Studies On The Phenotypic Stucture Of Phytophthora Infestans Populations And Its Management In Gansu, China

Potato is dominant industry of agriculture in Gansu province. The potato lateblight disease caused by Phytophthora infestans de Bary occurs frequently, and leadsto serious damage in main potato area. The prevalence of the disease is determined byphenotypic structure of P. infestans, cultivar resistance and environmental factors. Inthis study, the potato late blight disease is main research object, including phenotypicstructure of P. infestans, survival and germination of overwintering oospores in soil,field screening of pesticides, cultivar resistant determination, and field controldirected by disease forecasting system. This study provides theoretical foundation andtechnical support to formulate integrated management of the potato late blight disease.1. This study used international differential host R1-R11with single dominantresistance gene to determine race of75isolates of P. infestans from differentecoregions of potato production in Gansu province, and45races were determined,and the race l.2.3.4.5.6.7.8.9.l0.11occurred the highest frequently, and whichaccounted for22.67%ratio of determined isolates, was dominant race in Gansuprovince.2.186isolates of P. infestans were assessed for sensitivity to Metalaxyl and28.5%of the isolates were sensitive to Metalaxyl,15.6%of the isolates wereintermediate resistance to Metalaxyl, and55.9%of the isolates were high resistance toMetalaxyl. The high resistance isolates to Metalaxyl were found in different collectingplaces, and showed that the isolates resistance of P.infestans to Metalaxyl were highfrequency in Gansu province.3.147isolates mating types of P. infestans were determined by standard A1mating type and A2mating type. The result showed that there were4mating types ofP. infestans, such as A1mating type, A2mating type, A1A2mating type and SFmating type, which accounted for66.2%,20.4%,2.1%and16.3%, respectively.4. Survival and germination of overwintering oospores of P. infestans found thatcompatible mating strains of P. infestans A1and A2produce oospores abundantly inpaired cultures on tomato-rye agar medium.The survival rate of overwintering wasranged from19.57%to24.59%.The germination rate of overwintering was rangedfrom3.58%to8.49%, and there were no significant differences in germination rate ofoospores between alternating light at day/night and whole darkness at day/night.Furthermore, the soil extract liquid was more suitable for oospore germination thandistilled water. 5. mtDNA haplotype of P. infestans in Gansu were analyzed, the result showedthat their mtDNA haplotype were Ia and IIa, not Ib and IIb. The isolates of Iahaplotype were distributed in A1mating type, A2mating type and SF mating type,and accounted for28.00%,40.00%, and32.00%of determined isolates, respectively.90.00%ratio of IIa haplotype was A1mating types. There was not significantrelevance between race and mtDNA haplotype of P. infestans. The isolates of Iahaplotype were resistant to Metalaxyl.6. The field resistance of21cultivars (lines) was identified, and the resultshowed that the cultivar of Guorui-1, Lingxia0308-2,0527-4, Tianshui05-5-49-2and02-3-4was high resistance to P. infestans, the cultivar of Tianshui05-7-5,Tianshui6-3-4, Long6, P2and27-7was intermediate resistance to P. infestans, thecultivar of Long3, Zhongshu02175-200,0528-3, Zhuanglang05-7-1and9901-10wasintermediate resistance to susceptibility, the cultivar of Zhuanglang03-5-7,NongdaGDF, Dingxi05A-1, LK99, Shengjisuo03-1and Ailan1was susceptible to P.infestans.7The result of cultivar resistant identification in Lab showed that the cultivar ofLong7, Long8, Zhuangshu3and Qingshu9was resistant to all race of P. infestans.Therefore, the cultivar of Long3, Long5, Long9, and Long11was susceptible to partisolate of P. infestans.8The results of screening pesticides in field showed that500dilution water ofphosphite had perfect control effect to potato late blight, the control effect was68.00%-74.59%. The control effect of60%Flumorph mancozeb WP,50%FluazinamSC and DPX-QGU42SC was outstanding to potato late blight, the control effect was91.45%,88.32%,85.01%, respectively. Microbial agent Pythium Oligandrum WP was73.76%, however, for agricultural microbial agent Bacillus subtilis WP, the controleffect was only17.50%-43.78%.9Disease forecasting technical system was established by CARAH method, andwhich conducted successfully disease control of potato late blight in field. Thatformulating integrated management of the potato late blight provided technicalsupport for decision of administration in Gansu province.