A Preliminary Study On Phytophthora Infestans Collected From Fujian,Hunan And Anhui Provinces

Potato late blight,caused by Phytophthora infestans,is the main disease that troubled the development of the potato industry of the world.According to the report of FAO,the losses and hazards caused by potato late blight have exceeded the loses caused by rice blast and wheat rust,therefore,the organization has classified potato late blight as the world's largest crop disease.At present,the potato acreage and production of potato in China are largest in the world,therefore,the detection of the mating type,investigation of the composition and distribution of the physiological races and detection of sensitivity of P.infestans to fungicides are helpful to the sustainable development of potato industry of China.In this study,150 isolates of P.infestans were collected from Fuanand Xiapu in Fujian Province,collected from Fuan and Xiapu in Fujian Province,Yongshun in Hunan Province and Jieshou in Anhui Province.The mating type and physiological races of the isolates and their sensitivity to dimethomorph and propamocard were determined.Main results were summarized as follow:all isolates collected from Anhui Province in 2015 and 2016 are A1,in addition all isolates collected from Xiapu in Fujian and Yongshun in Hunan provinces are A1 A2,and the mating type of all isolates collected from Fuan in Fujian Province in 2016 are A1A2 while all isolates collected in 2016 are Al.'The dominant race of isolates from Fuan and Xiapu Fujian Province was 1.2.3.4.6.7.8.10 and 1.2.3.4.5.6.7.8.10 in 2015 and 2016,the frequency are both 50%;the virulence factors each strain carried was mean of 8.25 and 9.34 respectively in 2015 and 2016.The dominant race of isolates from Yongshun in Hunan Province was 1.2.3.4.5.6.7.8.9.10,2.3.4.5.6.7.8.9.10 and 1.2.3.4.5.6.7.8.9.10,1.2.3.4.5.6.7.8.10 in 2015 and 2016,the frequency is 25%and 28.57%;the virulence factors each strain carried was mean of 7.9 and 9.39 in 2015 and 2016.The dominant race of isolates from Jieshou in Anhui Province was 4.7 in 2015and 2016;8.25 and 9.34 virulence factors were each strain carried in 2015 and 2016.The EC50 values of dimethomorph ranged from 0.3769 ?g mL-1 to 0.5758 ?g mL-1,the EC50 values of propamocard ranged from 17.07 ?g·mL-1 to 21.34 ?g·mL-1.In order to understand whether the sexual reproduction caused by self-fertile may afftect the genetic structure of Phytophthora infesftans,the abortive rate of the oospores produced by self-fertile isolates was measured and MTT staining method was used to determine the oospore viability which were used to study the biological characteristics of self-fertile Phytophthora infestans isolates.The result show that the proportion of self-fertile isolates in Xiapu and Fuan in Fujian Province and Yongshun in Hunan Province had been changing with a highly significant rising trend from 2015 to 2016,of which in 2016 the self-fertile isolates occupied 100%of the P.infestans isolates,and the character of self-fertility was stable in clonal progeny of single zoospore.The oospores abortive rate of self-fertile isolates cultured on rye medium from Fijian and Hunan provinces during 2015-2016 was up to 74%to 100%.However,the proportion of healthy oosopres produced by self-fertile isolates in potato leave tissues was up to 54%to 68%,which was significantly higher than that on rye medium.In conclusion,Self-fertile P.infestans had become the dominant populations in Xiapu and Fuan of Fijian Province and Yongshun of Hunan Province,and the self-fertile isolates could produce a large number of healthy oospores in potato leaves.The resistance genes overcomed by isolates from Jieshou in Anhui Province were R4 and R7,while more resistance genes were overcomed by isolates from Fuan and Xiapu in Fijian Province and Yongshun in Hunan Province.In addition,there was no significant difference in resistance of the isolates collected in different years from same province to dimethomorph and propamocard;while there were differences in resistance of the isolates collected from different provinces:the inhibitory effect of dimethomorph on P.infetans from Fujian Province was stronger while on isolates from Anhui Province was weaker,the inhibitory effect of propamocard on P.infestans from Hunan Province was stronger than on isolates from Fujian and Anhui provinces.