Population Structure And Virulence Analyses Of Hessian Fly,Mayetiola Destructor (Say) (Diptera:Cecidomyiidae)

The Hessian fly,Mayetiola destructor（Say）,a major pest of wheat worldwide,is an important plant quarantine pest in China.To date,the invasion route,and the virulence of Hessian fly in China has not been researched.In this research,the population genetic structure of Hessian fly in China was assessed using the mitochondrial（12s r RNA）gene and nuclear marker（White）,the resistance of a total of 54 wheat cultivars was evaluated,the effect of temperature on resistance level of resistant cultivars was analyzed,the virulence of one Hessian fly population to 14 known resistance genes of wheat was determined.The main results are as follows:1.The length of mt DNA 12S r RNA gene fragment was 404 bp,only one haplotype was defined.Based on phylogenetic reconstruction and distance from sequence analysis of the mitochondrial 12S r RNA,we hypothesized that the four populations,i.e.Xinjiang,Spain,North America and Morocco populations share the common origin.2.The length of White gene fragment was 893 bp,12 alleles were detifined,The lowest F_ST value was between China and Spain,North America and Morocco populations popualtions.Neutrality test analysis revealed that Hessian fly populations in China have not been experienced expansion event.We hypothesized that the four populations i.e.Xinjiang,Spain,North America and Morocco populations share the common origin,and there were no introduction of Hessian fly occurred recently.3.Two of 54 cultivars of wheat,including Xindong 23 and Xindong 49,showed resistance to two Hessian fly populations in China at 18℃.The two resistant cultivars exhibited different level resistance related to Hessian fly popolations.,i.e.,the Xindong 23showed 58.7%and 78.6%of resistant plants to the Anxiang and Yangchang population,respectively,while the Xindong 49 showed a high resistance to the Anxiang population with 95%of resistant plants and low level resistance to Yangchang population with33.4%of resistant plants.The cultivar,Xindong 3,which once showed resistance to Hessian fly,became susceptible nowadys.These results suggests that the virulence of the Hessian fly in Xinjiang have changed,which may contributed to the outbreaks of Hessian flies in recent year in Xinjiang.4.Two selected resistant cultivars,Xindong 23 and Xindong 49,exhibited different resistance level related to temperatures.At 18～24℃,the percentage of resistant plants were decreased with temperature elevation,and reached 0 at 26℃,indicating that the resistance gene conferring resistanc in the two cultivars are temperature-sensitive.5.Six resistance genes,H5,H7H8,H14,H22,H25,and H26,were founded to be highly effective against the tested Hessian fly population,conferring resistance to>90%of plants containg one of these resistance genes,while five resistance genes H6,H17,H18,H20,and H31,were all susceptible at 18℃.The six resistant genes should be recommended as candidate genes in breeding and utilization in China.The above results confirm that the population of the Hessian fly in China is not introduced from central Asia,and no population expansion event has occurred.The virulence of Hessian fly has evolved since 1980s.The effect of temperature can affect the resistance of two screened resistant wheat cultivars.Six resistance genes were effective on the prevention of Hessian fly.These results may provide a useful information for understanding the reasons of the outbreak of Hessian fly in recent years,and making control strategy.