UNLOCKING QUINOA’S BUDDING POTENTIAL: OVERCOMING BARRIERS TO ITS ADOPTION AS A ROTATIONAL CROP IN WESTERN WASHINGTON AND BEYOND

Evan Domsic

Consumer demand for quinoa (Chenopodium quinoa Willd.) has risen drastically in recent decades, yet its broader adoption as crop outside the Andes has revealed several agronomic and postharvest challenges. This dissertation addresses three key aspects of quinoa production that limit its expansion into new environments: (1) postharvest pest susceptibility linked to seed saponin content, (2) preharvest sprouting, and (3) nutrient management and soil fertility guidelines for organic production systems.In the first study, I investigated the defensive role of saponins (bitter-tasting secondary metabolites that accumulate in quinoa seed coats and other plant tissues) against storage pests. Using six quinoa varieties (three “sweet,” low-saponin lines and three “bitter,” high-saponin lines), we conducted bioassays with the lesser grain borer (Rhyzopertha dominica) and red flour beetle (Tribolium castaneum). Sweet varieties supported dramatically higher progeny production for both species, with R. dominica averaging 158 progeny per replicate compared to only one on bitter varieties. Similarly, T. castaneum averaged 137 progeny on sweet varieties versus three on bitter varieties. These findings strongly suggest that saponins inhibit storage pest reproduction, providing empirical evidence for their function as a defense compound. As saponin-free “sweet” varieties gain popularity due to reduced processing requirements, breeders and growers should be aware of their increased vulnerability to pests during storage. The second study focused on preharvest sprouting, a significant issue with quinoa grown in regions with precipitation and humidity during quinoa maturation. To evaluate whether swathing can mitigate preharvest sprouting while maintaining grain quality, we conducted field trials in 2023 and 2024 in western Washington, USA, alongside a greenhouse experiment. Three varieties were swathed at intervals ranging from 70 to 133 days after sowing. Swathing between 85–110 days after sowing maintained or optimized yield, thousand seed weight, germination rate, and nutritional quality while minimizing exposure to weather that may cause preharvest sprouting. Extremely early swathing reduced germination, while delayed harvests decreased yield in field experiments. Across years, protein and amino acid concentrations varied by genotype and environment, but no consistent drawbacks were associated when swathing between 85 and 110 days after sowing. These results demonstrate that swathing is a viable management practice for quinoa production in high-moisture environments during quinoa maturation and senescence, and in some cases can not only maintain agronomic and nutritional qualities but increase them, when compared to direct combined controls. The third study addresses the lack of fertility management guidelines suited to organic cropping systems and explores the impact of differing organic matter-based amendments on quinoa nutritional quality. While quinoa is often promoted as a low-input crop, nitrogen availability has been shown to impact quinoa yield and protein content. Yet recommended fertilizer rates and amendment types remain poorly defined, and often mirror suggestions for other grain crops. From 2021–2023, on-farm field trials were conducted at two western Washington sites using two quinoa varieties (“106.49” and “104.88”) and organic amendments differing in carbon-to-nitrogen ratio (applied at 54–165 kg N ha⁻¹). Urea (112 kg N ha⁻¹) was included at the conventionally managed site. Fertility treatments influenced soil inorganic N and pH in all years but did not always impact yield and quinoa seed protein content. Amino acid and mineral profiles were largely determined by variety and rarely fertilizer treatment. These findings indicate that while amendment type and rate can alter short-term soil chemistry, yield and seed protein content, variety selection exerts greater control over quinoa’s amino acid profile and micronutrient content. Ultimately, variety selection may be a more effective method for increasing amino acid and micronutrient content in quinoa. Collectively, these studies address key barriers to quinoa’s successful integration into diverse agroecosystems outside its center of origin. By advancing our understanding of pest resistance, harvest management, and fertility practices, this dissertation aims to advance the knowledge of, and develop solutions for, the issues that limit the spread of quinoa into novel production regions.

UNLOCKING QUINOA’S BUDDING POTENTIAL: OVERCOMING BARRIERS TO ITS ADOPTION AS A ROTATIONAL CROP IN WESTERN WASHINGTON AND BEYOND

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