Triadimefon Sensitivity And Fitness Analysis Of Puccinia Striiformis F.sp.tritici From Fields In Tianshui Region

Wheat stripe rust caused by Puccinia striiformis f.sp.tritici（Pst）is an important fungal disease that endangers and seriously threatens the safety of wheat production all over the world.China as the world’s largest wheat stripe rust endemic area,where triadimefon has been applied in the fields for the prevention and treatment of Pst over 40years,which may present a certain risk of fungicide resistance.Therefore,it is urgent and necessary to collect Pst isolates from the field and determine their triadimefon resistance level.Tianshui region is located in the southern Gansu,and is considered as the“over summer region”and“source region”of Pst,therefore the samples of wheat leaves with Pst isolates were collected in Tianshui region,after purified and multiplicated,the effective concentration（EC50）values of triadimefon of Pst isolates were determined by using the detached leaf method.Based on the EC50 values,sensitive and resistant isolates were selected for the fitness properties test in order to evaluate the use efficiency of triadimefon,and the results are as follows:1.Resistance to triadimefon of Pst in Tianshui RegionIn this study,the EC50 of triadimefon of 69 collected in the fields of Tianshui were determined by using the detached leaf method.The EC₅₀ values varied from 0.142μg/m L to4.012μg/m L,with an average of 0.740μg/m L,the great variation indicated that the Pst has developed a certain resistance to triadimefon.Among the 69 tested Pst isolates,11 were triadimefon-resistant,with an average of 2.549μg/m L,58 were sensitive with an average of0.397μg/m L.The average resistance factor（Rf）of the 69 Pst isolates was 4.936,and resistance frequency reached 15.94%.2.Determination of parasitic fitness of Pst with different resistance to triadimefonBased on the results of triadimefon sensitivity test,five resistant and six sensitive isolates were selected for fitness components test,including urediniospore germination rate,spot daily increase,incubation period,sporulation period,sporulation intensity,uredinia length and lesion expansion rate.The principal component analysis（PCA）showed the fitness of the 69 Pst isolates were mainly determined by three principal components,the first principal component was the urediniospore viability and infection ability（consist of incubation period,urediniospore germination rate and lesion expansion rate）,the second principal component was sporulation capacity（consist of spots daily increase,sporulation period and sporulation intensity）,the third principal component was expansion ability（mainly consist of uredinia lenth）.The analysis of variance showed that compared with the sensitive Pst isolates,the resistant Pst isolates showed reduced urediniospore viability,infection ability,but there is no obvious difference both in sporulation and expansion capacity,the overall parasitic fitness of the triadimefon-resistant Pst isolates is lower than that of the sensitive.The data of correlation analysis between Log EC50 value and fitness of each isolate showed that the Log EC50 was significantly（p<0.05）correlated with the urediniospore germination rate（r=-0.909）,incubation period（r=0.967）,the lesion expansion rate（r=-0.818）.That is,the higher the triadimefon resistance of Pst,the lower the urediniospore germination rate,the longer period from inoculation to invasion of the leaves,colonization and re-generation of urediniospore;the lower expansion and infection ability.The results suggest the development of triadimefon resistance may reduce the fitness of Pst.