Response of Cotton (Gossypium barbadense L.) varieties to rate and time of mepiquat chloride application in middle Awash,Ethiopia.

Innate perennial nature of the cotton crop and suitable growing condition results in excessive vegetative growth at the expense of boll development. Plant growth regulators have, therefore, been studied and used as a means to manage the balance between vegetative and reproductive growth. This study was conducted to determine the effect of different rate and time of mepiquat chloride application on growth, yield, yield components, and fiber properties of cotton varieties (G. barbadense) in Middle Awash. The experimental treatments used were combinations of two varieties of G. barbadense, four rates (12.5, 25, 50 and 75 g a. i. ha-1 ) of mepiquat chloride arranged in seven application regimens considering different growth stages of cotton and untreated check. The treatments were laid out in a split plot design using the varieties as main plots and the mepiquat chloride applications as sub-plot with three replications. Mepiquat chloride significantly reduced plant height by 15 to 21% compared with untreated plants. Mepiquat chloride also reduced the number of main stem nodes per plant, height-to-node ratio, length of sympodial branch, nodes to first sympodial branch and number of nodes above white flower. Boll number, boll weight, boll retention, seed cotton yield and lint yield were significantly increased with application of mepiquat chloride. Treated plants produced 4 to 5 more bolls per plant as compared to the control and retained on average about 76% of the fruiting positions on sympodial branches while untreated plants retained only 57% of their fruiting on sympodial positions. The highest increases in seed cotton yield (427 and 408 kg ha-1) were recorded when mepiquat chloride was applied at the rates of 75 or 50 g a. i. ha-1, respectively at early bloom stage with additional late bloom application of 25 g a. i. ha-1. These treatments had highest suppression effect in vegetative growth. Therefore, sequential applications of 50 g a. i. ha-1 at early bloom followed by 25 g a. i. ha-1 towards the end of effective flowering could be recommended for reducing vegetative growth and at the same time improve yield. Treatments consisting late bloom applications tended to result in more positive responses. Mepiquat chloride had no effect on span length, uniformity ratio, micronaire value and strength. The results of this study support the perception that mepiquat chloride can be used to offset excessive vegetative growth and improve yield of cotton (G. barbadense) in Middle Awash area.