Abstract
Wheat (Triticum aestivum L.) is one of the world’s staple food crops and one of the most devastating foliar diseases attacking wheat is powdery mildew (PM). In Denmark only a few specific fungicides are available for controlling PM and the use of resistant cultivars is often recommended. In this study, two Chinese wheat landraces and two synthetic hexaploid wheat lines were used as donors for creating four multi-parental populations with a total of 717 individual lines to identify new PM resistance genetic variants. These lines and the nine parental lines (including the elite cultivars used to create the populations) were genotyped using a 20 K Illumina SNP chip, which resulted in 8,902 segregating single nucleotide polymorphisms for assessment of the population structure and whole genome association study. The largest genetic difference among the lines was between the donors and the elite cultivars, the second largest genetic difference was between the different donors; a difference that was also reflected in differences between the four multi-parental populations. The 726 lines were phenotyped for PM resistance in 2017 and 2018. A high PM disease pressure was observed in both seasons, with severities ranging from 0 to >50%. Whole genome association studies for genetic variation in PM resistance in the populations revealed significant markers mapped to either chromosome 2A, B, or D in each of the four populations. However, linkage disequilibrium between these putative quantitative trait loci (QTL) were all above 0.80, probably representing a single QTL. A combined analysis of all the populations confirmed this result and the most associated marker explained 42% of the variation in PM resistance. This study gives both knowledge about the resistance as well as molecular tools and plant material that can be utilised in marker-assisted selection. Additionally, the four populations produced in this study are highly suitable for association studies of other traits than PM resistance.
Highlights
Wheat (Triticum aestivum L.) is one of the world’s staple food crops and is responsible for feeding nearly 35% of the population (Paux et al, 2008)
The variance clearly shows that the multi-parental populations contain lines that are highly susceptible and lines that are highly resistant to powdery mildew (PM) and in all scoring dates and years we found high narrow sense heritability, making the populations ideal for association studies on PM resistance
In this study we identified a quantitative trait loci (QTL) on one of the homologous wheat chromosomes 2A, B, and D in four multi-parental populations
Summary
Wheat (Triticum aestivum L.) is one of the world’s staple food crops and is responsible for feeding nearly 35% of the population (Paux et al, 2008). Symptoms of PM are white powder-like colonies on leaves and stem which consists of mycelium and conidia. These symptoms may be followed by black overwintering sexual structures, cleistothecia, which may overwinter, release ascospores, and infect new host plants in the following growing season. Today’s cultivation of modern crops includes the use of semi-dwarf and dense cultivars in combination with a high nitrogen supply. This practice favors a rapid development of PM and can lead to severe epidemics. In order to control the disease, application of foliar fungicides is often recommended, but yield responses are variable depending on locality, timing and level of host resistance (Jørgensen et al, 2018). In Denmark, for instance, only a few fungicides are available for controlling PM and (Jørgensen et al, 2018) and use of resistant cultivars is recommended to promote integrated pest management (IPM) practices, which is considered to be the most environmental-friendly and efficient approach to control PM (Bennett, 1984; Uloth et al, 2016)
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