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Crop Science 41:1834-1837 (2001)
© 2001 Crop Science Society of America

CROP ECOLOGY, MANAGEMENT & QUALITY

Flowering and Yield Response of Cotton to Application of Mepiquat Chloride and PGR-IV

Stephen P. Biles*,a and J. T. Cothrenb

a Texas Agricultural Extension Service, 100 E. 3rd St. Suite 305, Sweetwater, TX 79556
b Texas A&M University, Soil and Crop Sciences Department, College Station, TX 77843-2474

* Corresponding author (biles-sp{at}tamu.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
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.

Abbreviations: EB, early bloom • GA, gibberellic acid • MC, mepiquat chloride • MHS, match head square • PGR, plant growth regulator • PHS, pinhead square


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE USE OF MC AND PGR-IV to regulate plant growth in cotton has been extensively researched and well documented. Plants treated with MC tend to be shorter and more compact than untreated plants (Jung et al., 1975; Willard et al., 1976; Stuart et al., 1984; Kerby, 1985; Cathey and Meredith, 1988; Hodges et al., 1991; Reddy et al., 1992). Height reduction is the result of reduced internode elongation (Kerr, 1976; Reddy et al., 1990, 1992). This height reduction is accomplished by reducing the concentration of GA in the plant. Lower GA concentrations affect movement between cells due to decreased cell wall relaxation, decreased cell wall plasticity, and increased cell wall stiffness (Behringer et al., 1990; Potter and Fry, 1993; and Yang et al., 1996). By increasing the amount of friction between cells, the ability of the cells to elongate and replicate is hampered. Thus, plant height is reduced.

MC also reduces leaf area (Stuart et al., 1984; Reddy et al., 1990). Fernandez et al. (1992) reported that, as a result of its effect on plant leaf area, MC induced a water-conservative behavior in cotton. However, Stuart et al. (1984) found that although MC-treated plants had as much as 33% less leaf area as untreated plants, no differences in seasonal water use were detected between untreated plants and plants treated with MC.

Other effects of MC treatment include increased fruit retention, earliness, and yield enhancement. Jung et al. (1975) found that MC treatment offset conditions leading to square abortion; while Cathey et al. (1988) found MC increased flower production in late-planted cotton. Earlier maturity is frequently a response to MC treatment (York, 1983a; Kerby, 1985). MC increases early-season fruiting and decreases the number of late-season bolls (Kerby et al., 1986). Although yield increases have been reported as a result of MC applications (Willard et al., 1976; Kerby, 1985), other research has found erratic yield responses (Stuart et al., 1984; Cathey et al., 1988; York, 1993a,b).

Oosterhuis and Zhao (1993a)(1994a,b) reported increased rooting in response to PGR-IV applications, a result that may have been caused by the IBA in the product. By increasing the root mass with IBA and promoting plant growth with GA, PGR-IV may enhance the plant's ability to tolerate drought and other environmental stresses. One potential benefit of stress tolerance would be increased yields through retention of fruit that otherwise would be lost. Yield has been increased frequently in response to PGR-IV application (Livingston et al., 1992; Oosterhuis and Zhao, 1993b; Robertson and Cothren, 1995; Hickey, 1996). Causes for these yield increases were from increased boll numbers and boll weight (Oosterhuis and Zhao, 1993b; Robertson and Cothren, 1993). However, the use of PGR-IV does not always increase yields (Locke et al., 1994; Cothren et al., 1996). Another benefit observed as a result of PGR-IV application is improved fiber quality (Robertson and Cothren, 1993).

One potential drawback to the use of PGR-IV is increased vegetative growth. Cadena and Cothren (1996) found that PGR-IV caused longer fruiting branches in cotton. Also, increased plant height has been observed as a result of treatment with PGR-IV (Oosterhuis and Zhao, 1993a; Livingston and Parker, 1994; Locke et al., 1994; Oosterhuis and Engilla, 1996). Robertson and Cothren (1993), however, reported that PGR-IV decreased plant height. In addition, varieties are known to respond differently to PGR-IV treatment with respect to plant height, yield and earliness (Livingston and Parker, 1994).

Because MC and PGR-IV frequently trigger desirable growth and development responses in cotton, the possibility of their combined use as a management strategy in cotton production has been suggested. Locke et al. (1994) found PGR-IV increased growth and square retention, and suggested MC could be used to control height when conditions tended to produce rank growth. Livingston et al. (1992) also proposed that both MC and PGR-IV might have beneficial, supplemental effects on yields when used at respective critical growth stages or stress levels.

Some research has been conducted to determine the compatibility of MC and PGR-IV. Guo and Oosterhuis (1994) found that PGR-IV and MC applied in a tank mixture increased yields; while Robertson and Cothren (1995) and Turner (1996) reported that by combining the PGRs, greater yields were obtained than by using either of them alone. Legé et al. (1996) also reported that the combined use of these products increased yields as a result of increased boll size.

Moreover, several studies have shown that by combining MC and PGR-IV, height control is attained. Turner (1996) indicated that combinations of PGR-IV and MC caused reductions in height similar to those observed when only MC was applied. And, in one instance, Oosterhuis et al. (1995) found that combined use of PGR-IV and MC resulted in greater height reductions than when MC is used alone.

Although considerable research has focused on MC and PGR-IV, little research on the effects of these PGRs on flowering has been performed. The objective of this research was to examine the effects of individual and sequential applications of MC and PGR-IV on flower production and flower survival.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Field experiments were conducted at the Texas A&M University Agricultural Experiment Station in Burleson County near College Station, TX, in 1996 and 1997. Cotton cultivar ‘Delta and Pine Land 50’ was planted 17 April 1996 and 9 April 1997 and grown under irrigated conditions at a population of 10 plants m-1 (98 423 plants ha-1). The soil type was a Ships clay (very fine, mixed, thermic Udic Chromustert) with a pH of 8.0. Nitrogen was applied each year as NH4NO3 at a rate of 134 kg ha-1. Insect and weed control was conducted according to the accepted agronomic practices for the area. Plots consisted of eight rows, 9.75 and 13.7 m long in 1996 and 1997, respectively, with a row spacing of 1.02 m. The population was thinned to 10 plants m-1 row prior to pinhead square (PHS), the developmental stage at which flower buds are approximately the size of the head of a pin.

The study consisted of three PGR treatments and an untreated check. The PGR treatments included: (i) a MC treatment consisting of two applications of 585.1 mL ha-1 of MC with the first application made at the match head square (MHS) stage of reproductive development and the second application made at the early bloom (EB) stage of development; (ii) a PGR-IV treatment consisting of applications of 146.3 mL ha-1 of PGR-IV applied at PHS, EB, and EB + 10 d; and (iii) a PGR-IV + MC treatment consisting of three applications, 292.6 mL ha-1 of PGR-IV applied at the PHS stage of development, 585.1 mL ha-1 of MC applied at PHS + 10 d, and 292.6 mL ha-1 of PGR-IV applied at EB. The experimental design was a randomized complete block with four replications.

In 1996, all treatments were applied with a backpack CO2–pressurized sprayer equipped with a hand-boom containing three Tee-jet 8002 nozzles per row, spaced 33.9 cm apart. Treatments were applied in 170.2 L ha-1 at a speed of 4.827 km h-1 and a pressure of 159 kPa. Application dates were 23 May, 31 May, 3 June, 18 June, and 1 July 1996 for PHS, MHS, PHS + 10 d, EB and EB + 10 d, respectively. In 1997, all treatments were applied with a self-propelled compressed-air sprayer equipped with two 8002 nozzles per row and calibrated to 142.2 L ha-1 at a speed of 5.63 km h-1 and a pressure of 240 kPa. Application dates were 27 May, 3 June, 5 June, 23 June, and 8 July 1997 for PHS, MHS, PHS + 10 d, EB and EB + 10 d, respectively.

Data collected consisted of dates of flower and boll opening and yield. Flower opening was measured by tagging all of the flowers on 1 m of row in each plot. Flowers were tagged every other day; white flowers were considered to have opened on the day of tagging, and pink flowers were considered to have opened the previous day. The tag number was recorded along with the day that the flower was white. Once a tagged flower had matured, it was hand-harvested. Information obtained from tagging the flowers included the average number of flowers per meter of row; total number of flowers per meter of row; and flower survival in 5-d increments and for the whole season. Flower survival was determined by calculating the percentage of flowers that produced harvestable bolls and yield. Seed cotton yield, lint yield, and bolls m-1 were also determined.

All data were analyzed by using the SAS (1985) general linear model procedure. Means were separated by using a protected LSD at a 0.05 level of significance. If no significance was detected for P = 0.05, means were separated by using a protected LSD at P = 0.10. All data were combined over years with years as a fixed variable.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Application of the PGRs resulted in plants with a greater number of flowers per meter per day (Table 1). The MC and PGR-IV + MC treatments increased the average of flowers per meter of row per day by 0.55 and 0.48, respectively, over the untreated control for the entire period of bloom. The average number of flowers per meter of row per day for the entire period of bloom did not differ between the PGR-IV treated plants and the untreated plants.


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  		Table 1. Average number of flowers per meter of row per day in 5-d increments and for the entire period of bloom, from the day of flowering through the 55th day after first flower, as influenced by different plant growth regulator PGR treatments, average of 1996 and 1997 data.

 
The differences in flower numbers was due to more flowers being produced at specific time periods. On Days 11 through 15 and on Days 16 through 20 after first flower, the MC-treated plants had 32 and 33% more flowers m-1 of row d-1, respectively, than the untreated plants after first flower. Plants in the PGR-IV and PGR-IV + MC treatments had 42 and 26% more flowers m-1 of row d-1, respectively, than did the control on Days 16 through 20 after first flower. No differences between treatments were observed on the other days of the measurement period.

By increasing the number of flowers per meter per day, plants treated with the PGRs accumulated more flowers per meter of row than untreated plants. The total numbers of flowers produced per meter at the end of flowering for the plants in the untreated control, MC, PGR-IV and PGR-IV + MC treatments were 178.9, 208.8, 193.0, and 205.0, respectively (Table 2).


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  		Table 2. Accumulated flower production from the 1st until the 55th day of flowering, as influenced by different growth regulator (PGR) treatments at the Texas A&M University Agricultural Experiment Station near College Station, TX, average of 1996 and 1997 data.

 
Mepiquat chloride-treated plants produced 12.5 more flowers m-1 of row than did plants in the untreated control by the 20th d of flowering, and more flowers per meter of row than untreated plants from the 35th d through the end of flowering. Cathey and Meredith (1988), also found that MC increased flower production in late-planted cotton. The MC treatment also caused plants to have 19.1 more accumulated flowers m-1 of row than plants in the PGR-IV treatment on the 40th d of flowering. PGR-IV application caused an increase in flower numbers per meter of row over the control on the 20th d of flowering and from the 35th d through the end of flowering.

The use of MC and PGR-IV in combination gave a numerically intermediate response to that of either of the PGRs used alone. More flowers were produced in the PGR-IV + MC treated plants than in the control plants by the 40th d of flowering through the end of flowering. No differences in accumulated flowers were observed between the different PGR treatments.

No differences were found between treatments for percentage of flowers retained to harvest at P = 0.05. The percentage of all flowers retained to maturity ranged from 40.4 to 42.0 for all treatments. One difference was noted for percentage flower retention between the treatments during flowering at P = 0.10. A 5.3% increase of fruit that bloomed between the 36th and 40th d of flowering survived to maturity in the PGR-IV + MC treatment than in the PGR-IV treatment.

All PGR treatments resulted in increased seed cotton and lint yields over the control (Table 3). MC-treated plants had 23 and 10% more seed cotton than the untreated and PGR-IV-treated plants, respectively. Applications of PGR-IV and PGR-IV + MC increased seed cotton yield over the untreated control 11 and 21%, respectively. Lint yields of the MC, PGR-IV, and PGR-IV + MC-treated plots were 18, 12, and 17% greater than the untreated plots, respectively. Lint yields did not differ between PGR treatments. The MC, PGR-IV, and PGR-IV + MC treated plots had 16, 10, and 14% more bolls m-1 of row than the untreated control plots, respectively.


View this table:
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  		Table 3. Seed cotton, lint yield, bolls per meter of row, percent ginout, and seed weight as influenced by different plant growth regulator (PGR) treatments at the Texas A&M University Agricultural Experiment Station near College Station, TX, average of 1996 and 1997 data.

 
The lack of a significant difference in lint yield between the MC and the PGR-IV treatments and between the PGR-IV treatment and the untreated control can be explained by the percentage ginout and seed weight of the treatments. The untreated control and PGR-IV treatment had a higher percentage of lint in the seed cotton than did the MC and PGR-IV + MC treatments. The cause for the difference in ginout involved differences in seed weight. Mean seed weight for the MC treatment was greater than that of the PGR-IV treatment and the control. The PGR-IV + MC treatment also had a greater seed weight than the control.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The data in this study indicates that the application of MC and PGR-IV positively influenced flowering in cotton. Since the percentage survival of flowers was not different between PGR treatments and the untreated control, it may be inferred that MC and PGR-IV affect fruit retention by retaining more fruit prior to bloom than untreated cotton, and not by increasing fruit survival after bloom. Furthermore, the use of these PGRs in sequential applications did not produce a synergistic effect, but only a numerically intermediate response to either of the PGRs used alone. No benefit was gained by the use of sequential applications of MC and PGR-IV over the use of MC alone. The addition of PGR-IV acted as an antagonist to the MC application. Thus, the use of sequential applications of MC and PGR-IV is not recommended.

Received for publication June 12, 2000.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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