Optimum temperature range for photosynthesis in celery (Apium graveolens)

Authors: Eriksen, Renee; Soule, Michelle

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2025
Publication Date: 1/23/2026
Citation: Eriksen, R.L., Soule, M.L. 2026. Optimum temperature range for photosynthesis in celery (Apium graveolens). Journal of the American Society for Horticultural Science. 151(2):79–88. https://doi.org/10.21273/JASHS05531-25.
DOI: https://doi.org/10.21273/JASHS05531-25

Interpretive Summary: Celery is usually grown in cool weather regions or cool weather seasons in the United States, and it can take more than 3 months to grow in the field. The peak production period is the Thanksgiving and Christmas holiday season, and in order to meet demands, American farmers in the coastal regions of California transplant celery to the field during the warm late summer/early fall months when temperatures can occasionally exceed 100 degrees F. These temperatures increase crop loss to a deadly plant disease called Fusarium wilt caused by a soil-borne fungus. This disease causes 100% crop loss in infested fields, especially during warm weather seasons. Researchers at the USDA-ARS in Salinas are breeding celery for resistance to this deadly plant disease, and studied photosynthesis in eight cultivars of celery to identify the range of temperatures that induce the best growth in celery, and also looked for variation in temperature tolerance among cultivars to use as breeding lines for improved resistance to Fusarium wilt during warm weather seasons. The range of temperatures that celery grows best is between 60-75 degrees F, and there was very little variation among the cultivars tested in heat tolerance.

Technical Abstract: Celery is grown in cool weather agricultural regions or cool weather seasons in the United States. The growing season typically requires about 90-100 days in the field, and therefore some plantings overlap with warmer, less ideal growing conditions. Fusarium oxysporum f sp apii race 4 is a highly virulent soil-borne pathogen that is spreading in the United States, and the pathogen induces significantly greater mortality during warm weather. Increased pathogen growth at high temperatures is likely the most important factor affecting this, but high temperature stress in celery may also contribute to crop mortality. We measured carbon assimilation in eight cultivars of celery to track the optimal temperature for carbon assimilation. Peak carbon assimilation rates were measured between 15-24º C, and there were no significant differences among the cultivars tested. All cultivars experienced significant declines in carbon assimilation when air temperatures were 38º C, though the hybrid cultivar Celx767 maintained slightly higher carbon assimilation rates at high temperatures. Physiological metrics of plant stress, including electrolyte leakage, FVFM ratios, chlorophyll A:B ratios, and chlorophyll: carotenoid ratios indicated increased stress at 45º C.