Inheritance and QTL analysis of dough rheological parameters in wheat

Abstract

A RIL population from two Australian wheats, Lang and CSCR6, was employed to evaluate the genetic variation and to detect QTL associated with dough rheological characters based on DArT and SSR markers and two environmental experiments. It was showed that the higher variation existed in the RIL for dough rheological characters, and so did much more abundant selection potentials that lacked in Chinese current commercial varieties. Nine additive QTLs for dough rheological characters were identified. Of which those for water absorption (WA) were located on chromosome 2A and 5A, stability time (ST) on 4B and 1B, breaking time (BT) on 1B, degree of softening (DS) on 1B, band width (BW) on 2B (two loci), evaluation value (EV) on 1B. And seven epistatic QTLs were screened out, and non-significant variance was found for the interaction between these epistatic QTLs and the environment. Correlation analysis indicated that there was a significantly positive relation between WA and development time (DT), and EV, whereas negatively related to BW. A significantly positive relation existed between DT, ST, BT and EV each other. They were negatively related to mixing tolerance index (MTI) and degree of softening (DS), both had a markedly positive relation.

Keywords

dough rheological characters / quality properties / QTL / DArT / additive effect

Introduction

Improving bread baking quality is one of the most important targets for quality breeding program in wheat. Bread baking quality is usually affected by the dough rheological parameters which are quantitatively inherited traits. There is a low efficiency for such kind of traits based on the phenotypic selection in traditional breeding. Genetic mapping and quantitative trait loci (QTL) analysis make it possible to dissect QTL controlling the quality traits and to increase the forecast feasibility of selection.

Quite a few studies have been carried out in QTL detection for quality characters by using various genetic populations and molecular markers in wheat. QTLs analysis on dough rheological characters and bread baking quality with 182 DH lines showed that the QTLs associated with dough water absorption were detected on chromosome 1A, 1B, 2A and 2D, as well as those were linked to dough development time on chromosome 1B, dough stability on 1A, 1B and 2A, dough strength and loaf volume on chromosome 2A and 3A (Kuchel et al., 2006). Eight QTLs associated with dough rheological parameters were identified by using 165 RILs, which gave 5.4%–26.6% explanation of phenotypic variance. Those on chromosome 3A and 5B also affected the grain hardness and protein content (Groos et al., 2004). Ninety-nine QTLs controlling 47 quality characters, including milling, dough rheological, baking, starch and noodle color etc., were screened out by McCartney et al. (2006) using 182 DH lines. They were located on 18 chromosomes, and of which, 44 were mapped to three major QTL clusters on chromosomes 1B, 4D and 7D. Major-effect QTLs were detected for grain and flour protein content, farinograph absorption, mixograph parameters and dietary fiber on chromosome 2BS. In another research, the dough properties of 204 RILs from a cross between wheat and spelt assessed in different environments indicated that nine QTLs were found for Zeleny sedimentation values explaining 47% of the phenotypic variance. For the alveograph parameters, 10 QTLs were found for baking strength, nine for tenacity, seven for configuration ratio, and four for elasticity index and extensibility (Zanetti et al., 2001). Also, analysis of dough rheological parameters with 165 DH lines found that the main additive QTL for dough rheological properties were located at the high- and low-molecular-weight glutenin loci. A new QTL on chromosome 5A for M-extensibility was detected, and the genotypic factors were the major determinants of dough strength (Ma et al., 2005).

The objectives of this study were to evaluate the genetic bases of an RIL population from wheat and spelt, and to identify QTLs controlling wheat dough rheological characters using SSR and DArT markers.

Materials and methods

Plant materials

The mapping population was RILs derived from a cross between an Australian hexaploid wheat and a spelt, Lang and CSCR6 (Ma et al., 2009). Lang is a high yielding cultivar extensively grown in Queensland and New South Wales, and CSCR6 belongs to the taxon T. spelt. Ninety-two RILs and the two parents were planted in Baoding and Zhangjiakou, Hebei province in 2010. The experiments were randomly arrayed with three replications, and four lines were planted for each RIL line with 2.5 m (40 seeds) in length and 25 cm spacing from each other.

Determination of dough rheological properties

Dough rheological properties were measured using a farinograph (Brabender, Germany) according to AACC method 54-21 (American Association of Cereal Chemists, 1983). The parameters include water absorption (WA), development time (DT), stability time (ST), mixing tolerance index (MTI), breaking time (BT), degree of softening (DS), band width (BW) and evaluation value (EV).

QTL analysis

The means, standard errors, skewness, kurtosis and correlation coefficients for the dough rheological characters of the RIL population were calculated by using a software, SPSS Statistics 17.0. Genetic mapping was conducted using 967 polymorphic DArT and 54 SSR markers, of which, 776 markers were located on 18 out of 21 chromosomes in wheat. The linkage groups were 912.9 cM long in total with an averaged interval of 1.2 cM between markers (Ma et al., 2009). The QTL analysis was carried out via QTL Network-2.1, and F significance test via Henderson method III. One dimensional scan was served to detect major-effect QTL, and two dimensional scan to detect epistatic-effect QTL. The Permutation method was employed to test QTL significance and probability level for whole genome scan was P=0.05. The distribution of various QTL effects were determined by Bayesian method based on Gibbs sampling (Yang et al., 2005, 2008).

Results and analysis

Phenotypic variation of the RIL population

The differences existed among the dough rheological properties in the RIL population and their parents (Tables 1, and 2). Higher WA, DT, ST, BT and EV were found for Lang than those for the male parent, CSCR6. Dough rheological properties of CSCR6 were more stable in two environments, whereas those of Lang varied more, as the DT, ST, BT and EV were 9.6/6.9, 18.9/6.4, 30/14.5 and 80/69 at Baoding/Zhangjiakou locations, respectively. All the dough rheological parameters were normally distributed in the RIL population, and high genetic variations were discovered between sites and RIL lines. The variation coefficients ranked as MTI>DS>ST>DT>BT>BW>EV>WA. Some dough rheological parameters showed a higher value than Chinese wheat cultivars, such as DT (8.95), ST (15.18), BT (23.19) and EV (74.72). It is valuable to the improvement of quality properties for Chinese common wheat. On all accounts, the tested RIL population and its parents contained abundant genetic variations and selection potentials in dough rheological properties.

Correlation analysis indicated that the WA was significantly positively related to DT and EV, and negative to BW. There was a significantly positive relation between DT, ST, BT and EV each other, and they were remarkably negatively related to MTI and DS (Table 3). All the marked relations among the characters determined suggest that there exists the genetic linkage or one-gene-multiple effect.

QTL analysis of dough rheological traits

The QTL analysis showed that nine QTLs were detected for the dough rheological traits, with additive effect and 5.81%–16.91% explanation of phenotypic variation (Table 4, Fig. 1). These QTLs were located on chromosome 1B, 2A, 2B, 4B and 5A, respectively, of which four on 1B with over 10.0% explanation of phenotypic variance. Two QTLs for ST located on 1B and 4B explained 16.91% and 6.74% phenotypic variance and could make the dough stability time increased 2.255 min and 1.352 min, respectively, which come from Lang’s alleles.

Two QTLs for WA located on 2A and 5A could give increased effects on flour water absorption via the alleles of Lang and CSCR6. The WPT-8832-WPT-1675 locus was simultaneously linked to four dough rheological traits, ST, BT, DS and EV, indicating the presence of one-gene-multiple effect. In addition, non-significant interaction effect was found for all the detected QTLs, suggesting that they are mainly controlled by additive loci, and more stable and easy for use.

Analysis of epistatic effect indicating that seven pairs of additive×additive effects of QTLs were identified for WA, BT, DS, MTI, BW, EV, involving chromosome 1B, 2A, 2B, 3A, 3B, 3D and 4A with 5.03%–11.70% explanation of phenotypic variance (Table 5). All the epistatic effects came from the interactions between non-linked loci, i.e. the interaction between different chromosomes. Moreover, no significant interaction was found between any epistatic effect and environment, showing the epistatic QTLs were impacted little by environment. A locus, WPT-6738-WPT-4153, appeared epistatic QTL with both WPT-0940-WPT-2559 and WPT-7614-WPT-5072.

It also can be seen that the nine additive QTLs (Table 4) and seven epistatic QTLs (Table 5) dealt with nine chromosomes. However, it seems that the additive QTL did not play a role in the epistatic.

Prediction superior line genotype

Based on the additive and epistatic effects, the genetic effects of all QTLs genotypic combinations were estimated for each trait. The combination with the maximum genetic effects was regarded as the superior line genotype. The general superior lines (GSL) of traits were predicted based on the genetic effects of QTLs estimated in the present study (Table 6). As all detected QTLs were seldom affected by environments, the genetic effects of superior lines from each environment were the same as those of GSL. The genetic effects of GSL for WA, ST, BT, and EV were the same as those of female parent, indicating P₁ is a superior line for improvement of these traits. Similarly, P₂ was a superior line for BW to be meliorated. However, the genetic effects of GSL for MTI and DS were obviously higher than those of parents, suggesting an over-parent dominant effect existing.

The QTL genotype (QG) of GSL for each trait was also predicted (Table 7), with the QQ expression of the alleles in a locus from P₁, whereas qq from P₂. The QG of GSL for the QTL controlling ST, BT and EV were the same as those of P₁. It can be seen that the QG of GSL for the same trait QTL on chromosomes were different from each other.

Discussion

Several dough rheological traits of RILs from two Anstralian wheats, Lang and CSCR6, were evaluated in two different environments and the QTLs controlling these traits were detected based on a genetic linkage map using DArT and SSR markers in the current study. Some previous studies demonstrated that DArT markers showed characteristic of a single locus and tended to distributing in gene-rich regions of chromosomes compared to AFLP, RFLP and SSR markers in hexaploid wheat (Jaccoud et al., 2001, Semagn et al., 2006; Peleg et al., 2008; Hong et al., 2009). Genetic mapping and QTLs detection were conducted using DArT markers by researchers (Semagn et al., 2006; Li et al., 2008; Mantovani et al., 2008; Peleg et al., 2008) as well as our present study, by which and some SSR markers, we constructed a map and identified four major QTL of dough rheological traits locating in the interval of WPT-8832-WPT-1675 on chromosome 1B. This as the same that QTL related to bread baking quality was detected in other populations (Kuchel et al., 2006; Elangovan et al., 2008), indicating 1B could be the enrichment region controlling the gluten intensity. QTLs detected in this study provided fresh instance for DArT application and source of selection for future wheat genetic improvement.

Most researchers considered that QTL detection was impacted by genetic populations and molecular markers that were used. Whether a QTL was able to be used for marker-aided selection or not, the most conservative way was to judge it could or not repeatedly appeared among populations and environments, and it was or not negatively correlated with the other important traits (Suprayogi et al., 2009). Actually, QTL with higher contribution ratio and large number of total QTL were more normally to be detected in a single environment than in multiple environments. Therefore it was suggested that QTL analysis should be carried out based on multiple environment test (Blanco et al., 2002). The QTL detected base on multiple environment tests were normally with higher LOD value and therefore were more truly inherited (Ma et al., 2007). The current study identified some QTLs related to dough DT, ST and BT at two locations, and they did not significantly interact with environment. This provides references for marker-assisted selection in quality breeding of wheat.

Dough rheological traits belong to the important processing properties in wheat. It was found that Australian wheats had longer dough DT and ST than those of Chinese varieties. So the dough viscosity deteriorated the quality of steamed bread making (Zhu et al., 2001). The results of this study showed that the RIL lines from two Australian wheats were markedly superior to those of Chinese commercial varieties in dough rheological properties. There was a high genetic variation for dough stability, mixing tolerance index and breaking time in the RIL population. Determination of dough rheological characters usually uses many a seeds, which makes a difficulty for their selection in early generations. This can be overcome via an indirect selection through a linked character to the dough rheological characters, such as using the sedimentation value that has a higher heritability and is closely linked to dough rheological characters (Li et al., 1990; Zhang et al., 2003; Yang et al., 2006).

As a whole, the detection of loci affecting the investigated traits in the RILs from Australian wheats may provide fresh opportunities for the application of marker-assisted selection to improve yield and quality.

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