Monitoring Of Resistance Of Rhizoctonia Solani To Thifuramide,Screening Of Resistance Gremplasm And Chemical Control Of Rice Sheath Blight In Heilongjiang

The incidence of rice sheath blight disease,which could cause substantial losses in rice production and quality is increasing by years in Heilongjiang.In fact,the combination of chemical control and resistant cultivars is the prevalent control measure.The lack of diversiy of fungicides,resulting in the declination of control efficiency.Therefore,it is necessary to find out efficient and low toxic fungicides or resistant cultivars.In this paper,the 120 samples were collected from 6 main rice growing areas in Heilongjiang Province,and the resistance of 99 strains of Rhizoctonia solani to hiamethoxam had been analyzed.Three inoculation methods of rice sheath blight were compared,Rhizoctonia solani strain FZ008,which was highly pathogenic has identified the resistance of 42main rice cultivars from Heilongjiang by peloton method.The 13 fungicides and the synergistic mixture of fungicides were tested by hypha growth rate method of Rhizoctonia solani and effective fungicides were selected to control rice sheath blight in the field.The main results are as follows.（1）The 120 samples were collected from 6 main rice growing areas in Heilongjiang Province,and 99 strains of Rhizoctonia solani were isolated by tissue separation method.（2）There were some differences in the sensitivity of Rhizoctonia solani to thifuramide in 6main rice growing areas in Heilongjiang Province.The average EC₅₀ of 34 strains in Harbin which had the most sensitivity to thifuramide was 196.9341 g/m L.The average EC₅₀ of 15 strains in Shuangyashan which showed the weakest sensitivity to thifuramide was 364.7323 g/m L.There was a significant difference of sensitivity of Rhizoctonia solani strains from two regions was analyzed by SPSS.There was no significant difference between Suihua,Mudanjiang,Qitaihe and Jiamusi.The sensitivity baseline of Rhizoctonia solani EC₅₀ was 253.8854 g/m L in Heilongjiang.According to the calculation of the overall resistance level,the resistance level was between 0.1567～3.3292,which were all less than 5.The study showed that the resistance level of Rhizoctonia solani in Heilongjiang was relatively low.Therefore,it was shown that Rhizoctonia solani was highly sensitive to thifuramide in most areas of Heilongjiang Province.But Qitaihe has certain resistance risks and need to be monitored continally.（3）Among the three methods,the peloton method,which caused severe disease had the best inoculation effect,short onset time and long spot length.The toothpick method caused moderate disease,which was easy to damage part of plant tissues and reduced disease resistance.The sclerotium method which aquired a complex grinding of the sclerotium caused the least degree of disease.Because this method need to take more time and energy.The sclerotium method was the least ideal method of inoculation compared with the former two methods.5 resistant,12 moderate resistant,19 susceptible and 6 sensitive rice cultivars were selected from 42 rice cultivars by the peloton method successfully.（4）The inhibitory effect and synergic of 13 different fungicides against Rhizoctonia solani were conducted by toxicity assay.Among them,the inhibitory effect of 75%oxime bacterium·pentazol WG was the best,with EC₅₀ of 0.0101 g/m L.20%Prothiazole SC,125g/m L fluconazole SC,24%thifuramide SC and 50%tebuconazole EC had a certain inhibitory effect on rice sheath blight because their EC₅₀were all less than 10 g/m L.Both the co-toxicity coefficient of prochloraz and epoxiconazole were greater than 100 at the ratios of 5,indicating additive or synergistic effects.At the ratio 4:1 of Prochloraz and epoxiconazole,the EC₅₀ was 10.0814μg/m L and the co-toxicity coefficient was 106.48,which performe a synergistic effect.At the ratio 1:2 of Prochloraz and epoxiconazole,the EC₅₀ was 2.9917μg/m L and the co-toxicity coefficient was 213.38.Synergistic effect was the strongest.Therefore,prochloraz and fluconazole were mixed at a mass ratio of 1:2 is reconmmended in field.（5）The experiment of spraying 5 fungicides in the field showed that the compound 30%prochloraz and fluconazole ME（1:2）had the best control effect of 89.69%.The medicine is highly safe to rice and an ideal agent for field control of rice sheath blight.The rice sheath blight be effectively controlled by 75%oxime bacterium·pentazol WG,50%hexazolol EC and 24%thifuramide SC,which were all higher than 80%.It is recommended to use alternately in the field.However,the effect was not good of 20%jinggangmycin AS and the control effect was only 49.85%.