Survey,Identification And Biological Characteristics Determination Of Tropical Forage Fungal Diseases

Tropical forage grasses are an very important part of forage production in China and the material basis for the development of tropical animal production.In the tropical area of China,the high temperature and high humidity climate conditions is very advantageous to the growth of tropical forages,however is also favorable to the growth and reproduction of plant pathogenic microorganisms which can lead to the occurrence and prevalence of forage grass diseases,sometimes result in serious losses both in yield and quality.Forage grass diseases have become one of the major limiting factors for the development of forage production.Thus the occurrence of fungal diseases of 34 main tropical forage grasses in four provinces including Hainan,Guangxi,Guangdong and Yunnan provinces were investigated in this study from 2014 to 2015.The pathogenic fungi of the diseases were identified by morphological and molecular biological methods,and the determination of the biological characteristics and indoor toxicity measurements of the fungicide for the most important pathogens whose damage are serious on gramineous forage grasses were studied.The results are as follows:1.66 kinds of fungal diseases were found from 34 kinds of tropical grasses.The pathogens isolated from them were classified in 10 genus,including Colletotrichum sp.,Fusarium sp.,Exserohilum sp.,Nigrospora sp.,Phoma sp.,Corynespora sp.,Curvularia sp.,Cercospora sp.,Alternaria sp.and Puccinia sp..Classification of species and the harmful severity of the pathogens were also summarized.2.The results of biological characteristics of the pathogens showed that most of pathogens have a strong adaptability to the environment conditions and adapt to a wide range of temperature and the pH value.They can also use a variety of carbon and nitrogen source.? Mycelium growth temperature of Phoma herbarum ranged from 25 to 32?,the optimum temperature was 25?,and the fatal temperature was 50? for 10 minutes;the optimum pH value for the mycelium growth was 5 to 8;glucose,sucrose and mannitol were suitable for the mycelium growth,but lactose was not propitious to mycelium growth;the best nitrogen source for mycelium growth was peptone,while urea was not conducive to the growth of mycelium.? Mycelium growth temperature of Fusarium oxysporum ranged from 25 to 32?,the optimum temperature was 28 ?,and the fatal temperature was 60 ? for 10 minutes;the optimum pH value for the mycelium growth was 9 to 11;maltose was the best carbon source for the mycelium growth,but lactose was not propitious to mycelium growth;the best nitrogen source for mycelium growth was peptone,while urea and asparagine were not conducive to the growth of mycelium.?Mycelium growth temperature of Nigrospora sphaerica ranged from 20 to 28 ?,the optimum temperature was 25?,and the fatal temperature was 50 ? for 10 minutes;the optimum pH value for the mycelium growth was 5 to 8;maltose and sucrose were the best carbon source for the mycelium growth,but lactose could not be used as the carbon source for mycelium growth;the best nitrogen source for mycelium growth were peptone or beef extract,while urea,glycine and asparagine were not conducive to the growth of mycelium.?Mycelium growth temperature of Curvularia sp.ranged from 25 to 32?,the optimum temperature was 28 to 32 ?,and the fatal temperature was 60 ? for 10 minutes;the optimum pH value for the mycelium growth was 6-8;glucose,sucrose and mannitol were the best carbon source for the mycelium growth,but lactose was not propitious to mycelium growth;the best nitrogen source for mycelium growth were peptone or beef extract,while urea was not conducive to the growth of mycelium.? Mycelium growth temperature of Exserohilum rostratum ranged from 25 to 32?,the optimum temperature was 28 to 32?,and the fatal temperature was 55? for 10 minutes;the optimum pH value for the mycelium growth was 6 to 9;most of the carbon source were suitable for the mycelium growth,but mannitol was not propitious to mycelium growth;the best nitrogen source for mycelium growth was NaNO3,while urea was not conducive to the growth of mycelium.?Mycelium growth temperature of Alternaria sp.ranged from 28 to 32?,the optimum temperature was 32?,and the fatal temperature was 55? for 10 minutes;the optimum pH value for the mycelium growth was 6 to 9;glucose,sucrose and maltose were the best carbon source for the mycelium growth,but fructose was not propitious to mycelium growth;situations of mycelium growth were different with different nitrogen source,the best nitrogen source for mycelium growth were beef extract and NaNO3,while peptone,asparagine and glycine were not conducive to the growth of mycelium,urea couldn't be used as the nitrogen source for mycelium growth.3.The indoor toxicity measurement of 11 tested fungicides against the six kinds of pathogenic fungi results showed that all fungicides could inhibit pathogen efficiently except iprodione which could only inhibit Alternaria sp.weakly;tebuconazole could inhibit all the six kinds of pathogenic fungi strongly and all the pathogens were sensitive to tebuconazole;myclobutanil could strongly inhibit the other 5 pathogenic funguses except Nigrospora sphaerica;carbendazim had weak toxicity to Exserohilum rostratum and Exserohilum rostratum was not sensitive to carbendazim,but it could strongly inhibit the other 5 pathogenic funguses.