A set of differential varieties (DVs) is a useful tool to identify blast resistance genes in rice (Oryza sativa L.) and to characterize the pathogenicity of the blast (Pyricularia grisea Sacc.) races. Yamada (1976) and Kiyosawa (1981) developed two sets of DVs targeting for nine and twelve resistance genes, respectively. These sets of DVs have a high differentiating ability on blast isolates from Japan, but are not so useful in the Philippines or the other tropical countries because some of DVs showed moderate resistance to a wide spectrum of blast isolates (Inukai et al 1994; Noda et al. 1999). Yanoria et al. (2000) tried to clarify the pathogenicities of blast isolates from the Philippines and selected 20 standard isolates using DVs by Yanamada (1976) and Kiyosama (1981), and other DVs. Tsunematsu et al. (2000) developed a set of DVs consisting of 31 monogenic lines, each carrying a single gene out of set of 24 different resistance genes - Pia, Pib, Pi11(t), Pi12(t), Pii, Pi3, Pik-s, Pik, Pik-p, Pik-h, Pik-m, Pi1, Pi7(t), Pish, Pit, Pita, Pita-2, Piz, Piz-5, Piz-t, Pi5(t), Pi9(t), Pi19(t), and Pi20. The lines were developed by several backcrosses between donor varieties and a Chinese Japonica-type, susceptible variety Lijiangxintuanheigu (LTH) as a recurrent parent. However, Tsunematsu et al. (2000) did not show all reaction patterns of each monogenic line to the standard isolates selected by Yanoria et al. (2000), and these lines were not yet morphologically characterized. This study aimed to characterize each monogenic line by investigating reactions for all 20 selected blast isolates and some morphological traits.

The reactions of 31monogenic lines were confirmed using the 20 blast isolates from the Philippines. Each line had a distinct reaction pattern except Pik, Pik-p, Pik-h, Pik-m, Pi1 and Pi7(t). The Pik alleles except for Pik-s showed the same reaction patterns. There is no incompatible isolate against two resistance genes, Pi19 and Pit, and Pish showed wide spectrum and moderate resistance to almost of isolates (Table 1).

Eight morphological traits were investigated in field conditions (short day, day length 11-12 h/day) and screen house (long day condition). The traits were culm length (CL), panicle

length (PL), leaf length (LL), leaf width (LW), panicle number (PN), days to heading (HD), % spikelet fertility (SF) and 100 seed weight (SW). The monogenic lines showed wide variation in each trait compared with the recurrent parent, LTH. The values of CL, PL, LW, LL and DAS were higher under screen house condition than field conditions. Although the variation in eight traits was recognized among monogenic lines, each line was already fixed (data are not shown). The set of monogenic lines have been distributed to more than 15 countries by the IRRI-Japan Collaborative Research Project or International Network for Genetic Evaluation of Rice (INGER), and is being used as a source of differential varieties against blast disease.

Acknowledgment

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

References

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