Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/29/2004
Publication Date: 2/1/2005
Citation: Eizenga, G.C., Refeld, R., Lee, F., Emerson, M., Xiang, G., Jia, Y., Yan, W. Identification of blast resistance genes in Indica rice germplasm. Rice Technical Working Group Meeting Proceedings. Abstract. p. 70-71.
Technical Abstract: Rice blast caused by Pyricularia grisea (Cooke) Sacc., is a major fungal disease of cultivated rice (Oryza sativa L.) in the US, and of irrigated rice worldwide. Indica rice, rice grown in tropical areas is one possible source of additional blast resistance genes (Pi-genes) that could be incorporated into US rice cultivars. Pi-ta is a major blast resistance gene introduced into the US cultivar Katy from the Vietnamese landrace Tetep and Pi-b is another major gene introduced into US cultivar Saber from the Chinese cultivar TeQing. A total of 94 rice (O. sativa L.) accessions were selected from approximately 1000 rice accessions screened in a field nursery for resistance to blast. In a different study, approximately 550 O. sativa accessions were genotyped with 180 microsatellite markers. Approximately half of these accessions were US rice cultivars and the other half from a more diverse origin. The main objectives of this study were to determine if new/novel resistance genes are present in the 94 selected accessions utilizing known molecular markers associated with these resistance genes and use microsatellite markers to determine the relatedness of the 94 accessions to each other and adapted rice cultivars. The accessions used in this study were those being brought through the US rice quarantine system for incorporation into the US rice germplasm collection (Germplasm Resources Information System). Blast inoculations were done in the field using standard protocols. Inoculations in the greenhouse followed standard procedures to identify resistance to the blast races IB-1 (ZN15), IB-49 (ZN52), IC-17 (ZN1), IE-1K (ZN19), IE-1 (ZN6), IG-1 (ZN39) and IH-1 (74L2). Plants were rated at the 4-5 leaf stage using a scale 0=no lesions to 9=dead leaves. 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 94 O. sativa accessions were visualized by fluorescent-labeled products, processed by an ABI 3700, and analyzed to detect polymorphisms in the PCR product. Once genotyped, the genetic distance (GD) between the O. sativa accession will be calculated using the following equation, GD=1-A/N, where A is the total number of microsatellite alleles shared by two accessions and N the total number of microsatellite loci scored between the two accessions. GD values can range from zero (all alleles in common) to unity (no alleles in common). In the field ratings for leaf blast, 89 of the 91 accessions tested had average ratings below 3.0 and 73 of the 77 accessions tested had ratings below 3.0 for panicle blast. In greenhouse testing, 90% or more of the accessions tested had average ratings below 2.0 for the blast isolates tested. Based on repeated screening, both the Pi-ta and Pi-b resistance genes were identified in 30 accessions with an additional entry having only Pi-ta and 29 accessions having only the Pi-b resistance gene. Thirty-four accessions did not have either Pi-b or Pi-ta. Fifteen of these 34 accessions had ratings of 1.0 or less for all field and greenhouse inoculations. The resistance of seven of these 34 accessions needs to be tested or reconfirmed in greenhouse inoculations. In summary, 15-22 accessions of the original 94 tested are potential sources of new and novel blast resistance genes. The data from the 180 microsatellite markers used to genotype the 94 accessions will be used to determine the genetic distance (GD) between the accessions. The GD data will be subjected to a hierarchical cluster analysis. Thes