Study On Alisma White Spot Caused By Ramularia Alismatis

Alisma white spot is considered as widespread destructive disease of Alisma plantago-aquatica in Sichuan in recent years. On this paper, first and systematically studied on biological characteristics, infection process and conditions of the pathogen, interior pharmaceutical screening, source of primary infection.The results are as follows:1.Biological characteristics of the R.alismatisResults showed that the temperature and pH value rage for mycelium growth and sporulation was 10～35℃,pH3～11.with the optimum at 28℃,pH 7,8. The carbon of diose could be effectively used by the pathogen,and the most suitable nitrogen sources was inorganic nitrates. Light on the pathogen growth and sporulation have no significant effect. It could grow and sporulate well on host juice medium.Conid were able to germinate in 10～35℃,pH3～10 and humidity of RH≥93%,the maximum rate of spore germination was in 28℃, pH7and water. In suitable condition, germination of conidia started within 1 hours and the percentage of germination reached above 90 % after 6 hours.The lethal temperature of pathogen conidia was 56℃.2.Infection process and conditions of the R. alismatisAfter inoculation,conidia of R. alismatis began to germinate within 2 hours.The pathogen was able to penetrate host through hypha.After the mycelium penetrated leaf cells,they could continue through the various cells.The best combination of temperature and time moisture as follows, temperature was 20～25℃, time moisture was 36～48h. The infection of Alisma plantago-aquatica by R. alismatis could be occured at 10 to 30℃, and the optimum temperature was 25℃. At 20℃and 25℃, the incubation period was 36 and 24 hour. The optimum wetness period rage for infecting leaf of Alisma plantago-aquatica by the pathogen was 36to48 hours, with the incubation period of 4 days and 3 days.3.The fungicides screening of laboratory and pot- plantsThe five fungicides were tested in laboratory to determine the effect on the mycelical growth and germination of conidia. The results showed that flusilazole inhibited the mycelial growth, but did not inhibit the germination of conidia. Copper sulfate inhibited the germination of conidia but did not inhibit the mycelial growth. Diniconazole and thiophonate-methyl were good fungicides on the inhibition of the mycelial growth and the germination of conidia. Mancozeb was the worse inhibition on spore germination and mycelial growthIn effective treatment of pot-plant ,choice the effective fungicides of inhibition on the mycelial growth and the germination of conidia,such as diniconazole,thiophonate-methyl,flusilazole,Copper sulfate.4.Study on source of primary infectionThe primary infection source of disease for carriers of the seeds, leaving the diseased leaves of trees and in the winter spores of disease wrack. Old leaves in the lower part of the original plants occurred, conidia by air currents, rain splash, continuously growing in cause further infection.