Multi-line varieties, mixtures of rice varieties and near-isogenic lines
(NILs) with different complete resistance genes have been reported to
be effective in controlling blast disease in Japan (Shindo and Horino
1989; Koizumi 1994; Koizumi and Fuji 1994; Nakajima et al. 1996).
To develop a multi-line variety that is adapted well to the tropical zone,
nine different kinds of single blast resistance genes - Pik, Pi7(t),
Pi3, Pi5(t), Pita-2, Piz, Piz-5,
Pish, and Pi9(t) - into an Indica-type genetic background,
specifically, line IR49830-7-1-2-2, a rainfed lowland rice with submergence
tolerance. Backcrossing was carried out at least six times, and nine kinds
of NILs for targeting these seven resistance genes were developed. These
NILs are already at the BC6F11-BC6F13 generation in 2004. They were designated
as IRBL, followed by the resistance gene and an abbreviation for the resistant
donor and /RL (for rainfed lowland) (Table 1).
The resistance genes in the IR49830-7-1-2-2 genetic background were investigated
based on a differential system, which consisted of differential varieties
(Tsunematsu et al. 2000) and 19 standard blast isolates (Pyricularia
grisea Sacc.) from the Philippine (Yanoria et al. 2000). At
least four genes -Pia, Pib, Pik-s, and Pita-
were detected. Genetic analyses based on allelism tests with the F2
populations derived from the crosses between IR49830-7-1-2-2 and differential
varieties confirmed the presences of these genes (data not shown).
Each NIL was investigated through its reactions against the standard blast
isolates, and the expected results were shown. Two NILs, IRBL9-W/RL and
IRBLz5-CA/RL, were broadly resistant as they showed resistance reaction
to all the isolates. Moderate resistance to several isolates and susceptibility
to a single but different isolate were exhibited by IRBLz-Fu/RL and ILBLsh-T/RL.
The reaction pattern of IRBLk-Ku/RL was the same with IRBL7-M/RL, and
these two NILs could not be differentiated based on the differential system
using the blast isolates collected from the Philippines by Tsunematsu
et al. (2000) and Yanoria et al. (2000). Two NILs, IRBL3-CP4/RL
and IRBL5-M/RL, also showed the same reaction patterns (Table 1). The
presence of introgressed resistance genes were also confirmed using by
allelism test in each NIL (data not shown).
The NILs are almost fixed for some of the morphological traits examined
such as heading date, culm length, panicle length, and panicle number,
and showed similarities with those of IR49830-7-1-2-2. Submergence tolerance
of the NILs were also investigated and almost NILs were considerably similar
with the recurrent parent IR49830-7-1-2-2 except for two NILs of Pi5(t)
that showed lower tolerance. (data not shown). Each NIL carried at least
five genes and was suitable for enhancing the blast resistance in rainfed
lowland rice ecosystem as a multiline variety.
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.
Koizumi, S., 1994. Effect of field resistance on leaf blast development
in mixtures of susceptible and resistant rice cultivars. Ann. Phytopathol.
Soc. Jpn. 60: 585-594.
Koizumi, S. and S. Fuji, 1994. Effect of mixtures of isogenic lines developed
from rice cvs. Sasanishiki and Nipponbare on blast development. Res. Bull.
Aichi Agric. Res. Ctr. 26: 87-97. (In Japanese, English summary)
Nakajima, T., R. Sonoda and H. Yaegashi, 1996. Effect of a multiline of
rice cultivar Sasanishiki and its near-isogenic lines on suppressing rice
blast disease. Ann. Phytopathol. Soc. Jpn. 62: 227-233.
Shindo, K. and O. Horino, 1989. Control of rice blast disease by mixed
plantings of isogenic lines as multilane cultivars. Bull. Tohoku Natl.
Agric. Expt. Stn. 39: 55-96. (In Japanese, English summary).
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.
Yanoria, M.J.T., T. Imbe, H. Tsunematsu, L.A. Ebron, D. Mercado, H. Kato
and Y. Fukuta, 2000. Pathogenicity of IRRI blast isolates to rice blast
resistance genes. Poster presented at the 4th International
Rice Genetics Symposium, October 22-27, 2000, International Rice Research
Institute, Manila, Philippines.