Svara, A. | bioRxiv Science

bioRxiv2025

A pan-generic marker panel for apples to enable genetic research and breeding across Malus species

AbstractWild Malus species harbor untapped genetic diversity to advance apple breeding, particularly for disease resistance and stress tolerance. However, existing marker panels, developed mainly using Malus domestica accessions, introduce ascertainment bias and limit detecting rare variants in wild species. We developed and validated a medium-density and cost-effective pan-generic 3K apple DArTag panel optimized to capture genome-wide variation across the Malus genus. The panel was constructed using conserved, syntenic, and collinear genomic blocks identified within the core genome of 13 Malus accessions for cross-species transferability. The panel was validated across three bi-parental mapping populations totaling 593 progeny. Across these populations, 2,461-3,234 SNP markers were polymorphic and 1,482-2,620 were informative. Each population contained over 900 multiallelic micro-haplotype loci, with several hundred loci exhibiting three or four distinct haplotypes. Markers were uniformly distributed across all 17 chromosomes, each containing between 60- 230 informative SNPs. The panel was further evaluated on 174 diverse germplasm accessions from 20 Malus species. It exhibited strong cross-species transferability, exceptionally low rates of missing data (<0.5%), and clear genetic differentiation between wild and domesticated accessions. Genome-wide association studies (GWAS) identified a major locus on chromosome 4 significantly linked to fruit length, weight, and width in addition to trait-specific associations on chromosomes 1, 6, 9, and 11. The cost-effectiveness of genotyping per sample (<$15), combined with these results, underscore the panels broad utility for quantitative trait locus (QTL) mapping in bi- parental and diverse populations, marker-assisted selection in the breeding programs, and genetic diversity analysis across the Malus genus.

genetics↗

bioRxiv2024

Advancing apple genetics research: Malus coronaria and Malus ioensis genomes and a gene family-based pangenome of native North American apples

Wild Malus species flourished in North America long before Europeans introduced domesticated apples. Malus coronaria and M. ioensis are native to the mid-western and eastern USA, while M. angustifolia and M. fusca grow in the southeast and west, respectively. They offer disease resistance, climate and soil adaptability, and horticultural traits for apple breeding. However, their utilization remains limited due to insufficient genomic resources and specific genetics. We report high-quality phased chromosome-scale assemblies of M. coronaria and M. ioensis, generated using long-read and conformation capture sequencing. Phylogenetic and synteny analysis indicated high relatedness between these two genomes and previously-published genome of M. angustifolia, and lower relatedness with M. fusca. Gene family-based pangenome of North American Malus identified 60,211 orthogroups containing 340,087 genes. Genes involved in basic cellular and metabolic processes, growth, and development were core to the existence of these species, whereas genes involved in secondary metabolism, stress response, and interactions with other organisms were accessory and are likely associated with adaptation to specific environments. Structural variation hotspots were mostly overlapping with high gene density. This study offers novel native North American Malus genome resources that can be used to identify genes for apple breeding and understand their evolution and adaptation.

genomics↗