| In recent years,maize white spot disease results in serious loses to wheat crops in Yunnan Province.The typical symptoms range from large area of maize leaf dead in the milk-ripe stage,leading to reduction in maize yield.Currently,there are limited studies on this disease in China and there are no reports on this emerging disease.In this study,the causative agent of maize white spot disease were identified,as well as the biological characteristics of the pathogenic fungi,chemical control,and resistance of different maize varieties to maize white spot disease were investigated,aiming to lay a theoretical foundation for the diagnosis,identification,and field control of maize white spot disease.The main findings of the study are as follows:1.The occurrence of maize white spot caused by Epicoccum latusicollum has been reported for the first time in China.In 2021,maize leaves with typical symptoms were collected from Aziying Township,Kunming City,Yunnan Province,and Jiulong Township,Luoping County,Qujing City,Yunnan Province,for the separation and purification of diseased spot tissue.Strains number five and nine were isolated from diseased leaves from two sampling sites,respectively.The pathogenic fungi were identified by morphological characteristics and molecular biology methods and verified by Koch’s postulates.Finally,we identified strains WS-1 and WS-191 as the pathogenic fungi of white spot disease.According to the results of morphological observation and phylogenetic tree analysis based on ITS,rpb2,tub2 and LSU gene sequences,we suggested that maize white spot in Yunnan Province is a new emerging disease reported for the first time in our country.The pathogen was finally identified as Epicoccum latusicollum.2.Biological characteristics of maize white spot pathogen showed that the mycelium grow faster on CAM medium.The pathogen mycelia grow in the temperature range of 5～35℃ The germination rate of pathogen spores reached 99.7% at 28℃,which was the optimum germination temperature.The germination rate of pathogen spores could reach 91.16% with the 100% relative humidity.Mycelia of pathogenic fungi can grow in the range of pH value4-11,and the best growth was recorded when the pH value is 5.The lethal condition of pathogenic mycelia was 50℃,at10 min.The lethal condition of pathogen conidia was 55℃ tested under 10 min.3.In addition,we tested the mycelium inhibition method to further screen the chemical agents in vitro.All the 7 fungicides tested had inhibitory effects on the growth of pathogenic fungal mycelium,but there were differences in the inhibitory effects among different agents.The next were 10% phenoxymethazole,25% pyrimethanil,and 18.7% propyrimethanil,80%mancozeb and 75% chlorothalonil.The control effect of fungicides showed that 18.7%propyrioxil emulsion and 25% phenylpropyl emulsion had the best control effect on maize white spot disease,which reached 69.43±1.18 % and 71.19±1.39%,respectively.4.The resistance of 622 new maize varieties tested in Southwest China in 2021 was investigated by using the method of natural disease in the field.The results showed that 4,184,216,186 and 32 maize varieties were highly resistant,resistant,moderately resistant,susceptible and highly susceptible to white spot of maize,respectively.They accounted for0.64%,29.58%,34.73%,29.90% and 5.14% of the total tested varieties.The method of artificial injection of natural infection was used to evaluate the resistance of 42 maize varieties.The resistant varieties tested were mainly medium resistant and resistant,and the susceptible varieties in the susceptible were mainly susceptible.In total,16 varieties showed moderate resistance,accounting for 38.10% of the total maize materials.Moreover,24 varieties showed resistance to disease,accounting for 57.14% of the total maize materials.Finally,4.76% of the total maize cultiavr were recorded with high susceptibility and high resistance. |
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