Virulence Analysis And Two Fugicides Resistant Evaluation Of Phytophthora Infestans Populations In Parts Of China

As one of the world’s third largest crop, potato impact country very substantial. Since the Irish famine at 19th century, people pay a lot attention to potato, especially potato late blight. It is a kind of oomycete disease which destructs plant strong caused by Phytophthora. infestans (Mont.) de Bary. The emergence and growing of P. infestans’fungicide resistance is a hot topic, which relate to potato quality and pesticide resisdues. In this experiment, we collected seven different habitat populations of P. infestans in China(Nanning、Fuzhou、 Dingxi、Qujing、Guyua、Anshun、Ningde), measured virulence and sensitivity to azoxystrobin、inprovilicarb, results are as follows:1. All tested P. infestans strains infected inoculated potato leaves successfully. Different strains could caused significant different plaque and had different incubation period, which described virulence of P. infestans differences between geographical origin and had connection with geographical origin.2. Azoxystrobin is a kind of strobilurin fungicide, stand for QoI. The test results showed that the frequency of the P. infestans in same concentration pictured unimodal distribution. The same P. infestans group had different relative growth rate (RGR) at different azoxystrobin lipid concentrations, different P. infestans groups had different relative growth rate at same azoxystribin concentrations too. Median lethal concentration(EC50) was 0.13±0.054, while there was no significant different between this 7 populations’ EC50 value.. In the study, the sensitivity baseline of EC50 was unimodal, the range was between 0.042 to 0.42. According apparent EC50 range,20% strains was sensitive,80% was anti-resistant strains. P.infestans population differentiation based on SSR marker loci (Fs) and azoxystrobin sensitivity groups degree (QST) comparing results showed that QST was was siginificent lower than FST (p< 0.01). QST< FST illustrated that azoxystrobin played the role of negative selection in the evolution of P.infestans’ anti-azoxystrobin.3. Experiment determination of P.infestans of iprovalicarb sensitivity showed that frequency distribution curve of 140 bacteria strains was unimodal in different iprovalicarb concentrations. A considerable part of the strains grow was promoted by low iprovalicarb concentration, which illustrated P.infestans was no longer sensitive to low iprovalicarb concentrations, but 0.6 and 0.8 ug/ml iprovalicarb could inhibit P.infesntans growth significant. Comparing Fst with QST based on iprovalicarb quantitative traits, QST< FST, the result indicated that iprovilicarb played a negative role in the anti-iprovilicarb selections as same as azoxystrobin, because this choice would result in the decrease of fungicide resistance’ genetic differentiation.The results showed that there was different virulence in different origins of P.infestans. different P.infestans strains and groups had different sensitivity to azoxystrobin and iprovalicarb, and suffered different resistant degrees. The comparison between QST and FST showed that P.infestans existed high cost of living facing azoxystrobin and iprovalicab. This study recommended that farmer use these two fungicides alternately or in combination with other fungicides in production, and with rational management to extend the service life of azoxystrobin and iprovalicarb.