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Cotton Seedling Metabolism as Influenced by Germination Temperature, Cultivar, and Seed Physical Properties¹

Growth rates of cotton (Gossypium hirsutum L.) seedlings are greatly reduced at minimal germination temperatures. Increased variability in the seedling growth rates are more apparent at low temperatures, and delayed emergence or seedling death result in more erratic and nonuniform stands. The pupose of this study was to determine if a specific area of metabolism might be controlling seedling growth at less than optimum germination temperatures. Cottonseed of four cultivars were separated into density and weight groups and germinated in the dark under two controlled temperature regimes (20 to 30 C and 15 to 25 C). Seedlings were harvested 3, 6, 9, and 12 days after planting and separated into cotyledons and seedling axes. Chemical analyses of each part were used to describe the utilization of cotyledonary reserves as related to seedling growth rates. At minimal temperatures, radicle growth rates were initially related to lipid use but by 6 days became more closely associated with non-lipid use. Specific cultivar differences existed with respect to seedling growth and non-lipid use, with N utilization being most affected. Mineral nutrient transfer varied according to cultivar and temperature with no apparent correlation with seedling growth. The results indicate that at optimum temperatures, seed maturity (density) and quantity of available substrate (weight) determine seedling growth rates irrespective of cultivar. Minimal temperatures resulted in a general decrease in metabolic activity. Genetic differences as to the extent of the reduction were quite apparent, however, and thus controlled seedling metabolism and growth rates. Seedling growth reductions due to temperature were related to problems associated with non-lipid metabolism, especially the protein fraction. The specific cause of this metabolic abnormality was not identified.

Key Words: Gossypium hirsutum L. • Lipid • Sugar • Protein • Minerals • Cotyledons • Seedling axis

² Associate professor and former graduate research assistant, Dep. of Plant and Soil Science, Texas Tech Univ., Lubbock, TX 79409.

Received for publication January 7, 1976.