Re-evaluating onion varieties in organic farming: Evidence from a decade of multi-environment trials

Onion landraces and traditional open-pollinated varieties are gaining renewed interest in organic farming due to their potential for regional adaptation, on-farm seed use, and distinct flavor profiles. However, comprehensive long-term field-based evaluations of their agronomic and quality traits remain scarce. This study assessed the agronomic performance, compositional quality, and environmental responsiveness of traditional open-pollinated onion varieties grown under certified organic conditions across diverse environments in Germany. Between 2014 and 2024, 19 field trials were conducted at seven research and on-farm locations. Three open-pollinated varieties, including one landrace, were evaluated alongside commercial references. Yield, quality traits, and environmental interactions were analyzed using meta-analyses, linear mixed-effects models (including site-year as a random effect), and principal component analysis. The landrace Birnenförmige (Bif) and the traditional open-pollinated variety Stunova (Stu) generally matched or approached the performance of commercial varieties. Birnenförmige showed the most consistent and statistically robust advantages in compositional traits, combining early maturity with high dry matter, sugar, and pyruvate levels. In contrast, Stunova—tested only at research stations—showed positive but more variable responses, with high fructan concentrations and favorable yield trends in early trial years. By comparison, the traditional open-pollinated variety Rijnsburger 4 (Rij) showed increased sensitivity to humid conditions, with reduced marketable yield and quality. Relative humidity negatively affected dry matter and sugar accumulation but tended to increase pyruvate levels, particularly in Stu. These findings underscore the importance of variety selection tailored to environmental conditions and organic production goals. Traditional open-pollinated onion varieties can contribute to the diversification and resilience of organic farming systems. Their distinct compositional profiles and climatic responses offer valuable options for producers seeking alternatives to hybrids in the context of organic seed system development and climate adaptation. • Traditional varieties matched hybrids in yield and exceeded them in quality. • Relative humidity shaped yield and quality traits across environments. • Birnenförmige maintained stable quality and early maturity under varied environments. • Stunova achieved high yields and dry matter content in research station environments. • Rijnsburger 4 showed reduced yield and quality under elevated humid conditions.