Submitted to: Proceeding Rice Disease in the Mediterranean and Breeding for Resistance
Publication Type: Proceedings
Publication Acceptance Date: 2/28/1995
Publication Date: N/A
Technical Abstract: Close cooperation among U.S. rice breeders and pathologists provided an excellent environment for characterizing U.S. pathotypes, determining inheritance of resistance and identifying sources of resistance. In the U.S. rice breeding program early-generation evaluation for blast resistance is conducted in upland nurseries, in which breeding lines are challenged in npolycyclic exposures to five broadly pathogenic pathotypes of Pyricularia grisea under conditions favorable to disease development. Acceptable resistance is based on performance relative to that of acceptable cultivars. We are now comparing resistances under both upland and flooded conditions; U.S. rice is irrigated. Flooded rice is more resistant than upland rice, but rice lines vary in degree of improved resistance. Race-specific resistance has not been abandoned as we seek to improve the more durable partial resistance. Certain race-specific resistance (Pi-) genes seem to provide some measure of residual resistance or are closely linked to genes which provide partial resistance to compatible pathotypes. Advanced lines are screened with eight or more distinct pathotypes to characterize them for the presence of Pi-genes. Pyramiding of Pi-genes is also an effective strategy. In dealing with this highly variable pathogen we are utilizing both race-specific and general sources of resistance. Each appears to perform more effectively in the presence of the other.