| Rice sheath blight caused by Rhizoctonia solani has become one of the major diseases of rice in the world,especially after the popularization of high yield varieties,which seriously affects the high quality and high yield of rice.The host of Rhizoctonia solani are very wide and the genetic diversity of Rhizoctonia solani is very serious.So far,no rice varieties with high resistance or complete immunity to rice sheath blight have been found.Nowadays,chemical control is the most effective way to control rice sheath blight.In this study,94 strains of Rhizoctonia solani isolated from Anhui Province were used as experimental strains.The sensitivity of Rhizoctonia solani isolated from Anhui Province to several common fungicides was determined by mycelial growth rate method,and the sensitivity baseline was established.The control effect of pyraclostrobin on rice sheath blight and its effect on the formation of infection structure of rice sheath blight were studied by the detached-leaf inoculation method.The differences of gene expression in the process of interaction between rice and pathogen after spraying pyraclostrobin were also studied by q RT-PCR.The main results are as follows:1.The sensitivity baseline of Rhizoctonia solani to four fungicides was established of Anhui Province.The sensitivity of 94 strains of Rhizoctonia solani to Jinggangmycin,thifluzamide,prothioconazole and pyraclostrobin fungicide was determined by mycelial growth rate method.The baseline of sensitivity of Rhizoctonia solani to four fungicides was 0.8348 μg / ml,0.0901 μg / ml,0.4323 μg / ml and 0.2422 μg / ml,respectively.From the point of view of sensitivity baseline,the sensitivity baseline of three kinds of fungicides were all at a low level,including thifluzamide,prothioconazole and pyraclostrobin.There was not significantly correlation between the sensitivity of all isolates to Jinggangmycin,thifluzamide and prothioconazole and the geographical origin of the strain.There was significantly correlation between the isolates geographical origin and their sensitivities to pyraclostrobin fungicides.And there was not significantly correlation among the four fungicides.2.The effects of pyrazoxystrobin on sclerotia formation and germination of Rhizoctonia solani were studied.Pyraclostrobin had a strong inhibitory effect on the formation of sclerotia of Rhizoctonia solani,and the number and dry weight of sclerotia decreased with the increase of the concentration of pyraclostrobin.When the concentration of pyraclostrobin was 0.01,0.1,1 and 2.5 μg / ml,the sclerotia formation rates was88.66%,53.19%,22.70% and 12.77% of the control,respectively.However,pyraclostrobin did not inhibit the germination of sclerotia.In the treatment of different concentrations of pyraclostrobin,the inhibition rate of sclerotia germination was 100%,but only inhibited the growth of mycelium after sclerotia germination.3.The action mode of pyrazoxystrobin on Rhizoctonia solani was clarified.The effect of pyrazoxystrobin on rice sheath blight was studied by in vitro leaf inoculation.The results showed that the concentration of fungicide was 145.8% μg/m L.The results showed that the treatment and protection effects of pyrazoxystrobin on rice sheath blight were49.54% and 66.98% respectively,indicating that pyrazoxystrobin had a certain control effect on rice sheath blight,and the protection effect was better than the treatment effect.After the leaves were stained with tissue transparency,it was found that the application of pyraclostrobin in different concentrations could significantly inhibit the spread of the hyphae of Rhizoctonia solani on the leaves of rice and the formation of the infection structure of the hyphae by optical microscope.4.The effects of pyraclostrobin on defense gene expression in host pathogen interaction were discussed.Rice leaves were sprayed with pyraclostrobin for 24 hours,then inoculated with Rhizoctonia solani.The genome of rice leaves at different time after inoculation was analyzed by q RT-PCR.The results showed that: PR1 a,PR1b,PR5,PAL and POX genes could be induced up-regulated in CK inoculation treatment,and the expression levels of the five genes reached the peak at 24 h after inoculation,and the expression levels of the five genes were significantly higher than CK-non inoculation treatment and chemical + inoculation treatment at 24 h and 48 h after inoculation,indicating that Rhizoctonia solani had successfully infected rice.At the same time,there was no significant difference in the expression of the five genes between CK-uninoculated treatment and chemical + inoculated treatment.The results showed that the spraying of pyraclostrobin on rice leaves could protect the leaves from the infection of rice sheath blight and had a good protective effect. |
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