Adaptation of wheat (Triticum aestivum L.) cultivars to southeastern U.S. environments could be improved if their vernalization responses were better defined. Vernalization responses of several cultivars of wheat and a triticale were assessed in 1985 and 1986 in Gainesville, FL (29 degrees 38'N lat.) using varying durations of natural winter (NW) cold exposure of potted plants and refrigerator (RF) exposure of germinating seeds. Five soft red winter wheat cultivars, Florida 301, Florida 302, Hunter, Coker 983, and Caldwell; a soft white spring wheat cultivar, Owens; a hard white wheat cultivar, Phoenix; and triticale (X Triticosecale Whittmack) cultivar Beagle 82 were investigated. Following cold exposures, all potted plants or vernalized, potted seeds were placed in a warm greenhouse at 18-h day length. Three types of vernalization responses were observed: (i) cold obligate (qualitative) requiring 6 to 8 wk of cold for heading and including Caldwell and Coker 983, winter-hardy types; (ii) cold stimulated (quantitative) heading earlier than the control with 2 to 4 wk of cold exposure and included Florida 302, Hunter, and Phoenix, mild-winter types; and (iii) cold neutral, not stimulated by cold exposure and included Owens, Beagle 82, and Florida 301, spring types. Heading of the cold-neutral cultivars was in the order Owens, Beagle 82, and Florida 301 and was delayed by increasing exposure to cold. Both NW and RF treatments were effective vernalization methods. While RF (constant 6 degrees C) required about four times the cold units, the duration of cold exposure required was similar for both methods. We conclude that fall-sown cultivars grown in the lower USA vary in vernalization response (ranging from cold obligate to cold neutral). Knowledge of this variation enhances opportunity for selection of cultivars to fit the narrow window of wheat adaptation in the southern USA.
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