Flowering and yield response of cotton to application of mepiquat chloride and PGR-IV

Few studies have documented the effects of mepiquat chloride (MC) (1,1-dimethyl piperidinium chloride) and PGR-IV [0.001% (w/v) indolebutyric acid (IBA), 0.001% gibberellic acid (GA)] on flowering. This study was conducted in an effort to better understand the effects of these two plant growth regulators (PGRs) on cotton (Gossypium hirsutum L.) flowering when applied alone or used in sequential applications. Field experiments conducted in 1996 and 1997 at the Texas A&M University Agricultural Experiment Station near College Station, TX, contained the following treatments: an untreated control, MC, PGR-IV, and a combination of both MC and PGR-IV applied sequentially (PGR-IV + MC). The MC and PGR-IV + MC treatments caused plants to have a season-long average of 0.55 and 0.48 more flowers m(-1) of row d(-1), respectively, than the untreated plants. All PGR treatments resulted in a higher rate of flowering than untreated plants between the 16th and 20th d of flowering. The MC treated plants also had 19.1 more total flowers per meter than PGR-IV treated plants by the 40th d of flowering. Treatment effect on flower survival was different only for flowers that bloomed between the 36th and 40th d of flowering. At this time, the PGR-IV + MC treated plants had a greater flower survival than plants treated with only PGR-IV. All PGR treatments resulted in increased yields and boll numbers. These studies indicate that the application of MC and PGR-IV, either in sequential applications or alone, increases both the rate of flowering and the number of flowers per meter of row, but does not impact the ability of flowers to survive to maturity.