Mapping QTLs with epistatic effects and QTL × treatment interactions for salt tolerance at seedling stage of wheat

Quantitative trait loci (QTLs) with additive (a), additive × additive (aa) epistatic effects, and their treatmental interactions (at and aat) were studied under salt stress and normal conditions at seedling stage of wheat (Triticum aestivum L.). A set of 182 recombinant inbred lines (RILs) derived from cross Xiaoyan 54 × Jing 411 were used. A total of 29 additive QTLs and 17 epistasis were detected for 12 traits examined, among which eight and seven, respectively, were identified to have QTL × treatment effects. Physiological traits rather than biomass traits were more likely to be involved in QTL × treatment interactions. Ten intervals on chromosomes 1A, 1D, 2A (two), 2D, 3B, 4B, 5A, 5B and 7D showed overlapping QTLs for different traits; some of them represent a single locus affecting different traits and/or the same trait under both treatments. Eleven pairs of QTLs were detected on seemingly homoeologous positions of six chromosome groups of wheat, showing synteny among the A, B and D genomes. Ten pairs were detected in which each pair was contributed by the same parent, indicating a strong genetic plasticity of the QTLs. The results are helpful for understanding the genetic basis of salt tolerance in wheat and provide useful information for genetic improvement of salt tolerance in wheat by marker-assisted selection.     

Assessing the importance of genotype × environment interaction for root traits in rice using a mapping population III: QTL analysis by mixed models

The phenotypic analysis of field experiments includes information about the experimental design, the randomization structure and a number of putative dependencies of environment and design factors on the trait investigated. In QTL studies, the genetic correlation across environments, which arises when the same set of lines is tested in multiple environments, plays an important role. This paper investigates the effect of model choice on the set and magnitude of detected root QTL in rice. Published studies on QTLs for root traits indicate that different results are obtained if varying genetic populations are used and also if different environmental conditions are included. An experiment was conducted with 168 RILs of the Bala × Azucena mapping population plus parents as checks under four environmental conditions (low light, low nitrogen, drought and a control environment). We propose a model that incorporates all relevant experimental information into a composite interval mapping approach based on a mixed model, which especially considers the correlation of genotypes in different environments. An extensive sequential model selection procedure was applied based on the phenotypic model, using the AIC to determine an appropriate random structure and Type 3 Wald F-tests for selection of fixed effects. In a first step we checked whether any of the fixed effects and random (nested) design effects could be dropped. Secondly, an appropriate covariance structure was chosen for genotype × environment interaction. In a third step Box-Cox transformations were applied based on residual analysis. We compared profiles of composite interval mapping scans with and without the inclusion of genotype × environment interaction and the experimental design information. Some distinct differences in profiles indicate that insufficient modeling of the non-QTL part can lead to an overly optimistic interpretation of QTL main effects in interval mapping. It is concluded that mixed model QTL mapping offers a reasonable way to separate environmental and genetic influences in the evaluation of quantitative genes and especially enables a more realistic assessment of QTL and QTL × environment effects than standard approaches by including all relevant effects.     

Impact of a decontamination step with peroxyacetic acid on the shelf-life,sensory quality and nutrient content of grated carrots packed under equilibrium modified atmosphere and stored at 7 °C

Peroxyacetic acid (PAA) is a strong oxidizer and exerts antimicrobial properties. The effect of a decontamination step with 80 and 250 mg L⁻¹ PAA on shelf-life of grated carrots stored under equilibrium modified atmospheric packaging at 7 °C was determined and compared with the shelf-life of unwashed and water-washed carrots. Microbial parameters, including total aerobic plate count, numbers of lactic acid bacteria, Lactobacillae and yeasts, and sensory quality were evaluated. Next to these parameters, atmospheric gas composition, pH and nutrient content were also monitored. The suggested packaging configuration prevented CO₂ accumulation, but at the end of the study anoxic conditions were reached for unwashed carrots and carrots washed with 80 mg L⁻¹ PAA. The microbial shelf-life of water-washed carrots was 4 d based on the yeast count, whereas the flavour was not acceptable after 5 d. The total aerobic plate count and the yeast count determined the shelf-life of carrots treated with 80 mg L⁻¹ PAA on 5 d, whereas the flavour was unacceptable after 7 d. None of the microbial parameters determined the shelf-life of carrots washed with 250 mg L⁻¹ PAA. However, this treatment had already a pronounced adverse effect on the initial sensory quality. Water washing already decreased the content of all individually studied nutrients (−16 to −28%), except for lutein content and the antioxidant capacity. Additional losses after adding PAA on day 0 were found for α-tocopherol and phenols. Regardless of the applied treatment, α- and β-carotene remained stable during storage, whereas ζ-carotene, lutein and α-tocopherol were unstable. The phenol content and the antioxidant capacity of unwashed, water-washed and 80 mg L⁻¹ PAA-treated carrots increased significantly at the end of the storage period, whereas no changes were found in carrots treated with 250 mg L⁻¹ PAA.On the condition that carrots were packed under an adequate EMA, the 80 mg L⁻¹ PAA treatment showed possibilities for extending shelf-life without pronounced effects on nutrient content.