Analysis Of Phenotype And SSR Genotype Of Phytophthora Infestans In Main Potato Production Areas In China

Late Blight,caused by Phytophthora infestans?Mont.?de Bary,is one of the most important potato diseases.Potato Late Blight prevalence is associated with the population structures of Phytophthora infestans.This study reveals the basic characteristics and dynamic changes of the population structures of Phytophthora infestans in potato production areas in China from 2017 to 2019,by testing mating type,lesion growth rate,latency period and simple sequence repeat?SSR?genotypes.The mating types of 478 strains were tested by the in-dish confrontation method.In 2017,the northern regions?Hebei Province and Shandong Province?were dominated by the A1 mating type?A1accounted for 94.7%,A2 accounted for 5.3%?,and the southern regions?Hubei Province,Hubei Province,Guizhou Province,and Yunnan Province?were dominated by the A2 mating type?A2 accounts for 97.5%,A1 accounts for 2.5%?;in 2018,the A1 mating type in the northern regions?Heilongjiang Province,Inner Mongolia,and Hebei Province?accounted for 100%,and the A2 mating type in the southern regions?Hubei Province and Yunnan Province?accounts for 100%;in 2019,the A1 mating type in the northern regions?Heilongjiang Province,Inner Mongolia,and Hebei Province?accounted for 100%and the A2 mating type in the southern regions?Hubei Province,Guizhou Province,and Yunnan Province?accounted for 100%.This shows that Phytophthora infestans in China is mainly asexually propagated.By observing the latency period?the time from inoculation to the symptom developed?of detached potato leaves,that were inoculated with Phytophthora infestans,it was found that the latency periods in southern regions?Hubei Province,Guizhou Province,and Yunnan Province?were longer than that in the northern regions?Hebei Province and Shandong Province??average 5.5 days in the northern regions and 4.3 days in the southern regions??P<0.001?.Using Image J to calculate the growth rate of lesions for three consecutive days,it was found that on the fourth day,there was a significant difference in the growth rate of lesions between the northern and southern regions?North:1.00 cm²/day,South:1.85 cm²/day??P<0.001?,on the 5th day,there was a significant difference in the growth rate of lesions between the northern and southern areas?North:1.55cm²/day,South:2.45cm²/day??P<0.002?,and on the 6th day,the difference disappeared?North:2.04cm²/day,South:1.71cm²/day??P>0.205?.By using the hemocytometer to count the number of sporangia?the number of sporangia produced by the lesions 10 days after infection?,it was found that the number of sporangia in the northern regions?6.0×10⁵??Hebei Province and Shandong Province?are not significantly different from the southern regions?6.3×10⁵??Hubei Province,Guizhou Province,and Yunnan Province??P>0.942?.Twelve pairs of SSR markers?Pi02,Pi4B,G11,Pi04,Pi63,Pi70,D13,SSR2,SSR4,SSR6,SSR8 and SSR11?were used for genotyping of538 strains,and 71 different genotypes were identified.Compared with the reference strain genotypes,it was found that the main genotype MLG6?87.9%?of Phytophthora infestans in the northern regions?Heilongjiang Province,Hebei Province,Inner Mongolia,and Shandong Province?was similar as the reference genotype misc_RU,the main genotype MLG63?43.8%?of Phytophthora infestans in southern regions?Hubei Province,Guizhou Province,and Yunnan Province?is similar with the reference genotype Blue₁3.The Microsatellite Genotyping?MLG?multi-site genotype study found that in 2017,there were 58 Phytophthora infestans genotypes in the southern regions?12 in Hubei Province,24 in Guizhou Province,and 22in Yunnan Province?,and 14 in the northern regions?2 in Hebei Province and 12 in Shandong Province?.In 2018,there were 12 genotypes of Phytophthora infestans in the southern regions?2 in Hubei Province and10 in Yunnan Province?,and 8 genotypes of Phytophthora infestans in the northern regions?2 in Hebei Province,2 in Heilongjiang Province,and 4in Inner Mongolia?.In 2019,there were 13 Phytophthora infestans genotypes in the southern regions?2 in Hubei Province,4 in Guizhou Province,and 7 in Yunnan Province?,and 8 genotypes of the Phytophthora infestans in the northern regions?3 in Hebei Province,2 in Heilongjiang Province,and 3 in Inner Mongolia?.Discriminant Analysis of Principal Components?DAPC?analysis results show that all Late Blight genotypes are divided into two groups.Group?mainly contains the Late Blight pathogens in the northern regions?Hebei Province,Shandong Province,Heilongjiang Province,and Inner Mongolia?,and Group??mainly contains the Late Blight genotypes in the southern regions?Hubei Province,Guizhou Province,and Yunnan Province?.