Dear Colleagues,

Wheat can grow in a wide range of climates and soil conditions and remains an important cereal crop around the globe. Extensive breeding efforts have gone into wheat improvement over the years, during the late twentieth and early twenty-first centuries, leading to the development of a large number of high-yielding cultivars with improved grain quality. It has also been subjected to enormous cytogenetic studies during the last century and extensive genetic and molecular studies over the past few decades. Thanks to recent genomic and technological advances, the complex wheat genome has now been sequenced along with the genomes and transcriptomes of many wheat cultivars. Moreover, intense analyses of different genes/gene families have also greatly improved our knowledge about their molecular functions and phenotypic effects in wheat. However, despite these strides, challenges persist, with diseases, pests, and abiotic stresses continuing to impact wheat production, amounting to billions of dollars per year in losses. Further increase in yield and better quality of wheat can be achieved through the improvement of resistance to different biotic and abiotic stresses. Improving our understanding of the resistance mechanisms, genetic variation, and resources available for breeding wheat can facilitate the development of superior wheat cultivars and management strategies for different stresses.

Topics of interest for this Special Issue of Plants encompass:

Biotic stress resistance:

1. Etiology and virulence dynamics
2. Epistasis, suppressors, and susceptibility factors
3. Major gene resistance
4. Quantitative resistance
5. Durable resistance
6. Recessive genes and temperature-sensitive or high-temperature resistance
7. All-stage and stage-specific resistance
8. Innate immunity
9. The mapping and cloning of resistance genes
10. The role of metabolism, signaling, and proteomics in plant disease resistance
11. Transcription factors in plant disease resistance
12. Small RNAs, transposable elements, and epigenetics in resistance
13. Systems biology for plant disease resistance
14. RNAi and dsRNA applications for developing resistance
15. Genome editing for developing resistance
16. Plant–microbe interactions
17. Plant-associated microbiome-mediated resistance

Abiotic stress resistance:

18. Seed dormancy and resistance to pre-harvest sprouting
19. Heat tolerance
20. Cold tolerance/winter hardiness
21. Drought tolerance/water-use efficiency
22. Salinity resistance
23. Waterlogging tolerance
24. The effects of elevated carbon dioxide (CO₂), ozone (O₃), and UV radiation
25. Nutrient use efficiency and the effects of excess and low nitrogen and other macro- and micro-nutrients

Common topics:

26. Resistance genes and molecular markers
27. Pre-breeding and alien introgression
28. Classical and modern resistance breeding methods
29. Marker-assisted breeding and genomic selection
30. Phenomics for biotic and abiotic stresses
31. Resistance breeding efforts: success stories
32. Plant resistance gene and variety databases
33. Domestic and international regulations for the use of wild and cultivated/mutant resistance germplasm and genome edited/genetically modified breeding lines

Original research articles and reviews, communications, and short notes are welcome.

Dr. Raman Dhariwal
Guest Editor

Manuscript Submission Information

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• cereal disease
• pathogen
• insects
• disease resistance
• dominant genes
• recessive genes
• herbivory and insect resistance
• defense mechanism
• defense signaling
• hormones
• secondary metabolism
• induced resistance
• systemic acquired resistance
• innate immunity
• seed dormancy
• pre-harvest sprouting
• cold tolerance

Multi-locus genome-wide association study reveals powdery mildew resistance loci in bread wheat

Ramandeep Kaur¹, Neeraj Kumar Vasistha¹*, Vinod Kumar Mishra², Arun Kumar Joshi^3,4, Mahesh Tripathi⁵, Raman Dhariwal⁶*

¹Department of Genetics, Plant Breeding and Biotechnology, Dr. Khem Sigh Gill Akal College of Agriculture, Eternal University, Baru Sahib, HP, India;

²Department of Genetics and Plant Breeding, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, UP, India;

³Borlaug Institute for South Asia, New Delhi, India;

⁴CIMMYT, New Delhi, India;

⁵Department of Agricultural Engineering, Dr. Khem Sigh Gill Akal College of Agriculture, Eternal University, Baru Sahib, HP, India;

⁶Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre, Lethbridge, AB, Canada

*Corresponding authors: neerajvasistha@gmail.com; Raman.Dhariwal@agr.gc.ca

Abstract: Powdery mildew, caused by the fungal pathogen Blumeria graminis f. sp. tritici (Bgt), is a major threat to bread wheat production worldwide. Although growing resistant cultivars is the most effective approach to managing this disease, current wheat cultivars have insufficient levels of resistance. To address this issue, we conducted a comprehensive genome-wide association study to identify chromosomal regions containing powdery mildew resistance loci from a diverse germplasm panel. The panel consisted of 286 bread wheat genotypes, which were extensively phenotyped for powdery mildew severity over three consecutive years (2020-21, 2021-22 and 2022-23) in field conditions following inoculation with virulent Bgt isolates. In addition, the panel was genotyped using the Illumina 90K SNP Infinium iSelect assay to obtain genome-wide SNP marker coverage. Principal component analysis revealed five sub-populations within the panel, and the number of principal components explaining 50% of the cumulative variation was used to control for population structure. Among various models used to detect significant marker-trait associations (MTAs), FarmCPU, a multilocus mixed model, was found to be the most effective. FarmCPU identified a total of 38 MTAs located on chromosomes 1D, 2B, 2D, 3A, 5B, and 6A at p≤0.001, with 10 MTAs consistently detected across years. These results identify new loci associated with powdery mildew resistance, which can be used to develop powdery mildew-resistant wheat cultivars.