Fungal endophytes boost salt tolerance and seed quality along a latitudinal gradient

Roberto Miño^1,2Gabriel I. Ballesteros^1,3*Karina B Ruiz⁴Ian S Acuña^1,3Marco A Molina-Montenegro^1,2,5*

• ¹Centro de Ecología Integrativa (CEI), Universidad de Talca, Talca, Chile
• ²Institute of Biological Sciences, University of Talca, Talca, Chile
• ³Dirección de Investigación, Vicerrectoría Académica, Universidad de Talca, Talca, Chile
• ⁴Química y Farmacia, Facultad de Ciencias de la Salud, Universidad Arturo Prat, Iquique, Chile
• ⁵Centro de Investigación y Estudios Avanzados de Maule, Vicerrectoría de Investigación y Estudios de Posgrado, Universidad Católica de Maule, Talca, Chile

Soil salinity threatens global food security, making salt tolerance a key agronomic trait. In this context, quinoa (Chenopodium quinoa Willd.), a halophytic pseudo-cereal with high nutritional value, has emerged as a resilient crop. While its physiological and morphological responses to salinity are well studied, the role of native endophytic microorganisms remains largely unexplored, especially across genotypes. This study hypothesizes that quinoa-associated endophytes contribute variably to salinity tolerance and seed quality across genotypes distributed along a 2,200 km latitudinal gradient (19°-39° S). Five quinoa genotypes were selected, and plants with (E + ) or without (E -) fungal endophytes were exposed to 0, 200, or 400 mM NaCl. Salinity tolerance was assessed via photochemical efficiency (Fv/Fm), gene expression (CqNHX1, encoding for a Na + /H + antiporter), and plant survival rates, while seed quality was evaluated by seed weight and protein content. Under salinity stress, native microbiomes provided beneficial, but genotype-dependent effects on stress tolerance and seed quality. Notably, E + plants exhibited no negative effects under non-saline conditions. These findings suggest that, in quinoa, fungal endophytes interactions shift from neutral to beneficial under salinity, with no trade-offs under normal conditions. Our results highlight the role of native microbiomes in enhancing quinoa resilience and nutritional value, reinforcing their importance for crop adaptation in the face of climate change.