Breeding Rice Cultivars with Durable Blast Resistance in Colombia

Abstract

Rice blast disease (Pyricularia grisea) is the most important rice production constraint in Latin America. One strategy to improve the durability of blast resistance is to pyramid resistance genes. To do this, we have conducted extensive studies on the genetic structure of blast pathogen populations in Colombia and Latin America; determined composition, distribution and frequency of the avirulences that underlie race variation; identified and incorporated resistance gene combinations into commercial rice cultivars using genetic markers; and continuously evaluated and selected breeding lines under high disease pressure and pathogen diversity. Rice differentials with known blast resistance genes have been used to study avirulence gene composition and frequency in the blast pathogen and to identify relevant resistance genes. The combination of the blast resistance genes (Pi-1, Pi-2, Pi-33) for which their corresponding avirulence genes are highly conserved in blast pathogen populations in Colombia has proven to confer stable blast resistance after several years of testing under high blast pressure in the field and greenhouse inoculations. Additional pathogen characterization of spontaneous mutations of the blast pathogen allowed the identification of the blast resistance genes Pi-b, Pi-9 and Pi-ta ², which will be needed for protecting rice cultivars from potential future changes in the avirulence/virulence genes in the blast pathogen population. Microsatellite markers highly linked to these blast resistance genes have been found from public databases facilitating the introgression and pyramiding of each of these six blast resistance genes into Latin American rice cultivars and elite lines derived from rice breeding programs aiming at developing rice cultivars with durable blast resistance.