Our objective was to evaluate and define effects of plant growth regulators on low and high temperature tolerance of cotton (Gossypium hirsutum L., cv 'McNair 220') plants grown under growth chamber conditions. Positive results have been obtained with mepiquat chloride (1,1-dimethylpiperidinium chloride)(MC).

For cold-treatment studies, cotton seeds were germinated in pellets and transplanted into 2.5 liter plastic pots containing a 1:200 mixture of Perlite and Hidalgo sandy clay loam (Typic Calciustoll). A 10-20-5 fertilizer was added to the mixture at the equivalent of 67.2 kg/ha of N. Plants were surface irrigated with equal amounts of rain water. The plants were kept in an open greenhouse (day temperatures: 38-35 C; night temperatures: 17-24 C) until they were subjected to a cold treatment. The plants were separated into three experimental groups. Each group had control (nontreated) plants, which were sprayed with distilled water, and plants sprayed with three MC concentrations: 40, 70, and 100 g a.i./ha (total volume was equivalent to 252 liter/ha). Exposure to cold treatments occurred 7 to 10 days after MC spray application. After cold treatment, the plants were returned to the greenhouse to record plant survival and growth. Experimental conditions and times of application (ages) follow.