Wheat germplasm is a fundamental resource for basic research, applied studies, and wheat breeding, which can be enriched normally by several paths, such as collecting natural lines, accumulating breeding lines, and introducing mutagenesis materials.  Ethyl methane sulfonate (EMS) is an alkylating agent that can effectively introduce genetic variations in a wide variety of plant species.  In this study, we created a million-scale EMS population (MEP) that started with the Chinese wheat cultivars ‘Luyan 128’, ‘Jimai 38’, ‘Jimai 44’, and ‘Shannong 30’.  In the M₁ generation, the MEP had numerous phenotypical variations, such as >3,000 chlorophyll-deficient mutants, 2,519 compact spikes, and 1,692 male sterile spikes.  There were also rare mutations, including 30 independent tillers each with double heads.  Some M₁ variations of chlorophyll-deficiency and compact spikes were inheritable, appearing in the M₂ or M₃ generations.  To advance the entire MEP to higher generations, we adopted a single-seed descendent (SSD) approach.  All other seed composites of M₂ were used to screen other agronomically important traits, such as the tolerance to herbicide quizalofop-P-methyl.  The MEP is available for collaborative projects, and provides a valuable toolbox for wheat genetics and breeding for sustainable agriculture.

Maize rough dwarf disease (MRDD), caused by Fijivirus, poses a significant threat to global maize production.  Using a recombinant inbred line (RIL) population derived from the resistant parent CML199 and the susceptible parent Zheng58, we identified three MRDD resistance QTLs on chromosomes 2, 6, and 9, accounting for 12.71, 5.89, and 11.04% of the total phenotypic variation, respectively.  Among them, the major locus qMrdd3 on chromosome 2 demonstrated incomplete dominance, conferring a resistance enhancement of 26.36–34.47% across diverse environments.  Fine-mapping refined qMrdd3 to a 227.7-kb interval containing five candidate genes, among which Zm00001d002441 was specifically upregulated in the resistant near-isogenic line (NIL-R) following RBSDV infection.  Additionally, two co-segregating markers were developed to facilitate efficient marker-assisted selection.  Introgression of qMrdd3 into Zheng58 and Chang7-2 enhanced field resistance by 38.84 and 26.47%, respectively.  This study provides a valuable genetic resource for MRDD resistance breeding through QTL dissection, elite germplasm development, and marker-assisted breeding.