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Effect of Temperature and Humidity Stress During Flowering on Safflower (Carthamus tinctorious L.)¹

Sensitivity of safflower (Carthamus tinctorius L.) during flowering to temperature and humidity stress and genetic variation for such sensitivity has been in question. Cultivars were grown in the greenhouse under similar conditions except for a 24-hr period during anthesis when they were exposed to temperature and humidity differentials in controlled environment chambers. Plants were exposed to these differentials on the day the second sequentially developing head began blooming, thus enabling measurement of sensitivity to temperature and humidity stress during pre-, post-, and anthesis stages of head development. Heads in anthesis and preanthesis were the most sensitive to temperature and humidity stresses. Seed yields of plants subjected to high humidity in low, medium, and high temperature were 10, I9, and 86% less, respectively, than those subjected to comparable temperatures with low humidity. Cultivars responded differently to the stresses for seed number, weight, and yield. Results of the experiment suggest that screening safflower genotypes for tolerance to temperature and humidity stress using controlled environment chambers is practical and a 24-hr exposure during anthesis is sufficient to differentiate genotypes.

Key Words: Controlled environment • Genetic variation

² Research Agronomist, Plant Science Research Division, Agricultural Research Service, US Department of Agriculture and Professor of Agronomy, Department of Agronomy and Plant Genetics, University of Arizona, Tucson, Arizona 85721.

Received for publication March 13, 1972.