| Summary: | Rice blast caused by Pyricularia grisea (Magnaporthe grisea) is the main limiting factor of rice production in Colombia. Resistance break down occurs after one to three years of cultivar release, with the exception of the commercial cultivars Oryzica Llanos 5 released in 1989 and Fedearroz 50 released in 1998. With the objective of developing rice cultivars with durable resistance to blast we have analyzed the genetic structure of blast pathogen populations using techniques such as MGR-DNA and rep-PCR fingerprinting and studied the diversity and frequencies of avirulence/virulence genes in the fungus. P. grisea in Colombia is mainly clonaI. Each clone or lineage exhibits a broad spectrum of virulence. However, some resistance genes are effective against all isolates of a linage. Avirulence genes vary in frequency, suggesting that these genes could be associated with pathogenic fitness. Therefore, the resistance genes corresponding to those avirulence genes would be more relevant in breeding for durable resistance. Our studies are allowing us to identify and predict the durability of resistance gene combinations based on the frequency of avirulence genes. We have identified the possible resistance genes present in our commercial rice cultivars and initiated a backcrossing program for incorporating desired combinations of resistance genes in rice varieties of Latin America through marker assisted selection, controlled inoculations with pathogenic isolates, and field evaluations.
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