Study On Population Structure Of Phytophthora Infestans And Control Efficiency Of Inducers And Fungicides Against Potato Late Blight

Potato late blight is a devastating disease in potato production,which can cause production in the year of disease outbreak.The pathogen is Phytophthora infestans,which can be sexually reproduced in a heterozygous manner,resulting in changes in the population structure of P.infestans.This study investigated the biological characteristics of P.infestans and the prevention and control of potato late blight.In order to provide theoretical basis and technical reference for high-yield and high-efficiency planting in the main potato producing areas and promote the industrialization process.A total of 92 P.infestans isolates collected from Heilongjiang province and Inner Mongolia in 2018 were determined for mating type.The results of mating type determination showed that three mating types were found in 92 P.infestans.A1,A2 and self-fertility were accounted for 88.1%,5.4% and 6.5% of the total isolates,respectively.Three mating types were found in the P.infestans isolates collected from Keshan county of Heilongjiang province.Of which,A1,A2 and self-fertility were accounted for 84.5%(49 isolates),5.2%(3 isolates)and 10.3%(6 isolates)of the total isolates,respectively.All the isolates(100%)collected from Yian county of Heilongjiang province were A1 mating type(8 isolates).Two mating types were found in the Yakeshi of Inner Mongolia.A1,A2 were accounted for 89.5%(17 isolates)and 10.5%(2 isolates)of the total isolates,respectively.All the isolates(100%)collected from Shiwei of Inner Mongolia were A1 type(8 isolates).Above results showed that the mating types of P.infestans isolates collected from Keshan county of Heilongjiang province and Yakeshi of Inner Mongolia were relatively richer than other two regions,but sexual reproduction was not found among the P.infestans isolates collected from other two main producing areas of potato.The mating types between different regions are also different,and the percentage is significantly different.Metalaxyl resistance of 92 P.infestans isolates were determined.The results of sensitivity to metalaxyl showed that 67.4% isolates were resistant to metalaxyl,30.4% isolates were moderate resistant to metalaxyl,and 2.2% isolates were sensitive to metalaxyl.But high metalaxyl sensitivity isolates were not found.The isolates of resistance to metalaxyl and moderate resistance to metalaxyl in Keshan county of Heilongjiang province were 65.5% and 31.1%,respectively.The isolates of resistance to metalaxyl and moderate resistance to metalaxyl in Yian county of Heilongjiang province were 62.5% and 37.5%,respectively.84.2% isolates were resistant to metalaxyl,and 15.8% isolates were moderate resistant to metalaxyl in Yakeshi of Inner Mongolia.42.9% isolates were resistant to metalaxyl,and 57.1% isolates were moderate resistant to metalaxyl in Shiwei of Inner Mongolia.The results suggested that P.infestans isolates occur in Heilongjiang province and Inner Mongolia have been produced metalaxyl resistance.For mt DNA haplotype analysis of P.infestans,two mt DNA haplotypes of Ia and IIa were found.Of which,82 isolates(89.1%)were IIa haplotype,and 10 isolates(15.2%)were Ia haplotype.Two haplotypes of Ia and IIa were identified in the 66 isolates collected from Heilongjiang province,which accounted for 15.2% and 84.8%,respectively.All the P.infestans isolates collected from Inner Mongolia were IIa haplotype(100%).The results showed that there were two mt DNA haplotypes of P.infestans in Heilongjiang province,and the dominant haplotype was IIa haplotype.The structure of mt DNA haplotype of P.infestans collected from Inner Mongolia city is single,only IIa haplotype.A total of 8 SSR genotypes were identified using two pairs of primers Pi4 G and Pi4 B,namely G-02,D-03,D-02,F-06,F-05,F-03,F-02 and F-01.8 SSR genotypes were found among the 66 isolates collected from Heilongjiang province,41 isolates(62.12%)of which were F-01 genotypes,which was dominant.The 26 isolates collected from Inner Mongolia,there are two SSR genotypes.Among them,22 isolates(84.62%)were F-01 genotype,and 4 isolates(15.38%)were G-02 genotype.Overall,the genetic diversity of P.infestans in Heilongjiang province is more complicated.The relationship between SSR genotypes of P.infestans and mating type and metalaxyl resistance in different regions could be further analyzed.The result showed that there were three mating types in the SSR dominant genotype F-01 analyzed in Heilongjiang province and Inner Mongolia.And there were isolates with high resistance,resistance and sensitive to metalaxyl.Above result indicated that there was no direct correlation between SSR genotype and mating type and resistance to metalaxyl.The sensitivities of P.infestans isolates to oxathiapiprolin,dimethomorph·pyraclostrobin and fluopicolide·propamocarb were determined by using the growth rate method.The EC50 value of P.infestans to oxathiapiprolin ranged from 0.000149 μg/m L to 0.000640 μg/m L,and the average EC50 value was(0.000359±0.000114)μg/m L.The results showed that oxathiapiprolin had higher activity against P.infestans.The EC50 value of dimethomorph·pyraclostrobin ranged from 0.1618 μg/m L to 0.2177 μg/m L,and the average EC50 value was(0.1908±0.0132)μg/m L.The EC50 value of fluopicolide·propamocarb ranged from 0.1623 μg/m L to 0.7089 μg/m L,and the average EC50 value was(0.3811±0.1078)μg/m L.There was no cross resistance between the three fungicides and metalaxyl.The single fungicide on the field control of potato late blight showed that the same fungicide was sprayed four times,and the single fungicide control effect from high to low was: fluorothiazolyl ethanone>fluopicolide·propamocarb>fluazina>dimethomorph>ovraclostrobin·dimethomorph>eugenol>matrine.The field control effect of different fungicide combination treatments to potato late blight showed that different fungicides were sprayed every 7 days in the field,and the combination treatments of fungicides with good control effect were: fluazinam + dimethomorph + fluorothiazolyl ethenone + fluopicolide·propamocarb,mancozeb + fluorothiazolyl ethanone + fluazinam + fluopicolide·propamocarb,fluazinam + fluopicolide·propamocarb + ovraclostrobin·dimethomorph + fluorothiazolyl ethanone,mancozeb + fluopicolide·propamocarb + ovraclostrobin·dimethomorph + fluorothiazolyl ethanone,mancozeb + dimethomorph + fluazinam + fluopicolide·propamocarb.The field control effect of the combination of fungicide and BABA to potato late blight showed that when the primary infection plants appeared in the field,it was sprayed with mancozeb + BABA,fluorothiazolyl ethanone + BABA,fluazinam + BABA and fluopicolide·propamocarb + BABA,respectively.The last control efficacy could reach 70.07%,the total yield was 2911.08 kg/667 m2,and the commodity potato rate and yield increase rate reached 76.45% and 60.72%,respectively.The results of sensitivity to BABA indicated that the BABA had no inhibitory effect on the mycelial growth and sporangial germination of P.infestans in vitro.The decrease of disease index and the increase of yield were mainly caused by its induce resistance to potato.Therefore,the combination treatments of the fungicide and the disease resistance inducers will be another safe and efficient way to control potato late blight in the field.The above results indicated that the population structure of P.infestans collected from Heilongjiang province became complicated year by year.The population structure of P.infestans collected from Inner Mongolia was relatively single.Chemical control is still the most effective way to effectively control potato late blight,and the use of chemical fungicide in combination with the resistance inducer BABA is one of the more effective and safe prevention strategies in the future.