Abstract:Rice blast caused by Magnaporthe grisea is an important rice disease.It causes serious damage to both yield and grain quality.Early detection and monitoring of the pathogen is crucial for disease control.After inoculating the pathogen on the susceptible cultivar Menggu and the widely planted cultivar Hexi 39,the symptom was observed and the total DNA of the diseased rice tissues was purified and detected by real time PCR.It was showed that the little necrotic spot occurred at 72 hours after inoculation on Mengu and Hexi 39.The typical symptom was observed at 168 hours after inoculation on Menggu rice,but at 190 hours after inoculation on Hexi 39.The amount of the pathogen in both rice cultivars increased and reached the highest level at 48 hours after inoculation and decreased after 72 hours.There was some difference between susceptible and widely planted cultivar in pathogen DNA amount.Pathogen DNA in both rice cultivars could be detected firstly at 12 hours after inoculation,with 7.2×103 copies in Menggu and 4.9×103 copies in Hexi 39.The results proved that the real time PCR technique could be used to detect M.grisea at early stage of infection.