Diffusional and Biochemical Limitations to Photosynthesis Under Water Deficit for Field-Grown Cotton.

Water deficit stress limits net photosynthetic rate (AN), but the relative sensitivities of underlying processes such as thylakoid reactions, ATP production, carbon fixation reactions, and carbon loss processes to water deficit stress in field-grown upland cotton require further exploration. Therefore, the objective of the present study was to assess (1) the diffusional and biochemical mechanisms associated with water deficit-induced declines in AN and (2) associations between water deficit-induced variation in oxidative stress and energy dissipation for field-grown cotton. Water deficit stress was imposed for three weeks during the peak bloom stage of cotton development, causing significant reductions in leaf water potential and AN. Among diffusional limitations, mesophyll conductance was the major contributor to the AN decline. Several biochemical processes were adversely impacted by water deficit. Among these, electron transport rate and RuBP regeneration were most sensitive to AN-limiting water deficit. Carbon loss processes (photorespiration and dark respiration) were less sensitive than carbon assimilation, contributing to the water deficit-induced declines in AN. Increased energy dissipation via non-photochemical quenching or maintenance of electron flux to photorespiration prevented oxidative stress. Declines in AN were not associated with water deficit-induced variation in ATP production. It was concluded that diffusional limitations followed by biochemical limitations (ETR and RuBP regeneration) contributed to declines in AN, carbon loss processes partially contributed to the decline in AN, and increased energy dissipation prevented oxidative stress under water deficit in field-grown cotton.

Differential sensitivities of photosynthetic component processes govern oxidative stress levels and net assimilation rates in virus-infected cotton.

Cotton (Gossypium hirsutum L.) leafroll dwarf virus disease (CLRDD) is a yield-limiting threat to cotton production and can substantially limit net photosynthetic rates (AN). Previous research showed that AN was more sensitive to CLRDD-induced reductions in stomatal conductance than electron transport rate (ETR) through photosystem II (PSII). This observation coupled with leaf reddening symptomology led to the hypothesis that differential sensitivities of photosynthetic component processes to CLRDD would contribute to declines in AN and increases in oxidative stress, stimulating anthocyanin production. Thus, an experiment was conducted to define the relative sensitivity of photosynthetic component processes to CLRDD and to quantify oxidative stress and anthocyanin production in field-grown cotton. Among diffusional limitations to AN, reductions in mesophyll conductance and CO2 concentration in the chloroplast were the greatest constraints to AN under CLRDD. Multiple metabolic processes were also adversely impacted by CLRDD. ETR, RuBP regeneration, and carboxylation were important metabolic (non-diffusional) limitations to AN in symptomatic plants. Photorespiration and dark respiration were less sensitive than photosynthetic processes, contributing to declines in AN in symptomatic plants. Among thylakoid processes, reduction of PSI end electron acceptors was the most sensitive to CLRDD. Oxidative stress indicators (H2O2 production and membrane peroxidation) and anthocyanin contents were substantially higher in symptomatic plants, concomitant with reductions in carotenoid content and no change in energy dissipation by PSII. We conclude that differential sensitivities of photosynthetic processes to CLRDD and limited potential for energy dissipation at PSII increases oxidative stress, stimulating anthocyanin production as an antioxidative mechanism.

Differential sensitivities of photosynthetic processes and carbon loss mechanisms govern N-induced variation in net carbon assimilation rate for field-grown cotton.

Nitrogen (N) deficiency limits the net carbon assimilation rate (AN), but the relative N sensitivities of photosynthetic component processes and carbon loss mechanisms remain relatively unexplored for field-grown cotton. Therefore, the objective of the current study was to define the relative sensitivity of individual physiological processes driving N deficiency-induced declines in AN for field-grown cotton. Among the potential diffusional limitations evaluated, mesophyll conductance was the only parameter substantially reduced by N deficiency, but this did not affect CO2 availability in the chloroplast. A number of metabolic processes were negatively impacted by N deficiency, and these effects were more pronounced at lower leaf positions in the cotton canopy. Ribulose bisphosphate (RuBP) regeneration and carboxylation, AN, and gross photosynthesis were the most sensitive metabolic processes to N deficiency, whereas photosynthetic electron transport processes, electron flux to photorespiration, and dark respiration exhibited intermediate sensitivity to N deficiency. Among thylakoid-specific processes, the quantum yield of PSI end electron acceptor reduction was the most sensitive process to N deficiency. It was concluded that AN is primarily limited by Rubisco carboxylation and RuBP regeneration under N deficiency in field-grown cotton, and the differential N sensitivities of the photosynthetic process and carbon loss mechanisms contributed significantly to photosynthetic declines.

Carbohydrate metabolism in the subtending leaf cross-acclimates to waterlogging and elevated temperature stress and influences boll biomass in cotton (Gossypium hirsutum).

Short-term waterlogging and chronic elevated temperature occur concomitantly in the cotton (Gossypium hirsutum) growing season. While previous research about co-occurring waterlogging and elevated temperature has focused primarily on cotton fiber, no studies have investigated carbohydrate metabolism of the subtending leaf (a major source leaf for boll development) cross-acclimation to aforementioned stressors. To address this, plants were exposed to ambient (31.6/26.5°C) and elevated (34.1/29.0°C) temperatures during the whole flowering and boll formation stage, and waterlogging (0, 3, 6 days) beginning on the day of anthesis. Both waterlogging and high temperature limited boll biomass (reduced by 1.19-32.14%), but effects of different durations of waterlogging coupled with elevated temperature on carbohydrate metabolism in the subtending leaf were quite different. The 6-day waterlogging combined with elevated temperature had the most negative impact on net photosynthetic rate (Pn) and carbohydrate metabolism of any treatment, leading to upregulated GhSusA and GhSusC expression and enhanced sucrose synthase (SuSy, EC 2.4.1.13) activity for sucrose degradation. A prior exposure to waterlogging for 3 days improved subtending leaf performance under elevated temperature. Pn, sucrose concentrations, Rubisco (EC 4.1.1.39) activity, and cytosolic fructose-1,6-bisphosphatase (cy-FBPase, EC 3.1.3.11) activity in the subtending leaf significantly increased, while SuSy activity decreased under 3 days waterlogging and elevated temperature combined relative to elevated temperature alone. Thus, we concluded that previous exposure to a brief (3 days) waterlogging stress improved sucrose composition and accumulation cross-acclimation to high temperature later in development not only by promoting leaf photosynthesis but also inhibiting sucrose degradation.

Cotton morphological traits tracking through spatiotemporal registration of terrestrial laser scanning time-series data.

Understanding the complex interactions between genotype-environment dynamics is fundamental for optimizing crop improvement. However, traditional phenotyping methods limit assessments to the end of the growing season, restricting continuous crop monitoring. To address this limitation, we developed a methodology for spatiotemporal registration of time-series 3D point cloud data, enabling field phenotyping over time for accurate crop growth tracking. Leveraging multi-scan terrestrial laser scanning (TLS), we captured high-resolution 3D LiDAR data in a cotton breeding field across various stages of the growing season to generate four-dimensional (4D) crop models, seamlessly integrating spatial and temporal dimensions. Our registration procedure involved an initial pairwise terrain-based matching for rough alignment, followed by a bird's-eye view adjustment for fine registration. Point clouds collected throughout nine sessions across the growing season were successfully registered both spatially and temporally, with average registration errors of approximately 3 cm. We used the generated 4D models to monitor canopy height (CH) and volume (CV) for eleven cotton genotypes over two months. The consistent height reference established via our spatiotemporal registration process enabled precise estimations of CH (R 2 = 0.95, RMSE = 7.6 cm). Additionally, we analyzed the relationship between CV and the interception of photosynthetically active radiation (IPAR f ), finding that it followed a curve with exponential saturation, consistent with theoretical models, with a standard error of regression (SER) of 11%. In addition, we compared mathematical models from the Richards family of sigmoid curves for crop growth modeling, finding that the logistic model effectively captured CH and CV evolution, aiding in identifying significant genotype differences. Our novel TLS-based digital phenotyping methodology enhances precision and efficiency in field phenotyping over time, advancing plant phenomics and empowering efficient decision-making for crop improvement efforts.

Characterization of Caulimovirid-like Sequences from Upland Cotton (Gossypium hirsutum L.) Exhibiting Terminal Abortion in Georgia, USA.

In this study, we investigated the potential involvement of endogenous viral elements (EVEs) in the development of apical tissue necrosis, resulting in the terminal abortion of upland cotton (Gossypium hirsutum L.) in Georgia. The high-throughput sequence analysis of symptomatic and asymptomatic plant tissue samples revealed near-complete EVE-Georgia (EVE-GA) sequences closely related to caulimoviruses. The analysis of EVE-GA's putative open reading frames (ORFs) compared to cotton virus A and endogenous cotton pararetroviral elements (eCPRVE) revealed their similarity in putative ORFs 1-4. However, in the ORF 5 and ORF 6 encoding putative coat protein and reverse transcriptase, respectively, the sequences from EVE-GA have stop codons similar to eCPRVE sequences from Mississippi. In silico mining of the cotton genome database using EVE-GA as a query uncovered near-complete viral sequence insertions in the genomes of G. hirsutum species (~7 kb) but partial in G. tomentosum (~5.3 kb) and G. mustelinum (~5.1 kb) species. Furthermore, cotton EVEs' episomal forms and messenger RNA (mRNA) transcripts were detected in both symptomatic and asymptomatic plants collected from cotton fields. No significant yield difference was observed between symptomatic and asymptomatic plants of the two varieties evaluated in the experimental plot. Additionally, EVEs were also detected in cotton seeds and seedlings. This study emphasizes the need for future research on EVE sequences, their coding capacity, and any potential role in host immunity or pathogenicity.

Variation in thermotolerance of photosystem II energy trapping, intersystem electron transport, and photosystem I electron acceptor reduction for diverse cotton genotypes.

Cotton breeding programs have focused on agronomically-desirable traits. Without targeted selection for tolerance to high temperature extremes, cotton will likely be more vulnerable to environment-induced yield loss. Recently-developed methods that couple chlorophyll fluorescence induction measurements with temperature response experiments could be used to identify genotypic variation in photosynthetic thermotolerance of specific photosynthetic processes for field-grown plants. It was hypothesized that diverse cotton genotypes would differ significantly in photosynthetic thermotolerance, specific thylakoid processes would exhibit differential sensitivities to high temperature, and that the most heat tolerant process would exhibit substantial genotypic variation in thermotolerance plasticity. A two-year field experiment was conducted at Tifton and Athens, Georgia, USA. Experiments included 10 genotypes in 2020 and 11 in 2021. Photosynthetic thermotolerance for field-collected leaf samples was assessed by determining the high temperature threshold resulting in a 15% decline in photosynthetic efficiency (T15) for energy trapping by photosystem II (ΦPo), intersystem electron transport (ΦEo), and photosystem I end electron acceptor reduction (ΦRo). Significant genotypic variation in photosynthetic thermotolerance was observed, but the response was dependent on location and photosynthetic parameter assessed. ΦEo was substantially more heat sensitive than ΦPo or ΦRo. Significant genotypic variation in thermotolerance plasticity of ΦEo was also observed. Identifying the weakest link in photosynthetic tolerance to high temperature will facilitate future selection efforts by focusing on the most heat-susceptible processes. Given the genotypic differences in environmental plasticity observed here, future research should evaluate genotypic variation in acclimation potential in controlled environments.

Cotton leafroll dwarf disease: An enigmatic viral disease in cotton.

TAXONOMY: Cotton leafroll dwarf virus (CLRDV) is a member of the genus Polerovirus, family Solemoviridae. Geographical Distribution: CLRDV is present in most cotton-producing regions worldwide, prominently in North and South America. PHYSICAL PROPERTIES: The virion is a nonenveloped icosahedron with T = 3 icosahedral lattice symmetry that has a diameter of 26-34 nm and comprises 180 molecules of the capsid protein. The CsCl buoyant density of the virion is 1.39-1.42 g/cm3 and S20w is 115-127S. Genome: CLRDV shares genomic features with other poleroviruses; its genome consists of monopartite, single-stranded, positive-sense RNA, is approximately 5.7-5.8 kb in length, and is composed of seven open reading frames (ORFs) with an intergenic region between ORF2 and ORF3a. TRANSMISSION: CLRDV is transmitted efficiently by the cotton aphid (Aphis gossypii Glover) in a circulative and nonpropagative manner. Host: CLRDV has a limited host range. Cotton is the primary host, and it has also been detected in different weeds in and around commercial cotton fields in Georgia, USA. SYMPTOMS: Cotton plants infected early in the growth stage exhibit reddening or bronzing of foliage, maroon stems and petioles, and drooping. Plants infected in later growth stages exhibit intense green foliage with leaf rugosity, moderate to severe stunting, shortened internodes, and increased boll shedding/abortion, resulting in poor boll retention. These symptoms are variable and are probably influenced by the time of infection, plant growth stage, varieties, soil health, and geographical location. CLRDV is also often detected in symptomless plants. CONTROL: Vector management with the application of chemical insecticides is ineffective. Some host plant varieties grown in South America are resistant, but all varieties grown in the United States are susceptible. Integrated disease management strategies, including weed management and removal of volunteer stalks, could reduce the abundance of virus inoculum in the field.

Estimating yield-contributing physiological parameters of cotton using UAV-based imagery.

Lint yield in cotton is governed by light intercepted by the canopy (IPAR), radiation use efficiency (RUE), and harvest index (HI). However, the conventional methods of measuring these yield-governing physiological parameters are labor-intensive, time-consuming and requires destructive sampling. This study aimed to explore the use of low-cost and high-resolution UAV-based RGB and multispectral imagery 1) to estimate fraction of IPAR (IPARf), RUE, and biomass throughout the season, 2) to estimate lint yield using the cotton fiber index (CFI), and 3) to determine the potential use of biomass and lint yield models for estimating cotton HI. An experiment was conducted during the 2021 and 2022 growing seasons in Tifton, Georgia, USA in randomized complete block design with five different nitrogen treatments. Different nitrogen treatments were applied to generate substantial variability in canopy development and yield. UAV imagery was collected bi-weekly along with light interception and biomass measurements throughout the season, and 20 different vegetation indices (VIs) were computed from the imagery. Generalized linear regression was performed to develop models using VIs and growing degree days (GDDs). The IPARf models had R2 values ranging from 0.66 to 0.90, and models based on RVI and RECI explained the highest variation (93%) in IPARf during cross-validation. Similarly, cotton above-ground biomass was best estimated by models from MSAVI and OSAVI. Estimation of RUE using actual biomass measurement and RVI-based IPARf model was able to explain 84% of variation in RUE. CFI from UAV-based RGB imagery had strong relationship (R2 = 0.69) with machine harvested lint yield. The estimated HI from CFI-based lint yield and MSAVI-based biomass models was able to explain 40 to 49% of variation in measured HI for the 2022 growing season. The models developed to estimate the yield-contributing physiological parameters in cotton showed low to strong performance, with IPARf and above-ground biomass having greater prediction accuracy. Future studies on accurate estimation of lint yield is suggested for precise cotton HI prediction. This study is the first attempt of its kind and the results can be used to expand and improve research on predicting functional yield drivers of cotton.

Carbon assimilation and distribution in cotton photosynthetic organs is a limiting factor affecting boll weight formation under drought.

Previous studies have documented cotton boll weight reductions under drought, but the relative importance of the subtending leaf, bracts and capsule wall in driving drought-induced reductions in boll mass has received limited attention. To investigate the role of carbon metabolism in driving organ-specific differences in contribution to boll weight formation, under drought conditions. Controlled experiments were carried out under soil relative water content (SRWC) (75 ± 5)% (well-watered conditions, control), (60 ± 5)% (moderate drought) and (45 ± 5)% (severe drought) in 2018 and 2019 with two cultivars Yuzaomian 9110 and Dexiamian 1. Under severe drought, the decreases of photosynthetic rate (Pn) and carbon isotope composition (δ13C) were observed in the subtending leaf, bract and capsule wall, suggesting that carbon assimilation of three organs was restricted and the limitation was most pronounced in the subtending leaf. Changes in the activities of sucrose phosphate synthase (SPS), sucrose synthase (SuSy), invertases as well as the reduction in expression of sucrose transporter (GhSUT1) led to variabilities in the sucrose content of three organs. Moreover, photosynthate distribution from subtending leaf to seeds plus fibers (the components of boll weight) was significantly restricted and the photosynthetic contribution rate of subtending leaf to boll weight was decreased, while contributions of bracts and capsule wall were increased by drought. This, in conjunction with the observed decreases in boll weight, indicated that the subtending leaf was the most sensitive photosynthetic organ to drought and was a dominant driver of boll weight loss under drought. Therefore, the subtending leaf governs boll weight loss under drought due to limitations in carbon assimilation, perturbations in sucrose metabolism and inhibition of sucrose transport.

Genotypic differences in thermotolerance are dependent upon prestress capacity for antioxidant protection of the photosynthetic apparatus in Gossypium hirsutum.

Numerous studies have illustrated the need for antioxidant enzymes in acquired photosynthetic thermotolerance, but information on their possible role in promoting innate thermotolerance is lacking. We investigated the hypothesis that genotypic differences in source leaf photosynthetic thermostability would be dependent upon prestress capacity for antioxidant protection of the photosynthetic apparatus in Gossypium hirsutum. To test this hypothesis, thermosensitive (cv. ST4554) and reportedly thermotolerant (cv. VH260) G. hirsutum plants were exposed to control (30/20 degrees C) or high-day temperature (38/20 degrees C) conditions during flowering and source leaf gas exchange, chlorophyll content and maximum photochemical efficiency (F(v)/F(m)) were measured for each treatment. The relationship between source leaf thermostability and prestress antioxidant capacity was quantified by monitoring the actual quantum yield response of photosystem II (PSII) (Phi(PSII)) to a range of temperatures for both cultivars grown under the control temperature regime and measuring antioxidant enzyme activity for those same leaves. VH260 was more thermotolerant than ST4554 as evidenced by photosynthesis and F(v)/F(m) being significantly lower under high temperature for ST4554 but not VH260. Under identical growth conditions, VH260 had significantly higher optimal and threshold temperatures for Phi(PSII) and glutathione reductase (GR; EC 1.8.1.7) activity than ST4554, and innate threshold temperature was dependent upon endogenous GR and superoxide dismutase (SOD; EC 1.15.1.1) activity. We conclude that maintaining a sufficient antioxidant enzyme pool prior to heat stress is an innate mechanism for coping with rapid leaf temperature increases that commonly occur under field conditions.

Heat stress-induced limitations to reproductive success in Gossypium hirsutum.

Using in vitro systems, numerous authors have cited the sensitivity of pollen tube growth to high temperature as a major cause of low yields for crops with valuable reproductive structures. We investigated the hypothesis that in vivo fertilization efficiency would be negatively affected by heat stress-induced changes in energy reserves and calcium-mediated oxidative status in the pistil. Gossypium hirsutum plants exposed to optimal (30/20 degrees C) or high day temperature (38/20 degrees C) conditions during flowering were analyzed for fertilization efficiency via UV microscopic observation of pollen tube-containing ovules and for soluble carbohydrates, adenosine triphosphate (ATP), calcium, antioxidant enzyme activity and NADPH oxidase (NOX; EC 1.6.3.1) activity in the pistil. Leaf measurements included gas exchange, chlorophyll content, quantum efficiency and ATP content of the subtending leaf on the day of anthesis. In the pistil fertilization efficiency, soluble carbohydrates, ATP content and NOX activity declined significantly, whereas water soluble calcium and glutathione reductase (EC 1.8.1.7) activity increased, and superoxide dismutase (EC 1.15.1.1) activity remained unchanged. In leaves, heat stress decreased photosynthesis, quantum efficiency and chlorophyll content, but increased stomatal conductance. We conclude that decreased source leaf activity either inhibits pollen development, tube growth through the style or guidance to the ovules as a result of an insufficient energy supply to the developing pistil. We further conclude that a calcium-augmented antioxidant response in heat-stressed pistils interferes with enzymatic superoxide production needed for normal pollen tube growth and fertilization of the ovule.

Short-term soil-waterlogging contributes to cotton cross tolerance to chronic elevated temperature by regulating ROS metabolism in the subtending leaf.

Chronic elevated temperature and soil-waterlogging events often occur concomitantly in the Yangtze River Valley; however, a clear understanding of the effects of aforementioned co-occurring stresses on antioxidant defense in cotton has not been attained. To address this, two temperature conditions during the whole flowering and boll development periods, and three soil-waterlogging levels (0, 3, 6 d) starting on the day of anthesis were established. In the current study, no siginificant difference was observed on plant performance for 3 d soil-waterlogging, whereas 6 d soil-waterlogging event and elevated temperature in isolation negatively affected plant performance (i.e. leaf area declined by 33.3% and 14.7% in AW6 (soil waterlogging for 6 d under ambient temperature regime) and EC (soil well-watered (SRWC(75 ±â€¯5) %) under elevated temperature for 2-3 °C) relative to AC (soil well-watered (SRWC(75 ±â€¯5) %) under ambient temperature regime)) and induced ROS (reactive oxygen species) production and scavenging mechanisms in the subtending leaf of cotton. SOD (superoxide dismutase), CAT (catalase), and POX (peroxidase) activities were increased, and ASA (ascorbic acid) concentration was enhanced due to higher H2O2 (hydrogen peroxide) and O2- accumulations. Whereas, APX (ascorbate peroxidase), DHAR (dehydroascorbate reductase) and GR (glutathione reductase) activities were inhibited under elevated temperature regime or waterlogging event, especially in the treatment of EW6 (soil waterlogging for 6 d under elevated temperature for 2-3 °C), which resulted in increasing H2O2 concentration and higher O2- generation rate. However, plants acclimated to a short-term waterlogging stress (3 d) performed a cross tolerance to chronic elevated temperature regime (leaf number increased by 11.4%, whereas the abscission rate decreased by 4.6% in EW3 (soil waterlogging for 3 d under elevated temperature for 2-3 °C) compared with EC (soil well-watered (SRWC(75 ±â€¯5) %) under elevated temperature for 2-3 °C)). Moreover, plants undergone a brief soil-waterlogging (3 d) induced higher GR activity and increased ASA concentration, along with enhanced SOD, CAT, POX activities, limiting H2O2 and O2- accumulation and reducing oxidative damage to membrane lipids as evidenced by reduced MDA (malondialdehyde) concentration when cotton was subsequently exposed to chronic elevated temperature regime.

OJIP-fluorescence parameters as rapid indicators of cotton (Gossypium hirsutum L.) seedling vigor under contrasting growth temperature regimes.

Vigorous seedling growth in cotton is desirable because it minimizes the negative impact of multiple early season stresses, and seedling vigor can be impacted by early season growth temperature or cultivar. OJIP fluorescence provides rapid information on a broad range of photosynthetic component processes and may be a useful surrogate for seeding vigor, but this possibility has not been evaluated previously in cotton. To this end, a controlled environment study was conducted with six cultivars selected based on seed characteristics that are widely indicative of vigor and under two growth temperature regimes (sub-optimal = 20/15 °C day/night temperature; optimal = 30/20 °C) for the first two weeks after seed germination. Thereafter multiple whole-plant vigor assessments were conducted along with extensive OJIP-fluorescence characterization in cotyledons. Growth temperature was the primary factor influencing multiple plant responses. Specifically, all whole-plant indicators of seedling vigor were negatively impacted by sub-optimal temperature as were all photosynthetic performance indices and quantum efficiencies. By comparison, most photosynthetic structural indicators or reaction center-specific fluxes were either unaffected or positively impacted by low growth temperature, largely because PSII antenna size increased. The performance index, PIABS, and the quantum efficiency, φEo, were the most sensitive to low growth temperature and exhibited the strongest relationships with whole-plant seedling vigor. Thus, OJIP parameters incorporating intersystem electron transport beyond PSII but not additional downstream processes may represent the most useful surrogates for whole-plant seedling vigor in cotton.

Chemical priming of seed alters cotton floral bud differentiation by inducing changes in hormones, metabolites and gene expression.

Fruiting branches and floral buds are forming well before squares are visible and determine cotton (Gossypium hirsutum L.) productivity. Pre-soaking with plant growth regulators (PGRs) affects the quantity of floral buds. However, studies illustrating the physiological mechanism of floral bud differentiation in response to PGRs are lacking. To address this, cotton seeds were primed with water (control), 5 mg L-1 gibberellic acid (GA3), 25 mg L-1 N6-benzyladenine (6-BA), and 150 mg L-1 dimethyl piperidinium chloride (DPC) respectively. Results showed that plants from seed pre-treated with GA3 and 6-BA differentiated more floral buds relative to control, while DPC application initiated less floral buds than control. GA3 and 6-BA application significantly increased the levels of zeatin riboside (ZR) by up-regulating IPT expression and gibberellic acid (GA3) but decreased the indole-3-acetic acid (IAA) content. Consequently, the ZR/IAA and GA3/IAA ratios were markedly increased, contributing to higher floral bud numbers. Contrasting results were observed for DPC treatment. Additionally, GA3 and 6-BA treatments up-regulated GhSOC1, GhMADS13 and GhAGL24 expression, which was associated with higher sucrose contents mainly attributed to higher endogenous ZR levels, inducing floral initiation. Whereas the GhMADS13 was down-regulated to suppress floral bud differentiation under DPC application. Surprisingly, the floral-associated genes were more sensitive to GA3 than 6-BA, which induced the differences in bud numbers at the beginning of flower bud differentiation. Thus, we conclude that seed pre-treated with PGRs affected hormone content, induced sugar accumulation in apical buds and regulated genes involved in floral induction, which impacted floral bud differentiation.

Physiological and biochemical changes during drought and recovery periods at tillering and jointing stages in wheat (Triticum aestivum L.).

Defining the metabolic strategies used by wheat to tolerate and recover from drought events will be important for ensuring yield stability in the future, but studies addressing this critical research topic are limited. To this end, the current study quantified the physiological, biochemical, and agronomic responses of a drought tolerant and drought sensitive cultivar to periods of water deficit and recovery. Drought stress caused a reversible decline in leaf water relations, membrane stability, and photosynthetic activity, leading to increased reactive oxygen species (ROS) generation, lipid peroxidation and membrane injury. Plants exhibited osmotic adjustment through the accumulation of soluble sugars, proline, and free amino acids and increased enzymatic and non-enzymatic antioxidant activities. After re-watering, leaf water potential, membrane stability, photosynthetic processes, ROS generation, anti-oxidative activities, lipid peroxidation, and osmotic potential completely recovered for moderately stressed plants and did not fully recover in severely stressed plants. Higher photosynthetic rates during drought and rapid recovery after re-watering produced less-pronounced yield declines in the tolerant cultivar than the sensitive cultivar. These results suggested that the plant's ability to maintain functions during drought and to rapidly recover after re-watering during vegetative periods are important for determining final productivity in wheat.

A Comparative Study of Integrated Crop Management System vs. Conventional Crop Management System for Cotton Yield and Fiber Quality With Respect to Fruiting Position Under Different Soil Fertility Levels.

In order to increase cotton productivity and optimize fiber quality on limited arable land, an integrated crop management system (ICMS), which combined with some optimal management practices, is projected to replace the conventional crop management system (CCMS) for cotton production in the Yangtze River valley. The seedcotton yield and fiber quality with respect to fruiting position under ICMS and CCMS were investigated in 2012 and 2013 in two fields differing in soil fertility. Reduced bolls on fruiting branches 1-10 (FB1-10) and at fruiting position 1-2 (FP1-2) on FB11-15 could not be fully compensated by increased bolls on FB16+ under CCMS, resulting in more seedcotton yield under ICMS relative to that under CCMS. Fiber at majority fruiting positions under CCMS were longer and stronger than those under ICMS, but CCMS increased the contribution of bolls on FB11+ to the cotton yield, which overall resulted in no significant change in fiber length and strength by management system at field level. The number of bolls at FP1-2 on FB1-5 under CCMS while the number of bolls on FB1-5 and at FP1-2 on FB1-5 were not significantly changed by soil fertility, resulting in diminished yield difference in soil fertility among ICMS relative to that of CCMS. The high soil fertility significantly increased seedcotton yield relative to low soil fertility, which was attributed to more number of bolls on FB11+ and higher seedcotton weight per boll at all fruiting positions. High soil fertility field not only recorded superior fiber quality on FB11+, but also increased the contribution of these bolls to the cotton yield relative to those in the low soil fertility field, resulting in no significant change in overall fiber quality among soil fertility. These findings demonstrate that by combining optimal management practices on infertile soils ICMS could minimize the yield differences due to soil fertility without sacrificing fiber quality.

In-field High Throughput Phenotyping and Cotton Plant Growth Analysis Using LiDAR.

Plant breeding programs and a wide range of plant science applications would greatly benefit from the development of in-field high throughput phenotyping technologies. In this study, a terrestrial LiDAR-based high throughput phenotyping system was developed. A 2D LiDAR was applied to scan plants from overhead in the field, and an RTK-GPS was used to provide spatial coordinates. Precise 3D models of scanned plants were reconstructed based on the LiDAR and RTK-GPS data. The ground plane of the 3D model was separated by RANSAC algorithm and a Euclidean clustering algorithm was applied to remove noise generated by weeds. After that, clean 3D surface models of cotton plants were obtained, from which three plot-level morphologic traits including canopy height, projected canopy area, and plant volume were derived. Canopy height ranging from 85th percentile to the maximum height were computed based on the histogram of the z coordinate for all measured points; projected canopy area was derived by projecting all points on a ground plane; and a Trapezoidal rule based algorithm was proposed to estimate plant volume. Results of validation experiments showed good agreement between LiDAR measurements and manual measurements for maximum canopy height, projected canopy area, and plant volume, with R2-values of 0.97, 0.97, and 0.98, respectively. The developed system was used to scan the whole field repeatedly over the period from 43 to 109 days after planting. Growth trends and growth rate curves for all three derived morphologic traits were established over the monitoring period for each cultivar. Overall, four different cultivars showed similar growth trends and growth rate patterns. Each cultivar continued to grow until ~88 days after planting, and from then on varied little. However, the actual values were cultivar specific. Correlation analysis between morphologic traits and final yield was conducted over the monitoring period. When considering each cultivar individually, the three traits showed the best correlations with final yield during the period between around 67 and 109 days after planting, with maximum R2-values of up to 0.84, 0.88, and 0.85, respectively. The developed system demonstrated relatively high throughput data collection and analysis.

Long-term exposure to slightly elevated air temperature alleviates the negative impacts of short term waterlogging stress by altering nitrogen metabolism in cotton leaves.

Short-term waterlogging and chronic elevated temperature occur frequently in the Yangtze River Valley, yet the effects of these co-occurring environments on nitrogen metabolism of the subtending leaf (a major source leaf for boll development) have received little attention. In this study, plants were exposed to two temperature regimes (31.6/26.5 °C and 34.1/29.0 °C) and waterlogging events (0 d, 3 d, 6 d) during flowering and boll development. The results showed that the effects of waterlogging stress and elevated temperature in isolation on nitrogen metabolism were quite different. Waterlogging stress not only limited NR (EC 1.6.6.1) and GS (EC 6.3.1.2) activities through the down-regulation of GhNR and GhGS expression for amino acid synthesis, but also promoted protein degradation by enhanced protease activity and peptidase activity, leading to lower organ and total biomass (reduced by 12.01%-27.63%), whereas elevated temperature inhibited protein degradation by limited protease activity and peptidase activity, promoting plant biomass accumulation. Furthermore, 2-3 °C chronic elevated temperature alleviated the negative impacts of a brief (3 d) waterlogging stress on cotton leaves, with the expression of GhNiR up-regulated, the activities of NR, GS and GOGAT (EC 1.4.7.1) increased and the activities of protease and peptidase decreased, leading to higher protein concentration and enhanced leaf biomass for EW3 relative to AW3. The results of the study suggested that exposure to slightly elevated air temperature improves the cotton plants' ability to recover from short-term (3 d) waterlogging stress by sustaining processes associated with nitrogen assimilation.

Assessing stomatal and non-stomatal limitations to carbon assimilation under progressive drought in peanut (Arachis hypogaea L.).

Drought is known to limit carbon assimilation in plants. However, it has been debated whether photosynthesis is primarily inhibited by stomatal or non-stomatal factors. This research assessed the underlying limitations to photosynthesis in peanuts (Arachis hypogaea L.) grown under progressive drought. Specifically, field-grown peanut plants were exposed to either well-watered or drought-stressed conditions during flowering. Measurements included survey measurements of gas exchange, chlorophyll fluorescence, PSII thermotolerance, pigment content, and rapid A-Ci response (RACiR) assessments. Drought significantly decreased stomatal conductance with consequent declines in photosynthesis (AN), actual quantum yield of PSII, and electron transport rate (ETR). Pigment contents were variable and depended on stress severity. Stomatal closure on stressed plants resulted in higher leaf temperatures, but Fv/Fm and PSII thermotolerance were only slightly affected by drought. A strong, hyperbolic relationship was observed between stomatal conductance, AN, and ETR. However, when RACiR analysis was conducted, drought significantly decreased AN at Ci values comparable to drought-stressed plants, indicating non-stomatal limitations to AN. The maximum rate of carboxylation and maximum electron transport rate were severely limited by drought, and chloroplast CO2 concentration (CC) declined substantially under drought along with a comparable increase in partitioning of electron flow to photorespiration. Thus, while stomatal conductance may be a viable reference indicator of water deficit stress in peanut, we conclude that declines in AN were largely due to non-stomatal (diffusional and metabolic) limitations. Additionally, this is the first study to apply the rapid A-Ci response method to peanut, with comparable results to traditional A-Ci methods.