ASHS 2025 Conference

Sustainable agricultural practices are essential to mitigating the impact of climate-induced stresses on crop production. Enhancing photosynthetic efficiency is a key strategy to boost yield, productivity, and resilience to stress, especially in organic farming. This study aimed to identify natural variation in leaf photosynthesis and uncover key genetic regulators of physiological and molecular responses in USDA spinach (Spinacia oleracea) germplasm under organic cultivation. 314 USDA organic spinach accessions and commercial checks were planted in an augmented design within an organic field in Uvalde, Texas. Gas exchange traits—including CO2 assimilation rate (A), carboxylation efficiency (CE), CO2 concentration in leaf air spaces (Ci), transpiration (E), CO2 efflux, stomatal conductance (gsw), and water use efficiency (WUEi)—as well as chlorophyll fluorescence metrics such as the efficiency of energy harvesting by oxidized (open) PSII reaction centers (Fv’/Fm’), quantum yield of PSII, electron transport rate, non-photochemical quenching, and photochemical quenching were measured using the LI-6800 portable photosynthesis system. The genome-wide association study (GWAS) was conducted on photosynthesis traits in 299 spinach accessions using 50,873 SNPs. Several SNP markers associated with different traits and candidate genes were identified. Our findings emphasize the value of combining high-throughput photosynthesis measurements with GWAS to reveal the genetic basis of photosynthetic variation in crop species.