Skim exome capture genotyping in wheat

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Abstract

Next-generation sequencing (NGS) technology advancements continue to reduce the cost of high-throughput genome-wide genotyping for breeding and genetics research. Skim sequencing, which surveys the entire genome at low coverage, has become feasible for quantitative trait locus (QTL) mapping and genomic selection in various crops. However, the genome complexity of allopolyploid crops such as wheat (Triticum aestivum L.) still poses a significant challenge for genome-wide genotyping. Targeted sequencing of the protein-coding regions (i.e., exome) reduces sequencing costs compared to whole genome re-sequencing and can be used for marker discovery and genotyping. We developed a method called skim exome capture (SEC) that combines the strengths of these existing technologies and produces targeted genotyping data while decreasing the cost on a per-sample basis compared to traditional exome capture. Specifically, we fragmented genomic DNA using a tagmentation approach, then enriched those fragments for the low-copy genic portion of the genome using commercial wheat exome baits and multiplexed the sequencing at different levels to achieve desired coverage. We demonstrated that for a library of 48 samples, ∼7–8× target coverage was sufficient for high-quality variant detection. For higher multiplexing levels of 528 and 1056 samples per library, we achieved an average coverage of 0.76× and 0.32×, respectively. Combining these lower coverage SEC sequencing data with genotype imputation using a customized wheat practical haplotype graph database that we developed, we identified hundreds of thousands of high-quality genic variants across the genome. The SEC method can be used for high-resolution QTL mapping, genome-wide association studies, genomic selection, and other downstream applications.

Multiscale temporal and spatiotemporal analysis of wheat blast infection‐like dynamics using vertical plant stratification, regression and Markov chain approaches

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Multiscale temporal and spatiotemporal analysis of wheat blast infection-like dynamics using vertical plant stratification, regression and Markov chain approaches

Deterministic and stochastic methods identified how WB intensity varies across scales. Temporally, WSB presented a higher disease intensity than WLB. At the spatiotemporal level, four types of infection-like changes were estimated.


Abstract

The spatiotemporal progress of wheat blast (WB) epidemics within the plant canopy remains poorly known due to complex pathogen–host–environment interactions. Although deterministic methods are popular and useful, robust stochastic methods, such as generalized additive models for location, scale and shape (GAMLSS) and probability matrix or Markov transition model (MTM), have seldom been used to analyse plant disease epidemics. Hence, both methods were employed to derive valuable insights into WB epidemiology at the vertical canopy level. We conducted experiments in three climatic zones in Bolivia, using three wheat cultivars, with disease data corresponding to different canopy positions (lower, L; middle, M; flag leaf, F; and spike, S). Using WB severity data (AUDPC, progress rate and maximum severity [K max]), we implemented the GAMLSS and MTM to test our hypothesis that WB is affected by host resistance, location and canopy level. Results showed that the AUDPC, progress rate and K max differed across sites, cultivars and canopy positions. Clearly, L and M canopies showed a lower progress rate than F and S. The disease showed an ascending movement from L and M canopies to F and S across locations and cultivars. However, descending transitions also occurred from M to L early or F to M canopy later in the season. Both ascending and descending movements can arise at a single state or several recurrent states, indicating indirect evidence of autoinfection within the canopy before and after spike emergence. Our findings contribute knowledge to improve monitoring and managing WB.

Expression analysis of candidate genes as indicators for commencing drought stress in starch potatoes

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Abstract

Drought stress is a major problem for potato production and will be of grave importance due to climate change and the resulting temperature peaks along with drought periods in the vegetative growth phase of potato. Plants, as sessile organisms, adapt to their environment morphologically as well as biochemically. To cope better with abiotic stresses like drought, plants developed strategies like reactive oxygen species (ROS) detoxification and fast reacting stomatal closure, as well as signalling cascades leading to a quick response to stress. This study aimed at analysing eight genes of interest, derived from a former proteomic study, and determining their suitability for detection of commencing drought stress in early growth stages of potato. For this aim, six starch potato genotypes, which differed in stress response in previous studies, were examined for plant growth and physiological parameters in two experiments in an open greenhouse after seven and 14 days of stress. Besides lower shoot biomass after drought stress, which was already visible after seven days and became stronger after 14 days, weaker root growth was also detected after 14 days. The observed differences between the experiments can presumably be explained by temperature peaks and high radiation prior to and during the first experiment, which took place earlier in the year. The expression of the eight genes was studied in young leaves of four genotypes after 7 days of water withdrawal. Gene expression patterns were dependent on the studied genes. Three genes, cell wall/vacuolar inhibitor of fructosidase (INH1), peroxidase 51-like (POD) and subtilase family protein (SBT1.7) showed consistent changes in gene expression after seven days of stress between all genotypes. The INH1 gene was found to be upregulated in all genotypes in two independent experiments after drought stress. This correlates with the results at the protein level, where INH1 was also found to be higher abundant in two genotypes of potato (Wellpott et al., DGG-Proceedings 10, 2021). Therefore, this gene might be an appropriate candidate for the detection of commencing drought stress in potato.

The antifungal activity of trans‐cinnamic acid and its priming effect in apple in response to Valsa mali

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The antifungal activity of trans-cinnamic acid and its priming effect in apple in response to Valsa mali

Trans-cinnamic acid not only plays a significant role in inhibiting the growth of Valsa mali, a fungus causing apple Valsa canker disease, but also in priming host defence.


Abstract

Valsa mali causes Valsa canker, one of the most destructive diseases on apple trees, leading to severe losses for the apple industry in China. Considering the development of fungicide resistance and the harmful effects of chemical residues, it is urgent to identify alternatives to control this disease. Trans-cinnamic acid (t-CA), a compound with good antibacterial, antitumour and anti-inflammatory properties, is widely used in food, medicine and other industries. However, the antifungal activity of t-CA against V. mali and its regulatory role in apple defence against biotic stresses are unclear. Based on a metabolomic assay, we found that Malus yunnaensis (Valsa canker-resistant) twigs infected with V. mali dramatically accumulated t-CA. Exogenous application of t-CA effectively inhibited V. mali growth on potato dextrose agar. The EC50 value of t-CA inhibiting mycelial growth was 200 μg/mL. Malus prunifolia (Valsa canker-susceptible) leaves and twigs pretreated with t-CA had significantly enhanced V. mali resistance. The t-CA application increased salicylic acid but reduced jasmonic acid levels in leaves and twigs. Moreover, the contents of phenolic acids and flavonoids increased in t-CA-treated samples. In addition, t-CA increased the activities of phenylalanine ammonia-lyase, β-1,3-glucanase and chitinase. These results indicate that t-CA plays a significant role in inhibiting V. mali growth and priming apple defence.

Integrating de novo QTL‐seq and linkage mapping to identify quantitative trait loci conditioning physiological resistance and avoidance to white mold disease in dry bean

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Abstract

White mold (WM), caused by the ubiquitous fungus Sclerotinia sclerotiorum, is a devastating disease that limits production and quality of dry bean globally. In the present study, classic linkage mapping combined with QTL-seq were employed in two recombinant inbred line (RIL) populations, “Montrose”/I9365-25 (M25) and “Raven”/I9365-31 (R31), with the initial goal of fine-mapping QTL WM5.4 and WM7.5 that condition WM resistance. The RILs were phenotyped for WM reactions under greenhouse (straw test) and field environments. The general region of WM5.4 and WM7.5 were reconfirmed with both mapping strategies within each population. Combining the results from both mapping strategies, WM5.4 was delimited to a 22.60–36.25 Mb interval in the heterochromatic regions on Pv05, while WM7.5 was narrowed to a 0.83 Mb (3.99–4.82 Mb) region on the Pv07 chromosome. Furthermore, additional QTL WM2.2a (3.81–7.24 Mb), WM2.2b (11.18–17.37 Mb, heterochromatic region), and WM2.2c (23.33–25.94 Mb) were mapped to a narrowed genomic interval on Pv02 and WM4.2 in a 0.89 Mb physical interval at the distal end of Pv04 chromosome. Gene models encoding gibberellin 2-oxidase proteins regulating plant architecture are likely candidate genes associated with WM2.2a resistance. Nine gene models encoding a disease resistance protein (quinone reductase family protein and ATWRKY69) found within the WM5.4 QTL interval are putative candidate genes. Clusters of 13 and 5 copies of gene models encoding cysteine-rich receptor-like kinase and receptor-like protein kinase-related family proteins, respectively, are potential candidate genes associated with WM7.5 resistance and most likely trigger physiological resistance to WM. Acquired knowledge of the narrowed major QTL intervals, flanking markers, and candidate genes provides promising opportunities to develop functional molecular markers to implement marker-assisted selection for WM resistant dry bean cultivars.