Boll Abscission Research Articles

Identification of SSR markers linked to the abscission of cotton boll traits and mining germplasm in Cotton

BackgroundCotton is an economically important crop. It is crucial to find an effective method to improve cotton yield, and one approach is to decrease the abscission of cotton bolls and buds. However, the lack of knowledge of the genetic and molecular mechanisms underlying cotton boll abscission traits has hindered genetic improvements.ResultsPearson’s correlation analysis revealed a significant positive correlation between boll abscission rates 1 (AR1) and boll abscission rates 2 (AR2). A genome-wide association study was conducted on 145 loci that exhibited high polymorphism and were uniformly distributed across 26 chromosomes (pair). The study revealed 18, 46, and 62 markers that were significantly associated with boll abscission, fiber quality, and yield traits (P < 0.05), explaining 1.75%–7.13%, 1.16%–9.58%, and 1.40%–5.44% of the phenotypic variation, respectively. Notably, the marker MON_SHIN-1584b was associated with the cotton boll abscission trait, whereas MON_CGR5732a was associated with cotton boll abscission and fiber quality traits. Thirteen of the marker loci identified in this study had been previously reported. Based on phenotypic effects, six typical cultivars with elite alleles related to cotton boll abscission, fiber quality, and yield traits were identified. These cultivars hold great promise for widespread utilization in breeding programs.ConclusionsThese results lay the foundation for understanding the molecular regulatory mechanism of cotton boll abscission and provide data for the future improvement of cotton breeding.

Integrated analysis of the transcriptome and metabolome reveals the molecular mechanism regulating cotton boll abscission under low light intensity

BackgroundCotton boll shedding is one of the main factors adversely affecting the cotton yield. During the cotton plant growth period, low light conditions can cause cotton bolls to fall off prematurely. In this study, we clarified the regulatory effects of low light intensity on cotton boll abscission by comprehensively analyzing the transcriptome and metabolome.ResultsWhen the fruiting branch leaves were shaded after pollination, all of the cotton bolls fell off within 5 days. Additionally, H2O2 accumulated during the formation of the abscission zone. Moreover, 10,172 differentially expressed genes (DEGs) and 81 differentially accumulated metabolites (DAMs) were identified. A KEGG pathway enrichment analysis revealed that the identified DEGs and DAMs were associated with plant hormone signal transduction and flavonoid biosynthesis pathways. The results of the transcriptome analysis suggested that the expression of ethylene (ETH) and abscisic acid (ABA) signaling-related genes was induced, which was in contrast to the decrease in the expression of most of the IAA signaling-related genes. A combined transcriptomics and metabolomics analysis revealed that flavonoids may help regulate plant organ abscission. A weighted gene co-expression network analysis detected two gene modules significantly related to abscission. The genes in these modules were mainly related to exosome, flavonoid biosynthesis, ubiquitin-mediated proteolysis, plant hormone signal transduction, photosynthesis, and cytoskeleton proteins. Furthermore, TIP1;1, UGT71C4, KMD3, TRFL6, REV, and FRA1 were identified as the hub genes in these two modules.ConclusionsIn this study, we elucidated the mechanisms underlying cotton boll abscission induced by shading on the basis of comprehensive transcriptomics and metabolomics analyses of the boll abscission process. The study findings have clarified the molecular basis of cotton boll abscission under low light intensity, and suggested that H2O2, phytohormone, and flavonoid have the potential to affect the shedding process of cotton bolls under low light stress.

Cloning and Bioinformatics Analysis of GhArfGAP in Cotton (Gossypium hirsutum) Boll Abscission Layer With Ethylene Treatment.

With the continuous growth of the human population, the demand for fiber is also rising sharply. As one of the main fiber plants available globally, cotton fiber yield (Gossypium hirsutum) is affected by boll abscission, which is related to the formation of the abscission layer. Therefore, we explored the formation of the abscission layer in cotton. The formation of the abscission layer in the cotton boll stalk was promoted by exogenous ethylene. It was found that both the number of the Golgi apparatus and the number of stacking layers increased in the dissociated cells. The GhArfGAP gene family in cotton was screened by the bioinformatics method, and the species and evolutionary relationship of the GhArfGAP gene family were analyzed. qRT-PCR showed that GhArfGAP13, GhArfGAP15, GhArfGAP25, and GhArfGAP34 in cotton had spatiotemporal-specific expression patterns. Subcellular localization suggested that GhArfGAP25 played a role in the Golgi apparatus. The expression of GhArfGAP25 in transgenic Arabidopsis thaliana is increased in the roots, stems, and leaves. Finally, we found that ethylene could induce the formation of the abscission layer in cotton. GhArfGAP13, GhArfGAP15, GhArfGAP25, and GhArfGAP34 might regulate the changes in the Golgi apparatus in the abscission layer. Taken together, the findings provide new ideas for the study of the formation of cotton abscission.

Feeding Behavior and Fruiting Form Damage by Bollworm (Lepidoptera: Noctuidae) in Bt Cotton.

Bt technologies have played a major role in the control of bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), in cotton. Variation in expression levels among varieties and plant parts, along with selection pressure on bollworm populations, has led to the development of resistance to some Bt proteins. Trials were conducted to evaluate how cotton varieties expressing different Bt proteins affect bollworm larval behavior and their damage in flowering cotton. Differences in larval recovery were observed among cotton varieties at 3 d with 3-gene Bt cotton having the lowest recovery and non-Bt cotton having the greatest recovery. Loss of bloom tags and abscission of small bolls at the site of infestation affected bollworm larval recovery among varieties. Day after infestation was the main factor that affected bollworm movement across all varieties. Number of total damaged fruiting forms by an individual bollworm larva was different among all varieties. Overall, flower bud (square) and fruit (boll) damage by an individual larva was lower on 3-gene cotton than 2-gene cotton and non-Bt cotton. An individual larva damaged fewer squares on 2-gene cotton than non-Bt cotton, but boll damage from bollworm was similar among 2-gene cotton and non-Bt cotton. The level of square and boll damage in 2-gene cotton has increased compared to previous research further supporting the occurrence of bollworm resistance to Cry proteins. The 3-gene cotton containing the Vip3A gene experienced low levels of damage and survival. These results will be important for improving management recommendations of bollworm in Bt cotton technologies.

Global cotton production under climate change – Implications for yield and water consumption

Abstract. Being an extensively produced natural fiber on earth, cotton is of importance for economies. Although the plant is broadly adapted to varying environments, the growth of and irrigation water demand on cotton may be challenged by future climate change. To study the impacts of climate change on cotton productivity in different regions across the world and the irrigation water requirements related to it, we use the process-based, spatially detailed biosphere and hydrology model LPJmL (Lund–Potsdam–Jena managed land). We find our modeled cotton yield levels in good agreement with reported values and simulated water consumption of cotton production similar to published estimates. Following the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) protocol, we employ an ensemble of five general circulation models under four representative concentration pathways (RCPs) for the 2011–2099 period to simulate future cotton yields. We find that irrigated cotton production does not suffer from climate change if CO2 effects are considered, whereas rainfed production is more sensitive to varying climate conditions. Considering the overall effect of a changing climate and CO2 fertilization, cotton production on current cropland steadily increases for most of the RCPs. Starting from ∼65 million tonnes in 2010, cotton production for RCP4.5 and RCP6.0 equates to 83 and 92 million tonnes at the end of the century, respectively. Under RCP8.5, simulated global cotton production rises by more than 50 % by 2099. Taking only climate change into account, projected cotton production considerably shrinks in most scenarios, by up to one-third or 43 million tonnes under RCP8.5. The simulation of future virtual water content (VWC) of cotton grown under elevated CO2 results for all scenarios in less VWC compared to ambient CO2 conditions. Under RCP6.0 and RCP8.5, VWC is notably decreased by more than 2000 m3 t−1 in areas where cotton is produced under purely rainfed conditions. By 2040, the average global VWC for cotton declines in all scenarios from currently 3300 to 3000 m3 t−1, and reduction continues by up to 30 % in 2100 under RCP8.5. While the VWC decreases by the CO2 effect, elevated temperature acts in the opposite direction. Ignoring beneficial CO2 effects, global VWC of cotton would increase for all RCPs except RCP2.6, reaching more than 5000 m3 t−1 by the end of the simulation period under RCP8.5. Given the economic relevance of cotton production, climate change poses an additional stress and deserves special attention. Changes in VWC and water demands for cotton production are of special importance, as cotton production is known for its intense water consumption. The implications of climate impacts on cotton production on the one hand and the impact of cotton production on water resources on the other hand illustrate the need to assess how future climate change may affect cotton production and its resource requirements. Our results should be regarded as optimistic, because of high uncertainty with respect to CO2 fertilization and the lack of implementing processes of boll abscission under heat stress. Still, the inclusion of cotton in LPJmL allows for various large-scale studies to assess impacts of climate change on hydrological factors and the implications for agricultural production and carbon sequestration.

An Arabidopsis E3 ligase HUB2 increases histone H2B monoubiquitination and enhances drought tolerance in transgenic cotton

SummaryThe HUB2 gene encoding histone H2B monoubiquitination E3 ligase is involved in seed dormancy, flowering timing, defence response and salt stress regulation in Arabidopsis thaliana. In this study, we used the cauliflower mosaic virus (CaMV) 35S promoter to drive AtHUB2 overexpression in cotton and found that it can significantly improve the agricultural traits of transgenic cotton plants under drought stress conditions, including increasing the fruit branch number, boll number, and boll‐setting rate and decreasing the boll abscission rate. In addition, survival and soluble sugar, proline and leaf relative water contents were increased in transgenic cotton plants after drought stress treatment. In contrast, RNAi knockdown of GhHUB2 genes reduced the drought resistance of transgenic cotton plants. AtHUB2 overexpression increased the global H2B monoubiquitination (H2Bub1) level through a direct interaction with GhH2B1 and up‐regulated the expression of drought‐related genes in transgenic cotton plants. Furthermore, we found a significant increase in H3K4me3 at the DREB locus in transgenic cotton, although no change in H3K4me3 was identified at the global level. These results demonstrated that AtHUB2 overexpression changed H2Bub1 and H3K4me3 levels at the GhDREB chromatin locus, leading the GhDREB gene to respond quickly to drought stress to improve transgenic cotton drought resistance, but had no influence on transgenic cotton development under normal growth conditions. Our findings also provide a useful route for breeding drought‐resistant transgenic plants.

SHEDDING OF FRUITING STRUCTURES IN COTTON: FACTORS, COMPENSATION AND PREVENTION

&lt;p&gt;The fruiting potential of advanced cotton cultivars is not a limiting factor for achieving yield targets but retention of squares and flowers for successful maturation into bolls is major challenge. In this article, we focused on why shedding occurs, its mechanism, yield losses, plant self-compensation, effects on plant growth and possible management to ameliorate its adverse effects. We concluded that it is quite unfair to blame single factor, instead it is an integrated effect of plant and stress factors i.e., high temperature, drought, thick plant stand, insects and diseases etc. contribute to accelerate shedding which ranges about 40-50%. The stresses induce the excessive production of degrading enzymes like pectinase, cellulose and hydrolase, while ethylene and abscisic acid is produced excessively to hasten the degradation process for shedding. The physiological disturbance contributes 7-35 and 42-64% abscission of unopened flowers and bolls, respectively. The square and flower are more frequent to shedding at high temperature compared to immature bolls. The flowers and boll shedding up to 30% is tolerable limit because cotton can recover yield provided weather support the crop later in season. The self-regulated abscission of floral parts is not easy to control under field conditions, however, the adverse effects of stress mediated shedding can be ameliorated with girdling and avoiding pest and stressful conditions, application of plant growth regulator (PGR) to control vegetative growth and abscisic acid (abscission promoter) and ethylene inhibitors like naphthalene acetic acid, silver thiosulfate and 1-methylcyclopropene.&lt;/p&gt;

Ethylene Inhibitors Increase Net Assimilation Rate and Cotton Boll Dry Matter Under Drought

Although the ethylene inhibitors role on reduction rate of boll abscission in cotton plants submitted to drought is being recently reported, its effects on photosynthesis performance and on cotton boll dry matter across the sympodial branch is scarce. Thus, the objective of this study was to evaluate the cotton photosynthesis and its boll dry matter performance across the reproductive branches via positional mapping in plants sprayed with ethylene inhibitors and submitted to water deficit. 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action and aminoethoxyvinylglycine (AVG), an inhibitor of its synthesis, were sprayed on cotton plants alone and in association. Treatments were composed by (T1) control, where deionized water was sprayed; (T2) sprayed with AVG at 0.15 g a.i. L-1; (T3) 1-MCP at 0.076 g a.i. L-1; (T4) AVG at 0.15 g a.i. L-1 plus 1-MCP at 0.076 g a.i. L-1; (T5) AVG at 0.15 g a.i. L-1 twice at each seven days; (T6) 1-MCP sprayed at 0.076 g a.i. L-1 twice using the same interval and (T7) AVG at 0.15 g a.i. L-1 plus 1-MCP at 0.076 g a.i. L-1 twice at each seven days. The ethylene inhibitors sustained higher photosynthesis performance and higher boll dry mass across reproductive branches independent of compound, its combination or entries number. Highlight that a AVG (T2) or its 1-MCP association in two entries (T7) showed the best performance for dry matter accumulation, especially in the two first reproductive branches, while they maintained the highest photosynthesis rates at the end of stress period.

Effect of 1-MCP on Cotton Plants under Abiotic Stress Caused by Ethephon

Many environmental stress factors have been identified to increase square and boll abscission and thus result in reduced cotton yield. Under stress conditions, ethylene is elicited. Ethylene peaks before abscission to promote the formation of the abscission layer and plays a major role in early season square and boll abortion in cotton (Gossypium hirsutum L.). In addition, ethylene stimulates the leaf senescence process. Thus, it is desirable to protect plants from ethylene-induced fruit loss and premature leaf senescence under stress conditions. The objective of this study was to evaluate the ability of 1-methylcyclopropene (1-MCP) to protect cotton plants against abiotic stress caused by ethephon (ethylene promoting effect). Field studies using a randomized complete block design with four replications were conducted in 2010 and 2011 at Texas A&M AgriLIFE Research Farm in Burleson County, TX. Eight treatments that consisted of two 1-MCP rates (0 and 10 g a.i. ha-1) in combination with four ethephon rates (0, 146, 292, 438 mL&middotha-1) were imposed at the first flower (FF) stage of the development. 1-MCP increased plant height and number of main stem nodes in both years. In addition, 1-MCP-treated plants exhibited greater membrane integrity and increased photosystem II quantum efficiency and thus delayed senescence in both years. These potentials for yield increase were realized in 2011 with 1-MCP treatment exhibiting a higher lint yield. In 2012, although 1-MCP treatment increased number of open fruit and open fruit weight per plant significantly, no significant lint yield increase was detected.

Effect of 1-MCP on Boll Development and Subtending Leaves of Cotton (&amp;lt;i&amp;gt;Gossypium hirsutum&amp;lt;/i&amp;gt; L.) Plants

Ethylene regulates multiple physiological processes in cotton (Gossypium hirsutum L.) ranging from square and boll abscission to senescence. This field study investigated the effect of an ethylene inhibiting compound 1-methylcyclopropene (1-MCP) on boll development and the corresponding subtending leaves. The study was conducted in 2011 and 2012 at the Texas A & M Agri-LIFE Research Farm in Burleson County, TX. The study consisted of two rates of 1-MCP (0 and 10 g a.i. ha-1) applied at one and two weeks after first flower. Boll development and subtending leaves were studied on the tagged flowers during the growing season. 1-MCP treatment increased cotton boll weight at 20 days after flowering. This study showed that 1-MCP-treated subtending leaves exhibited decreased membrane damage and lipid peroxidation, and higher chlorophyll content and photosynthetic efficiency at 20 to 30 days after flowering. The healthier state of subtending leaves should have provided more carbohydrates for the fruits which could partially explain the reason for the increased boll weight. However, this beneficial effect of 1-MCP did not last to the end of the growing season and failed to result in a yield increase ultimately. Multiple applications or extending effective duration of 1-MCP is desirable to enhance the activity of 1-MCP to make a significant difference in cotton yield.

Toxicity of Selected Insecticides and Insecticide Mixtures in a Glass-Vial Bioassay of Southern Green Stink Bug (Hemiptera: Pentatomidae) from Central Texas

The southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae), is cosmopolitan in distribution and feeds on a multitude of food and fiber crops. It induces abscission of bolls of cotton, Gossypium hirsutum L., and reduces seed cotton yield, gin-turnout, and fiber quality. Also, the bug vectors bacterial and fungal pathogens causing necrosis of the locule and rotting the bolls. Control options are mostly dependent upon and limited to the use of insecticides. Data are needed to assess the toxicity of currently available insecticides and develop baseline mortality data to monitor resistance of the insect to insecticides in Central Texas. We studied the toxicity of selected organophosphate and pyrethroid insecticides in a glass-vial bioassay to adult southern green stink bugs captured in blacklight traps. Dicrotophos was six times more toxic than acephate to southern green stink bug. Toxicity of acephate and chlorpyrifos was comparable. The order of toxicity of pyrethroids to southern green stink bug was γ-cyhalothrin > zeta-cypermethrin > λ-cyhalothrin > Cypermethrin > bifenthrin. Mixtures of technicalgrade active ingredients were 4- to 7.5-fold more toxic to southern green stink bug compared to commercially-formulated insecticides. The lesser efficacy of the commercial formulations suggests the active ingredients used in the mixtures failed to potentiate, probably because of lack of additivity or synergism in the composition of active ingredients in the formulations. The inert and other ingredients in the formulations may have played a part as well.

Verde Plant Bug (Hemiptera: Miridae) Feeding Injury to Cotton Bolls Characterized by Boll Age, Size, and Damage Ratings

The verde plant bug, Creontiades signatus (Distant), has been present in south Texas for several years but has more recently been documented as an economic threat to cultivated cotton, (Gossypium hirsutum L. Our studies over 2 yr (2009 and 2010) and two locations (Weslaco and Corpus Christi, TX) investigated feeding-injury of the verde plant bug to a range of cotton boll age classes defined by boll diameter and accumulated degree-days (anthesis to the time of infesting) for first-position cotton bolls infested with the plant bugs. The most detrimental damage to younger cotton holls from verde plant bug feeding was boll abscission. Cotton bolls <04 accumulating daily degree-days (ACDD), or a boll diameter of 1.3 cm were subject to 60-70% higher boll abscission when compared with the noninfested controls. Significantly higher boll abscission occurred from verde plant bug injured bolls compared with the controls up to 162 ACDD or a mean boll diameter 2.0 cm. Cotton seed weights were significantly reduced up to 179 ACDD or a boll diameter of 2.0 cm at Weslaco in 2009, and up to 317 ACDD or boll diameter 2.6 cm for Weslaco in 2010 when compared with the noninfested controls. Lint weight per cotton boll for infested and noninfested bolls was significantly reduced up to 262 ACDD or boll diameter 2.5 for Corpus Christi in 2010 and up to 288 ACCD or boll diameter 2.6 cm for Weslaco, TX, in 2010. Damage ratings (dependant variable) regressed against infested and noninfested seed-cotton weights showed that in every instance, the infested cotton bolls had a strong and significant relationship with damage ratings for all age classes of bolls. Damage ratings for the infested cotton bolls that did not abscise by harvest showed visual signs of verde plant bug feeding injury and the subsequent development ofboll rot; however, these two forms of injury causing lint and seed mass loss are hard to differentiate from open or boll-locked cotton bolls. Based on the results of both lint and seed loss over 2 yr and four studies cotton bolls should be protected up to approximately 300 ACDD or a boll diameter of 2.5 cm. This equilibrates to bolls that are 12-14 d of age dependent upon daily maximum and minimum temperatures.

1-Methylcyclopropene and Aminoethoxyvinylglycine effects on yield components of field-grown cotton

Biotic and abiotic stresses can alter the hormone balance and trigger the activation of pathways involved in the cotton stress responses, resulting in the abscission of squares, flowers and young bolls and consequent reductions in the seed cotton yield and fiber yield. As part of the mechanism that primarily regulates the protective response of plants against stresses, ethylene is considered a key hormone involved in this response, and increased ethylene synthesis has been observed when plants are subjected to stress. Thus, the development of strategies aimed to mitigate their negative effects can reduce the shed rate of reproductive structures and positively impact cotton productivity. For this purpose, 1-methylcyclopropene (1-MCP), a compound that inhibits the action of ethylene, and aminoethoxyvinylglycine (AVG), an ethylene synthesis inhibitor, were sprayed on cotton plants to investigate their effects on the seed cotton yield (SCY), fiber yield (FY), fiber percentage (% Fiber) and final stand of plants (STAND) during two cotton growth seasons (2010 and 2011). To this end, experiments were performed in a randomized complete block design with five replicates. Our results demonstrate that the inhibitors of ethylene synthesis and action increased the seed cotton and fiber yield during both growing seasons. The results obtained after AVG spraying in the initial reproductive phase (first square emission) presented the highest values for the cotton yield components and are the first record of the success of this method in Brazil.

Boll weevil feeding preference on squares at different ages and square shedding time of cotton cultivars

The boll weevil is considered the major pest of cotton in the Western Hemisphere due to the large potential for direct destruction of fruiting bodies, survival on the fallow ground and dispersal ability. The purpose of this study was to evaluate the feeding preference of Anthonomus grandis for squares at different ages, as well as the abscission of attacked squares on five cotton cultivars. The experiment was conducted in Jaboticabal, SP, Brazil, in 2010 and 2011. Newly formed squares of the cultivars NuOPAL, DeltaOPAL, FMT-701, FMX-910 and FMX-993 were chosen and labeled for daily observations. Each evaluation was based on the registration of the age (days) at which the squares were fed to A. grandis and the time (days) from the first hole of boll weevil feeding until boll abscission. Results indicated a greater preference of the boll weevil for squares of the cultivars FMT-701, FMX-910 and FMX-993 than of the cultivars NuOPAL and DeltaOPAL. A. grandis prefers smaller two-day-old squares of the cultivars NuOPAL and FMX-910 and larger, seven-day-old bolls of the cultivars DeltaOPAL, FMT-701 and FMX-993. All feeding punctured squares fell on the ground, and the time of square abscission was independent on the age and cultivar of the square and was 1 to 2 days after the first feeding puncture. Key words: Anthonomus grandis, host plant, injury, Gossypium hirsutum.

Stink Bug Feeding Induces Fluorescence in Developing Cotton Bolls

BackgroundStink bugs (Hemiptera: Pentatomidae) comprise a critically important insect pest complex affecting 12 major crops worldwide including cotton. In the US, stink bug damage to developing cotton bolls causes boll abscission, lint staining, reduced fiber quality, and reduced yields with estimated losses ranging from 10 to 60 million dollars annually. Unfortunately, scouting for stink bug damage in the field is laborious and excessively time consuming. To improve scouting accuracy and efficiency, we investigated fluorescence changes in cotton boll tissues as a result of stink bug feeding.ResultsFluorescent imaging under long-wave ultraviolet light showed that stink bug-damaged lint, the inner carpal wall, and the outside of the boll emitted strong blue-green fluorescence in a circular region near the puncture wound, whereas undamaged tissue emissions occurred at different wavelengths; the much weaker emission of undamaged tissue was dominated by chlorophyll fluorescence. We further characterized the optimum emission and excitation spectra to distinguish between stink bug damaged bolls from undamaged bolls.ConclusionsThe observed characteristic fluorescence peaks associated with stink bug damage give rise to a fluorescence-based method to rapidly distinguish between undamaged and stink bug damaged cotton bolls. Based on the fluorescent fingerprint, we envision a fluorescence reflectance imaging or a fluorescence ratiometric device to assist pest management professionals with rapidly determining the extent of stink bug damage in a cotton field.

Efficacy of Cry1Ac:Cry1F Proteins in Cotton Leaf Tissue Against Fall Armyworm, Beet Armyworm, and Soybean Looper (Lepidoptera: Noctuidae)

Cotton, Gossypium hirsutum L., plants expressing Cry1Ac and Cry1F insecticidal crystal proteins of Bacillus thuringiensis Berliner (Bt) were evaluated against selected lepidopteran pests including fall armyworm, Spodoptera frugiperda (J. E. Smith), beet armyworm, Spodoptera exigua (Hübner), and soybean looper, Pseudoplusia includens (Walker). Studies were conducted in a range of environments, challenging various cotton tissue types from several varieties containing a combination of Cry1Ac and Cry1F proteins. In fresh tissue bioassays of mature leaves and squares (flower buds) and in artificial field infestations of white flowers, plants containing Cry1Ac:Cry1F significantly reduced levels of damage (leaf defoliation, bract feeding, penetrated squares and bolls, and boll abscission) and induced significantly greater mortality (90-100%) of fall armyworm compared with that on non-Bt cotton plants. Plants containing Cry1Ac:Cry1F conferred high levels (100%) of soybean looper mortality and low levels (0.2%) of leaf defoliation compared with non-Bt cotton. Beet armyworm was relatively less sensitive to Cry1Ac:Cry1F cotton plants compared with fall armyworm and soybean looper. However, beet armyworm larval development was delayed 21 d after infestation (DAI), and ingestion of plant tissue was inhibited (14 and 21 DAI) on the Cry1Ac:Cry1F plants compared with that on non-Bt cotton plants. These results show Cry1Ac:Cry1F cotton varieties can be an effective component in a management program for these lepidopteran pest species. Differential susceptibility of fall armyworm, beet armyworm, and soybean looper larvae to Cry1Ac:Cry1F cotton reinforces the need to sample during plant development and respond with a foliar insecticide if local action thresholds are exceeded.

Nitrophenolates spray can alter boll abscission rate in cotton through enhanced peroxidase activity and increased ascorbate and phenolics levels

Field studies were conducted from 2002 to 2005 to evaluate foliar spray of Atonik (a plant growth regulator (PGR) containing nitrophenolates) on cotton boll abscission rate by assessing various reactive oxygen species (ROS) contents, antioxidant content and antioxidant enzyme activity from 1 to 9 days after anthesis (DAA). The result indicated that the nitrophenolate spray reduced hydrogen peroxide (H(2)O(2)), superoxide anion (O(2)(-)) accumulation, lipid peroxidation (malondialdehyde--MDA), lipoxygenase (LOX) activity and membrane permeability relative to the control. Antioxidant enzyme activity (superoxide dismutase, SOD; ascorbate peroxidase, APX; peroxidase, POX; glutathione peroxidase, GSH-Px) was significantly increased by the nitrophenolate spray. The POX (217%) and GSH-Px (242%) activities were enhanced compared with APX (7.7%) activity at 9 DAA. Enhanced accumulation of ascorbate (245%), phenol (253%) and proline (150%) was observed in nitrophenolate-sprayed plants compared with control at 9 DAA. Because ascorbate content is increased by higher dehydroascorbate reductase (DHAR) enzyme activity, the ascorbate was able to replenish reducing equivalents to phenoxyl radicals, resulting in an increase of phenolic compounds. The increased phenolic acid content may be involved in scavenging the ROS produced in developing cotton boll. The role of DHAR and glutathione reductase (GR) in keeping higher levels of reduced ascorbate and low levels of endogenous H(2)O(2) in the developing cotton boll may be the prerequisite for boll retention. Based on the present work, we conclude that nitrophenolate-sprayed plants counteracted the deleterious effects of ROS by the peroxide/phenolics/ascorbate system, which causes reduced boll abscission and increased yield.

Relationships of Abscised Cotton Fruit to Boll Weevil (Coleoptera: Curculionidae) Feeding, Oviposition, and Development

Abscised cotton, Gossypium hirsutum L., fruit in field plots planted at different times were examined to assess adult boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), use of squares and bolls during 2002 and 2003 in the Lower Rio Grande Valley of Texas. Although boll abscission is not necessarily related to infestation, generally more bolls abscised than squares and abundances of fallen bolls were not related to the planting date treatments. During 2003, fallen squares were most abundant in the late-planted treatment. Although large squares (5.5-8-mm-diameter) on the plant are preferred for boll weevil oviposition, diameter of abscised squares is not a reliable measurement because of shrinkage resulting from desiccation and larval feeding. Fallen feeding-punctured squares and bolls were most abundant in late plantings but differences between fallen feeding-punctured squares versus fallen feeding-punctured bolls were found in only one treatment in 2003. During the same year, fallen oviposition-punctured squares were more numerous in the late-planted treatment than in the earlier treatments. Treatment effects were not found on numbers of oviposition-punctured bolls, but fallen oviposition-punctured squares were more common than bolls in the late-planted treatment compared with earlier treatments each year. Dead weevil eggs, larvae, and pupae inside fallen fruit were few and planting date treatment effects were not detected. Living third instars and pupae were more abundant in fallen squares of the late-planted treatment than in the earlier treatments and bolls of all three treatments. This study shows that fallen squares in late-planted cotton contribute more to adult boll weevil populations than bolls, or squares of earlier plantings.

Influence of &lt;I&gt;Nezara viridula&lt;/I&gt; Feeding on Cotton Yield, Fiber Quality, and Seed Germination

The influence of southern green stink bug, Nezara viridula (L.), adults (males and females) and fourth to fifth instars on cotton, Gossypium hirsutum L., boll abscission, seedcotton yield, fiber quality, and seed viability was evaluated in field studies conducted during 2004 and 2005. Cotton bolls representing several age classes ranging from 0-600 heat units were individually infested with a specific gender or life stage of southern green stink bug. Adults and nymphs induced abscission of bolls that accumulated 0-280 heat units after anthesis. Seedcotton yield was significantly lower in bolls infested with adults (males and females) and late instars through approximately 500 heat units after anthesis. Southern green stink bug feeding on bolls significantly affected the physical fiber properties of micronaire (measure of fiber fineness or maturity), strength, uniformity, and fiber length. Discolored cotton lint in the stink bug-infested bolls was more common than in noninfested bolls. Seed germination and development of normal seedlings for seed harvested from stink bug-infested bolls that accumulated < or =500 heat units beyond anthesis were significantly lower compared with noninfested bolls. No significant differences in boll abscission, yield, fiber quality, and seed germination were detected between southern green stink bug males and females or between adults and fourth to fifth instars.

Crop Responses to Elevated Carbon Dioxide and Interactions with Temperature

SUMMARY Carbon dioxide concentration [CO2] and temperature are major environmental factors that affect plant growth, development and yield. Increases in [CO2] above present levels will improve productivity of cotton crop because of improved carbon exchange rates, vegetative growth and number of reproductive organs (bolls). In contrast, increase in temperatures above optimum decrease cotton yield due to increased boll abscission and smaller boll size. Doubling of [CO2] did not ameliorate the adverse effects of high temperature on reproductive growth (boll abscission or boll size) or fiber quality. Thus, it is concluded that in future climates, if increases in [CO2] are associated with higher temperatures, cotton yield and quality will decrease particularly in regions where present temperature are near to optimum.