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CROP ECOLOGY, PRODUCTION & MANAGEMENT

Early Flower Bud Loss and Mepiquat Chloride Effects on Cotton Yield Distribution

^a Entomology Dep., 402 Life Sciences Bldg., Louisiana State Univ. Agricultural Center, Baton Rouge, LA 70803 USA
^b Agronomy Dep., 104 Sturgis Hall, Louisiana State Univ. Agric. Center, Baton Rouge, LA 70803 USA

ckennedy{at}agctr.lsu.edu

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Abscission or abortion of the initial cotton (Gossypium hirsutum L.) flower buds or bolls increases the importance of retaining fruit on adjacent or subsequent fruiting positions. Use of the plant growth regulator mepiquat chloride (MC) (N, N dimethylpiperidinium chloride) improves boll retention on lower reproductive branches (sympodia), reduces vegetative growth, and in some cases reduces upper sympodial productivity. Our objective was to determine the effect of doses and application timings of MC and different levels of early flower bud removal on within-plant yield distribution. Zero or an average of two or four flower buds located at first positions on lower sympodia were removed from each plant prior to MC applications at two field locations in 1992. This bud loss resulted in higher retention at second positions on lower sympodia and on slightly higher sympodia. Two biweekly doses of 24.5 g ha^-1 of MC applied at early bloom also enhanced compensation and yield on lower sympodial second positions. Primarily at one location, four weekly MC doses of 12.25 g ha^-1 each beginning when buds were 1 cm long resulted in increased monopodial branch yield when there was moderate early bud loss. Depending on field location, one or the other of the MC treatments reduced the number of fruiting positions and yield on higher sympodia when fruit retention on lower sympodia was high. Loss of early buds, which resulted in small increases in vegetative growth, ameliorated this effect. The biological responses produced by early bud loss and MC treatments interacted positively. After early bud loss, plants treated with MC generally improved compensation on lower sympodia without negative effects on upper sympodia.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
IT IS GENERALLY ACCEPTED that the yield potential of modern cotton cultivars depends on retention of first position bolls on lower (earlier) sympodia (Mauney, 1984; Jenkins et al., 1990). Regardless of many production practices involved in protection of fruiting forms on these positions, they can still abscise because of insect feeding or physiological stress (Guinn, 1982). Moreover, a certain amount of fruit loss early in the season is allowable from the standpoint of being below the economic injury level (Bagwell et al., 1999; Parker et al., 1991; Ring and Benedict, 1993). Cotton has an indeterminate growth habit, and the loss of fruiting forms from the earliest positions has resulted in more productive fruiting from later-developed positions that partially to fully compensate for earlier losses (Dale, 1959; Kletter and Wallach, 1982; Ungar et al., 1987). An increased vegetative growth occurs as well (Eaton, 1955; Kennedy et al., 1986). If the yield potential of a crop is high, then early fruit loss can result in vegetative growth and reproductive growth that is not balanced. Shedding of additional fruiting structures could occur because of this. Research reported in the review by Krizek (1986) and work by Guinn (1974) provide considerable evidence for the necessity of adequate sunlight in the proximity of young (<14 d) bolls for retention to occur. Rapid and excessive increase in leaf area may result in reduced light intensity via mutual shading in the lower portion of the canopy that could induce fruit shed. Moreover, increased leaf area would tend to reduce penetration of insecticides into the canopy (James and Jones, 1985; Sassenrath-Cole et al., 1994), thus reducing efficacy of insect control and increasing the potential for loss of compensatory fruiting structures via insect feeding. Alternatively, the amount of effective compensation may be related to the spatial distribution of the compensating fruiting forms. Sadras' review (1995) suggested translocation of assimilates may be limited by phyllotaxis and increased distance between major source leaves and compensatory sinks. Likewise, Wells and Meredith (1984) indicated earlier transition to reproductive growth (a longer reproductive period) was highly related to improved yields of modern vs obsolete cultivars.

Mepiquat chloride is a plant growth regulator used in cotton production to reduce vegetative growth. After application, subsequently produced mainstem and branch internodes are shorter, and leaves have less area (Cathey and Meredith, 1988; Willard, 1979). One of the major benefits of MC is retarded plant growth under conditions favorable for excessive vegetative growth. These conditions include late planting or delayed early growth, excesses of nitrogen when soil moisture content is adequate, and a delay or reduction in fruit set (Cathey and Meredith, 1988; York, 1983; Kerby et al., 1996). Mepiquat chloride also enhances retention of early buds and bolls (Wilde et al., 1988; Kerby et al., 1986), thus enhancing earlier crop maturity.

Yield response to MC has been variable, ranging from negative (Crawford, 1981) to no response (Wallace et al., 1993; Niles and Bader, 1986) to a positive effect (Kerby et al., 1983). Yield differences generally were small when conditions favored early boll set. Early boll set produced a strong reproductive sink and thus slowed vegetative growth. However, when boll set was in any way delayed and excessive vegetative growth existed, yield increases associated with MC were greater (Kerby et al., 1983). After early flower bud loss, application of MC could, therefore, ameliorate problems of balance between vegetative and reproductive growth and/or adjust the spatial distribution between compensating fruit and major source leaves by enhancing retention on lower sympodia. The latter would also tend to make a faster transition in partitioning assimilate from vegetative to reproductive growth. Although a positive response to MC after early fruit loss has been suggested (Parvin and Stewart, 1989; Kerby et al., 1996; Fletcher et al., 1994; Munier et al., 1994), no definitive research has been attempted to study this relationship. It was our objective to determine how different amounts of early flower bud loss at or near the economic threshold level combined with applications of MC at varying doses and stages of crop development would affect yield and yield distribution on the plant.

	Materials and methods

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Seed of variety `Deltapine 50' was sown on 5 May 1992 at St. Joseph, LA, in a Commerce silt loam (fine-silty, mixed, nonacid, thermic, Aeric Fluvaquent) and on 15 May 1992 at Baton Rouge, LA in a Mhoon silt loam (fine-silty, mixed, nonacid, thermic, Typic Fluvaquent). The distance between locations was about 240 km. Plant populations were hand thinned to approximately 10 plants m^-2 by the third leaf stage at both locations. In some cases at Baton Rouge, initial plant populations were slightly less than this density. Plot size was four, 1-m-wide by 6-m-long rows at St. Joseph and three, 1-m-wide by 6-m-long rows at Baton Rouge.

Treatments for the removal of flower buds consisted of the removal of 0, 20, or 40% of all buds 10 to 14 d after buds were easily visible. The largest buds were approximately 1 cm long at the time of removal. The number of buds to be removed was determined by counting all buds in a five-plant group. The appropriate percentage of buds was removed from each plant before moving to the next group of five plants within the row. The first fruiting position on lower sympodia was the primary source of buds at that time and the emphasis of the debudding was to remove those particular buds although a few Position 2 buds may have been removed. There were about 8 to 10 buds plant^-1 at the time of removal. Because this was a field experiment, some abscission may have occurred beyond the treatment. The bud loss treatments were defined as minimum, moderate, and maximum. Although our bud loss treatments were artificial, Ungar et al. (1989) found similar natural frequencies under fairly normal production situations. The level of bud removal approximated the economic threshold range at which time control measures would be implemented for several insect pests (Bagwell et al., 1999). Therefore, under best management practices, these levels of bud loss would be at to slightly above the level of acceptability.

The three MC treatments were untreated (0 MC), low rate multiple (LRM), and early bloom (EB). The LRM treatment was initiated 14 d after flower buds were just visible (pin head square stage) and consisted of four weekly applications of 12.25 g MC ha^-1. The third MC treatment (EB) was initiated at early bloom (one white bloom/6 m of row) and consisted of 2 biweekly applications of 24.5g ha^-1. Thus LRM and EB treatments received the same total amount of MC (49 g ha^-1) but at different doses and stages of crop development. All applications were made with a hand-held CO₂-powered boom, with one nozzle per row. Travel speed of 4.8 km h^-1 regulated by a metronome (Wolf and Edmisten, 1985), CO₂ pressure of 276 kPa, and nozzle size (TX-18) were used to achieve an application volume of 187 1 ha^-1. Standard management practices were utilized throughout the season. A vigorous insecticide regimen consisting of applications scheduled on five to seven day intervals was implemented to minimize additional fruit loss due to insect damage.

At about 2 wk after blooming ceased, a 2-m section of an inside row was fruit mapped and archived according to the BOLOCATE computer program of Kennedy et al. (1990). The same 2-m section was hand harvested and box mapped (Jenkins et al., 1990) at the end of the season. With both methods, sympodia (fruiting branches) were partitioned into zones of four consecutive mainstem nodes beginning at the node where most plants initiated the first sympodium. Most plants initiated sympodia at mainstem Node 5 at St. Joseph and mainstem Node 6 at Baton Rouge. Zone 1 consisted of mainstem Nodes 5 through 8 at St. Joseph and Nodes 6 through 9 at Baton Rouge. Zone 2 consisted of mainstem Nodes 9 through 12 at St. Joseph and Nodes 10 through 13 at Baton Rouge. Zone 3 consisted of mainstem nodes above 12 and 13 for St. Joseph and Baton Rouge, respectively. Bolls were separated into first, second, and third and beyond sympodial node locations within respective zones. Bolls on monopodia (vegetative branches) were pooled and placed in a separate zone. Within each zone and node location, boll numbers were determined, and the seed cotton was ginned for determination of lint weight. Overall lint yield was determined from 4 m of row and consisted of yields obtained from box-mapping procedures combined with hand-harvested yields from an additional 2-m section of an inside row. Yields were then converted to kg lint ha^-1. Average plant height to the nearest 0.01 m was determined at the end of the season from all plants within the 2-m section of row in each plot used for mapping and yield collection. The height:node ratio was determined on the basis of the mainstem node number quantified at the time of fruit mapping.

All treatments were placed in a factorial arrangement within a randomized complete block with four replications at St. Joseph and three replications at Baton Rouge. Data were statistically analyzed as a replicated location randomized complete block factorial design using the general linear models procedure (SAS Institute, 1979). Yield distribution data were subjected to analysis of covariance because of the occasional differences in plant population at Baton Rouge. The least square means procedure was used for mean separation (SAS Institute, 1979).

	Results and discussion

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Vegetative Growth
Mepiquate chloride application reduced plant height and the height to mainstem node ratio 11 and 4%, respectively (Table 1) . Dose and timing of MC did not matter as LRM and EB treatments produced similar results. Early bud loss resulted in moderate increases in vegetative growth. With the maximum amount of bud loss, plant height was increased by about 12% above the control when averaged across all MC treatments and locations (Table 1).

View larger version (27K): [in this window] [in a new window]   Fig. 1 Effect of early flower bud loss and mepiquat chloride (MC) applications on fruiting efficiency of lower and mid-level sympodia, Positions 1 and 2. Averaged across two locations in 1992 for cv Deltapine 50. = Mean symbols or bars subtended by the same letter are NS (P 0.05). EB = two bi-weekly applications of 24.5 g MC ha-1 beginning at early bloom. LRM = four weekly applications of 12.25 g MC ha-1 beginning when earliest buds were 1 cm long. Minimum = no buds manually removed. Moderate and Maximum = 20% and 40% of buds removed, respectively, when there were about 8 to 10 buds plant-1. Zone 1 = pooled sympodia off mainstem Nodes 5 through 8 and 6 through 9 for St. Joseph and Baton Rouge, respectively. Zone 2 = pooled sympodia off mainstem Nodes 9 through 12 and 10 through 13 for St. Joseph and Baton Rouge, respectively

View larger version (26K): [in this window] [in a new window]   Fig. 2 Effect of early flower bud loss and mepiquat chloride (MC) applications on lint weight of Position 1 and 2 bolls of lower and mid-level sympodia. Averaged across two locations in 1992 for cv Deltapine 50. = Mean symbols or bars subtended by the same letter are NS (P 0.05). = Mean symbols subtended by the same letter are NS (P 0.1). EB = two bi-weekly applications of 24.5 g MC ha-1 beginning at early bloom. LRM = four weekly applications of 12.25 g MC ha-1 beginning when earliest buds were 1 cm long. Minimum = no additional flower buds removed. Moderate and Maximum = 20% and 40% of buds removed, respectively, when there were about 8 to 10 buds plant. Zone 1 = pooled sympodia off mainstem Nodes 5 through 8 and 6 through 9 for St. Joseph and Baton Rouge, respectively. Zone 2 = pooled sympodia off mainstem Nodes 9 through 12 and 10 through 13 for St. Joseph and Baton Rouge, respectively

Position 2 yield on lower (Zone 1) sympodia was enhanced 25% by the EB treatment compared with no MC application (Table 2). Accordingly, averaged across bud loss treatment, boll set was increased 21% and lint per boll was increased (not significantly) 7% with the EB treatment compared to no MC application (Fig. 1 and 2). Kerby et al. (1983, 1986) found EB applications of MC resulted in more open bolls and greater retention at Position 2 and beyond on lower mainstem sympodia. Alternatively, McCarty et al. (1989) and Kerby et al. (1989) found LRM applications did not result in increased retention and yield at Position 2 and beyond. Our data on lower (Zone 1) sympodia generally reflect the results of these earlier studies. This enhancement of Position 2 fruit-set and yield would improve compensation effects by providing a greater sink strength on lower sympodia. This would allow for a faster transition from vegetative sink strength to reproductive sink strength. Wells and Meredith (1984) showed that yield improvement in modern cultivars is related to an earlier transition from vegetative to reproductive development. The application of MC after early bud loss helps to maintain this transition.

Interactions between bud loss treatments and MC applications occurred for yield and yield components within Zone 3 sympodia and monopodia. The greatest monopodial yield occurred with the LRM treatment and moderate early bud loss. This combination resulted in almost twice as much lint as any other treatment combination (Table 2). There was a three way interaction with location (P 0.10) and much of the increase shown on Table 2 was attributable to the Baton Rouge location. Monopodial productivity after MC application has had mixed results. Kerby et al. (1986) found numerically, but nonsignificantly, higher monopodial productivity with EB application of MC. However, Bourland and Watson (1990) indicated a significant increase in monopodial productivity under MC treatment (dose and timing not indicated) when the crop was planted late. On the highest sympodia (Zone 3), an interaction between early bud loss and MC application varied between locations (Table 3) . The biggest differences occurred at Baton Rouge where the EB treatment produced about 64% less lint in Zone 3 with minimum bud loss compared to when the level of early bud loss was maximum. At St. Joseph, the EB treatment was not altered by early bud loss. However, the LRM treatment at St. Joseph had about 31% less lint with the minimum early bud loss than with the maximum loss treatment. At Baton Rouge the LRM treatment effect when coupled with early bud loss was inconsistent for reasons we could not determine.

Total Lint Yield
An interaction between MC application and bud loss treatment occurred for total lint yield (Fig. 3) . The LRM treatment had peak yields with moderate early bud loss, producing yields that were 10% greater than the control or LRM treatments with maximum bud loss. The application of MC at early bloom was deleterious to yield unless accompanied by increasing early bud loss. Yields increased 12% with increasing early bud loss under the EB treatment of MC. Results indicated that conditions for high yield potential existed in this study. Under these conditions, loss of early flower buds would have a neutral to negative effect on crop yield (Sadras, 1995).

View larger version (60K): [in this window] [in a new window]   Fig. 3 Effect of early flower bud loss and mepiquat chloride (MC) applications on lint yield of cv Deltapine 50 averaged across two locations in 1992. = bars topped with the same letter are NS (P 0.05). Yield determination was based on hand harvest from 4m2. EB = two bi-weekly applications of 24.5 g MC ha-1 beginning at early bloom. LRM = four weekly applications of 12.25 g MC ha-1 beginning when earliest buds were 1 cm long. Minimum = no additional flower buds removed. Moderate and Maximum = 20% and 40% of buds removed, respectively, when there were about 8 to 10 buds plant-1

	Conclusions

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Our results support previous research findings on the compensating ability of cotton after early loss of fruiting forms. With early bud loss at or slightly above the level that would trigger control inputs to avoid further losses (economic injury), the use of MC was of general benefit, increasing yields significantly in some cases. Mepiquat chloride improved the retention and yield at Position 2 nodes on lower sympodia, which helped maintain sink strength in the lower portion of the plant. Monopodial productivity also improved with the LRM treatment. The potential for MC application to reduce productivity of sympodia on the upper portion of the plant was generally eliminated by slight increases in vegetative growth. This vegetative growth was stimulated by relatively small amounts of early bud loss. The differences shown in this study were not considered dramatic but did reflect what might occur under commercial production. We suspect the mechanisms shown here would be the same in fields prone to more excessive vegetative growth although responses might vary in amplitude.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as manuscript no. 97-09-0004.

Received for publication August 4, 1999.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Cook, D. R. Articles by Kennedy, C. W. Search for Related Content PubMed Articles by Cook, D. R. Articles by Kennedy, C. W. Agricola Articles by Cook, D. R. Articles by Kennedy, C. W.