Determination of host responses to Magnaporthe grisea on detached rice leaves using a spot inoculation method

Through the use of standard assays, where conidia of the pathogen Magnaporthe grisea are sprayed onto rice, it is impossible to determine the exact number of conidia in any given area and to predict the locations of disease lesions in the rice blast system. To develop a localized, quantitative inoculation of M. grisea, a novel spot method was investigated. Serially diluted Tween 20 was added to M. grisea conidial suspensions in 0.25% (wt/vol) gelatin to promote adherence of conidia on detached rice leaves. Standard assays indicated no deleterious effects of Tween 20 to rice blast development and 0.02% (vol/vol) Tween 20 was necessary for promoting adherence of spore suspensions to the detached leaves. The spot method was evaluated using three well -characterized races of M. grisea and confirmed with standard assays. Disease reactions of rice to four predominant races of M. grisea were tested concurrently using the spot method and standard assays. Successful application of this assay will help identify novel sources of rice blast resistance and evaluate virulence of M. grisea to aid in breeding resistance to rice blast.