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Blast, caused by Pyricularia grisea Sacc., is often an important impediment in the production of rice in temperate and tropical areas. It is also very important in Iran. To study components of partial resistance in some Iranian rice cultivars namely Anbarboo,
Tarom mahalli, Domsiah, Nemat and Neda along with IR64, Moroberekan, San Huang Zhan-2, Co39 and Vandana from IRRI but with different origins, were greenhouse tested in an upland nursery experiment at IRRI, Philipines. The experiment was conducted in a Randomized Complete Block Design (RCBD) with three replications. Traits in this study consisted of infection type(IT), lesion number (LN), lesion size ( LS, mm2 ), percent diseased leaf area (DLA, or disease severity %), latent period (LP, day), and sporulation capacity ( SC, spore/gram fresh wieght). Results showed that, the cultivars differed significantly in IT, LN, DLA, LP and SC. Nemat , Neda and Co39 exhibited high rates of all traits showing susceptible reaction. IR64 and Vandana, two indica type cultivars, were intermediate being considered as partially resistant cultivars. Anbarboo, Tarom mahalli, Domsiah, Moroberekan and San Huang Zhan-2 were resistant to single blast isolates in greenhouse as well as field races of blast. Using the area under disease progress curves as a measure of relative disease progress in the nursery, disease development on Anbarboo, Tarom mahalli, Domsiah, and San Huang Zhan-2 was slight, on IR64 it was intermediate and on Nemat, Neda and Co39 high. There was a good match observed between greenhouse and field results. This suggests that race-specificity in the field was not important in determining the rank order of these cultivars for either susceptibility or resistance and for achieving durable resistance,
cultivars with partial resistance are preferred.