Inbreeding depression in diploid potato: genetic basis, deleterious load, and breeding mitigation

The development of diploid hybrid potato derived from traditional tetraploid clonal cultivars is a key breakthrough for modern potato breeding. However, severe inbreeding depression severely restricts the breeding and application of homozygous inbred lines. This narrative review systematically elaborates the phenotypic characteristics of inbreeding depression in diploid potato, and explores the accumulation mechanism of deleterious load driven by long-term clonal propagation and polyploid genetic buffering. Continuous selfing elevates genome-wide homozygosity, which exposes recessive deleterious variants and further causes comprehensive declines in plant vigor, reproductive capacity, tuber yield, tuber quality and stress tolerance. We then summarize multiple quantitative evaluation systems for inbreeding depression and genetic load, and sort out a series of targeted breeding interventions, including genomic prediction, marker-assisted selection, CRISPR-Cas9 genome editing and hybrid complementation. Each technical strategy is discussed with explicit discussion of its practical limitations. Finally, we discuss the research prospects of genome design breeding for purging deleterious variants, and distinguish laboratory research progress from large-scale industrial application. This review establishes an explicit logical framework linking deleterious load, genomic homozygosity, phenotypic deterioration and breeding strategies, and provides theoretical references for the innovation of diploid potato inbred line breeding.