Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2006
Publication Date: 4/25/2006
Citation: Eizenga, G.C., Agrama, H.A., Lee, F.N., Yan, W., Jia, Y. 2006. Molecular and agronomic characterization of newly introduced blast resistant rice germplasm. Crop Science. 46:1870-1878. Interpretive Summary: Plant breeders often use cultivars developed in other countries to broaden the background of the improved cultivars being developed. Blast and sheath blight are major fungal diseases of cultivated rice in the USA. In the past 15 years, blast resistance genes from the Vietnamese rice named Tetep and the Chinese rice named Teqing, have been incorporated into U.S. rice varieties. To expand the background of U.S. cultivars, most rice breeding programs are attempting to incorporate additional resistance genes from rice cultivars grown outside the USA. To make these non-U.S. cultivars (germplasm) more useful to rice breeders, the germplasm is evaluated for a number of characteristics including resistance to blast and sheath blight. DNA markers can be used to further characterize rice germplasm and identify disease resistance genes. In this study, resistance to U.S. blast races was observed in 85 of approximately 1,000 newly introduced rice germplasm lines (accessions). These accessions are possible sources of new blast resistance genes that could be incorporated into U.S. rice varieties. DNA markers identified the blast resistance genes in the 85 accessions that were initially found in Tetep and Teqing. Twenty-five of the 85 accessions had resistance to U.S. blast races and did not have the blast resistance genes already incorporated into U.S. rice cultivars from Tetep and Teqing. Based on DNA markers, eleven of the 25 accessions were closely related to each other but the remaining 14 accessions were more distantly related. Eleven DNA markers were found which may assist in identifying new blast resistance genes. Also, 19 DNA markers associated with sheath blight resistance were identified for further study. It is very likely that one or two of the rice germplasm accessions identified in this study will be the source of new blast resistance genes. These new resistance genes are of primary importance to U.S. rice breeding programs and ultimately, the U.S. rice industry.
Technical Abstract: Blast, Pyricularia grisea Cav., and sheath blight, Rhizoctonia solani Kühn, are major fungal diseases of cultivated rice (Oryza sativa L.) in the USA. Resistance to U.S. blast races was observed in 85 newly introduced rice accessions, indicating these accessions are possible sources of unique blast resistance genes (Pi-genes) that could be incorporated into U.S. rice varieties. The genes Pi-ta and Pi-b have been introduced into U.S. varieties and characterized molecularly. Objectives of this study were to identify Pi-ta and Pi-b in the aforementioned accessions, determine the relatedness between accessions using SSR markers, and identify SSR markers associated to blast and sheath blight resistance traits. Twenty-five accessions were identified with resistance to U.S. blast races and had neither the Pi-ta nor Pi-b gene. Based on 125 SSR markers distributed over the rice genome, eleven of the 25 accessions were closely related to each other but the remaining 14 accessions had varying levels of genotypic diversity, including two accessions selected from crosses with O. glaberrima, one from the Philippines and one from Ivory Coast. Blast resistance traits were associated with 37 of the 125 SSR markers and sheath blight traits with 19 markers. Of the 37 blast-associated markers, 26 were located in chromosomal regions of previously identified as containing Pi-genes. The remaining eleven markers will provide the basis for discovering additional Pi-genes.