Rice Genetics Newsletter, Vol. 21

Rgn21

27.

Identification of blast resistance genes in IRRI-bred rice (Oryza sativa L.) varieties

L.A. EBRON¹, Y. FUKUTA^1,2*, T. IMBE³, H. KATO³, H. TSUNEMATSU², M.J. TELEBANCO-YANORIA¹, G.S. KHUSH¹ and M. YOKOO⁴

1) Plant Breeding, Genetics, and Biochemistry, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines
2) Department of Biological Resources, Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki, 305 Japan
3) Department of Rice Research, National Institute of Crop Science 2-1-18 Kannondai, Tsukuba, Ibaraki, 305-8518 Japan
4) Life and Environmental Sciences, University of Tsukuba, Tennodai, Tsukuba, Ibaraki, 305-8572 Japan
* Corresponding Author, E-mail: y.fukuta@cgiar.org, Tel: +63-2-580-5600, Fax: +63-2-580-0606

The genetic constitution for blast resistant of rice varieties bred at the International Rice Research Institute (IRRI) is poorly characterized. Several factors may account for this situation, including the lack of a differential system for identification of blast resistance genes. In addition, indica type varieties are genetically complex for blast resistance (Mackill et al. 1985, Yu et al. 1987), making genetic studies difficult. The genetic characterization of resistance in IRRI-bred varieties was undertaken following a differential system based on the gene-for-gene relationship between rice resistance genes and avirulence genes in the blast pathogen.

The resistance genes in 42 IRRI-bred rice varieties were examined based on the reaction patterns of monogenic differentials (Tsunematsu et al. 2000) against 14 isolates of blast, Pyricularia grisea Sacc., from the Philippines. These varieties were classified into seven variety groups (VG) based on the presence of Pi20, Pita, and Pik^† (one of Pik alleles except for Pik-s). They were found to carry seven genes: Pi20, Pita, Pik^†, Pib, Pik-s, Piz-t, and Pii or Pi3 were found in them.

To confirm these genes, genetic analyses were carried out using BC₁F₂ progenies derived from crosses of IRRI varieties with a susceptible Indica-type variety, CO39, as recurrent parent, and allelism tests between IRRI varieties and differential varieties. Some varieties contained novel genes Pia, Pib, Pik-s, and Piz-t, which could not be estimated by reaction patterns due to the masking effects of wide spectrum genes, Pi20, Pita, and Pik^†. Among the genes identified, two genes, Pib and one of Pik alleles (Pik-s or Pik^†), were found in almost all IRRI-bred varieties (Table 1).

The duplication of number and kind of resistance genes in IRRI-bred varieties might reflect the genetic relatedness of several leading varieties (IR8, IR24, IR36, or their hybrid progenies) that were often used as the crossing parents in these pedigrees. This study demonstrated the utility of the differential system in elucidating the genetic constitution for blast resistance of IRRI varieties. The information produced from this study is very important in relation to rice blast resistance breeding using IRRI-bred rice varieties.

Acknowledgment

This study was carried out under the IRRI-Japan Collaborative Research Project (Phase III and IV) donated from Ministry of Agriculture, Forestry, and Fisheries, and Ministry of Foreign Affairs of Japan.

References

Mackill, D.J., J.M. Bonman, H.S. Suh and R. Srilingam, 1985. Genes for resistance to Philippine isolates of the rice blast pathogen. RGN 2: 80-81.

Tsunematsu, H., M.J.T. Yanoria, L.A. Ebron, N. Hayashi, I. Ando, H. Kato, T. Imbe and G.S. Khush, 2000. Development of monogenic lines of rice for blast resistance. Breed. Sci. 50: 229-234.

Yu, Z.H., D.J. Mackill and J.M. Bonman, 1987. Inheritance of resistance to blast in some traditional and improved rice cultivars. Genetics 77(2): 323-326.