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Selection of Safflower for Tolerance to Temperature and Humidity Stress During Flowering¹

Safflower (Carthamus tinctorius L.) was exposed to temperature and humidity stress in the greenhouse and parameters were developed to evaluate response to this stress in segregating populations. The rank for seed yield of the cultivars (‘N4051’, ‘Pacific 1’, ‘Rio’, and ‘Gila’,) exposed to temperature and humidity stress in the greenhouse was similar to that obtained in a previous study using controlled environment chambers. A fertility index (FI) measuring number of seed per unit of head area of the primary head was closely associated (r = 0.90) with actual fertility, number of aborted ovaries, and seed number. FI was a rapid method of evaluating response to humidity and temperature stress in populations segregating for head size and seed number per head.

In a cross between Pacific 1 (tolerant to humiditytemperature stress) and Rio (much less tolerant), FI of the F₁ was not significantly different from the midparent. In mean generation analysis using an additive dominance model, the observed FI means for the P₁, P₂, F₁, F₂, B₁, and B₂ generations were highly significantly different from the expected generation means, suggesting mostly epistatic gene action. There was response to divergent selection for FI in the F₂ generation; the means of the F₃ bulks for low and high FI selection were significantly different (0.005 > P > 0.001).

Key Words: Carthamus tinctorius L. • Fertility index

² Research agronomist, SEA, USDA, and professor, Dep. of Plant Sciences, Univ. of Arizona.

Received for publication November 19, 1977.