title: Mapping QTLs for cold tolerance at germination and the early seedling stage in rice (Oryza sativaL.).
abstract: Cold tolerance is an important breeding target in rice production. We studied quantitative trait loci (QTLs) controlling cold tolerance at germination (CTG) and early seedling (CTS) stages, using recombinant inbred lines derived from ajaponica×indicacross. CTG was evaluated based on the percentage rate of germination at 15 °C for 12 days after pre-incubation of imbibed seeds at 20 °C for 2 days. For CTS, seven-day-old seedlings grown at 25 °C were subjected to two consecutive periods of three-day cold stress at 4 °C with an intervening eight-day recovery at 25 °C. CTS evaluation was according to an arbitrary five-point rating system at the fifth day of recovery after each stress period. No correlations were found between CTG and CTS, while a weak correlation was detected between CTS after the first and second stress. By the composite interval mapping, five QTLs for CTG explaining 5.7%-9.3% of the total phenotypic variance (PVE) and nine for CTS with PVE of 5.8%-35.6% were detected. Only one of these QTLs was common, indicating growth-stage specificity of cold tolerance. Four of the five QTLs after the second cold stress were different from the ones after the first cold stress. Analysis of variance test showed significant interactions between alleles at the QTL sites and the two stress conditions with respect to the mean CTS scores. A possible involvement of cold acclimation and usefulness ofjaponicagermplasms in breeding for cold tolerance inindicarice was discussed.
authors.affiliation: Department of Agricultural Biology, Faculty of Agriculture, University of Ruhuna , Mapalana , Sri Lanka.
authors.forename: Aloka Lanka
authors.initials: AL
authors.lastname: Ranawake
authors.affiliation: Plant Breeding and Biotechnology Division, Philippine Rice Research Institute, Science City of Munoz , Nueva Ecija , Philippine.
authors.forename: Oliver Escano
authors.initials: OE
authors.lastname: Manangkil
authors.affiliation: Hyogo Institute of Agriculture, Forestry and Fishery , Kasai , Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Yoshida
authors.affiliation: Department of Bioresource Science, Laboratory of Plant Breeding, Graduate School of Agricultural Science, Kobe University , Kobe , Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ishii
authors.affiliation: Department of Agrobioscience, Laboratory of Plant Genetics, Graduate School of Agricultural Science, Kobe University , Kobe , Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Mori
authors.affiliation: Department of Agrobioscience, Laboratory of Plant Genetics, Graduate School of Agricultural Science, Kobe University , Kobe , Japan.
authors.forename: Chiharu
authors.initials: C
authors.lastname: Nakamura
keywords: cold acclimation; cold tolerance; germination; growth stage specificity; quantitative trait loci (QTLs), recombinant inbred lines (RILs); rice (Oryza sativa L.)