RESUMEN
Arbuscular mycorrhizal fungi (AMF) are obligate plant symbionts of most land plants. In these organisms, thousands of nuclei that are either genetically similar (homokaryotic) or derived from two distinct parents (dikaryotic) co-exist in a large syncytium. Here, we investigated the impact of these two nuclear organizations on the mycorrhizal response of potatoes (Solanum tuberosum) by inoculating four potato cultivars with eight Rhizophagus irregularis strains individually (four homokaryotic and four dikaryotic). By evaluating plant and fungal fitness-related traits four months post inoculation, we found that AMF genetic organization significantly affects the mycorrhizal response of host plants. Specifically, homokaryotic strains lead to higher total, shoot, and tuber biomass and a higher number of tubers, compared to dikaryotic strains. However, fungal fitness-related traits showed no clear differences between homokaryotic and dikaryotic strains. Nucleotype content analysis of single spores confirmed that the nucleotype ratio of AMF heterokaryon spores can shift depending on host identity. Together, these findings continue to highlight significant ecological differences derived from the two distinct genetic organizations in AMF.