Evaluation of the pathogenicity of several Fusarium species isolated from rice seed in laboratory and tracing of seeds transmission of rice bakanae disease

The fungal infection of rice seeds with Fusarium species, is a major problem for farmers in Iran and the world. Determining the pathogenicity of Fusarium species in rice fields might be helpful in development of strategies for management of the relevant diseases. In this research, the pathogenicity of forty seven isolates of Fusarium belonged to Fusarium fujikuroi, F. incarnatum, F.prolifratum, F. thapsinum, F. andyazi, F. oxysporum, F. graminearum and F. merismides obtained from rice seeds in Mazandaran, Guilan, Golestan, Khuzestan and Fars provinces were investigated. The pathogenicity test was performed by rice seed dressing method using spore suspension as inoculum in invitro, nursery and the paddy field. Percentage of healthy, unhealthy and dead seedlings recorded and percentage of disease incidence was determined. Also, the transmission rate of bakanae disease by seeds from the laboratory to the nursery and the paddy was determined. The results showed that all isolates were pathogenic on rice seedling and reduced germination percentage compared to control, and only one isolate of F. merismoides was non-pathogenic. F. fujikuroi isolates had the highest disease incidence rate. In addition, there was a significant difference among Fusarium species, isolates of each species and the five provinces in terms of disease incidence. Based on the disease incidence, 2.1% of the isolates placed in the non-pathogenic group, 25.6% of the isolates were in the moderate pathogenic, 34.1% of the isolates were pathogenic and 38.2% considered as severe pathogenic group. In this research, the rate of disease transmission from contaminated seeds to the nursery was 38%., but after seed disinfection, with fungicide, the transmission rate of the disease dropped from 38% to 3.6%. These results show the importance of rice seed treatment with fungicides for the control of bakanae disease.