The rice populations were tested at experiment stations of the China National Rice Research Institute located either in Hangzhou, Zhejiang, check details or Lingshui, Hainan (Table 1). In all the trials, the planting density was 16.7 cm between plants and 26.7 cm between rows. For the F2-type populations in BC2F6, heading date (HD) and 1000-grain weight (TGW) were scored on a single-plant basis. For the NILs in either BC2F5 or BC2F7, a randomized complete block design with two replications was used. Each line was grown in a single row of 12 plants. HD was scored for each plant and averaged for each

replication. At maturity, the middle five plants in each row were bulk-harvested and measured for grain yield per plant (GY), number of panicles per plant (NP), number of grains per panicle (NGP) and TGW. Total DNA was extracted following the method of Zheng et http://www.selleckchem.com/products/ve-821.html al. [19]. PCR amplification was performed according to Chen et al. [20] except that the products were visualized on 6% non-denaturing polyacrylamide gels using silver staining.

Polymorphic markers located in the target region included 17 SSR markers (Fig. 2), all of which were selected from the Gramene database (http://www.gramene.org/). For the F2-type populations in BC2F6, linkage maps were constructed with MAPMAKER/EXP 3.0 [21], and genetic distances in centiMorgans (cM) were derived using the Kosambi function. QTL analysis was performed with composite interval mapping implemented in Windows QTL Cartographer 2.5 [22]. Using 1000 permutation test, the critical LOD values at P = 0.05 were determined,

ranging from 1.75 to 2.03. Putative QTL were claimed at a LOD threshold of 2.1. For the NIL populations in BC2F5 and BC2F7, two-way analyses of variance (ANOVA) were performed to test phenotypic differences between the two homozygous genotypic groups in each NIL set, with a mixed model using SAS procedure GLM [23] as previously described [24]. When significant differences (P < 0.05) were detected, the same model was applied to estimate the genetic effects of the QTL, including additive effect and the proportions of phenotypic variance explained. Since QTL for TGW on the long arm of chromosome 1 showed significant QTL × QTL interaction but no significant main effect in the ZS97/MY46 RIL population [17], it remained unknown whether the QTL effect could be detected in the genetic background Cell press of ZS97. To avoid the risk of wasted effort in population development, marker analysis and field trials, it was necessary to test the effect using NILs at an early generation stage. Therefore, when NILs with sequential segregating regions in the target region became available in BC2F5, they were grown at two locations for primary validation of the QTL effect. Two-way ANOVA for testing phenotypic differences between two homozygous genotypic groups in each of the three NIL sets are shown in Table 2. In populations I and II, no significant effect was detected for any traits.