Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: February 29, 2004
Publication Date: February 1, 2005
Citation: Eizenga, G.C., Xiang, G., Jia, Y., Lee, F. 2005. Identification of disease resistance in the Oryza spp. and following its introgression into cultivated rice with DNA markers. Rice Technical Working Group Meeting Proceedings. Abstract p. 115. Technical Abstract: Rice wild relatives (Oryza spp.) are an important source of novel genes for rice improvement. Previous studies of 21 Oryza spp. accessions identified resistance to rice sheath blight (Rhizoctonia solani Khhn) and rice blast (Pyricularia grisea (Cooke) Sacc.) in these wild Oryza spp. accessions via greenhouse screening methods. Subsequently, selected Oryza spp. accessions were backcrossed to the US long grain 'Ahrent' and US medium grain 'Bengal'. Recently, DNA markers were developed to determine the presence of Pi-ta and Pi-b, two major blast resistance genes in US cultivated rice. Pi-ta is a major blast resistance gene introduced into 'Katy' from the Vietnamese landrace Tetep and Pi-b is another major gene introduced into 'Saber' from Chinese cultivar TeQing. In a different study, a set of 180 microsatellite markers was used to genotype 550 rice (O. sativa) accessions with about one half representing germplasm used in US rice breeding programs and one half representing international rice germplasm. The objectives of this study were to 1) determine the resistance of the remaining Oryza spp. using greenhouse methods, 2) identify Pi-ta and Pi-b in the Oryza spp. accessions and selected progeny, 3) genotype the Oryza spp. accessions, and 4) use selected polymorphic microsatellite markers to follow the introgression of Oryza spp. DNA into Ahrent and/or Bengal. The 56 accessions included in this study represented the following Oryza spp.: O. alta, O. australiensis, O. barthii, O. glumaepatula, O. latifolia, O. meridionalis, O. nivara, O. officinalis, O. rufipogon and the O. sativa cultivated parents for crossing. The blast and sheath blight inoculations were done in the greenhouse and rated using standard protocols. The blast races (isolates) used were IB-1 (ZN15), IB-33, IB-49 (ZN51), IB-54, IC-17 (ZN48), IE-1 (ZN5), IE-1K (ZN19), IG-1 (ZN39) and IH-1 (74L2) and the sheath blight isolate 95KBNT collected near Stuttgart, Arkansas in 1995. Genomic DNA was extracted from leaf tissue using a CTAB method or the DNeasy Plant Mini Kit per the manufacturer's instructions. Three pairs of Pi-ta dominant primers, one pair of pi-ta recessive primers and one pair of Pi-b dominant primers were used to determine the presence of Pi-ta, pi-ta and Pi-b, respectively. The presence or absence of these PCR products was visualized on a 1% agarose gel. The 180 microsatellite markers used to genotype the Oryza spp. accessions were visualized by fluorescent-labeled products, processed by an ABI 3700, and analyzed to detect polymorphisms in the PCR product. Once genotyped, approximately 30 polymorphic markers will be selected to follow the introgression of the Oryza spp. chromatin into the cultivated parent. At least one marker will be located on each of the 24 rice chromosome arms. Other polymorphic markers will be selected based on their proximity to known resistance genes. Sheath blight tolerance was identified in the initial Oryza spp. confirming an IRRI report of sheath blight tolerance in these accessions. This tolerance was diluted when initial backcrosses were made to the cultivated rice parent. Resistance to all US blast races was not identified in any of these accessions. As a result of backcrossing with selected Oryza spp. there are small populations of 1) Ahrent by five different O. nivara, one O. nivara/O. sativa, one O. barthii and one O. rufipogon accession(s) in the BC3. or BC4 and 2) Bengal by two different O. nivara and one O. nivara/O. sativa accession(s) in the BC4 that have been developed. Results from screening the Oryza spp. accessions with the four PCR-based markers for Pi-ta indicate the Pi-ta gene is present in an O. barthii, O. rufipogon and O. nivara/O. sativa accession(s). The screening of the remaining Oryza spp. for Pi-ta and all accessions with the PCR-based Pi-b marker for the Pi-b gene is still being completed. Data analysis is in progress that will give the genotype of each Oryza spp. accession included in this study based on the 180 microsatellite markers used in the earlier study of O. sativa germplasm. Once the genotyping analysis is complete, approximately 30 microsatellite markers will be selected from the aforementioned 180 markers to follow the introgression of selected O. barthii, O. nivara and O. rufipogon accessions into the cultivated rice parent of either Ahrent or Bengal. Since recombination occurs more frequently in the distal region and most introgression involves distal rather than proximal chromatin, polymorphic markers located in distal regions will be given preference.