Identification of conditional QTL provides an alternative way for exploring the genetic relationship of related quantitative traits. The only difference from general QTL mapping is that the phenotypic data used in conditional QTL mapping is the target trait values conditioned on related traits. A statistical method was initially proposed for analyzing conditional genetic effects and variance

components [19], and had been mainly used in developmental quantitative genetics [20], [21] and [22]. With the combination of QTL mapping, conditional QTL mapping was widely used to dissect the genetic basis of agronomic traits in rice, maize and soybean at different developmental stages [23], [24], [25], [26], [27], Fluorouracil solubility dmso [28] and [29]. Zhao et al. also used this approach to dissect the genetic interrelationship between two traits at the level of individual

QTL, and to identify additional small-effect QTL that were not detected in unconditional Selleck ICG-001 mapping [30]. In this study, an RIL population, derived from a single cross of high-oil line By804 and regular line B73, was used to: map unconditional and condition QTL for oil, protein and starch content in maize kernels; explore the genetic interrelationships among three quality traits based on identified conditional and unconditional QTL. An RIL population consisting of 245 F7:8 lines derived from a cross Terminal deoxynucleotidyl transferase between regular inbred line, B73, and high-oil inbred line, By804 (derived from BHO after 13 selection cycles), was utilized in the present study. The RIL population, along with its parents, was evaluated in a randomized complete block design with three replications at the Agronomy Farm, China Agricultural University, Beijing, over two years (2005 and 2006). Each line was grown in a single row of 3 m with a planting density of 45,000 plant ha− 1. The row-to-row distance was kept at 67 cM. For each line, more than six plants in each row were pollinated with bulked pollen collected within the row.

Only pollinated ears were harvested at maturity, and equal amounts of grains from each harvested ear were bulked for measuring oil, protein and starch content. Two hundred and twenty four RILs with sufficient amounts of well-developed kernels from three field replications over two years were utilized for phenotyping. For each line, approximately 200 randomly chosen kernels from the bulked grain were analyzed by a VECTER22/N near-infrared analyzer (Bruker Corporation, Germany) for oil, protein and starch content. Genomic DNA was extracted from young leaves of 245 RILs using the CTAB method [31]. DNA amplification procedure was: template DNA 50 ng, 0.67 μmol L− 1 of each forward and reverse primer, 1.5 μL of 10 × PCR reaction buffer, 2.5 mmol L− 1 MgCl2, 0.2 mmol L− 1 of each dNTP, Taq DNA polymerase of 0.