| The purpose of this paper is to evaluate the risk of resistance in Rhizoctonia cerealis to fungicides. In the study the resistance selection of Rhizoctonia cerealis to tebuconazole,validamycin,propiconazole,difenoconazle,fludioxoni and also the cross-resistance of each resistant strain were carried out; Then the difference on some biological characters such as the growth rate and dry weight of the mycelium,pathogenicity and the capacity of producing sclerotia were studied; The inhibition of PH and irradiate on sensitive and resistant strains was also studied;At last the resistance mechanism was studied. The results could be summaried as follows:1.The studies of resistance selection showed the resistance of Rhizoctonia cerealis had reached 33.37 fold to tebuconazole, 49.24 fold to validamycin, 33.26 fold to propiconazole, 39.96 fold to difenoconazle and 20.04 fold to fludioxoni after treated 36-time in the laboratory. After 8 successive incubation on the free-fungicide PDA, the resistant strains could maintain their resistance.2.The cross-resistance of each resistant strain to fungicides was as follows: The R-validamycin strain had high positive resistance to propiconazole and difenoconazle,the resistance to propiconazole and difenoconazle were 10.95 fold and 48.58 fold respectively, while had little influence on the resistance to tebuconazole and fludioxoni,the resistance were 2.55 fold and 1.78 fold respectively; The R-tebuconazole strain had high positive resistance to triadimefon,propiconazole,validamycin,thiram and difenoconazole, the resistance were 31.2 fold,22.8 fold,16.9 fold,15.8 foldand 15.5 fold respectively, while the resistance to fludioxoni was only 1.6 fold; The resistance of R- propiconazole to tebuconazole,validamycin,difenoconazole were 11.83 fold,23.26 fold,21.38 fold respectively, while had negative resistance to fludioxoni, the resistance was 0.316 fold; The resistance of R- difenoconazole strain to propiconazole,tebuconazole,vacidamycin were 56.45 fold,25.48 fold and 46.10 fold respectively, the resistance to fludioxoni was 0.75 fold, also had negative resistance; The resistance of R- fludioxoni strain to tebuconazole and validamycin were 3.42 fold and 2.87 fold, had negative resistance to propiconazole and difenoconazole, the resistance were 0.65 fold and 0.76 fold respectively.3.In biological characters, the sensitive strain had higher growth rate and dry weight than resistant strains; The resistant strains had higher pathogenicity and produced more sclerote than sensitive strain. The sensitive and resistant strains showed little differences in inhibition of pH and irradiate.4.The sensitive strain was more sensitive than resistant strains in low osmotice pressure. But when the osmotice pressure was high ,the resistant strains were more sensitive than strains, the result showed that the function of the cell membrane of resistant strains were changed.5.Ergosterol yields of R-tebuconazole strain was higher than that of sensitive strain, and the inhibition rate of tebuconazole to sensitive strain was higher than to resistant strain. At concentration of 0.5 ug/ml, the inhibition rate to sensitive strain was 41.94%, while to resistant strain was only 20.37%; At concentration 0.1 ug/ml, the inhibition rate to sensitive strain was 32.05%, while to resisant strain was only 8.43%.6.The esterase isoenzyme zymogram showed that the sensitive strain and R-tebuconazole strain all have five obvious enzyme bands. The difference of the color of the band whose Rf was 0.56 shows that the resistance of Rhizoctonia cerealis to tebuconazole was concerned with the changes of esterase.7.After inoculated the sensitive and resistant strains respectively, the activities of peroxidase(POD) and polyphenol oxidase(PPO) were all changed ; after inoculated the sensitive strain, the activities of POD and PPO of wheat were increased more than that inoculated resistant strains. The result showed that the sensitive strains had higher pathogenicity to wheat seedli...
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