Mepiquat chloride seed treatment and germination temperature effects on cotton growth, nutrient partitioning, and water use efficiency

Cotton seed (Gossypium hirsutum L. cv. Stoneville 825), treated with 0, 0.2, 1.0, and 2.0 g active ingredient (a.i.) mepiquat chloride (MC) kg^–1, was evaluated for the effect of MC on early plant growth. Emergence rate and total emergence of MC-treated seed and control were similar regardless of germination temperature. However, the number of leaves and squares and the dry weight of leaves, stems, and roots for hydroponically grown cotton plants were significantly lower at lower germination temperatures (15°C for 3 day/30°C for 1 day and 15°C for 4 days) than at higher germination temperatures (30°C for 4 days and 30°C for 3 days/15°C for 1 day). All MC treatments significantly decreased the number of nodes, leaves, and squares, as well as dry weight of leaves, stems, and roots, as compared to control plants at 28 days after emergence. MC seed treatments also significantly reduced plant height and total leaf area compared to controls. Water-use efficiency (WUE) was significantly lower for the 1.0 g a.i. MC treatment than for control plants. In general, the highest rate of MC seed treatment resulted in greater concentrations of calcium, phosphorus, and nitrogen in plant leaves and stems and also in greater concentrations of magnesium, phosphorus, and nitrogen in roots than in controls.