conditional qtl mapping
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Abstract Background: Dynamic regulations of QTLs still remain mysterious. Single segment substitution lines and conditional QTL mapping, functional QTL mappings are ideal materials and methods to explore epistatic interactions, expression patterns and functions of QTLs for complex traits.Results: Based on single segment substitution lines five QTLs on plant height in rice were identified first in this paper, and then their epistatic interactions, expression patterns and functions were systemmatically studied by tailing after each QTL. Unconditional QTL mapping showed the five QTLs were with significant effects at one or more stages, all of which increased plant height except QTL1. They interacted each other as homeostatic mechanisms to regulate plant height with negative effects before 72d after transplanting and positive since then. Conditional QTL mapping revealed the expression quantities and periods for the five QTLs and their epistases. Temporal expression pattern was verified again by selective expressions of QTLs in specific periods. QTL1 expressed negatively while QTL2 and QTL4 positively, mainly occurring in the periods from 35 to 42d and from 49 to 56d after transplanting. Epistatic expressions were dispersedly in various periods, mainly with negative effects before 35d while positive since then. Functional QTL mapping discovered the five QTLs brought the inflexion point ahead of schedule, accelerated the growth and the degradation, and changed the peak of plant height, while their interactions had the opposite effects approximately. This paper uncovered the dynamic rules of five QTLs and their interactions on plant height systematically, which will be helpful to understand the genetic mechanism for developmental traits.Conclusions: Five single segment substitution lines were tested with significant additive, dominant and epistatic effects of QTLs on plant height. Additive and dominant expressions were mainly in two periods, while epistasis dispersedly. The five QTLs and their interactions significantly regulated the developmental trajectory of plant height.

AbstractGrain filling is an important growth process in formation of yield and quality for barley final yield determination. To explore the grain development behavior during grain filling period in barley, a high-density genetic map with 1962 markers deriving from a doubled haploid (DH) population of 122 lines was used to identify dynamic quantitative trait locus (QTL) for grain filling rate (GFR) and five grain size traits: grain area (GA), grain perimeter (GP), grain length (GL), grain width (GW) and grain diameter (GD). Unconditional QTL mapping is to detect the cumulative effect of genetic factors on a phenotype from development to a certain stage. Conditional QTL mapping is to detect a net effect of genetic factors on the phenotype at adjacent time intervals. Using unconditional, conditional and covariate QTL mapping methods, we successfully detected 34 major consensus QTLs. Moreover, certain candidate genes related to grain size, plant height, yield, and starch synthesis were identified in six QTL clusters, and individual gene was specifically expressed in different grain filling stages. These findings provide useful information for understanding the genetic basis of the grain filling dynamic process and will be useful for molecular marker-assisted selection in barley breeding.

SUMMARYFlour whiteness (FW) is an important factor in assessing flour quality and determining the end product quality. It is an integrated sensory indicator reflecting flour colour and is negatively correlated with protein content. In order to dissect the genetic relationship between FW and its five related traits at the quantitative trait locus (QTL)/gene level, a recombinant inbred line population was evaluated under three environments. Quantitative trait loci for FW were analysed by unconditional and conditional QTL mapping. Four unconditional additive QTLs and 16 conditional additive QTLs were detected across the three environments. Of these QTLs, only one major additive QTL (Qfw1D1-1) was consistently identified using both unconditional and conditional QTL analysis. This QTL was independent of flour colour a* (a function of red-green with a positive a* for redness and negative for greenness) and b* (a green-blue value with positive value for yellowness and negative for blueness) and was only slightly affected by flour protein content. A minor additive QTL (Qfw4A-4) was also detected using these two QTL mapping methods, being independent of flour colour a* and b*. Five unconditional and ten conditional epistatic minor QTLs were detected, from which only one pair (Qfw3A-10/Qfw6B-6) was identified by both unconditional and conditional QTL mapping, also independent of flour colour a* and b*. The major QTL (Qfw1D1-1) identified in the current study for the first time can be used for improving wheat FW in marker-assisted breeding.