Abstract: A double haploid (DH) population including 120 lines derived from a cross between indica rice (Oryza sativa L.) TN1 and japonica rice CJ06 was used to detect quantitative trait loci (QTLs) for 10-trait relative values of alkali damage at germination period and early seedling stage under 0.15% Na₂CO₃ stress. Correlation analyses showed that alkali damage rate in germination period (ADG) had significant positive correlation with relative germination energy (RGE), relative germination rate (RGR) and relative germination index (RGI), and alkali damage rate at early seedling stage (ADS) had significantly correlation with relative seedling height (RSH), relative root length (RRL), relative root number (RRN) and relative seedling dry weight (RDW). ADG and ADS can be used as evaluation indexes of alkaline tolerance in rice. By using QTLNetwork 2.0 software, 14 additive QTLs and 13 epistatic QTLs controlling the tolerance to alkali were mapped. Two main effect QTLs were detected in same region, RM251–RM3280, on chromosome 3, and three main effect QTLs were mapped between RM3286 and RM1279 on chromosome 7. Epistasis analysis showed that some epistatic loci, like RM1–RM1195, RM1358–RM290, RM1279–RM505, and RM1246– RM519 on chromosome 1, 2, 7, and 12 respectively were important under alkali stress, included two or more epistatic QTLs, in-dicating that the QTLs displayed their effects through different ways of interaction. Among the key loci under alkali stress one may be pleiotropic or some closely linked each other. Comparing QTLs with those found in other researches, some alkali resis-tance QTLs were likely to be in the same region with some salt resistance QTLs. A presume was made that QTLs in this article might include two types, one for resistance to ions (K⁺ or Na⁺) stress and other for resisttance to high pH stress, the latter may play an important role for tolerance to alkali. Many rice varieties have different resistance QTLs for alkali stress; we can pyramid them through marker-assistant selection to breed varieties suitable to growth in saline-alkalized land.

Key words: Rice, Alkali stress, Quantitative trait locus, Double haploid population