LAUSR

Abstract Weedy red rice (Oryza sativa; WRR), a close relative of cultivated rice, is a highly competitive weed that commonly infests rice fields and can also naturally interbreed with rice. Useful genes for biotic stress have been maintained in WRR and can be explored for breeding. Here we describe genetic and physiological traits of WRR that can be beneficial in preventing major rice diseases. Rice blast, caused by the hemibiotrophic fungal pathogen Magnaporthe oryzae, and sheath blight disease, caused by the necrotrophic pathogen Rhizoctonia solani, are the two most damaging biotic stresses of rice. Many major and minor resistance genes and QTL have been identified in cultivated and wild rice relatives. However, novel QTL were recently found in the two major U.S. biotypes of WRR, blackhull-awned (BH) and strawhull-awnless (SH), suggesting that WRR has evolved novel genetic mechanisms to cope with these biotic stresses. Twenty-eight accessions of WRR (PI 653412–PI 653439) from the southern USA were characterized and placed in the National Small Grains Collection, and are available for identification of novel genetic factors to prevent biotic stress.