GENOMIC CHARACTERIZATION OF RICE GERMPLASM
Location: Dale Bumpers National Rice Research Center
Title: Exploring genetic diversity and potential novel disease resistance genes in a collection of rice wild relatives
Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 2005
Publication Date: February 1, 2009
Citation: Eizenga, G.C., Agrama, H.A., Lee, F.N., Jia, Y. 2009. Exploring genetic diversity and potential novel disease resistance genes in a collection of rice wild relatives. Genetic Resources and Crop Evolution. 56:65-76.
Interpretive Summary: At times, plant breeders have used wild relatives of crop plants to incorporate desirable traits into the adapted crop plants. Often these are genes that were lost during the process of domesticating the given crop plant. In the case of rice, breeders have incorporated genes for biotic and abiotic stress that were found in the wild relatives of rice into adapted rice cultivars. In a few cases, like incorporation of resistance to the grassy stunt virus and tolerance to acid soils, the resulting varieties are exciting success stories. Blast and sheath blight are major fungal diseases of cultivated rice in the USA. This study identified resistance to blast and sheath blight in some accessions (lines) of the rice wild relatives that were tested for disease resistance. DNA markers were used to determine how related the different accessions of rice wild relatives were to each other and to cultivated rice. This information will be important in selecting resistant accessions from different backgrounds. The possible location of novel blast and sheath blight resistance genes was postulated based on data from the disease testing, DNA markers, and statistical computations. Future studies will verify the location of these resistance genes, so these genes can be incorporated into cultivated rice adapted to the USA. New resistance genes are of primary importance to U.S. rice breeding programs and ultimately, the U.S. rice industry.
Wild relatives of rice (Oryza spp.) and introduced rice (O. sativa) germplasm are important sources of novel resistance (R-) genes for rice improvement. Rice sheath blight, caused by Rhizotonia solani, and leaf blast, caused by Magnaportha oryzae, are major fungal diseases of rice worldwide. To identify novel R-genes, a group of Oryza spp. accessions represented by O. alta, O. australiensis, O. barthii, O. glaberrima, O. glumapatula, O. latifolia, O. meridionolis, O. nivara, O. officinalis, and O. rufipogon, and a group of O. sativa accessions, originating from international sources and the USA, were evaluated for their disease reaction and genotyped with 176 microsatellite (SSR) markers. Cluster analysis grouped most Oryza spp. accessions with the same species or a closely related Oryza spp. Only a few Oryza spp. accessions grouped with the O. sativa accessions. Analysis of the genotypic data in the software Structure revealed that the Oryza spp. accessions were assigned into eight different subpopulations and fit well into eight different backgrounds. Marker-trait associations between the SSR markers and disease reactions to blast and sheath blight were ascertained using the software TASSEL. For the Oryza spp. group, associations with blast disease were identified in 10 different chromosomal regions and five of the 10 were not located near known blast R-genes. Three associations were discovered with sheath blight disease for the Oryza spp. group, and one was not near previously reported sheath blight QTL. For the O. sativa group, one association with blast disease was ascertained that had not been previously reported. These newly identified regions may represent novel R-genes that will be the basis of future investigations.