011 and 2013.1.A set of SSR markers was developed from a genomic library of A.solani used to study population genetic structure of 268 A.solani sampled from four locations in Heilongjiang,Henan,Fujian and Yunnan.The result indicated that seven SSR markers were moderately diverse,selectively neutral and possibly unlinked.Population genetic analysis from four provinces also indicated that genetic variation of A.solani in China was high.About 2/3 of 123 genotypes were detected only once and genotype diversity measured by the standardized Shannon index ranged between 0.82 and 0.92 in the populations.Although clones were detected in multiple populations separated by thousands of kilometres,random association among SSR loci was found in half of the populations assayed.On average,nearly six copies of genetic material were exchanged among these populations each generation and no isolation by distance was detected.It is hypothesized that the joint effects of cryptic sexual reproduction and human-mediated gene flow may account for the observed population genetic structure of A.solani in China.2.Though carrying a functional MAT1 gene,A.alternata is considered to be an asexual fungi(Deuteromycete).Population genetic analysis on A.alternata population diversity and the spatiotemporal dynamics of MAT1 genes from four potato cropping regions in China between 2011 and 2013 used the combination of SSR markers and MAT1 mating type genes.The result demonstrated that identical genotypes were recovered from different locations separated by hundreds of kilometers of geographic distance and spanned across many years,consisting with the expectation of asexual species.However,high genotype diversity,equal frequency of MAT1-1 and MAT1-2 within and among populations,no genetic differentiation(overall Gst=0.002)and phylogenetic association between the isolates from the two mating types,combined with random association amongst neutral markers in some field populations,suggested that sexual reproduction may also play important roles in the epidemics and evolution of the pathogen.In conclusion,A.alternata may adopt an epidemic mode of reproduction with fewer cycles of sexual reproduction,facilitating its adaptation to changing environments and making control more difficult in agriculture.3.Population genetic structure in the 688 A.alternata isolates collected from 17 fields across China was characterized using the seven SSR markers developed from A.solani in the previous chapter and the evolutionary mechanisms.The result displayed that there was almost no significant genetic distance differentiation between individuals from different populations.Pairwise genetic differentiation in the pathogen populations was low,suggesting frequent gene flow has occured among populations,though significant isolation by distance was detected.Further analysis indicated that NSR was the main donator of genetic material(source population)while SWR was the main receptor of genetic material(sink population).No bottleneck was detected in the 17 A.alternata populations and the population of the pathogen was in expansion.In conclusion,the study uncodes population genetic dynamics and evolutionary mechanism of the pathogens causing potato early blight and provides important knowledge of sustainable management of the disease.