In this regard, identification of yield-enhancing QTL that do not have significantly adverse effects on heading date would be preferable. Grain yield per plant in rice is determined by three components, panicles per plant, number of grains per panicle, and grain Sunitinib weight. It has been shown that increased grain weight

has played a major role in enhancement of yield potential in modern Chinese rice varieties [15] and [16]. Therefore, identification of minor QTL for grain weight, especially those showing no significant adverse effects on heading date, would facilitate the development of high-yielding rice varieties. In a previous study using recombinant inbred lines (RILs) derived from an indica rice cross between maintainer PARP inhibitor line Zhenshan 97 (ZS97) and restorer line Milyang 46 (MY46) of Shanyou 10, a popular three-line rice hybrid, multiple QTL for grain weight on the long arm of chromosome 1 showed significant QTL × QTL effects, but no significant main effect [17]. In addition, this chromosome region had no significant effect on heading date in the same population [18]. Using populations segregating in an isogenetic background, the objectives of the present study were (i) to separate

different QTL for grain weight in the interval RM11448–RM11974 on the long arm of chromosome 1 and (ii) to test the effects of these QTL on heading date and other yield traits. Rice populations having sequential segregating regions between RM11448 and RM11974 on the long arm of chromosome 1 were established in the generations BC2F5, BC2F6 and BC2F7. They were derived from the

indica rice cross ZS97/MY46 as described below and illustrated in Fig. 1. An F9 plant of ZS97/MY46 was selected and backcrossed to ZS97 for two generations. One BC2F2 carrying a heterozygous segment extending from RM11448 to RM11974 was identified. In the resultant BC2F3 population, three plants were selected, which carried heterozygous segments covering the intervals RM11448–RM11615, RM11448–RM11787 and RM11615–RM11974, respectively. Three BC2F4 populations were produced, from which populations having the same sequential segregating regions (Fig. 2) were advanced for three generations. Firstly, non-recombinant homozygotes were filipin identified from each of the three BC2F4 populations and selfed to produce homozygous lines. Three sets of near isogenic lines (NILs) were established and named B2F5-I, B2F5-II and B2F5-III, respectively (Table 1). Meanwhile, one heterozygote was selected from a segregating line in each of the three BC2F4 populations, in which the entire segregating region in the given population identified was heterozygous. From the selfed seeds three populations segregating in an F2 pattern were produced and named B2F6-I, B2F6-II and B2F6-III, respectively (Table 1). Then, non-recombinant homozygotes were identified from each of the three BC2F6 populations and selfed to produce homozygous lines.