Biological Activity Of A Novel Fungicide Pyrametostrobin To Sphaerotheca Fuliginea On Cucumber And Its Resistance Risk Assessment

Pyrametostrobin, a candidate strobilurin fungicide developed by Shenyang Research Institute of Chemical Industry, has not commercialized yet. It was reported that, pyrametostrobin can give good control of cucumber downy mildew, wheat powdery mildew and cucumber powdery mildew with as long as 14-d efficacy duration, it can be transported inside wheat plants. In this study, the systemic activity of pyrametostrobin inside cucumber plants, action mode of pyrametostrobin against Sphaerotheca fuliginea and efficacy of pyrametostrobin in controlling Sphaerotheca fuliginea in greenhouses were studied, and the risk of resistance to pyrametostrobin in Sphaerotheca fuliginea was assessed. The major result were reviewed as followed.1. Results in the assay on potted cucumber seedling and adult palnts showed that, pyrametostrobin has good preventive, curative and eradicative activity against Sphaerotheca fuliginea, also its efficacy lasts longer than azoxystrobin in controlling cucumber powdery mildew (over 75 percent 14d after spray at 200μg a.i./mL of pyrametostrobin 20EC on cucumber cotyledons), besides, its preferable properties of uptake and transmission are mainly reflected by lateral translocation, translaminar translocation and acropetal traslocation inside cucumber plants, but its sysplastic movement is poor .2. Pyrametostrobin 20EC gives good control of powdery mildew both on potted cucumber plants and on the cucumber plants growing in the greenhouses, and is safe to cucumber's growth and reproduction. In the trial on potted cucumber plants, controlling efficacy of 70.91%～87.75% is given by spray of pyrametostrobin 20EC at the rate of 50～150 g a.i./hm2, and controlling efficacy of over 80% is accquired 7 days after 4 sprays of pyrametostrobin 20EC by 50～150 g a.i/hm2 at the interval of 7～10 d in the field trial on cucumber plants.3. Sensitivity to pyrametostrobin of 45 isolates of Sphaerotheca fuliginea from cucumber greenhouses ( no strobilurin fungicides treeated) of Hebei, Shandong and Shenyang in potted cucumber seedlings test ranges from 0.34μg a.i./mL to 25.82μg a.i./mL, with average 12.24±0.07μg a.i./mL. The frequency distribution of the EC50 values for the 45 isolates is a unimodal curve. It suggests that there is no resistant subpopulation among the 45 isolates. Thus, these sensitivity data also could be used as a baseline for monitoring the shift of sensitivity in Sphaerotheca fuliginea population to pyrametostrobin. 4. It was found that the isolates sensitive, weakly rensistant, moderately resistant and highly reisitant to pyrametostrobin account for 43.13%, 41.18%, 14.71% and 0.98%, respectively, among the 102 isolates of Sphaerotheca fuliginea collected from the greenhouses or plastic tunnels (strobilurin fungicides, such as azoxystrobin, kresoxim-methyl, pyraclostrobin were used to some extents, but pyrametostrobin was not used before) of Hebei, Shandong and Shenyang during 2007～2009.5. 5 pyrametostrobin-resistant mutants of Sphaerotheca fuliginea are accquired by 2 parent isolates sensitive to pyrametostrobin in 10 Ultroviolet mutagensis tests and subcultures on cucumber coletydons treated by pyramentostrobin at EC90, the frequency of mutants resistant to pyrametostrobin is 2.0×10-7. The 5 pyrametostrobin-resistant mutants are 18.45～77.79 times less sensitive than their parent isolates. No positively correlated cross resistance exists between pyrametostrobin and the DMI fungicides, such as myclobutanil, tebuconazole and difenoconazole, but the positively correlated cross resistance exists between pyrametostrobin and azoxystrobin. 2 pyrametostrobin-resistant mutants are less aggressive in in fection than their parent isolate, 3 pyrametostrobin-resistant mutant keep their pathogenicity like their parent isolate. In absence of fungicides, 5 pyrametostrobin-resistant mutants are more competitive than their parent isolates and remain resistant to pyrametostrobin after 10 subcultures on cucumber seedlings untreated with fungicides.6. Based on the sensitivity to pyramentostrobin in isolates of Sphaerotheca fuliginea detected before the practical usage of pyrametostrobin, variation of sensitivity to pyrametostrobin under the condition of lab, and the biological characteristics of mutants resistant to pyramentostrobin accquired bu UV irritation and fungicide selection, a high risk of reisistance to the candidate strobilurin fungicide pyrametostrobin is supposed to exists in...