Boll Retention Research Articles

Physiological causes of cotton fruit abscission under conditions of high temperature and enhanced ultraviolet‐B radiation

An experiment was conducted in sunlit controlled environment growth chambers to determine the physiological mechanisms of fruit abscission of cotton (Gossypium hirsutum L. cv. NuCOTN 33B) grown in high temperature and enhanced ultraviolet (UV)‐B radiation. Six treatments included two levels of optimum (30/22°C) and high (36/28°C) day/night temperatures and three levels of biologically effective UV‐B radiation (0, 7, and 14 kJ m−2 per day). Both the temperature and UV‐B treatments were imposed from seedling emergence through 79 days after emergence (DAE). High temperature did not negatively affect either leaf net photosynthetic rates (Pn) or abscission of cotton squares (floral buds with bracts) but significantly decreased boll retention. Plants exposed to 7 kJ UV‐B radiation retained 56% less bolls than the 0 kJ UV‐B control plants at 79 DAE, despite no significant differences in leaf Pn measured at squaring and flowering. At 53 DAE, leaf Pn of plants grown in high UV‐B radiation (14 kJ m−2 per day) decreased by 11%, whereas total non‐structural carbohydrate (TNC) concentrations in the leaves, floral buds, and young bolls decreased by 34, 32, and 20%, respectively, compared with the control plants. The high UV‐B radiation significantly increased square abscission. Square abscission was not related to leaf TNC concentration but closely correlated with TNC in floral buds (r = −0.68, P < 0.001). Young boll abscission was highly correlated with TNC concentrations in both the leaves (r = −0.40, P < 0.01) and the bolls (r = −0.80, P < 0.001). Our results indicate that non‐structural carbohydrate limitation in reproductive parts was a major factor associated with fruit abscission of cotton grown under high temperature and enhanced UV‐B radiation conditions.

Differences in in vitro Pollen Germination and Pollen Tube Growth of Cotton Cultivars in Response to High Temperature

High-temperature environments with >30 degrees C during flowering reduce boll retention and yield in cotton. Therefore, identification of cotton cultivars with high-temperature tolerance would be beneficial in both current and future climates. * Response to temperature (10-45 degrees C at 5 degrees C intervals) of pollen germination and pollen tube growth was quantified, and their relationship to cell membrane thermostability was studied in 12 cultivars. A principal component analysis was carried out to classify the genotypes for temperature tolerance. * Pollen germination and pollen tube length of the cultivars ranged from 20 to 60 % and 411 to 903 microm, respectively. A modified bilinear model best described the response to temperature of pollen germination and pollen tube length. Cultivar variation existed for cardinal temperatures (T(min), T(opt) and T(max)) of pollen germination percentage and pollen tube growth. Mean cardinal temperatures calculated from the bilinear model for the 12 cultivars were 15.0, 31.8 and 43.3 degrees C for pollen germination and 11.9, 28.6 and 42.9 degrees C for pollen tube length. No significant correlations were found between pollen parameters and leaf membrane thermostability. Cultivars were classified into four groups based on principal component analysis. * Based on principal component analysis, it is concluded that higher pollen germination percentages and longer pollen tubes under optimum conditions and with optimum temperatures above 32 degrees C for pollen germination would indicate tolerance to high temperature.

Response of flower and boll development to climatic factors before and after anthesis in Egyptian cotton

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 29:167-179 (2005) - doi:10.3354/cr029167 Response of flower and boll development to climatic factors before and after anthesis in Egyptian cotton Z. M. Sawan1,*, L. I. Hanna2, W. L. McCuistion3 1Cotton Research Institute, 2Central Laboratory for Design and Statistical Analysis Research, and 3National Agricultural Research Project, Agricultural Research Center, Ministry of Agriculture & Land Reclamation, 9 Gamaa St., 12619 Giza, Egypt *Email: zmsawan@hotmail.com ABSTRACT: Understanding the impact that climatic factors have on cotton production may help physiologists to determine possible control mechanisms which influence the flowering of cotton plants. This study was conducted to investigate the nature of the effects of climatic factors prevailing prior and subsequent to either flowering or boll setting on flower and boll production and retention in Egyptian cotton Gossypium barbadense L. Two uniform field trials using the cotton cultivated variety Giza 75 were carried out at the Agricultural Research Center, Giza, Egypt. Randomly chosen plants were used to record daily numbers of flowers and bolls during the production stage (68 d in Season I and 62 d in Season II). The daily records of the climatic factors (air temperature, diurnal temperature range, evaporation, soil surface temperature, sunshine duration, and humidity) were recorded during the entire period of production and also for the 15 d periods before and after anthesis. The effects of climatic factors on flower and boll production were quantified in non-limiting management techniques. Relationships in the form of simple and multiple correlations were computed between climatic factors and flower and boll production and retention. The data indicated that evaporation, minimum humidity and sunshine duration were the most effective climatic factors during preceding and succeeding periods on boll production and retention. There was a negative correlation between flower and boll production and either evaporation or sunshine duration, while the same correlation with minimum humidity was positive. Thus, it appeared that low evaporation rate, reduced sunshine duration and high humidity would enhance flower and boll formation. Accordingly, the deleterious effects of climatic factors on cotton production could be minimized through applying appropriate production practices, which would control and adjust the impact of these factors and thus potentially lead to an important improvement in cotton yield in Egypt. KEY WORDS:Boll retention · Evaporation · Flower and boll production · Humidity · Sunshine duration · Temperature Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 29, No. 2. Online publication date: August 22, 2005 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2005 Inter-Research.

Effect of glyphosate application timings and methods on glyphosate-resistant cotton

Under certain conditions, application of glyphosate to glyphosate-resistant (GR) cotton can lead to fruit shedding and yield reductions. Field studies were conducted at the Texas Agricultural Experiment Station using GR cotton, cv. ‘DeltaPine 5690RR’, to determine if application method and timing affect cotton fruit retention. Glyphosate at 1.12 kg ai ha−1was precisely postdirected (PD), postdirected with 25% foliage coverage (PDFC), or applied over the top (OT) at the 8- or 18-leaf stage after an initial topical application of 1.12 kg ha−1glyphosate at the four-leaf stage. In one of the years of this study, 8 PD, 18 PDFC, and 18 OT reduced yield. In 1999 and 2000, 8 PDFC and 8 OT applications of glyphosate caused yield loss, mainly due to lower mean boll weight. Glyphosate applied topically at the eight-leaf stage also affected the Position 1 boll retention throughout the plant in both years. Glyphosate contact with leaves and stems should be avoided when applying glyphosate after the four-leaf stage to prevent possible yield loss.

Growth and physiological responses of cotton (Gossypium hirsutum L.) to elevated carbon dioxide and ultraviolet‐B radiation under controlled environmental conditions

ABSTRACTBetter understanding of crop responses to projected changes in climate is an important requirement. An experiment was conducted in sunlit, controlled environment chambers known as soil–plant–atmosphere–research units to determine the interactive effects of atmospheric carbon dioxide concentration [CO2] and ultraviolet‐B (UV‐B) radiation on cotton (Gossypium hirsutum L.) growth, development and leaf photosynthetic characteristics. Six treatments were used, comprising two levels of [CO2] (360 and 720 µmol mol−1) and three levels of 0 (control), 7.7 and 15.1 kJ m−2 d−1 biologically effective UV‐B radiations within each CO2 level. Treatments were imposed for 66 d from emergence until 3 weeks after the first flower stage. Plants grown in elevated [CO2] had greater leaf area and higher leaf photosynthesis, non‐structural carbohydrates, and total biomass than plants in ambient [CO2]. Neither dry matter partitioning among plant organs nor pigment concentrations was affected by elevated [CO2]. On the other hand, high UV‐B (15.1 kJ m−2 d−1) radiation treatment altered growth resulting in shorter stem and branch lengths and smaller leaf area. Shorter plants at high UV‐B radiation were related to internode lengths rather than the number of mainstem nodes. Fruit dry matter accumulation was most sensitive to UV‐B radiation due to fruit abscission. Even under 7.7 kJ m−2 d−1 of UV‐B radiation, fruit dry weight was significantly lower than the control although total biomass and leaf photosynthesis did not differ from the control. The UV‐B radiation of 15.1 kJ m−2 d−1 reduced both total (43%) and fruit (88%) dry weights due to smaller leaf area and lower leaf net photosynthesis. Elevated [CO2] did not ameliorate the adverse effects of UV‐B radiation on cotton growth and physiology, particularly the boll retention under UV‐B stress.

Boll Retention and Boll Size among Intrasympodial Fruiting Sites in Cotton

Competition among cotton (Gossypium hirsutum L.) bolls for assimilates may affect boll retention and size, making it an important factor affecting productivity. A 4‐yr field study was conducted on Commerce silt loam to evaluate relationships among fruiting sites (FS) on sympodial branches of cotton receiving preplant fertilizer N rates of 0, 28, 56, 84, 112, 140, or 168 kg ha−1 or a preplant + sidedress application of 56 + 56 kg ha−1 each year. For each FS on each sympodium, there were four possible competition levels based on boll retention or abscission at FS 1, 2, and 3. Competition levels were determined by natural retention or abscission of fruit. Boll retention and weight were influenced by competition level, year, sympodia, FS location on the sympodia and by N rate. Competition effects on boll retention were affected by N rate but not by sympodia. Conversely, competition effects on boll weight were not affected by N rate but were affected by sympodia. Boll weight at FS 1 increased when bolls were retained at FS 2 and 3. Retention of a boll at FS 1 increased boll retention at FS 2 but decreased boll weight at FS 2. In contrast, boll weight at FS 2 increased when bolls were retained at FS 3, or at FS 1 and 3. Fertilizer N increased boll weight at FS 2, except when a competing boll was present at FS 1. Apparent increased competition among FS on a sympodium had favorable effects on boll retention and on boll weight except for FS 2 when FS 1 retained a boll and FS 3 did not retain a boll.

Boll Retention and Boll Size among Intrasympodial Fruiting Sites in Cotton

Boll Retention and Boll Size among Intrasympodial Fruiting Sites in Cotton

Glyphosate-induced reductions in pollen viability and seed set in glyphosate-resistant cotton and attempted remediation by gibberellic acid (GA3)

Glyphosate treatments to glyphosate-resistant (GR) cotton can cause increased fruit loss compared with untreated plants, likely due to reductions in pollen viability and alterations in floral morphology that may reduce pollination efficiency. This study was conducted to determine whether both stamen and pistil are affected by glyphosate treatments by measuring seed set from reciprocal reproductive crosses made between glyphosate-treated GR, untreated GR, and conventional nontransgenic cotton. Pollen viability was 51 and 38% lower for the first and second week of flowering, respectively, in GR plants treated with a four-leaf postemergence (POST) treatment and an eight-leaf POST-directed treatment of glyphosate than in GR plants that were not treated. Seed set per boll was significantly reduced when the pollen donor parent was glyphosate treated vs. untreated for the first 2 wk of flowering. There were no significant differences between treatments applied to male parents as measured by seed set at Weeks 3 and 4 of flowering. Seed set was not influenced by glyphosate treatments applied to female parents at any time. Retention of bolls resulting from crosses was reduced by glyphosate treatment of male parents during the first and third week of flowering but was not affected by glyphosate treatment of female parents. The application of gibberellic acid (GA), which has been shown to reverse male sterility in tomato (Lycopersicon esculentum L.) and to enhance boll retention in cotton, was investigated for similar effects in glyphosate-treated GR cotton. The GA treatments to glyphosate-treated plants increased the anther–stigma distance 12-fold, stigma height, and pollen viability in the second week of flowering but decreased the number of seeds in second-position bolls on Fruiting branches 1 through 3, decreased the number of first-position bolls per plant, and increased the number of squares in comparison with glyphosate-treated GR plants not receiving GA. Although GA applications to glyphosate-treated GR cotton have some remedial effect on pollen viability, the GA-induced increase in the anther–stigma difference exacerbates the increase in anther–stigma distance caused by glyphosate, resulting in low pollination.

Relationships between climatic factors and flower and boll production in Egyptian cotton ( Gossypium barbadense)

Fruiting of cotton plant is determined and influenced by cultivar, climatic conditions, management practices and pests. An understanding of the flowering and boll retention patterns of cotton cultivars can contribute to more efficient and economical crop management. The objective of this investigation was to study the effect of various climatic factors on flower and boll production of Egyptian cotton. This could be used in formulating advanced predictions of the effect of certain climatic conditions on the production of Egyptian cotton. Two uniform field trials, using cotton Gossypium barbadense cv. Giza 75 were carried out in 1992 and 1993 at the Agricultural Research Station, Agricultural Research Center, Ministry of Agriculture, Giza, Egypt, to investigate the relationships between climatic factors, flower and boll production. Climatic factors included maximum and minimum air temperatures along with their difference, evaporation, surface soil temperature (grass temperature or green cover temperature) at 0600 and 1800 h°C −1, sunshine duration, maximum and minimum humidity and wind speed. The effects of climatic factors on flower and boll production were quantified in the absence of water and nutritional deficits and damage effects of insects. Results obtained indicate that evaporation, sunshine duration, humidity, surface soil temperature at 1800 h, and maximum air temperature, were the important climatic factors that significantly affect flower and boll production of Egyptian cotton. Consequently, applying appropriate specific cultural practices that minimize the deleterious effect of these factors will lead to an improvement in cotton yield.

Interval of days required for determining efficient relations between climatic factors and cotton flower and boll production

The cotton plant (Gossypium spp.) is sensitive to numerous environmental factors. This study was aimed at predicting effects of climatic factors grouped into convenient intervals (in days) on cotton flower and boll production compared with daily observations. Two uniformity field trials using the cotton (G. barbadense L.) cv. Giza 75 were conducted in 1992 and 1993 at the Agricultural Research Center, Giza, Egypt. Randomly chosen plants were used to record daily numbers of flowers and bolls during the reproductive stage (60 days). During this period, daily air temperature, temperature magnitude, evaporation, surface soil temperature, sunshine duration, humidity, and wind speed were recorded. Data, grouped into intervals of 2, 3, 4, 5, 6, and 10 d, were correlated with cotton production variables using regression analysis. Evaporation was found to be the most important climatic variable affecting flower and boll production, followed by humidity and sunshine duration. The least important variables were surface soil temperature at 0600 and minimum air temperature. The 5-d interval was found to provide the best correlation with yield parameters. Applying appropriate cultural practices that minimize the deleterious effects of evaporation and humidity could lead to an important improvement in cotton yield in Egypt. Key words: Cotton, flower production, boll production, boll retention

Developing management options for mepiquat chloride in tropical winter season cotton

Little research had been conducted on managing cotton growth using mepiquat chloride (MC) during the tropical winter season. Three experiments were conducted over three seasons. Early season internodes (first nine nodes) were long compared to temperate climates. Consequently the effect of MC applied, as multiple or single doses, from four nodes to first flower was evaluated. MC dramatically reduced height and node number in proportion to a total amount of MC up to 45 g/ha, r 2=0.66 and r 2=0.81, respectively; this response was independent of the frequency of treatment. Lint yields were high averaging 2143, 2415 and 2312 kg/ha for the three seasons. Despite the number of fruiting branches declining linearly with the amount of MC lint yields were decreased ( p<0.05) in only 2 of the 28 treatments. There was a trend to increased yield (106.5%) compared with untreated plants where between 9 and 18 g/ha MC was intercepted. There was no economic effect of MC on lint quality. Yield compensation for reduced fruiting branches due to MC was via a linear increase in boll retention over all fruiting sites and vegetative branch bolls, which peaked with 35 g/ha of MC for each yield component. Where >35 g/ha was intercepted yields were the same or reduced compared to untreated plants. Compensation via boll size, possibly related to position, was implicated in this yield response. Thus treatment with 9–18 g/ha of MC, between 4 and 11 nodes, provided a compromise between suppressing plant height for operational efficiency, and optimising these yield components. Crop monitoring techniques based on the length of internodes could not aid MC treatment decisions because critical lengths, developed for temperate locations, were always exceeded and there was rarely a yield response to MC. An explanation came from the independence to MC of the height-to-nodes ratio prior to flowering. Monitoring techniques based on predicting the height and node number response from the MC concentration within the plant showed promise. MC did not affect time to maturity despite ≤15-day reduction in main-stem flowering period due to MC. This difference was attributed to high and increasing end-of-season temperatures synchronising maturity in bolls from later flowers, and it was possible vegetative branch bolls, increased by MC, matured after main-stem bolls. It was suggested future research consider modelling the MC response, irrigation interactions, the cultivar response, the effect on duration of flowering, and the interaction between MC and yield compensation from insect damage.

Influence of seasonal variability and conservation tillage on flower production and boll retention of Bt cotton (Gossypium hirsutum)

An experiment was conducted at Central Institute for Cotton Research, Nagpur, Maharashtra, to monitor flower and boll production in Bt transgenic cotton (Gossypium hirsutum L.) hybrid (RCH 2 Bt. hybrid) as influenced by climatic factors and conservation tillage practices in selected treatments. Two reduced tillage (RT) systems, with limited soil disturbance in the form of inter-culture operations (RT1) and no soil disturbance (RT2), were compared with the conventional tillage treatment (CT). The tillage treatments comprised subplots with and without green ma- nure. Conservation-tillage treatments had 1215% more bolls retained on a plant than the conventional tillage. Ir- respective of the tillage systems, flower and boll production varied among years. Flower production correlated negatively with the maximum and minimum temperature (P

Effect of over-expression of an E. coli fructose 1,6-bisphosphate aldolase gene in planta on photosynthesis, carbon metabolism and plant growth

Fructose 1,6 biphosphate aldolase (fda) is an enzyme catalyzing a reversible reaction converting triose phosphate to fructose 1,6 bisphosphate. This reaction occurs in both chloroplast (the Calvin cycle and starch synthesis) and cytosol (sucrose synthesis and glycolysis). To study whether fda plays any important roles in controlling photosynthesis, metabolic flux and plant growth we have successfully increased its activity in planta by transforming an E. coli class II fda gene into tobacco, potato and cotton under the control of a constitutive promoter. This E. coli fda enzyme differs from its plant counterpart which is a class I enzyme in that the E. coli enzyme is a metalloaldolase and the plant enzyme is a Schiff base-forming aldolase. When expressed in planta, the E. coli fda protein is specifically targeted into chloroplast through a chloroplast targeting sequence. Transgenic cotton plants expressing the E. coli fda showed up to 6-fold increase in fda activity, little effect on photosynthesis, but altered carbon partitioning and significant increase in starch accumulation in leaves. Under the standard greenhouse conditions trangenic cotton plants showed improved boll retention and lint yield. Significant increase in root biomass and tuber yield were observed in the transgenic tobacco and potato, respectively.

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

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.

Dynamics of non-structural carbohydrates in developing leaves, bracts and floral buds of cotton

Development of cotton ( Gossypium hirsutum L.) squares (i.e. floral buds with bracts) is fundamental for yield formation. A 2-year field study was conducted to determine dry weight (DW) accumulations of cotton leaves, floral bracts and floral buds, and the changes in concentrations of non-structural carbohydrates (hexoses, sucrose and starch) in these tissues during square ontogeny as affected by fruiting positions within the plant canopy. During square development, DW accumulation of a subtending sympodial leaf and floral bracts followed a sigmoid growth curve with increasing square age, whereas the DW increase of a floral bud followed an exponential curve. Main-stem node (Node 8, 10 or 12) and branch position (proximal vs. distal) within a plant canopy significantly affected DW accumulations of the leaf, bracts and floral bud. Starch was the dominant non-structural carbohydrate in the three tissues, accounting for more than 65% of total non-structural carbohydrates (TNC). Subtending leaf TNC increased as square age increased. The bracts exhibited a smaller change in TNC than leaves. Non-structural carbohydrate concentration was the lowest in 10-day-old floral buds, and had little change during the first 15 days of square development. Within 5 days prior to anthesis, the floral-bud TNC increased dramatically, tripling at the time of floral anthesis compared with 15-day-old floral buds. Square age and fruiting position significantly affected non-structural carbohydrate concentrations of subtending leaves, bracts, and floral buds. The correlation did not exist between final boll retention and non-structural carbohydrate concentrations of floral buds at different fruiting positions under normal growth conditions. The pattern of floral-bud non-structural carbohydrates during square ontogeny suggests that major events in carbohydrate metabolism occur just prior to anthesis.

COTTON RESPONSES TO SHADE AT DIFFERENT GROWTH STAGES: GROWTH, LINT YIELD AND FIBRE QUALITY

Photosynthetic photon flux density (PPFD) has variable effects on cotton (Gossypium hirsutum) plant growth, development and lint yield, but little is known about the responses of yield, yield components and fibre quality to low PPFD at different developmental stages. Field studies were conducted in 1993–95 to determine the effects of an 8-d period of shade (63% reduction in PPFD) imposed at different developmental stages (pinhead square (PHS), first flower (FF), peak flower (PF) and boll development (BD)) on cotton growth, lint yield, yield components and fibre quality. Shade for 8 d at the early square stage did not affect cotton growth and yield. Shade during FF, PF and BD increased fruit abscission, and decreased specific leaf weight, dry matter accumulation, lint yield, fibre micronaire, and fibre strength compared with the unshaded control. The detrimental effect of shade on yield increased with later growth stages. Shade at the FF, PF and BD stages decreased lint yield by 18, 34 and 52% in 1993, and by 18, 21 and 29% in 1994 respectively compared with the unshaded control. Shade caused the greatest decrease in the dry weight (DW) of fruits (squares + flowers + bolls) and the smallest decrease in leaf DW among leaves, stems and fruits. Of the three yield components (boll number, boll weight and lint percentage), boll number was the most sensitive to shade. Shade during squaring and early flowering had little effect on average boll weight, and did not affect lint percentage. Decreased yield of cotton shaded during FF and PF appeared to be related to decreased boll retention. Shade during BD decreased both boll retention and average boll weight. Under shade conditions, fibre micronaire and fibre strength were decreased, while other fibre properties were unaffected. These results help explain the yield response of field-grown cotton to low PPFD stress.

Temperature Regime and Carbon Dioxide Enrichment Alter Cotton Boll Development and Fiber Properties

Temperature and atmospheric carbon dioxide concentration [CO2] affect cotton (Gossypium hirsutum L.) growth and development, but the interaction of these two factors on boll and fiber properties has not been studied. An experiment was conducted in naturally lit plant growth chambers to determine the influence of temperature and atmospheric [CO2] on cotton (cv. DPL‐51) boll and fiber growth parameters. Five temperature regimes were evaluated: the 1995 temperature at Mississippi State, MS; the 1995 temperature minus 2°C; and the 1995 temperature plus 2, 5, and 7°C. Daily and seasonal variation and amplitudes were maintained. Atmospheric [CO2] treatments were 360 (ambient) and 720 μL L−1. Boll number, boll growth, and fiber properties were measured. Boll size and maturation periods decreased as temperature increased. Boll growth increased with temperature to 25°C and then declined at the highest temperature. Boll maturation period, size, and growth rates were not affected by atmospheric [CO2]. The most temperature‐sensitive aspect of cotton development is boll retention. Almost no bolls were retained to maturity at 1995 plus 5 or 7°C, but squares and bolls were continuously produced even at those high temperatures. Therefore, the upper limit for cotton boll survival is 32°C, or 5°C warmer than the 1995 U.S. Mid‐South ambient temperatures. The 720 μL L−1 atmospheric [CO2] had about 40% more squares and bolls across temperatures than the 360 μL L−1 [CO2]. Fibers were longer when bolls grew at less than optimal temperatures (25°C) for boll growth. As temperature increased, fiber length distributions were more uniform. Fiber fineness and maturity increased linearly with the increase in temperature up to 26°C, but decreased at 32°C. Short‐fiber content declined linearly from 17 to 26°C, but was higher at higher temperature. As for boll growth and developmental parameters, elevated atmospheric [CO2] did not affect any of the fiber parameters. Changes in temperature, however, had a dramatic effect on boll set and fiber properties. The relationships between temperature and boll growth and developmental rate functions and fiber properties provide the necessary functional parameters to build fiber models under optimum water and nutrient conditions.

Relationships among Final Plant Map Indices in Acala Cotton

In cotton (Gossypium hirsutum L.) crop management, the practice of collecting detailed structural data just prior to harvest, called final plant mapping, may provide useful information about the crop's response to its environment and to management actions. The objective of this study was to analyze final plant map data taken in Acala cotton in the San Joaquin Valley, California, to determine whether relationships exist that might be useful in data interpretation. Five years of data taken from statewide variety trials were used to develop a statistical model. Data in each year were collected at eight locations for five cultivars. Seven parameters were most substantially related to cotton lint yield, boll retention, and earliness. These parameters were number of vegetative branches, percentage boll retention in the bottom five fruiting branches, late season boll retention, plant height, number of first position bolls, late season boll retention, and number of main stem nodes in the zone of the plant contributing 95% of the total bolls. These quantities provide useful information in interpreting an Acala cotton crop's performance. The model was compared with data from a sixth year. This comparison generally supported the conclusions drawn based on the 5 yr of data. The relationships between plant map indices and yield are not sufficiently precise to enable them to be used in yield forecasting, but they do provide a useful means to evaluate the effects of environmental conditions and management strategies.

Cotton responses to different light–temperature regimes

A series of experiments investigating the interactive effects of light and temperature on vegetative growth, earliness, fruiting, yield and fibre properties in three cultivars of cotton, was undertaken in growth rooms. Two constant day/night temperature regimes with a difference of 4 °C (30/20 and 26/16·5 °C) were used throughout the growing season in combination with two light intensities (75 and 52·5 W m−2).The results showed that significant interactions occurred for most of the characters studied. Although the development of leaf area was mainly temperature-dependent, plants at harvest had a larger leaf area when high temperature was combined with low rather than with high light intensity. Leaf area was least in the low temperature–low light regime. However, the plants grown under the high temperature–low light combination weighed the least.Variations in the number of nodes and internode length were largely dependent on temperature rather than light. Light did, however, affect the numbers of branches, sympodia and monopodia. The first two of these were highest in the high light–high temperature regime and the third in the low light–low temperature regime.All other characters, except time to certain developmental stages and fibre length, were reduced at the lower light intensity. Variation in temperature modified the light effect and vice versa, in a character-dependent manner. More specifically, square and boll dry weights, as well as seed cotton yield per plant, were highest in high light combined with low temperature, where the most and heaviest bolls were produced. But flower production was favoured by high light and high temperature, suggesting increased boll retention at low temperature, especially when combined with low light. Low temperature and high light also maximized lint percentage.Fibres were shortest in the high temperature–high light regime, where fibre strength, micronaire index and maturity ratio were at a maximum. However, the finest and the most uniform fibres were produced when high light was combined with low temperature.Cultivar differences were significant mainly in leaf area and dry matter production at flowering.

Physiologic and Yield Responses of Shaded Cotton to the Plant Growth Regulator PGR-IV

The plant growth regulator PGR-IV has been reported to improve the growth, boll retention, and yield of cotton (Gossypium hirsutum L.) under optimum growing conditions. However, little is known about the response of cotton to PGR-IV under low light stress. A 3-year field study was conducted to determine if applying PGR-IV before an 8-day period of shade (63% light reduction) benefitted the growth and yield of shaded cotton. Shading during early squaring did not affect yield. Shading after the first flower stage significantly increased leaf chlorophyll concentration and fruit abscission and decreased the leaf photosynthetic rate, nonstructural carbohydrate concentrations, and lint yield. Foliar application of PGR-IV at 292 mL ha−1 at early squaring and first flower did not improve the leaf photosynthetic rate of shaded cotton. However, shaded plants receiving PGR-IV had higher nonstructural carbohydrate concentrations in the floral buds and significantly lower fruit abscission than the shaded plants without PGR-IV. Applying PGR-IV to the foliage before shading resulted in a numeric increase (6–18%) in lint yield compared with shaded plants without PGR-IV. The decreased fruit abscission from the application of PGR-IV was associated with improved assimilate translocation. The yield enhancement from foliar application of PGR-IV was attributed to increased fruit retention. However, the average boll weight of shaded plants with PGR-IV tended to be lower than that of shaded plants without PGR-IV. Lint percentage was not affected by PGR-IV. Foliar application of PGR-IV appears beneficial for increasing the fruit retention of shaded cotton.