ARS | Publication request: Host active defense responses occur within 24 hours after pathogen inoculation in the rice blast system

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 10, 2007
Publication Date: October 8, 2007
Citation: Wang Zhonghua, Jia, Y., Lin, H., Valent, B., Rutger, J.N. 2007. Host active defense responses occur within 24 hours after pathogen inoculation in the rice blast system. 4th Intl. Rice Blast Conference, October 8-14, 2007, Changsha, China. p. 37.

Technical Abstract: Phenotypic, cytological and molecular responses of rice to the fungus M. grisea were studied using rice cultivars and lesion mimic plants. Cultivar Katy was susceptible to several virulent Magnaporthe grisea isolates. A Sekiguchi-like lesion mimic mutant of Katy (LmmKaty) has shown enhanced resistance to these isolates. Lesion mimic phenotype of LmmKaty was rapidly induced by virulent M. grisea isolates or by avirulent isolates only at high levels of inoculum. Autofluorescence (a sign of an active defense response) was visible under ultraviolet light 24 h after localized inoculation in the incompatible interaction, whereas autofluorescence was not evident in the compatible interaction. Autofluorescence was also observed in LmmKaty 20 h after pathogen inoculation, thus indicating that rapid cell death is a mechanism of LmmKaty to restrict pathogen invasion. Rapid accumulation of defense related (DR) gene transcripts, phenylalanine ammonia lyase and ß-glucanase, was observed beginning at 6 h and was obvious at 16 h and 24 h in an incompatible interaction. Rapid transcript accumulation of PR-1 and chitinase had occurred by 24 h after inoculation in an incompatible interaction. Accumulation of these transcripts was delayed in a compatible interaction. These results indicate that host active defense responses occur 24 h after pathogen inoculation and that LmmKaty exhibits enhanced resistance to M. grisea. We suggest that the autofluorescence and expression of the DR genes after heavy inoculation are important cytological and molecular markers respectively for early determination of the host response to M. grisea in the rice blast system. This knowledge provides an important basis for developing strategies to control the rice blast disease.