Crop Science 41:1522-1529 (2001)
© 2001 Crop Science Society of America
CROP PHYSIOLOGY & METABOLISM
Leaf Pigment and Canopy Photosynthetic Response to Early Flower Removal in Cotton
Randy Wells*
Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695-7620
* Corresponding author (randy_wells{at}ncsu.edu)
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ABSTRACT
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Loss of reproductive organs from cotton (Gossypium hirsutum L.) often results in compensatory growth that culminates in altered morphologic, physiologic, and photosynthetic patterns. This field study examined the change in leaf chlorophyll (Chl) and anthocyanin (Ant) contents and their relationship to canopy photosynthetic patterns in response to the removal of flowers for the first 2 wk of flowering. Flower removal caused an extended flowering period in all years except 1995 when temperatures were highest. The largest yield differences occurred in 1994, while there were no significant differences in any other year. Differences in canopy photosynthesis occurred on at least one date in each year that measurements were made. In 1997, significant differences were observed on four dates and plants from the removal treatment had 15% larger area under the seasonal photosynthetic curve. Chlorophyll concentrations were higher in leaves from the flower removal treatment after 100 d after planting. Anthocyanin levels were higher in controls during the same period, indicating significant negative relationships between Ant levels and either Chl a/b ratio or Chl concentration. Pigment differences late in plant ontogeny appeared to be associated with delayed senescence of plants from the removal treatment. While pigment levels late in development were associated with canopy photosynthesis, not all treatment differences could be related to Chl loss. In 2 yr, significant differences in canopy photosynthesis occurred prior to differences in Chl concentration, implicating other morphological and physiological adaptations in response to early fruit loss.
Abbreviations: A, absorbance • Ant, anthocyanin • Chl, chlorophyll • DAP, days after planting
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INTRODUCTION
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LOSS OF REPRODUCTIVE ORGANS from cotton can be induced by a myriad of causes (Guinn, 1982). Such losses can elicit many morphological and physiological responses, including compensatory growth (Sadras, 1995). Sadras (1995) suggested that fruit loss may enhance photosynthetic rate in cotton, and subsequently, work by Holman and Oosterhuis (1999) confirmed that canopy photosynthesis was increased on two dates after fruit loss due to insect damage. Canopy photosynthesis was 21% greater in infested than noninfested plants at 4 wk after the initiation of flowering. Infested plants also exhibited 4% greater light penetration than control plants. Sadras (1996) found greater radiation-use efficiency in plants that lost fruit when grown in favorable (low population, high N) but not unfavorable growth (high population, low N) conditions. It is not known what long-term changes are induced by fruit loss in cotton canopy photosynthetic patterns during the reproductive period.
Brook et al. (1992) suggested that loss of early fruit may lengthen the duration of canopy development causing greater light interception by the plant canopy and increased leaf N concentration. Sadras (1996) found leaf N concentration followed a pattern of decline in one out of two cultivars (CS7S) grown under favorable growth conditions (low population, high N). Leaf N concentration has been successfully estimated in cotton by means of concentrations of leaf chlorophyll (Chl) measured with a hand-held meter that measures leaf transmittance in the 400- to 500-nm and 600- to 700-nm ranges (Feibo et al., 1998). Significant linear regressions between N, expressed on both a leaf dry weight and leaf area basis, and Chl values were found over numerous growth stages and two locations (r2 
0.58, P < 0.01). Chlorophyll values generated with the hand-held meter and Chl contents measured by the methods of Chen and Chen (1984) were linearly related and highly significant, regardless of growth stage (r2 0.73, P < 0.01). The reddening of cotton leaves has also been associated with low leaf N concentrations in F1 hybrids with heavy fruit loads (Bhatt et al., 1982) and reduced amino acid levels of prematurely reddened cotton leaves. The red color has been identified as anthocyanin (Ant), which is unmasked by chlorophyll breakdown (Combrink, 1988).
Disappearance of chlorophyll from leaves is one of the most prominent indications of senescence and its rate of degradation is a dependable criterion of leaf senescence and loss of photosynthetic capacity (Gepstein, 1988). Since Brook et al. (1992) suggested that fruit loss may affect canopy duration, one would expect delayed canopy senescence. Both Chl and Ant have good potential as indicators of physiological decline of cotton leaves during senescence.
The present study was conducted to test the hypothesis that early fruit removal would result in altered leaf pigment concentrations, canopy senescence, and photosynthetic patterns throughout an extended period of reproductive development. Specific objectives include the determination of leaf Chl concentration, leaf Ant concentration, canopy photosynthesis, and yield in response to fruit removed during the first 2 wk of reproductive growth.
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MATERIALS AND METHODS
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Cultural Practices and Treatments
A field study was conducted from 1994 through 1997 at the Central Crops Research Station in Clayton, NC. The studies in 1994 and 1997 were on a Dothan sandy loam (fine-loamy, siliceous, thermic Plinthic Kandiudult). In 1995 and 1996, the studies were on a Wagram loamy sand (fine-loamy, siliceous, thermic Arenic Kandiudult). Seed of upland cotton, ‘Deltapine 50’, was sown in excess on 28 April 1994, 2 May 1995, 14 May 1996 and 12 May 1997. Plants were thinned in all years to 10 plants m-2 at the three to four true-leaf stage. The experimental design was a randomized complete block with four replications. Plants were grown in four 0.96-m-wide rows that were 7.6 m long. Approximately 6 wk before planting in all years, 14 kg N, 14 kg P and 160 kg K ha-1 were broadcast on all plots. At planting, an additional 29 kg N ha-1 was applied. At approximately 50 d after planting (DAP), 27 kg N, 13 kg P, and 54 kg K ha-1 were sidedressed. Insecticide applications at planting consisted of 0.94 kg a.i. ha-1 aldicarb [2-methyl-2-(methylthio) propionaldehyde O-(methyl-carbomoy)oxime] applied in-furrow. Later insecticide applications occurred weekly and consisted of either 0.07 kg a.i. ha-1 esfenvalerate [(S)-cyano(3-phenoxyphenyl)methyl-(S)-4 chloroalpha-(1-methylethyl) benzene acetate] or 0.03 kg a.i. ha-1 lambda-cyhalothrin ([1
(S*),3(Z)]-(±)-cyano-(3-phenoxyphenyl methyl-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropane-carboxylate). Water stress was minimized with overhead, sprinkler-irrigation on the dates indicated in Fig. 1. Other cultural practices were typical of the region. In 1996, some measurements were curtailed early and yield was not determined becaue of a hurricane which occurred on 5 and 6 September.
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Fig. 1. Weekly rainfall and applied irrigation (A), cumulative heat units (B), and quadratic regressions of weekly accumulated heat units against weeks after planting (C) from 1994 to 1997. Rainfall totals do not reflect irrigation applied. *, ** represent significance at P = 0.05 and 0.01, respectively.
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There were two treatments, an untreated control and plants from which all flowers were removed for the first 2 wk of flowering. All red and white flowers were removed from a bordered row on a Monday, Wednesday, and Friday schedule. This treatment will be henceforth referred to as the flower removal treatment. During the first week of flowering, newly emerging (5–10 cm2) main stem and first position sympodial leaves were tagged with jewelers tags. These leaves were used for pigment analysis.
Flower Counts and Heat Units
White flowers were counted approximately once per week from the same row where the flowers were removed. Counts of flowers in the removal treatments began on the first measurement day after the removal treatments were completed. Daily heat units were calculated in each year using the following equation: heat units (HU) = [(Tmax + Tmin)/2] - 15.5°C, where, Tmax and Tmin were the maximum and minimum daily temperatures in °C, respectively. Daily temperatures were recorded at Raleigh, NC.
Pigment Analysis
Pigment measurements were made on three leaf discs (0.3 cm2 each) taken from tagged leaves, avoiding veinal tissue. Chlorophyll concentration was determined by extraction with 3 mL dimethylformamide (DMF) for 48 h in the dark at 4°C. Concentrations of Chl and Chl a/b ratio of DMF extracts were determined spectrophotometrically (Moran, 1982). Anthocyanin was determined from three leaf discs extracted with 3 mL acidified methanol (10 mL conc. HCl/L) for 48 h in the dark at 4°C. Absorbance (A) of the extracts was determined at 530 nm (peak absorption by Ant) and 658 nm (peak absorbance by Chl degradation products) and Ant was calculated after Mancinelli et al. (1998) by the following formula:
Both Ant and Chl determinations were continued until no tagged leaves were found.
In each year, evaluations of pigment concentration were made at different vertical positions on the main stem. In addition to the leaves tagged as described above, main stem leaves that were two nodes above, two nodes below, and four nodes below the tagged leaf were analyzed for Chl and Ant. Measurements were made at the four selected nodes on four dates in each year except 1996, starting when Chl and Ant differences between the treatments were observed and continuing approximately every week thereafter.
Canopy Photosynthesis
Canopy photosynthesis of the control and flower removal plants was measured in 1995, 1996, and 1997 with a closed LI-6200 infrared gas analyzer system (LI COR Inc., Lincoln, NE) in combination with a mylar-covered, aluminum frame chamber (Wells, 1991). The chamber fit into aluminum soil bases that formed a trough and created an air tight seal when filled with water. Internal air circulation was maintained with an internally mounted blower capable of an air flow of 9060 L min-1. Measurements were made between 1030 and 1430 h over a 30-s to 1-min period at approximately weekly intervals. During measurements, photosynthetic photon flux density was 1200 µmol m-2 s-1 or greater.
Yield
Seedcotton was hand-harvested from the flower removal row and a bordered row in the control. Harvest dates were 19 Sept. and 25 Oct. 1994, 10 and 27 Oct. 1995, and 30 Oct. and 12 Nov. 1997. No yield was determined in 1996 because of severe lodging and boll loss as a result of hurricane-force winds. Boll weight was determined by dividing the seedcotton weight by the number of bolls harvested. The number of bolls was not determined at the second harvest in 1995 and 1997. Seedcotton was ginned on a 12-saw gin. After ginning, lint percentage was determined by dividing the lint weight by the seedcotton weight and multiplying by 100.
Statistical Analysis
All data were statistically analyzed by the General Linear Models (GLM) procedures Institute Inc., 1987). Significant year x treatment interactions prevented presentation of mean values for Chl, Ant, canopy photosynthesis, and yield. Regression analyses of the relationships between leaf pigments and photosynthesis were performed by PROC GLM (SAS Institute Inc., 1987). Linear, quadratic, and cubic functions were sequentially added as long as significant combinations were found. Regressions of weekly mean minimum and maximum temperature against weeks after planting were performed using PROC REG and the maximum R2 improvement technique.
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RESULTS AND DISCUSSION
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Environment
All years had similar cumulative rainfall totals at 15 wk after planting (Fig. 1A). After that time, a great divergence occurred between the years. A hurricane in 1996 caused that year's cumulative total after 15 wk to be much greater than any other year. In contrast, 1997 was much drier than 1995 and 1996, which had intermediate rainfall totals.
Cumulative heat units were similar for 1994 and 1997 throughout the growth period (Fig. 1B). Greater early heat unit accumulation characterized 1996 as compared with the other years, while 1995 had greater late accumulation. These trends are more easily discernable as second order regressions of heat units accumulated weekly against time (Fig. 1C).
Alteration of Reproductive Patterns
The loss of flowers for 2 wk resulted in a second increase in flower production that was seen in all years, except 1995 (Fig. 2). This second proliferation of flowering was not observed in the control. These modifications indicate that fruit loss was greater than naturally occurring abscission. In contrast, no effect on the resultant flowering pattern was observed in 1995. All yearly losses, however, resulted in time-dependent compensation because there was a delay in boll maturity as measured as the percentage of seedcotton at the first harvest (Table 1), except in 1996 when no final harvest was made. Similar maturity responses have been reported by a number of investigators (Guinn, 1985; Kennedy et al., 1991; Pettigrew et al., 1992; Jones et al., 1996; Heitholt, 1997).
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Fig. 2. White blooms m-2 as a function of days after planting for control and flower removal treatments from 1994 to 1997. Numbers in parentheses indicate the probability level associated with significant differences on individual dates.
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Table 1. Effect of flower removal on cotton yield and yield components during 1994, 1995, and 1997 at Clayton, NC.
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Fiber yield averaged over all years was 8% larger for the control than the flower removal treatment (Table 1). Treatment x year interaction was also significant and reflects the numerically greater yield of the flower removal treatment that was not significant in 1995. Only 1994 had yield differences that were significant between treatments when analyzed by year. There was a greater weight per boll in response to flower removal than in the controls, indicating that allocation of assimilates to bolls was affected in addition to fruit initiation. Similarly, Jones et al. (1996) found no yield response to early flower removal (3rd week and earlier) but found boll dry weights to inversely reflect lower boll numbers in response to removal of early and late flowers. Holman and Oosterhuis (1999) reported significantly reduced yield, seven more days to reach five nodes above white flower, and increased weight per boll in response to insect infestation that cause 33% floral bud abscission. Both Heitholt (1997) and Pettigrew et al. (1992) found some degree of increase in weight per boll in response to hand removal of floral buds. Alternatively, Kennedy et al. (1986) and Pettigrew et al. (1992) reported a reduction in weight per boll in response to floral bud removal with ethephon [(2-chloroethyl)phosphonic acid].
The lack of treatment effect on flowering and yield in 1995 in comparison with the other years may be due to temperature during reproductive development (Fig. 1C). Regressions of weekly mean minimum and maximum temperatures against time are shown in Fig. 3. Minimum temperatures were higher than the other years starting at 12 wk after planting and lasting throughout development. This period closely approximates the beginning of anthesis. The maximum temperature mimicked the trend seen in minimum temperature but the magnitude of difference with the other years was not as great. High temperatures have been reported to greatly reduce reproductive efficiency in cotton (Reddy et al., 1992). In their study, day/night temperature regimes of 30/20, 35/25, and 40/30°C resulted in 434.2, 57.0, and 3.6 g boll weight per kg plant tissue, respectively. In our study, loss of fruit due to high temperature may have contributed to the lack of compensatory response in 1995. Fruiting forms may have been lost in such large numbers because of high temperatures that manual removal merely eliminated flowers that would have abscised due to high temperature stress.
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Fig. 3. Regressions of weekly mean minimum and maximum temperature (T) as a function of weeks after planting for control and flower removal treatments from 1994 to 1997. Regressions were performed using SAS Proc Regression with maximum R2 improvement techniques. ** represents significance at 0.01.
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Canopy Photosynthesis
Differences in canopy photosynthesis between control and flower removal treatments were found on only one date (108 DAP) in 1995 (Fig. 4). Despite this singular date difference there was a significantly (P = 0.06) greater area under the photosynthetic curve of the removal treatment (8%) than for the control. A similar difference in the area under the curve was found in 1996 but the difference was not significant. There was a significant difference (P = 0.09) at 106 DAP between the treatments in 1996. On the other hand, 1997 resulted in four dates on which significant differences were observed and a 15% greater area under the curve for the removal treatment.
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Fig. 4. Canopy photosynthesis per unit ground area as a function of days after planting for control and flower removal treatments from 1995 to 1997. Numbers in parentheses indicate the probability level (P) associated with significant differences on individual dates. The integrated area under the photosynthetic curve was expressed as a percentage of the control. NS signifies no significant difference.
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The greater canopy photosynthesis of the flower removal treatment, while similar to photosynthetic differences induced by floral bud loss due to insect damage reported by Holman and Oosterhuis (1999), shows differences induced over an extended portion of reproductive growth. Similarly, Sadras (1996) reported increased seasonal radiation use efficiency in high N, low population conditions. The increased radiation use efficiency was attributed to better light penetration brought about by more internodes, longer internodes and more vertically positioned sympodia, presumedly due to reduced boll mass on the sympodia. Holman and Oosterhuis (1999) also found significantly increased light penetration (4%) in plant canopies that were infested with insects. In 1996 and 1997, there was no variation in canopy photosynthesis between the treatments on the first date(s) of measurement. The removal of flowers which are low in dry weight could account for the lack of treatment effect in the short term, since their presence or absence would have little effect. The continued development of early bolls on control plants would rapidly gain mass over a few weeks, thus contributing to the difference between treatments.
Alterations in Leaf Pigments
Years with treatment responses in flowering pattern also exhibited alterations in Chl concentration during later stages of leaf ontogeny (Fig. 5). During 1994, 1996, and 1997, statistically greater Chl concentrations were evident in the tagged leaves from the flower removal treatment than from the control plants. The differences in Chl concentration were not consistent between the control and removal treatment in 1995, reflecting the lack of difference in flowering pattern. Changes in Chl concentration in the first position sympodial leaf in response to flower removal were similar to those seen in the main stem leaves (Fig. 6). Chlorophyll a/b ratio generally did not change (data not shown) which indicates little reorganization in Chl between the Chl-protein complexes within the thylakoids in response to flower removal (Burkey and Wells, 1991).
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Fig. 5. Chlorophyll concentration of tagged main stem leaves as a function of days after planting (DAP) for control and flower removal treatments from 1994 to 1997. Numbers in parentheses indicate the probability level associated with significant differences on individual dates.
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Fig. 6. Chlorophyll concentration of tagged, first position, sympodial leaves as a function of days after planting for control and flower removal treatments from 1994 to 1996. Numbers in parentheses indicate the probability level associated with significant differences on individual dates.
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Increases in anthocyanin content that coincided with declining Chl concentration in the tagged leaves (Fig. 7). In all years except 1995, Ant began to increase between 100 and 110 DAP which coincided with a decline in Chl. The Chl a/b ratio and Chl concentration per unit leaf area were significantly associated in a negative curvilinear manner (Fig. 8). Because of this negative relationship, the ratio of Chl to Ant (Fig. 9) generally mimicked the patterns in Chl (Fig. 5); however, the differences between treatments were enhanced. The appearance of Ant was not merely due to a loss of Chl, but rather an active synthesis. This finding is in contrast to that of Combrink (1988) who indicated that Ant appearance was due to decreases in Chl concentration.
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Fig. 7. Anthocyanin concentration of tagged main stem leaves as a function of days after planting for control and flower removal treatments from 1994 to 1997. Absorbances were adjusted to indicate what 1.0 cm2 of leaf would have yielded. Numbers in parentheses indicate the probability level associated with significant differences on individual dates.
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Fig. 8. Relationship between anthocyanin level and either chlorophyll a/b ratio (A) or chlorophyll concentration (B). Each symbol represents mean values of four replications within treatment, date, and year.
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Fig. 9. Chlorophyll/anthocyanin ratio of tagged, main stem leaves as a function of days after planting (DAP) for control and flower removal treatments from 1994 to 1997. Numbers in parentheses indicate the probability level associated with significant differences on individual dates
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Leaves measured both above and below the tagged leaf showed similar declining Chl and increasing Ant trends in all years (data not shown). These differences at different nodal positions were not always significant, but the trends correspond with those seen in the tagged leaves.
The data presented herein indicate that the greater Chl level and longer duration of leaves from plants from the flower removal treatment was due to a delayed leaf senescence and not to a greater initial leaf Chl concentration. One might expect that expanding leaves, tagged when the flower removal treatment was initiated, would exhibit a greater Chl concentration because of reduced assimilate demand from competing fruit. This condition was not found since maximum Chl concentrations were similar for the two treatments. Similarly, Sadras (1996) found little difference in leaf N concentration between control and fruit removal plants shortly after initiation of the removal treatments.
Canopy photosynthesis during all years was significantly associated with average Chl concentration (Fig. 10A) and Chl/Ant ratio (Fig. 10C) of tagged main stem leaves measured after 100 DAP when Chl concentration was declining. Canopy photosynthesis was linearly associated with both chlorophyll concentration (r2 = 0.68, P = 0.001) and Chl/Ant ratio (r2 = 0.68, P = 0.01), suggesting that the declining leaf Chl was limiting canopy photosynthesis. Alternatively, average Ant content was associated negatively with canopy photosynthesis (r2 = 0.51, P = 0.001), which is not surprising based on the relationships of both Chl content and Chl a/b ratio to Ant content (Fig. 8). Sadras (1996) reported a significant relationship between radiation-use efficiency and leaf N concentration. Despite this association, higher leaf N in the removal treatment was observed in only one of four cultural combinations (cv. CS7S, high N, and low population).
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Fig. 10. Relationship between canopy photosynthetic rate (Pn) and either chlorophyll concentration (A) or anthocyanin level (B), or chlorophyll/anthocyanin ratio (C). Each symbol represents mean values of four replications within treatment, date, and year. Dates were after 100 d after planting, when canopy photosynthetic rates were declining and their nearest date of corresponding pigment measurement.
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Despite the associations between canopy photosynthesis and leaf pigments, not all differences due to treatments can be attributed to pigment concentration differences. For example, significant canopy photosynthetic differences in 1997 were observed at 99 DAP, prior to the development of treatment differences in leaf Chl concentration, Ant concentration, or Chl/Ant ratio (Fig. 5, 7, and 9, respectively). Even in the shortened measurement period of 1996, no difference in Chl concentration of the tagged leaf was seen at 104 DAP, 2 d prior to a significant difference between treatments (P = 0.09) in canopy photosynthesis. These observations agree with the suggestion of Sadras (1996) that radiation-use efficiency could not be completely explained by leaf N content. The other attributing factor was reduced light extinction coefficients induced by lessened boll loads on the sympodia (Sadras, 1996) and increased light penetration into the canopy (Holman and Oosterhuis, 1999) that had reduced boll loads because of insect infestation.
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SUMMARY
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In 3 of 4 yr, the flower removal treatment induced time dependent alterations in fruit development. The exception was 1995, when high temperatures during reproductive growth may have rendered flower removal ineffective because of physiological stress. Canopy photosynthetic patterns during reproductive growth partially reflected the altered flowering patterns but not completely. In 1995, when little effect was seen in flowering pattern, the area under the canopy photosynthesis curve was significant. This difference in integrated canopy photosynthesis occurred despite a significant treatment difference for only one measurement. Canopy photosynthesis was associated positively with Chl concentration after late season decreases were observed in Chl concentration. While this relationship existed, differences in canopy photosynthesis were observed in 1996 and 1997 (Fig. 4) before treatment differences in Chl concentration of tagged leaves were apparent (Fig. 5 and 6). These data indicate that while canopy duration and canopy photosynthesis was certainly affected by flower removal, there were other more subtle alterations induced by the absence or presence of developing bolls. These alterations may include modified leaf angles caused by the weight of bolls on branches, and hence, changing light extinction coefficients.
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ACKNOWLEDGMENTS
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The author wishes to thank John B. Graeber and Gary A. Little for their hard work in completing this study.
Received for publication June 26, 2000.
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REFERENCES
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- Bhatt, J.G., M.R.K. Rao, E. Appukuttan, and A.R.S. Nathan. 1982. Leaf reddening in hybrids of cotton. Comm. Soil Sci. Plant Anal. 13:151–156.
- Brook, K.D., A.B. Hearn, and C.F. Kelly. 1992. Response of cotton, Gossypium hirsutum L., to damage by insect pests in Australia: Manual simulation of damage. J. Econ. Entom. 85:1367–1377.
- Burkey, K.O., and R. Wells. 1991. Response of soybean photosynthesis and chloroplast membrane function to canopy development and mutual shading. Plant Physiol. 97:245–252.[Abstract/Free Full Text]
- Chen, F.M., and S.W. Chen. 1984. Determining the chlorphyll contents of plant leaves by acetone/ethanol mixture assay. For. Sci. Comm. 2:4–8.
- Combrink, N.J.J. 1988. An hypothesis concerning the development of the red leaf disorder in cotton. So. African J. Plant Soil 5:110–111.
- Feibo, W., W. Lianghuan, and X. Fuhua. 1998. Chlorphyll meter to predict nitrogen sidedress requirements for short-season cotton Gossypium hirsutum L. Field Crops Res. 56:309–314.
- Gepstein, S. 1988. Photosynthesis. p. 1347–1351. In. L.D. Noodén and A.C. Leopold (ed.) Senescence and aging in plants. Acad. Press, New York.
- Guinn, G. 1982. Causes of square and boll shedding in cotton. USDA Tech. Bull. 1672. p. 1–22. U.S. Gov. Print. Office, Washington, DC.
- Guinn, G. 1985. Fruiting of cotton. III. Nutritional stress and cutout. Crop Sci. 25:981–986.[Abstract/Free Full Text]
- Heitholt, J.J. 1997. Floral bud removal from specific fruiting positions in cotton: Yield and fiber quality. Crop Sci. 37:826–832.[Abstract/Free Full Text]
- Holman, E.M., and D.M. Oosterhuis. 1999. Cotton photosynthesis and carbon partitioning in response to floral bud loss due to insect damage. Crop Sci. 39:1347–1351.[Abstract/Free Full Text]
- Jones, M.A., R. Wells, and D.S. Guthrie. 1996. Cotton response to seasonal patterns of flower removal: I. Yield and fiber quality. Crop Sci. 36:633–638.[Abstract/Free Full Text]
- Kennedy, C.W., W.C. Smith, Jr., and J.E. Jones. 1991. Chemical efficacy of early square removal and subsequent productivity of superokra-leaf cotton. Crop Sci. 31:791–796.[Abstract/Free Full Text]
- Mancinelli, A.L., A.M. Hoff, and M. Cottrell. 1988. Anthocyanin production in Chl-rich and Chl-poor seedlings. Plant Physiol. 86: 652–654.[Abstract/Free Full Text]
- Moran, R. 1982. Formulae for determination of chlorophyllous pigments extracted with N,N-dimethylformamide. Plant Physiol. 68: 1376–1381.
- Pettigrew, W.T., J.J. Heitholt, and W.R. Meredith, Jr. 1992. Early season floral bud removal and cotton growth, yield, and fiber quality. Agron. J. 84:209–214.[Abstract/Free Full Text]
- Reddy, K.R., H.F. Hodges, and V.R. Reddy. 1992. Temperature effects on cotton fruit retention. Agron. J. 84:26–30.[Abstract/Free Full Text]
- Sadras, V.O. 1995. Compensatory growth in cotton after loss of reproductive organs. Field Crops Res. 40:1–18.
- Sadras, V.O. 1996. Cotton responses to simulated insect damage: radiation-use efficiency, canopy architecture, and leaf nitrogen content as affected by loss of reproductive organs. Field Crops Res. 48:199–208.
- SAS Institute Inc. 1987. SAS user's guide: Statistics. SAS Institute, Inc., Cary, NC.
- Wells, R. 1991. Soybean response to plant density: Relationships among canopy photosynthesis, leaf area, and light interception. Crop Sci. 31:755–761.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
