ARS | Publication request: UNIFORM INFECTION AND DETERMINATION OF HOST RESPONSES TO MAGNAPORTHE GRISEAON DETACHED RICE LEAVES USING SPOT INOCULATION

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2002
Publication Date: N/A

Interpretive Summary: Rice blast disease caused by the fungal pathogen Magnaporthe grisea is one of the most devastating agricultural diseases worldwide. Rice blast disease is spread by fungal spores that are deposited onto the plant by drizzle deposition, dew, etc. Immediately after attaching to the rice leaf, fungal spores begin to germinate and infect the leaf. However, only a few infection sites can be obtained in the laboratory even after extensive spraying with conidial spore suspensions. Therefore, we developed a spot inoculation method to produce a more uniform infection on detached rice leaves with various fungal isolates and to examine the pathogenicity of fungal isolates on detached rice leaves in the laboratory. Fungal spores were suspended in 0.25% gelatin and a series of dilutions of Tween-20 was added to the suspension. Standard infection assays in the greenhouse indicated no side effects of Tween-20 or gelatin to rice blast development. Microscopic examination was used to distinguish between cell death due to blast infection and cell death due to hypersensitive response. Several known fungal isolates were used to verify this method. Successful application of this infection assay will help to identify novel sources of rice blast resistance and accelerate breeding programs searching for a broad-spectrum rice blast resistance.

Technical Abstract: A spot inoculation method to produce more uniform infection on detached rice leaves by Magnaporthe grisea spores was developed. Spores were suspended in 0.25% gelatin and serially diluted with Tween-20. Standard pathogenicity assays in the greenhouse indicated no deleterious effects from Tween-20 or gelatin to rice blast development. Microscopic examination was used to distinguish between cell death due to blast infection and cell death due to hypersensitive response. The spot inoculation method was evaluated using three well-characterized M. grisea isolates and results were confirmed with standard pathogenicity assays in the greenhouse. Using the spot inoculation method, disease reactions of four representative isolates of M. grisea with differential rice varieties were critically evaluated. Successful application of this assay will help to identify novel sources of rice blast resistance and evaluation of virulence of M. grisea to aid in breeding a broad-spectrum of rice blast resistance.