Advances on the identification and characterization of broadspectrum blast resistance genes in rice

Rice blast,caused by the fungus Magnaporthe grisea,is one of the most devastating diseases in rice production.Because of high strain diversity,the resistance of most rice cultivars is relatively short.Therefore, identification and utilization of broad-spectrum resistance genes in rice breeding has been considered as the most effective and economical strategy to control this disease.By far,about forty blast resistance genes have been identified,but only eight of them confer broad-spectrum resistance,and were mapped or cloned successfully. Pi9,Pi2 and Piz-t were cloned using a map-based cloning strategy or PCR-based homology cloning method.All of them encode highly homologous NBS-LRR proteins and are a member of a multi-gene family.The cloned genes provide valuable insights into the molecular basis of the broad-spectrum resistance and the evolutionary mechanisms of different blast resistance gene clusters in rice.Because of the rich rice genetic resources of blast resistance in China,identification and utilization of the broad-spectrum blast resistance genes will play an important role in stable rice production in the future.