Boll Retention Research Articles

A Comparison of Scenarios for the Effect of Global Climate Change on Cotton Growth and Yield

If global surface temperatures change as projected because of radiative and physiological effects of a changing environment, we should expect important changes in crop production in the 21st Century. Experiments were conducted at ambient and twice ambient atmospheric CO2 concentrations at five temperatures. The 1995 temperature in Mississippi was used as a reference with the other temperatures being 1995 minus 2˚C, and 1995 plus 2, 5 and 7˚C. Daily and seasonal variation and amplitudes were maintained. Seedlings had 4–6 times as much leaf area and dry weight at 20 d after emergence when grown at 28˚C as at 23˚C (1995 ambient) average temperature during that growth period. Number of days to first square, flower, and open boll decreased as temperature increased. Double atmospheric CO2 did not affect these developmental rates. Temperatures above 28˚C, or 1995 average whole-season temperatures, were detrimental to mid- and late-season boll retention and growth. No fruits were retained to maturity at 1995 plus 5 or 7˚C. However, whole season vegetative growth was not significantly reduced by temperature 5–7˚C above the 1995 ambient conditions. Twice ambient CO2 caused about 40% increase in vegetative dry matter accumulation across temperatures. In a separate experiment, similar results were obtained on fruiting cotton grown at a range of temperatures based on long-term average US Midsouth July temperatures. Therefore, if global warming occurs as predicted, food and fibre production in such high-temperature and humid environments may be more limited to vegetative structures and the animals that consume vegetative structures.

Cotton Flowering and Boll Retention in Different Planting Configurations and Leaf Shapes

AbstractNarrow rows have the potential to increase boll numbers and lint yield of cotton (Gossypium hirsutum L.) compared with conventional row spacing. To optimize production in this system, it is important to know whether narrow‐row‐induced boll number increases are a result of increased seasonal flowering or increased boll retention. The objective of this study was to determine flower production (no. m−2), boll retention [(bolls/flowers) ✕ 1001, main stem node number, and yield as affected by row spacing and plant density. Field experiments were conducted in 1991 and 1992 on a Bosket fine sandy loam in narrow (51 or 76 cm) and wide rows (102 cm) using the normal‐ and okra‐leaf isolines of DES 24‐8 ne cotton. Plant densities were 5, 10, 15, and 20 plants m−2 in 1991 and 2, 3, 5, 10, and 15 plants m−2 in 1992. Averaged across leaf types and plant densities, 51‐cm rows increased the number of flowers by 12% and yield by 4% compared with 102‐cm rows in 1991. Boll retention was 40% for both row spacings. In 1992, averaged across leaf types and plant densities, 76‐cm rows increased the number of flowers by 21% and yield by 6% compared with 102‐cm rows. Boll retention was actually higher in 102‐cm rows (42%) than 76‐cm rows (36%). In general, plant density and the number of main stem nodes had little effect on flower numbers or boll retention. High plant densities tended to reduce the number of main stem nodes per plant. Averaged across row spacings, plant densities, and years, boll retention for normal‐leaf was higher than for okra‐leaf (50 vs. 29%). Results indicate that increased flower production rather than increased boll retention was responsible for the small narrow‐row yield increase.

Supplemental Boron, Boll Retention Percentage, Ovary Carbohydrates, and Lint Yield in Modern Cotton Genotypes

AbstractCotton (Gossypium hirsutum L.) is sometimes grown on soils with low B concentration. However, most of the literature regarding the effects of supplemental B on cotton was obtained from obsolete, low‐yielding genotypes rather than modern, high‐yielding genotypes. Therefore, the objective of this study was to determine the effects of soil‐ and foliarapplied B on leaf blade B concentration, boll retention, and lint yield of modern cotton genotypes. In 1991, three genotypes (DES 119, DES 24‐8 ne normal leaf, and DES 24‐8 ne okra leaf) and in 1992, two genotypes (Deltapine 20 and Deltapine 5415) of cotton were grown in the field on a Beulah fine sandy loam (coarse‐loamy, mixed, thermic Typic Dystrochrepts) having 0.11 mg kg−1 hot water extractable B concentration. Treatments included preplant soil and foliar (first flower to end of bloom) B (78% Na2B8O13·4H2O, 20% Na2B4O7·5H2O) applications for seasonal totals of 0, 0.89, or 1.78 (1992 only) kg B ha−1. The lowest rate of foliar‐applied B increased leaf blade B concentration from 25 to 70 mg kg−1 in 1991 and from 54 to 108 mg kg−1 in 1992. In 1992, the highest rate of foliar B applications resulted in a leaf blade concentration of 154 mg B kg−1. Soil‐applied B did not alter leaf blade B concentration in 1991, but slightly increased leaf blade B concentration in 1992 from 54 to 71 mg kg−1. Soil B concentrations were higher during the midseason than the preplant period, suggesting that preplant soil B analysis may not accurately foreshadow soil B supply during the season. Soil B or foliar B applications did not affect boll retention percentage, flower number, or lint yield in either year. Supplemental B did not affect boll distribution in 1991, but in 1992, foliar B applications increased the percentage of fruit on monopodial branches. In both years, supplemental B did not greatly affect fiber properties with the exception that supplemental B increased fiber micronaire reading of Deltapine 20 in 1992. The results suggest that modern cultivars may not always need supplemental B when soil B concentration is moderately low.

Receptacle and Ovary Assimilate Concentrations and Subsequent Boll Retention in Cotton

Assimilate supply or flux to developing cotton (Gossypium hirsutum L.) bolls (fruits) may help determine whether those bolls are retained or abscised. Most bolls that abscise tend to do so within a few days post anthesis (DPA), and little is known about the relationship between assimilate levels in young fruiting forms and their relationship to boll retention. Therefore, the objective of this study was to determine the relationships of young receptacle and ovary assimilate levels to boll retention among genotypes and sympodial branch positions. Eight genotypes of cotton (four cultivars and four leaf‐type isolines) were grown in the field in 1989 and 1990 using conventional cultural practices. Boll retention percentages (bolls/tagged flowers) and assimilate concentrations of excised receptacles and ovaries at Fruiting Positions 1, 2, and 3 were determined at 5 d preanthesis, 0 DPA, and 2 DPA. Position 1 boll retention (54 to 75%) was greater than that of Position 2 (19 to 45%) but the concentrations of soluble sugars in their excised receptacles and ovaries were similar. Variation in retention among genotypes at Position 1 was either small or nonsignificant but was significant at Position 2. Boll retention, glucose, and starch concentration of Position 2 MD 65‐11 super okra‐leaf bolls were lower and N concentration higher than the other genotypes. However, assimilate levels did not appear to explain the variation in retention among the eight genotypes. Other factors, such as C metabolism in ovules, may need to be examined in order to explain the physiological reasons for differences in boll retention.

Cotton Boll Retention and Its Relationship to Lint Yield

Fruit retention helps determine cotton (Gossypium hirsutum L.) yield. Study objectives were to (i) characterize genotypic variation in whole‐plant boll retention percentage, (ii) determine the relationship between retention and lint yield, and (iii) characterize timing, stage, and frequency of fruiting‐form abscission over two seasons in eight field‐grown genotypes: normal‐, sub okra., okra‐, and super okra‐leaf isolines of MD 65‐11 and four commonly grown higher‐yielding cultivars. Flower production was higher in okra‐ (238 m−2) and super okra‐leaf (323 m−2) than in normal (160 m−2) and sub okra.leaf (164 m−2) isolines, but boll retention was lower in okra‐ (29%) and super okra‐leaf (21%) than in the normal‐ (42%) and sub okra‐leaf (45%), so lint yields did not differ significantly among isolines. The cultivars averaged 16% more flowers, 33% more bolls, and 37% higher lint yield than normal‐leaf MD 65‐11, but lint yield correlated with boll retention (r = 0.84*; P < 0.05) when super okra‐ and okra‐leaf types were excluded. Genotypes differed slightly in distribution of mature bolls on mainstem nodes and on sympodial branch positions. Deltapine 90 produced fewer bolls (73%) on lower mainstem nodes (8–20) than the other genotypes (86–92%), reflecting its full‐season fruiting habit. Distribution of open bolls on sympodial fruiting positions differed between normal‐leaf (98% at Positions 1 and 2) and super okra‐leaf MD 65‐11 (88%). The other genotypes produced 94 to 96% of their bolls at Positions 1 and 2, which differs significantly from both extremes. When seven of these genotypes and three others were grown in the greenhouse and observed for development of squares and bolls, the normal‐leaf types shed more small squares (bract width >2 cm) but fewer bolls than did the okra‐ and super okra‐leaf types.

Cotton White Flower Counts and Yield with and without Early-Season Pest Control

Cotton (Gossypium hirsutum L.) yield is related to the number of flowers produced and the number of bolls retained. Flower production and boll retention are influenced by a wide range of factors including, but not limited to; cultivar selection, planting date, pest control, water stress, and fertilization. This field study was conducted to determine the relationship between white flower counts and yield as related to two levels of early-season pest control. Linear and quadratic regression models were tested to determine the best-fit relationship between yield and average weekly white flower counts, accumulated weekly flower counts, and flower counts made during specific 100 degree-day (DD) increments. The study used 12 to 15 planting dates each year and two levels of early-season pest control. The highest positive correlations between white flower counts and yield occurred with flowers counted at Week 6 (21–27 July). Coefficients (r2) between average weekly white flower counts and yield at Week 6 were 0.56 and 0.73 for the Temik-TSX and untreated check plots, respectively. The highest positive correlations between flower counts and yield at the various 100 DD increments occurred at 1600 to 1700 accumulated DD. In general, higher correlations between weekly white flower counts and yield were determined for the untreated check than for the Temik-TSX treatment. The significant correlations at Week 6 and at 1600 to 1700 DD occurred around the time of peak flowering.

Temperature Effects on Cotton Fruit Retention

AbstractTemperature is a major environmental factor that affects cotton (Gossypium hirsutum L.) production. Temperatures of 35 to 40°C are frequently observed in cotton‐producing areas. High‐temperature environments are sometimes associated with cotton sterility and boll retention problems; however, there is little specific information available on cotton sensitivity to temperature. We conducted a series of experiments in naturally lit growth chambers where the temperature was accurately controlled so we could measure its effects on cotton fruiting site production, abscission of flower buds (squares), flowers, and bolls. Cotton plants grown from seedlings at 40°C for 12 h d−1 shed all their squares. Plants grown from seedlings in the natural environment, then exposed to daytime temperatures of 30, 35, or 40°C during the fruiting period accumulated 47, 5.7, and <1%, respectively, of their mass as bolls. The time of day when plants were exposed to high temperature did not influence percent boll retention. Number of bolls produced, bolls retained, and percent retention were progressively reduced as time per day at 40°C was increased. Three week exposure to 40°C for 2 or 12 h d−1 resulted in 64 or 0% bolls, respectively, retained on the plants. Cultivars appeared to be similar in sensitivity to high temperature. Cultivars tolerant to short periods of high temperature would probably be more productive in today's environment and increased tolerance to high temperature will be even more essential in a warmer environment.

A comparison between drip and furrow irrigation in cotton at two levels of water supply

Optimal soil water status improves cotton yields by increasing flower production and boll retention and by controlling the time to maturity. Drip irrigation presumably improves the soil water regime thus leading to higher crop yields but the extent of its potential in cotton is unclear. A two-year experiment was carried out on a sandy loam soil at Cordoba, Spain, aimed at comparing drip against furrow irrigation in cotton ( Gossypium hirsutum L.). The irrigation methods were tested using a split-split-plot design which included two irrigation amounts and two or three cultivars each year. The advantage of one method over the other varied from year to year. The furrow irrigation treatments yielded significantly more than drip irrigation yields in 1985 but less in 1986. The differences in yield were explained by the crop water relations and the seasonal evapotranspiration. The 1986 results pointed to an advantage for drip irrigation under deficit irrigation conditions. Water application efficiency was 30% higher in the drip irrigation treatments indicating a definitive advantage of this method under limited water supply. Midday leaf water potential fluctuated along the season in both drip and furrow irrigation. The fluctuations were related to the irrigation events but not to the soil water deficit.

Pesticides and Cotton: Effect on Photosynthesis, Growth, and Fruiting

Field studies were conducted in 1972 and 1986 to determine the effect of selected, commercial insecticides and acaricides (pesticides) on growth, fruiting patterns, and yield of ‘Acala SJ-2’ cotton, Gossypium hirsutum L. There was a strong tendency in the 1972 study toward less boll retention in plots treated “season-long” with methyl parathion at all test sites, as well as a significant reduction in the weight of lint cotton at one site. In the 1986 study, four weekly applications of methyl parathion significantly reduced mesophyll conductance, boll retention, number of mature and open bolls per plant, number of first position bolls per plant on mainstem nodes 5-7, weight of lint cotton at harvest, and dry weight accumulation of fruiting forms. None of the other pesticides tested in the 1986 study, including chlordimeform, significantly increased any plant growth parameter when compared with the control.

COTMAP, a Technique for Evaluating Structure and Yield of Cotton Plants

Analysis of the structure and fruiting behavior of cotton, Gossypium hirsutum L., is complicated by its indeterminate growth habit and size variation among individual plants. We present COTMAP, a technique in which the primary fruiting sites (first and second sympodial positions) are individually mapped and fruit on remaining sites are considered collectively. Yield variables calculated by COTMAP include total bolls, boll distribution, and boll retention in prime fruiting sites. Plant structure variables include node of first fruiting branch, number of monopodia, number of sympodia, number of effective sympodia, number of sympodia with at least two flowering positions, total number of main axis nodes, plant height, and average internode length. Data from three tests of mepiquat chloride (N,N‐dimethyl‐piperidinium chloride) on cotton are used to illustrate the mapping technique. The COTMAP technique has been used to distinguish variation in structural characteristics and fruiting pattern of cotton plants associated with genetic differences, growth regulators, and insect damage.

Fruiting of cotton IV. Nitrogen, abscisic acid, indole-3-acetic acid, and cutout

Decreases in growth, flowering rate, and fruit (boll) retention of cotton ( Gossypium hirsutum L.) characterize cutout, a hiatus in fruiting. Nitrogen deficiency hastens cutout, and has been reported to cause an increase in the concentration of abscisic acid (ABA), a growth-inhibiting hormone. A field experiment was conducted with ‘Deltapine 61’ cotton to determine possible effects of N deficit on the concentrations of ABA and the growth-promoting hormone, indole-3-acetic acid (IAA), in cotton fruiting branches in relation to their growth, flowering rate, and boll retention. Three harvests were made during the fruiting cycle in 1987 to determine if the ABA concentration of fruiting branches increased or IAA concentration decreased as growth decreased during the season. Three harvests were made the next season (1988) to determine possible changes in concentrations of ABA and IAA in flower buds and flowers. Fruiting branches were always shorter on low-N than on high-N plants, and fruiting branches that developed late in the season were much shorter than those that developed early. The ABA concentrations in fruiting branches decreased after 9 July and ABA concentrations were always lower in fruiting branches of low-N than high-N plants. Therefore, the results do not support the hypothesis that ABA accumulates in N-deficient cotton fruiting branches and inhibits their growth. Decreasing concentrations of IAA, however, could have been a cause of decreased growth of fruiting branches. The IAA content of fruiting branches decreased during the fruiting cycle, and was lower in low-N than in high-N plants except in the last harvest. ABA increased and IAA decreased in 3-day-old bolls as boll retention decreased. The concentrations of ABA in flower buds and flowers did not increase during the season and were not affected by N deficiency. Likewise, the concentrations of IAA in flower buds and flowers were not affected by N. The concentration of IAA in flower buds decreased during the season, however. In general, the results support the hypothesis that the IAA of cotton fruiting branches is affected by N deficit, decreases during the fruiting cycle, and may be a factor in the decreases in growth, flowering, and boll retention commonly referred to as cutout.

Cotton Square Damage by the Plant Bug, Lygus hesperus (Hemiptera: Heteroptera: Miridae), and Abscission Rates

Numbers of Lygus Hesperus Knight per 50 net sweeps and numbers of abscised and lygus bug damaged squares per cotton plant terminal were counted weekly. Square abscission and square damage showed a high positive correlation with L. hesperus numbers ( r = 0.92, n = 7, for week of count and r = 0.69, n = 63, for June through July) and with square age ( r = 0.96, n = 20); fruit set on first and second sympodial branch positions showed a high negative correlation with L. Hesperus numbers ( r = -0.65, n = 25, for zero to six bugs per 50 sweeps). Comparisons of the proportion of squares damaged by lygus bugs between the terminal 5 nodes, terminal 10 nodes, and all nodes on one to three dates per location indicate that the terminal 5 nodes provide a reliable estimate of L. Hesperus feeding damage to squares. Our calculations indicate that before 1 August each lygus bug collected in the sweep net indicates a potential for 23,400 abscised plus damaged squares per hectare on the day of sample. Boll retention in relation to lygus bug numbers is presented. This information is expected to provide guidance when developing management strategies for L. hesperus on cotton. Square damage and loss can be used to estimate need for pesticide use and for refining the lygus bug: square ratio as an estimator of treatment threshold.

Changes in Free and Conjugated Indole 3-Acetic Acid and Abscisic Acid in Young Cotton Fruits and Their Abscission Zones in Relation to Fruit Retention during and after Moisture Stress

Experiments were conducted with field-grown cotton (Gossypium hirsutum L.) in 1985 and 1986 to determine effects of water deficit on levels of conjugated indole 3-acetic acid (IAA) and abscisic acid (ABA) in young fruits (bolls) and their abscission zones in relation to boll retention. Tissues were harvested three times during an irrigation cycle in 1985. They were harvested twice during an irrigation cycle and once after irrigation in 1986 to determine extent of recoveries of measured parameters. As reported earlier, the free IAA content of abscission zones decreased with moisture stress. Irrigation caused a partial recovery in free IAA content of abscission zones and caused a partial recovery in rate of boll retention. In contrast to free IAA, conjugated IAA increased with water deficit, both in 3-day-old bolls and in their abscission zones. Bolls contained much more ester IAA than their abscission zones. Some, but not all, of the increase in ester IAA in bolls during moisture stress could have come from a conversion of amide-linked IAA. Amide IAA decreased slightly during stress and increased after irrigation, but the concentration was low relative to ester IAA. Free and conjugated ABA both increased during stress and decreased after irrigation. However, the concentration of conjugated ABA remained relatively high in abscission zones. Ester IAA, being more resistant than free IAA to enzymic destruction during stress, may hasten recovery of fruit retention after relief of stress by providing a source of free IAA in abscission zones to inhibit continued abscission.

Concentrations of Abscisic Acid and Indoleacetic Acid in Cotton Fruits and Their Abscission Zones in Relation to Fruit Retention

An experiment was conducted with field-grown cotton (Gossypium hirsutum L.) to determine the effects of drought and an increase in available photosynthate on the abscisic acid (ABA) and indoleacetic acid (IAA) contents of 3-day-old bolls and their abscission zones. Photosynthate availability was manipulated by removing about two-thirds of the plants to permit increased irradiance, and thus photosynthesis, in the plant canopy. The demand for photosynthate was decreased by removing all bolls from the remaining plants. The thinning and defruiting operations were performed about 3 weeks after first flower. Control plants were neither thinned nor defruited. Effects of water deficit were observed by making three harvests at different times during a 2-week irrigation cycle. Increasing the availability of photosynthate increased boll retention, but had relatively little effect on the concentrations of ABA and IAA in bolls. However, it did increase the concentration of IAA in abscission zones. Water deficit increased the ABA content of bolls and abscission zones and decreased the IAA content of bolls and abscission zones. Across all treatments, the IAA content of abscission zones was positively correlated, and the ABA content of bolls was negatively correlated, with boll retention. The results indicate that stresses change the hormonal balance in ways that are consistent with observed increases in fruit abscission.

Fruiting of Cotton. III. Nutritional Stress and Cutout1

Decreases in growth, flowering, and fruit (boll) retention of cotton (Gossypium hirsutum L.) occur during the season in many modern cultivars even though it is an indeterminate plant. if they are pronounced, these decreases are commonly referred to as cutout. If cutout occurs too early it may decrease yield. Conversely, complete and permanent cutout at the end of the season would facilitate the control of insect pests. Cutout is strongly affected by boll load and may occur because of competition for photosynthate, a change in hormonal status, or both. Previous results indicated that changes in free abscisic acid (ABA) did not correlate with the decreases in growth, flowering, and boll retention that occurred as boll load increased during the season. Therefore, experiments were conducted in the field to test the hypothesis that cutout occurs when the demand for photosynthate exceeds the supply. The supply of photosynthate per plant was manipulated by thinning the plant population at different times to permit better light penetration (irradiance) into the canopy and thus increase total photosynthesis per plant. The demand for photosynthate was manipulated by partial defruiting. All flowers were removed during the first 3 weeks of flowering. Thinning at the start of the season caused individual plants to produce more flowers and bolls, but did not alter the timing of changes in flower production and boll retention rates during the season. Carrying capacity per plant varied inversely with plant population. Thinning later in the season caused an immediate increase in boll retention and a subsequent increase in flowering rate. Decreasing the demand by removing flowers early in the season caused subsequent and rather prolonged increases in flowering and boll retention rates. Early defruiting also moderated the decline in growth rate late in the season. Decreases and subsequent increases in flowering rate lagged behind the changes in growth and boll retention because flowering rate was determined by prior events (production and retention of flower buds). The results are consistent with the hypothesis that growth, flowering, and boll retention decrease when the demand for photosynthate increases and exceeds the supply. Therefore, an increase in photosynthesis should permit more bolls to be set before cutout.

Abscisic Acid and Cutout in Cotton

A decline in growth, flowering, and boll (fruit) retention is referred to as cutout in cotton (Gossypium hirsutum L.). Fruit load affects cutout, possibly through hormonal effects. Experiments were conducted to test the hypothesis that fruits are a source of abscisic acid (ABA) that moves into fruiting branches and growing points where it inhibits growth, flowering, and boll retention. Removal of the flower or young boll at the first node of fruiting branches did not decrease the ABA content of fruiting branches or the abscission zone at the second node. Effects on ABA content of the boll at the second node varied. In one field test, ABA content of bolls at the second node decreased with successive harvests as bolls were removed from first node positions of several fruiting branches. Thus, the effect was cumulative and was not limited to individual branches. Removal of the flower or boll at the first node increased boll retention at the second node. Removal of all flowers during the first 3 weeks of flowering delayed the decreases in growth, flowering, and boll retention that occurred as fruit load increased. But, the ABA content of fruiting branches and mainstem apices was not decreased by early defruiting and did not increase with increasing fruit load. The results do not support the hypothesis that fruits are a source of ABA that moves into fruiting branches and growing points where it then inhibits growth, flowering, and boll retention.

The effect of Terpal on the yield and yield components of oil-seed rape (Brassica napus L.)

The objective of this study was to examine the effect of the chemical growth regulator Terpal (a mixture of mepiquat chloride and ethephon or 2 chloroethyl phosphonic acid) on the pattern of branching, plant height and yield components of winter oil-seed rape (cv. Jet Neuf). Mepiquat chloride (a quaternary ammonium compound with similar antigibberellin properties to cycocel) was developed as a morphoregulator for cotton where it has been shown to reduce plant height, shorten internodes and increase boll retention (Willard et al. 1977). The activity of ethephon has been attributed to its release of ethylene which influences a wide range of developmental processes, for example fruit abscission and ripening (Chatterjee, 1977; Gvozdenovic, Dulic & Slavic, 1978), growth retardation (Van Andel & Verkerke, 1978) and also the extent of lodging in cereals (Hill, Joice & Squires, 1982).

Effects of Topping Pima Cotton on Lint Yield and Boll Retention1

AbstractSubstantial mid‐ and late‐season topping of American Pima cotton (Gossypium barbadense L.) plants occurs in field plantings. Lygus bug (Lygus hesperus Knight) feeding is the apparent cause of topping. The effects of mid to late‐season topping on lint yield and several yield components of ‘Pima S‐4’ cotton were examined. Topping of Pima S‐4 cotton in mid‐July, early‐August, and mid‐August reduced plant height, reduced the number of main stem nodes, increased boll set on top fruiting branches, and resulted in additional branch nodes on top fruiting branches. Plants topped 17 July produced 300%, 100%, and 60% more bolls on the first, second, and third branch, respectively, below the point of topping than did the check plants. The effect was less when topping was later in the season. The yield patterns in lower branches were not different from the checks. Topping did not affect: 1) lint yield (3 years), 2) number of bolls set, 3) seed/boll, 4) lint/boll, 5) lint/seed, 6) seed weight, 7) days to boll maturity, or 8) pink bollworm infestation. Fruit set was not delayed by topping. Fruiting points, which aborted on normal plants, produced bolls on topped plants up to the potential for the cultivar and environment. This has important implications for studies on insect damage to plants and for efforts to increase lint yield by reducing boll abscission.

Application of Time Series Analysis to Investigate Crop and Environment Relationships1

AbstractCorrelation techniques are important tools for investigating relationships between crop growth and environment. However when applied to a time series the presence of autocorrelation affects the estimates of correlations between two observed series, an effect which is sometimes overlooked in studies reported in the literature. Appropriate statistical techniques are needed to ensure that proper inferences can be made from these observations. Empirical time series modeling has the potential for removing autocorrelations in many of these cases. To test the feasibility of this technique the relationship between boll retention in cotton (Gossypium hirsutum L.) and 5‐day average minimum temperature during the growing season was investigated with 3 years of data. The best fitting autoregressive moving average models were selected for the observed time series for each of the 3 years. Residual series, observed minus predicted values, were computed from the estimated time series models for boll retention and minimum temperature and were free of autocorrelation. Negative crosscorrelations were found between the residual series for boll retention and average minimum temperature for the 5‐day periods beginning with 10 days and 1 day prior to anthesis, respectively. The negative relationship suggests that high nighttime temperatures accumulated over 5‐day periods prior to and during anthesis increase boll shedding. We conclude that time series modeling is an effective technique to aid the identification of relationships between agronomic variables measured in time sequences.

Effect of Blooming Date on Boll Retention and Fiber Properties in Cotton1

Six cultivars of upland cotton (Gossypium hirsutum L.) were studied to determine the influence of blooming date on boll retention and selected fiber properties in experiments conducted over 3 years at a single location. Flowers were tagged at weekly intervals; and after frost, bolls within plots were harvested by tagging dates. Records were kept by dates of blooms tagged/row, tagged bolls set/row, and percent tagged bolls set/row. Fiber properties (2.5% span length, 50% span length, uniformity index, micronaire, and 1/8‐inch gauge stelometer) were also studied to determine their patterns of variation.In general, blooms tagged increased from the beginning of the flowering season until shortly after mid‐season, then declined to form a fairly symmetrical distribution. Boll set increased rapidly during the first 3 weeks of the season, then gradually decreased. Percentage boll set was highest at the first of each season, then declined fairly continuously. As a consequence, shedding rate increased in a linear fashion as the seasons progressed. In one instance, it appeared that the cotton plant exhibited increased boll retention efficiency when blooms were limited. The 2.5 and 50% span length measurements exhibited similar distributions within each of the 3 years; however, both showed moderately different patterns between years. Their means did decrease fairly steadily, particularly during the latter part of each season. Evidence in 1 year suggested that about a week's delay was required to obtain a response in the longer fibers comparable to that in the shorter ones. Uniformity index was higher at the end of each season than in midseason; and in 2 of ~ years, it was also higher at the first of the season. All cultivars except one displayed lower micronaires at the end of the flowering season than at the beginning. The 1/8‐inch gauge stelometer reading also declined toward the end of the flowering period.Relative performance among cultivars for each trait and their differential response patterns over the season are discussed in the text.