Population Dynamics of the Rice Blast Pathogen in a Screening Site in Colombia and Characterization of Resistance

Abstract

Rice blast disease caused by Pyricularia grisea Sacc., the anamorph of Magnaporthe grisea (Hebert) Barr, is the main rice production constraint in Colombia. Development of resistant cultivars has been the preferred means of controlling this disease; however, development of resistant cultivars with durable blast resistance has been a very difficult task, especially in areas where rice is grown continuously such as in Colombia, and where the climatic conditions are highly conducive to blast. In general, blast resistance is defeated by the pathogen shortly after cultivar release (Correa-Victoria and Martinez, 1994). Major efforts are being made at CIAT to understand the high pathogen variation observed, often reported as the main cause of resistance breakdown (Correa-Victoria et al., 1994). An extensive study of P. grisea diversity in Colombia was initiated in 1990 by analyzing the population structure in the country. We have analyzed extensively the virulence diversity and virulence spectrum of several hundred isolates collected from different rice cultivars. Isolates have been inoculated under greenhouse conditions onto rice cultivars with known resistance genes, rice commercial cultivars released in Colombia over a period of 30 years, sources of durable blast resistance, the international set of host differentials, and a set of near isogenic lines carrying known resistance genes.