Genotype-dependent responses of Andean and Coastal quinoa to plant population density for yield and its physiological determinants in Northwest Argentina

Context. In quinoa, similar yields are found under a wide range of plant population densities due to its phenotypic plasticity.Aims. This study aimed to identify optimal plant population densities for achieving attainable yields, in relation to the most adapted genotype for a given environment.Methods. Andean (RQ252 and RQ420) and Coastal (Titicaca and Puno) genotypes were tested at conventional (14 plants/m(2)) and low (7 plants/m(2)) plant population densities, in Dry Valley and Highland mega-environments for 2 years.Key results. More than 64% of total variation was explained by genotype, location, and interaction effects for grain yield, biomass, and harvest index. For these variables, the genotype x location x plant population density term presented the highest percentage of variation among triple and quadruple interaction terms. In the Highlands, grain yields decreased with plant population density for Andean genotypes (30-40%), in contrast to lower reductions for Coastal genotypes (9-20%). In the Dry Valleys, no effect of plant population density was found for all genotypes. In the Highlands, reductions in biomass and harvest index explained grain yield response, in parallel with increases in small grain percentage of up to 16% when frosts came early, related to uneven maturity at low plant population density.Conclusions. Attainable yields in Northwest Argentina were achieved by exploring local adaptation and response to plant population density of Andean genotypes in the Highlands, in contrast to stable yields of Coastal genotypes through locations and plant population densities.Implications. Understanding genotype-dependent responses to plant population density according to Northwest Argentina mega-environments can reduce yield gaps in quinoa production and refine breeding strategies.