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A total of 119 blast (Magnaporthe grisea (Hebert) Barr.) isolates collected from the Philippines, were characterized for their pathogenicities using 19 rice (Oryza sativa L.) differential varieties (DVs) targeting for 18 resistance genes. These isolates were classified into 31 groups based on the reaction patterns to 9 DVs for targeting 9 resistance genes, Pia, Pib, Pii, Pit, Pita, Pish, Pi3, and Piz-5, at first, and then further divided into 70 pathotypes considering the reaction pattern of the other 9 DVs for the other resistance genes, Pik, Piz, Pi1, and Pi20(t). Twenty isolates that have differentiating ability, stable reactions and good sporulating ability were selected. The reactions of these isolates were confirmed using the monogenic lines as a set of DVs for targeting 24 resistance genes, Pia,

Total spikelet number per panicle (TSN) is one of the most important traits associated with rice yield potential. This trait was assessed in a set of 334 chromosomal segment introgression lines (ILs: BC3-derived lines), developed from new plant type (NPT) varieties as donor parents and having the genetic background of an indica-type rice variety IR64. Among the 334 ILs, five lines which had different donor parents and showed significantly higher TSN than IR64 were used for genetic analysis. Quantitative trait locus (QTL) analysis was conducted using F2 populations derived from crosses between IR64 and these ILs. As a result, a QTL for high TSN (one from each NPT donor variety) was detected on common region of the long arm of chromosome 4. The effect of the QTL was confirmed by an increase in TSN of five near-isogenic lines (NILs) developed in the present study. The variation in TSN was found among these NILs, attributing to the panicle architecture in the numbers of primary, secondary and tertiary branches. The NILs for TSN and the SSR markers linked to the TSN QTLs are expected to be useful materials for research and breeding to enhance the yield potential of rice varieties.

Tillering is one of the most important agronomic traits related to grain production in rice (Oryza sativa L.). A japonica-type variety, Aikawa 1, is known to have low-tiller number. The detailed location of a low-tillering gene, Ltn, which has been localized on chromosome 8 in Aikawa 1, was confirmed by molecular mapping. Using BC5F2 individuals derived from a cross between IR64 and Aikawa 1, the low-tillering gene was mapped to an interval defined by SSR markers ssr5816-3 and A4765. This was designated as Ltn because there was no reported gene for tillering in the region of chromosome 8. Through high-resolution linkage analysis, the candidate region of Ltn was located between DNA markers ssr6049-23 and ind6049-1 corresponding to 38.6 kbp on the Nipponbare genome sequence. These DNA markers, which were tightly linked to Ltn, are useful for marker-assisted selection in breeding studies.