We investigated the mode of inheritance and map location of field resistance to rice blast in the elite rice strain Chubu 111, and yield under severe blast conditions. Chubu 111 carries the complete resistance gene Pii, although field testing showed this strain to be susceptible to infection. The level of field resistance of Chubu 111 was so high that chemicals used to control blast were not required, even in an epiphytotic area. Genetic analysis of field resistance to blast in 149 F 3 lines derived from a cross between Chubu 111 and the susceptible cultivar ÔMineasahiÕ suggested that field resistance is controlled by a dominant gene, designated Pi39(t), that cosegregates with the single sequence repeat marker loci RM3843 and RM5473 on chromosome 4. Comparative studies of polymorphism at RM3843 among Chubu 111 and six cultivars or lines in its pedigree suggested that the donor of the resistance gene was the Chinese cultivar ÔHaonaihuanÕ. Marker-assisted selection of Pi39(t) should be useful in rice-breeding programmes for field resistance to blast.

New Rice for Africa (NERICA) is a general name for interspecific rice varieties derived from a cross between the high-yielding Asian rice (Oryza sativa L.) between locally adapted African rice (Oryza glaberrima Steud.). Eight NERICAs were evaluated for cold tolerance (CT) at the reproductive stage and compared with their O. sativa parents and three Japanese standard rice varieties over 3 years. Cold tolerance was evaluated based on the filled grain ratio (FGR) after cold water irrigation. The FGR was greatly reduced by cold water irrigation. NERICA 1, 2 and 7 had higher FGR (51.9-57.9 %), while NERICA 6, 15 and 16 had lower FGR (6.2-14.5 %). NERICA 1, 2 and 7 were less affected by cold stress, with a 31 % mean reduction in FGR, while NERICA 6, 15 and 16 were greatly affected, with their FGRs being reduced by more than 80 %. NERICA 3 and 4 were moderately affected by cold stress, with about 45 % reduction rate in FGR. FGR significantly influenced the grain weights of the varieties with strong positive correlations (r = 0.83-0.91; P < 0.001), and thus, similar trends in grain weights were observed. Grain weights were reduced by 61.7-96.4 % under cold stress. NERICA 1, 2 and 7 showed significantly better performance than NERICA 3 and 4, while NERICA 6, 15 and 16 performed poorly under cold water irrigation. The Japanese varieties Koshihikari (very tolerant) and Ozora (moderately tolerant) were more affected by cold water irrigation than NERICA 1, 2 and 7. On the basis of the mean reduction rate (%) in FGR under cold stress, the varieties were classified as follows: NERICA 1, 2 and 7 as tolerant; NERICA 3 and 4 as moderately tolerant; and NERICA 6, 15 and 16 as susceptible to cold stress. However, NERI-CA 7 grain yields were lower under cold stress due to both greatly reduced number of panicles per plant and number of spikelets per panicle. Therefore, NERICA 1 and 2 are suitable candidates for production in the highland regions of East Africa and should be promoted for production.

No abstract

ノ ー ト 複数の栽培環境におけるイネいもち病圃場抵抗性遺伝子 pi21 の収量性に対する影響 坂 紀邦 1,2) ・冨田 桂 3) ・永野邦明 4,5) ・片岡知守 6,7) ・安東郁男 8,9) ・永吉嘉文 10) ・中込弘二 6) ・ 山口誠之 6) ・前田英郎 8) ・佐藤宏之 8) ・石井卓郎 7,11) ・寺島竹彦 1,12) ・水上優子 1,13) ・福岡修一 14) 1) 愛知県農業総合試験場・山間農業研究所，豊田市，〒 441-2513 2) 現：愛知県農業総合試験場・作物研究部，安城市，〒 446-0066 3) 福井県農業試験場，福井市，〒 918-8215 4) 宮城県古川農業試験場，大崎市，〒 989-6227 5) 現：宮城県北部地方振興事務所，大崎市，〒 989-6117 6) 農研機構・東北農業研究センター，大仙市，〒 014-0102 7) 農研機構・九州沖縄農業研究センター，筑後市，〒 833-0041 8) 農研機構・作物研究所，つくば市，〒 305-8518 9) 現：農水省・農林水産技術会議事務局，千代田区，〒 100-8950 10) 宮崎県総合農業試験場，宮崎市，〒 880-0212 11) 農研機構・近畿中国四国農業研究センター，福山市，〒 721-0975 12) 現：愛知県新城設楽農林水産事務所，北設楽郡，〒 441-2301 13) 愛知県農業総合試験場，長久手市，〒 480-1101 14) 農業生物資源研究所，つくば市，〒 305-8602