Effect Of Non-fungicide Pesticides On Growth And Pathogenicity Of Rhizoctonia Cerealis Vander Hoeven

The effects of nine herbicides and 14 insecticides on mycelia growth, sclerotia forming, pathogenicity and the activities of three cell wall-degrading enzymes (pectinase, cellulase, hemicellulase) in vitro of Rhizoctonia cerealis were studied.The results indicated that all 23 pesticides tested had inhibition effects on the mycelia growth with defferent degrees, and the inhibition increased with concentration, but with pesticides. At the concentration of 50mg/L, the inhibitions of fenoxaprop, cyflithrin, deilamethrin, acetaniprid, alphamethrin, cyflithrinand pushiya were higher than that of jingangmycin( 86.28%); whereas tribenuron, dicamba, monocrotophos and omethoate were of little inhibition at the same concentration; some pesticides ,for example pushiya and phoxim ,could also affect the colony shape and color of R. cerealis.Toxicity test showed that the EC50 varied with pesticides. The EC50 of fenoxaprop, deilamethrin, acetaniprid, cyflithrin and pushiya was lower than l0mg/L. At the recommended field rate, the theory inhibition of fenoxaprop, butachlor, mailening, phoxim and chlorpyrifos even exceeded that of jinggangmycin (88.6%) .Microscopic observation indicated that the shape of treated mycelia deformed in varying degrees, including unusual constriction, intumescent, contortion, branching frequently, more intertwining and deformation. Microscopic measurment indicated that the intervals of mycelia branches were shortened significantly when treated with fenoxaprop, cyflithrin, deilamethrin and so on. However the intervals became slight longer when treated with omethoate and trichlorphon.The numbers of sclerotia decreased significantly when treated with pesticides at the concentration of 50mg/L.Pectinase, cellulase and hemicellulase were also produced in vitro from R.cerealis after treatment, but their activities were affected with various degrees. Compared with the control, majority treatments could promote the activity of hemicellulase, and the effect on the activity of pectinase was less than that of other two enzymes.Inoculating experiment with potted plants showed that fenoxaprop, cyflithrin, cyflithrin, pushiyacould inhibited the pathogenicity of R.cerealis at the concentration of 50mg/L, and the inhibition reached 40% or more. No effects wre found with dicofol andmonocrotophos, whereas omethoate and mailening enhanced the pathogenicity slightly.When subcultured the colonies formed on treated medium with concentration of 50mg/L , the effects on mycelia growth sclerotia forming and pathogenicity of R. cerealis relented.Periodic sampling observation indicated that,during the invading of mycelia into boot cellulars , the time of invading was delayed in some treatments when compared with control, and they could not further more penetrated and expanded vicinity cellulars after invading.Insertion method was applied first time for inoculating R. cerealis , and compared with mycelia plugs clasp stem method. The results showed that: the disease appeared faster and more uniformly with insertion method. With its convenient to operate, insertion method is suitable for R. cerealis inoculating, especially for seedling inoculation.