| Corn Brown Spot is a common disease of maize in agricultural production, which is caused by the infection of Physoderma maydis and occurring in corn-producing areas all over the country, especially in some regions ,such as Shandong, Hebei, Henan and Jiangsu.Owing to the extension of straw returning technology and extensive planting of susceptible variety, the disease is becoming more and more serious in recent years.At present, there is little study about the disease both at home and abroad. Control effects of two fungicides to the disease was analyzed, in the term of influences about the two fungicides to spatial distribution of the disease, chlorophyll content and net photosynthetic rate of the ear leaf, root activity and the yield.Occurence of disease in different leaves and the effect of which on chlorophyll content,photosythesis character, key enzymes of carbon assimilation and protective enzymes and root activity, providing theoretical basis for quick survey of the disease,forcast of yield loss and scientific prevention.1. The spore germination method was used to determine the toxicities of tebuconazole, mancozeb and hymexazol to Physoderma maydis and field trials were conducted to ascertain the effects of 80% mancozeb WP, 430g/L tebuconazole SC and 70% hymexazol WP on pathogenicities and control efficiencies when spray applied at 8-leaf stage. The results showed that mancozeb exhibited great inhibition to the germination of the resting sporangia, with the values of EC50 66.71mg/L.However,tebuconazole had little effect. The pathogenicity was effectively lowered by the treatments of mancozeb and tebuconazole,which suppressed the occurrence of corn brown spot below the ear leaf and increased the content of chlorophyll,net photosynthetic and root activity,the control effect of which were88.99% and 94.23%,and had the the highest yield, that increased by 31.48% and 33.21% compared with CK.2. Field trials of quantitative artificial inoculation about 2 years were conducted to ascertain the effect of spatial distribution of brown spot in maize of 10-leaf stage, silking stage and filling stage, and the effect of which on growth vigor, chlorophyll content and photosynthetic characteristic of leaves at different positions, root activity and grain yield. The results showed that brown spot could extend to 8 leaf and 12 leaf after 10-leaf stage and silking stage, the disease grades of 5～6-leaf and 8～9-leaf in which were maximum. The growth vigor, photosynthetic characteristic, chlorophyll content , root activity and grain yield of the plants, the maximum disease grade of the leaves in which was 1 to 2, were not significantly different with the healthy, while they were lower than healthy plants when disease grade was 5; net photosynthetics and chlorophyll contents of 4～6-leaf about plants in 10-leaf stage and 8～10-leaf about plants in silking stage and filling stage were higher than the healthy, and increased as leaf position elevate, while7～9-leaf and 11～13-leaf were opposite, when disease grade was 3 to 4;the growth vigor, root activity and yield components, such as grainweight per ear, mass per 1000, ear length and kernel, were significantly lower than the healthy when disease grade was 3 to 5.3. Field trials of quantitative artificial inoculation about 2 years were conducted to ascertain the spatial distribution of brown spot in maize of 10-leaf stage, silking stage and filling stage, and the effect of which on key enzymes of carbon assimilation and protective enzymes of leaves at different positions. Results showed that while the maximum disease grade of the leaves was 5, brown spot in maize of 10-leaf stage could extend to 8 leaf, the disease grade of 6 leaf was the maximum, SOD, POD, CAT, PEPase, RUBPase activity of which were reduced by 17.28%, 32.17%, 18.45%, 33.07% and 49.84%,while MDA content was increased by 94.54%; brown spot in maize of silking stage could extend to 12 leaf, the disease grade of 8 leaf was the maximum, activities of the five enzymes were reduced by 40.70%, 65.89%,36.18%, 40.74% and 51.97%,while MDA content was increased by 164.20%; brown spot in maize of filling stage could extend to 12 leaf, the disease grade of 8 leaf was the maximum, activities of the five enzymes were reduced by 33.39%, 44.64%, 43.08%, 35.88% and 58.53%,while MDA content was increased by 107.75%.
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