Lint Yield Increase Research Articles

Photosynthetic Rate, Stomatal Conductance and Leaf Area in Two Cotton Species (Gossypium barbadense and Gossypium hirsutum) and their Relation with Heat Resistance and Yield

Gossypium barbadense L. (Pima) and Gossypium hirsutum L. (upland) cottons are the two major fibre producing species grown in the south-western United States, where lint yields are adversely affected by high temperatures. In these environments, heat-adapted upland cultivars show higher yields and heat resistance than advanced Pima cultivars. Recent studies with an historical series of commercial Pima cultivars have shown that increases in lint yield and heat resistance are tightly coupled to increases in stomatal conductance and photosynthetic rate, and to decreases in leaf area. In the present study, Pima S-6 and Pima S-7 (advanced Pima cultivars) and Deltapine 90 (advanced upland cultivar) were compared under field and laboratory conditions to determine whether the physiological and morphological gradients found in the Pima historical series extrapolate to upland cotton. In the field, Deltapine 90 showed 25–35% higher stomatal conductance, 35–50% higher photosynthetic rate and 45% smaller leaf area than Pima S-6. The higher photosynthetic rate and stomatal conductance of Deltapine 90 leaves were partially related to their sun-tracking ability. In gas exchange experiments that prevented sun-tracking, the two cultivars had comparable photosynthetic rate as a function of incident radiation, while stomatal conductance was higher in upland cotton. In the 25–35°C range, photosynthetic rate as a function of temperature remained nearly constant in both cultivars, and was higher in upland cotton at all temperatures. Stomatal conductance showed a strong temperature-dependence, and conductance value and the slope of the stomatal response to temperature were higher in Deltapine 90. In progeny from a cross between Deltapine 90 and Pima S-7, the segregation of stomatal conductance in F1 and F2 populations showed a clear genetic component. These results indicate that the differences in photosynthetic rate, stomatal conductance and leaf area associated with increases in lint yield and heat resistance in the Pima historical series are also evident in a comparison between advanced cultivars of upland and Pima cotton. Upland cotton could be used as a source of genetic variation for high stomatal conductance in Pima breeding programs.

Performance of Commercial Cotton Cultivars under Elevated Densities of Tobacco Budworm

AbstractThe development of improved cultivars is essential for continued economic production of cotton, Gossypium hirsutum L. Information is limited on how different cotton cultivars compare under elevated densities of tobacco budworm, Heliothis virescens (F.), an economically important cotton pest. Seven field tests were conducted between 1988 and 1992 to evaluate cotton cultivars grown under elevated densities of tobacco budworm (TBW). Cultivars were grown under two regimes: (i) artificial elevated infestation, w/TBW, and (ii) elimination of tobacco budworm, w/o TBW. Elevated densities of TBW (w/TBW) significantly reduced yields compared with w/o TBW, but reduction varied among years and tests. The regression equation for lint yield w/TBW on lint yield w/o TBW was Y = −111.0 + 0.6X. Thus, for every 1.0 kg of lint yield increase per hectare due to cultivar improvement, the corresponding increase under artificial TBW infestation was only 0.6 kg. The regression coefficient for lint percentage on lint yield w/o TBW was Y = 30.85 + 0.006X. These data show that cotton breeders have developed high‐yielding cultivars, but that progress is still needed in the development of resistance to the tobacco budworm injury. They also show that, as cultivars with higher yield potential were developed, these cultivars were better able to tolerate damage by the tobacco budworm. The parity between yield increase per se and yield under elevated densities of tobacco budworm is not 1.0:1.0, but rather 1.0:0.6. This is a useful and practical level of parity.

Productivity and Tobacco Budworm Resistance of Cotton Developed between 1890 and 1986

There is a paucity of information on the relationships between modern (i.e., released in or after 1978) and historically obsolete cotton (Gossypium hirsutum L.) cultivars with respect to their ability to yield when grown in the presence of high levels of tobacco budworm (TBW), Heliothis virescens F. The objective of this study was to compare 18 cultivars of cotton developed between 1890 and 1986 for ability to yield when grown with and without TBW infestations. This comparison was accomplished by growing cultivars for 2 yr under two regimes: (i) artificial infestation with TBW (w/TBW) and (ii) complete control of all insect pests (w/o TBW). The regression equation for lint percentage w/o TBW on lint yield w/o TBW was Y = 26.8 + 0.0076 X, with an R2 of 0.58. Thus, lint percentage has increased 0.76% for every 100 kg ha‐1 increase in lint yield. Theregression equation for number of bolls w/o TBW on lint yields w/o TBW was y = 73,689 + 402 X, with an R2 of 0.83. The regression equation for lint yield w/TBW on lint yield w/o TBW was Y = ‐48.4 + 0.69 X, with an JP of 0.84. Thus, for every 1.00 kg of lint yield increase due to breeding during the 96‐yr period there was a corresponding lint yield increase under TBW infestation of only 0.6 kg. The newer cultivars yielded more than the older cultivars, with number of boils per unit area and lint percentage being the primary components involved in increased yields. Some of the newer cultivars yielded as much w/TBW as some of the older cultivars w/o TBW. In addition, the newest cultivar (DES 119; 1986) yielded significantly more than any other cultivar when grown w/o TBW. It also yielded significantly more when grown w/TBW than any cultivar developed before 1982.

Analysis of Effects of Atmospheric Carbon Dioxide and Ozone on Cotton Yield Trends

AbstractCotton (Gossypium hirsutum L.) yields have declined since 1964 despite improvements in technology and introductions of higher‐yielding cultivars. Cotton scientists have been unable to identify exact causes of the yield decline. For the past 25 yr, global atmospheric CO2 concentration ([CO2]) has been increasing due to the increased burning of fossil fuels; cotton has been found to be sensitive to [CO2]. Cotton has also been found to be sensitive to atmospheric ozone concentration ([O3]) at levels that occur regularly where it is grown.To analyze the effects of [CO2] and [O3] on cotton‐yield trends, simulations were made using the cotton crop model GOSSYM. Input data for simulations were obtained from cotton breeders' trial sites located at Florence, SC; Stoneville, MS; College Station, TX; Phoenix, AZ; and Fresno, CA.The simulated effects of the [CO2] and [O3] on cotton yields changed from location to location due to interactions with soil, plant, and atmospheric variables and with nutrient levels in the soil. Given enough N, the increased [CO2] would probably result in a 10% increase in lint yield. Due to N stress sometime during the growing season, however, the plants could not fully utilize the increased [CO2]. Ozone concentration increased during the period of cotton‐yield decline, and this increase in [O3] was found to affect simulated cotton yields adversely. It appears that O3 is one of the contributing factors to the yield decline. Overall O3 had a more adverse effect on simulated cotton yields at locations where O3 was present at higher concentrations, i.e., Phoenix, AZ and Fresno, CA.

Estimation of Heat Tolerance Improvement in Recent American Pima Cotton Cultivars

AbstractImproving cotton (Gossypium spp.) heat tolerance (ability to set bolls in high temperature environments) has been an important aspect of the American Pima (Pima) cotton (G. barbadense L.) breeding program for over 25 years. However, heat tolerance is difficult to quantify. This report estimates change in heat tolerance of Pima cotton through yield response over 30 years in six Arizona counties that differ in elevation and mean summer temperatures. Pima cotton/upland cotton (G. hirsutum L.) lint yield percentages were compared for each county by regression with year of production. County mean yield percentages were also compared with elevations. Pima cotton yields as percentages of upland cotton yields increased in five of the six counties over the 30‐year period. Pima lint yield increased from 57 % of upland yield in 1956 to 75 % in 1985 when averaged over the six counties. This increase represents an estimated 206 kg lint ha‐1 in addition to any upland yield increase. Comparison of regression coefficients suggest that nearly 50 % of the 30‐year lint yield increase of Pima cotton at lower elevations was the result of increased tolerance to high temperature in improved cultivars. County 30‐year mean Pima cotton lint yields as percentage of upland cotton yield increased significantly (P < 0.001) from 52.2% to 82.1 % as county elevations increased from 37 m to 1273 m (cooler summer temperatures). These results support reports of greater heat tolerance for upland cotton than Pima cotton, but also show that the difference between species has been reduced substantially by breeding in the last 30 years.

Evaluation of Chlordimeform for Cotton Yield Enhancement1

Greenhouse and field studies were conducted to evaluate the effects of multiple applications of chlordimeform on the growth and development of cotton, Gossypium hirsutum. L., plants, and on early season insect populations. Plants were sprayed six times with chlordimeform either alone or in combination with fenvalerate at 5- to 7-d intervals, beginning at the six-leaf stage of plant development. In the absence of early season insects and when insect populations were maintained at a relatively low level, no increases in lint yield occurred on the chlordimeform-treated plants. However, yield increases did occur and insect populations became lower in these treated plots when early season insect populations in the test area were relatively high. None of the treatments influenced the boll components boll Size, seed index, lint index, and lint percentage, or the fiber properties length, strength, and micronaire.

Effects of Yield Components on Lint Yield of Upland Cotton with High Fiber Strength1

Seeds/boll, lint/seed, and bolls/m2 were determined for several PD breeding lines and check cultivars of Upland cotton, Gossypium hirsutum L., representative of distinct breeding stages in the simultaneous improvement of lint yield and fiber strength. These yield components were calculated from seed cotton yield, boll size, seed size, and lint percentage measured on the stocks in one or more tests conducted for at least 3 years on the Pee Dee Experiment Station, Florence, S.C. from 1956 to 1972. The objective of the present study was to determine the influence of each component on lint yield and its breeding implication in improvement programs.Most southeastern commercial cultivars averaged 36 seeds/boll as compared with 33 for PD lines. Seeds/boll can be increased by crossing PD lines with southeastern commercial cultivars and selecting for this characteristic. It might be possible to increase lint yields of PD lines by increasing seeds/boll, which should increase seed surface area for greater lint production. Lint/seed advanced slightly as lint percentages were improved in early developed PD lines. Lint/seed was increased significantly after the introduction of the C 6‐5 breeding line because lint percentage and seed size advanced greatly. This component has not influenced yield of recent PD lines appreciably because boll size has declined and lint percentage has remained relatively constant. Bolls/m2 has been the major component contributing to lint yields of PD lines. Except for the rapid increase in lint yield from the higher level of lint percentage and larger bolls and seeds derived from C 6‐5, increases in lint yields have paralleled increases in bolls/m2 We suspect that we will be concerned more with maintaining, rather than increasing, bolls/m2 as we develop future PD breeding lines.

Recurrent Selection for Lint Percent within a Cultivar of Cotton (Gossypium hirsutum L.)1

We conducted this study to determine if a modified form of recurrent selection for lint percent within a cotton (Gossypium hirsutum L.) cultivar, ‘Deltapine 523,’ could improve lint yield. Three cycles of selection, beginning in 1965, were completed, with selection for lint percent being practiced first on a plant basis and then on a progeny‐row basis. Plant populations of 430, 828, and 800 plants were used to initiate the S1, S2, and S3 populations, respectively. From each population, 16 progenies were ultimately selected on the basis of high lint percent, and 8 crosses were made among them to initiate the next cycle. In each cycle, an equal number of seeds from each of the 16 selections were combined to form the bulk populations tested in 1971. Eight progenies selected in the S3 for higher 2.5% span length were bulked and designated as the S3L. population.In 1971, Deltapine 523 (S0) and the four selected populations were grown in replicated experiments at four locations. Mean lint precent was 33.8, 35.4, 36.6, 38.0, and 37.1 for the S0, S1, S2, S3, and S3L. populations, respectively. The S2, S3, and S3L populations produced significantly greater lint yield than did S0 and S1. As lint percent was increased by selection, there were concurrent decreases in seed index and 50 and 2.5% span length. Selection for fiber length in the S3 population restored most of the fiber length previously lost. As lint percent was increased by selection, there were simultaneous increases in lint index, seeds per boll, and Micronaire. No consistent trend or change was observed for boll size, number of bolls per plot, fiber strength, and fiber elongation. The primary cause of the increase in lint yield resulting from selection for lint percent was the association of lint percent with increased number of seeds per boll and higher lint index.The genetic variability for lint percent within the S1 and S2 populations was found to be 188 and 83%, respectively, as compared to that of the S0 population. The genetic variability for an unselected trait, boll size, was similar, with the S1 and S2 populations expressing 233 and 186%, respectively, as much variability as that of the S0 population.

Effect of Soil Moisture During Early Stages of Development on Growth and Yield of Cotton Plants1

AbstractThe effect of three irrigation treatments on the vegetative development of two cultivars of upland cotton (Gossypium hirsutum L.) was studied in two experiments conducted under different climatic conditions. The treatments differed until the middle of flowering and were designated as L (no irrigation), M (regular), and H (early and excessive irrigation). From mid‐flowering onwards all plots were irrigated regularly.In both experiments, treatment L resulted in a slower growth rate, smaller plants, fewer nodes and fruiting branches, and smaller leaf area index (LAI), and dry matter (DM) weight throughout the season. Small differences were found between the effects of treatments M and H. No excessive vegetative development was observed in this study. The highest rates of DM production were associated with LAI values between 2.0 and 3.0.A close relationship was found between, lint yield, DM production and leaf area duration (LAD). Only small increases in lint yield were associated with LAD and DM exceeding values of 100 days and 600 g/m2, respectively, at the end of the main flowering period. Smaller values of LAD and DM, however, were associated with reduced lint yield. Vegetative development was slower under the high temperatures prevailing in the Bet‐She'an valley than in the Coastal Plain area. Lint yield produced from the first cycle of flowering was lower in Bet‐She'an than in the Coastal Plain, but additional yields were produced in Bet‐She'an from the second cycle of flowering.