SPAD Chlorophyll Content Research Articles

Screening Iranian endemic coriander genebank germplasm for drought tolerance using a new multivariate statistical method

Drought is one of the serious abiotic factors influencing crop production such as coriander. Development of tolerant genotypes is prevented by the lack of effective selection criterion. Objectives of this study were evaluation of coriander accessions for water deficit stress and introduce a new multivariate method to select drought tolerant genotypes. For investigation of 19 traits, 16 Iranian endemic coriander genotypes were grown in a glasshouse under control and water deficit stress conditions. Shoot dry weight (SDW), fruit weight per plant (FWPP), fruit number per plant (FNPP) and umbel number per plant (UNPP) were decreased (Susceptibility Index>38%) under water deficit stress condition compared with the control condition. While the mean values of root dry weight (RDW) and root to shoot ratio (RTSR) were increased 1.49% and 97.33% under water stress condition, respectively. Because of high inheritance, high expected genetic gain, high genotypic correlation with together, well response to drought stress and high explanation of FWPP variation in regression model, the FWPP, branch number per plant (BNPP), FNPP and SPAD chlorophyll content in grain filing stage (SCCIGFS) traits were selected to screen coriander genotypes for drought tolerance in coriander. The principal component analysis mediated method (PCAMM) indicated as comprehensive criterion to screen drought tolerant genotypes. This method was highly heritabl, able to separate the Fernandez described A, B, C and D groups, no multicollinear and using multiple drought tolerance related traits. The PCAMM results showed that G13, G16, G2 and G12 genotypes belonged to Fernandez described A, B, C and D groups, respectively.

Genetic diversity and candidate genes for transient waterlogging tolerance in mungbean at the germination and seedling stages.

Mungbean [Vigna radiata var. radiata (L.) Wilczek] production in Asia is detrimentally affected by transient soil waterlogging caused by unseasonal and increasingly frequent extreme precipitation events. While mungbean exhibits sensitivity to waterlogging, there has been insufficient exploration of germplasm for waterlogging tolerance, as well as limited investigation into the genetic basis for tolerance to identify valuable loci. This research investigated the diversity of transient waterlogging tolerance in a mini-core germplasm collection of mungbean and identified candidate genes for adaptive traits of interest using genome-wide association studies (GWAS) at two critical stages of growth: germination and seedling stage (i.e., once the first trifoliate leaf had fully-expanded). In a temperature-controlled glasshouse, 292 genotypes were screened for tolerance after (i) 4 days of waterlogging followed by 7 days of recovery at the germination stage and (ii) 8 days of waterlogging followed by 7 days of recovery at the seedling stage. Tolerance was measured against drained controls. GWAS was conducted using 3,522 high-quality DArTseq-derived SNPs, revealing five significant associations with five phenotypic traits indicating improved tolerance. Waterlogging tolerance was positively correlated with the formation of adventitious roots and higher dry masses. FGGY carbohydrate kinase domain-containing protein was identified as a candidate gene for adventitious rooting and mRNA-uncharacterized LOC111241851, Caffeoyl-CoA O-methyltransferase At4g26220 and MORC family CW-type zinc finger protein 3 and zinc finger protein 2B genes for shoot, root, and total dry matter production. Moderate to high broad-sense heritability was exhibited for all phenotypic traits, including seed emergence (81%), adventitious rooting (56%), shoot dry mass (81%), root dry mass (79%) and SPAD chlorophyll content (70%). The heritability estimates, marker-trait associations, and identification of sources of waterlogging tolerant germplasm from this study demonstrate high potential for marker-assisted selection of tolerance traits to accelerate breeding of climate-resilient mungbean varieties.

Influence of High Temperature Stress on Morpho-physiological and Yield Traits of Blackgram (Vigna mungo L.) Genotypes

A field experiment was conducted at College farm, Agricultural College, Bapatla, Acharya N.G. Ranga Agricultural University during summer, 2022 and 2023 to study the influence of high temperature stress on morpho-physiological and yield traits of blackgram genotypes. The experiment was carried out in randomized block design with 30 treatments and 2 replications. The study revealed that among the thirty blackgram genotypes screened for their tolerance to high temperature stress at flowering stage, the genotype, TBG-129, LBG-1015 and PU-1804 were found to withstand high temperature stress and maintain higher SPAD chlorophyll content, and higher seed yield per plant indicating tolerance to high temperature stress during both the years. These blackgram genotypes can be further used as donors in the pulse breeding program for development of heat resilient varieties.

Evaluation of Drought Tolerance in USDA Tomato Germplasm at Seedling Stage

Drought, a crucial abiotic stressor, markedly reduces the growth and yield of tomato crops (Solanum lycopersicum L.). Consequently, adopting drought-resistant cultivars and implementing breeding programs to enhance drought tolerance have emerged as enduring solutions to alleviate the adverse effects of drought in various tomato cultivation regions. In this study, 68 United States Department of Agriculture (USDA) tomato accessions were assessed in a controlled greenhouse experiment, encompassing both water deficit treatment and a control group subjected to standard watering conditions. The experiment was arranged in a randomized complete block design with three replications. The results of this study pinpointed four accessions, PI 365956, PI 584456, PI 390510, and PI 370091, as drought-tolerant accessions. Additionally, high broad-sense heritability was revealed for leaf wilting, leaf rolling, and SPAD chlorophyll content (total leaf chlorophyll). Furthermore, positive correlations were found among parameters associated with leaf wilting, leaf rolling, and SPAD chlorophyll content. The findings offer valuable insights for tomato breeding initiatives, especially those focused on enhancing drought tolerance in elite cultivars. Future studies will expand the evaluation to include a larger pool of tomato accessions and conduct a genome-wide association study to identify single nucleotide polymorphism (SNP) markers for molecular breeding in tomatoes.

Metal Micronutrient and Silicon Concentration Effects on Growth and Susceptibility to Pythium Root Rot for Hydroponic Lettuce (Lactuca sativa)

The objectives were to evaluate the effects of increasing metal micronutrient concentrations and silicon (Si) concentrations on plant growth and susceptibility to Pythium root rot with hydroponically grown lettuce (Lactuca sativa). In the first experiment, lettuce was grown in hydroponic solutions with metal micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) supplied at either 0, 2.5, 5, or 10 mg∙L−1. A standard commercial hydroponic solution was also included as a control, with metal micronutrients supplied at 2 Fe, 1 Mn, 0.5 Cu, and 0.5 Zn mg∙L−1. In the second experiment, hydroponic lettuce was grown with Si at 0, 7, 14, 28, and 56 mg∙L−1. Hydroponic treatment solutions for both experiments were either dosed with Pythium myriotylum (Pythium treatment) at 1.80 × 104 oospores per L or deionized water as a non-Pythium control. Data were collected on leaf SPAD chlorophyll content, shoot height and width, total plant fresh mass, and root disease severity. Increasing the Cu concentration in solution decreased Pythium disease severity but reduced lettuce growth and yield. Increasing the concentration of the other metal micronutrients also tended to reduce lettuce growth but had no significant influence on root disease. Supplementing the hydroponic solution with Si had no effect on Pythium root disease severity and slightly decreased lettuce growth at 56 mg∙L−1 Si. Results of this study suggest that the management of micronutrients and Si nutrition is not an effective strategy and, at best, a risky strategy for controlling Pythium in hydroponic lettuce. Growers would likely benefit from maintaining metal micronutrient and Si concentrations within the ranges of (in mg∙L−1) 0.5 to 5.5 for Fe, 0.1 to 2.0 for Mn, 0.1 to 0.6 for Cu, 0.1 to 0.6 for Zn, and 0 to 28 for Si for many hydroponic crops. Supplementing Si has the potential to negatively influence plant growth and quality for certain plant species, and testing is necessary to evaluate phytotoxicity risks prior to implementing in commercial practice. Overall, successful mitigation of root rot pathogens in commercial hydroponic production requires the combination of proper sanitation, best management and cultural practices, appropriate hydroponic system design, and the implementation of a water treatment system with proper design and a multi-barrier approach.

Florescimento de Lantana em jardim vertical indoor em ambiente com restrição de luz

ABSTRACT: The time spent by urban residents indoors has been increasing annually, thus, prioritizing the enhancement of indoor spaces into green spaces to improve the quality of life. Even with limited environmental conditions indoors, an active living wall and LED light techniques have enabled us to explore indoor green environments. In the present study, the yellow/orange-colored flowers invasive ornamental species,Lantana camara‘splendens’, was cultivated in 4.0 m2 of the active living wall under a non-decorative LED lamp, adjusted to optimize performance in the coverage area. This study evaluated the development of lantana in the active living wall under different light intensities (135 watts and 90 watts) in a room with light restriction. Parameters such as plant height, flowering, SPAD chlorophyll content, and vegetative cover were analyzed. The results indicated that Lantana camara ‘splendens’ is suitable for use in active living walls and blooms at a low light intensity when the light is uniformly applied.

Root Electrical Capacitance Can Be a Promising Plant Phenotyping Parameter in Wheat.

As root electrical capacitance (CR*) was assumed to depend on the stem properties, the efficiency of measuring CR* at flowering for whole-plant phenotyping was assessed in five wheat cultivars in three replicate plots over two years. Linear regression analysis was used to correlate CR* with plant-size parameters and flag-leaf traits (extension and SPAD chlorophyll content) at flowering, and with yield components at maturity. The plot-mean CR* was correlated with the plot leaf area index (LAI), the chlorophyll quantity (LAI×SPAD), and the grain yield across years. At plant scale, CR* was found to show the strongest positive regression with total chlorophyll in the flag leaf (flag leaf area × SPAD; R2: 0.65-0.74) and with grain mass (R2: 0.55-0.70) for each cultivar and year (p < 0.001). Likewise, at plot scale, the regression was strongest between CR* and the LAI×SPAD value (R2: 0.86-0.99; p < 0.01) for the cultivars. Consequently, CR* indicated the total plant nutrient and photosynthate supply at flowering, which depended on root uptake capacity, and strongly influenced the final yield. Our results suggested that the polarization of the active root membrane surfaces was the main contributor to CR*, and that the measurement could be suitable for evaluating root size and functional intensity. In conclusion, the capacitance method can be applied for nondestructive whole-plant phenotyping, with potential to estimate root and shoot traits linked to the nutrient supply, and to predict grain yield. CR* can be incorporated into allometric models of cereal development, contributing to optimal crop management and genetic improvement.

Co-implementation of tillage, irrigation, and fertilizers in soybean: Impact on crop productivity, soil moisture, and soil microbial dynamics

Due to depleting water supplies and the cultivation of high water-demanding crops like rice, water deficit in crop production has become a major concern, especially in semi-arid regions of South Asia. Soybean has been considered a possible substitution for high-water-demand crops with improved water productivity and nutrient quality. However, due to inefficient and injudicious water and fertilizer management, the overall productivity and profitability of soybean is quite low. Hence, a three-year field investigation was carried out using strip-strip plot design with three replications to study the individual and combined effects of tillage, irrigation, and fertilizer levels on crop yield and quality, soil moisture and soil microbial dynamics. Results revealed that zero tilled-flat beds (ZTFB) and conventional tilled-raised beds (CTRB) reduced the irrigation water requirement by 5.15–5.45 and 3.12–3.49 cm ha −1 , respectively, compared to conventional tilled-flat beds (CTFB). Moreover, CTRB enhanced seed yield by 8.1–31.5 %, biomass yield by 6.5–34.1 %, crop water productivity (CWP) by 27.2–30.9 %, and irrigation water productivity (IWP) by 55.2–57.5 % over CTFB. Similarly, in 2016 and 2017, CTRB had higher SPAD-chlorophyll content (34.3 and 33.2 in the top leaves) and normalized difference vegetation index (NDVI) (0.51 and 0.71) values than CTFB and ZTFB. At 0.0–0.30 m soil depth, ZTFB showed the highest soil moisture content of 11.2 % and 22.5 %, respectively, leading to the highest relative water content (RWC) of 76.7–78.7 % in soybean leaves. As a result, ZTFB took 4–8 days longer to mature than CTFB, delaying the sowing of the following wheat crop. During the 2016–2018 growing seasons, irrigation applied at the depletion of available soil moisture (DASM) by 25 % and 100 % rate of recommended fertilizer (RRF) achieved significantly higher crop, biomass yields, protein yield, SPAD, NDVI, and CWP than irrigation at lower levels. Interaction effects revealed that combinations of CTRB and ZTFB + 25 % DASM + 100 % RRF strategies generated significantly (P ≤ 0.05) higher seed yield, biomass yield, and CWP. At the same time, ZTFB had significantly higher alkaline and acid phosphatase activity than CTRB, whereas the latter had significantly higher soil microbial biomass carbon. In comparison to individual use of these crop management methods, the results of this study showed planning soybean either in CTRB or ZTFB, irrigating at 25 % DASM, and fertilizing crops with 100 % RRF could help achieve higher crop and water productivity, thus sustaining soybean production in India and adjoining regions with similar agro-ecology. • Tillage, irrigation and fertilizer rates on soybean growth were studied in three years. • CTRB+DASM 25 % + 100 % fertilizer rate enhanced soybean yield and resource use efficiency. • Due to higher soil moisture content, a soybean grown in ZT-flat beds matures later.

Multiplication of Arbuscular Mycorrhiza on Chickpea and their Co-inoculative Impact with Trichoderma sp. on Chilli Wilt

Fusarium wilt has emerged as a serious problem in all chilli growing areas of India. Due to difficulties in disease management and lack of stable genetic resistance in chilli cultivars, integration of arbuscular mycorrhiza and Trichoderma were used to manage the disease. Different mycorrhizal fungi were raised and maintained on chickpea in earthen pots. A further experiment was conducted and Plant height, Root length, Dry weight of root and shoot, Mycorrhizal colonization (Phillips and Hayman method), Sporocarp number (Gerdemann and Nicolson method), SPAD chlorophyll content (SPAD meter) and NPK content were investigated. The present investigation deals with the beneficial effect of Glomus intraradices and Trichoderma harzianum on chilli wilt under greenhouse. In soil (Chickpea) sporocarp population of Glomus intraradices (5283) in 100 g soil and mycorrhizal colonization of Glomus intraradices (87 per cent) was observed. Chilli plant showed a significant increase in the Plant height, Root length, Dry weight of root and shoot, SPAD chlorophyll content and NPK content as compared to control. The results revealed that mixed Fusarium oxysporum + Glomus intraradices + Trichoderma harzianum inoculation contribute best growth and development of chilli plant under greenhouse experiment at 90 days after transplanting.

Impact Assessment of Different Level of Mycorrhiza on the Growth Parameters and Nutrient Content of Capsicum annum

Soil microbes play an important role in the biogeochemical cycling of nutrients and their availability to plants, which is important for sustaining soil health and agricultural sustainability. In light of this, vesicular arbuscular mycorrhiza (VAM) plays an important function. Hyphae of VAM can reach far beyond the plant root zone, allowing it to obtain nutrients from a considerably larger region of soil. Mycorrhiza improves plant nutrition by facilitating the uptake of minerals such as phosphorus and immobile trace elements such as zinc, cobalt, magnesium, iron, copper, molybdenum, and others. Mycorrhiza improves plant growth, productivity and yield by increasing the rate of photosynthesis. In the present study Glomus fasciculatum was tested on Capsicum annum plant with different inoculum levels (100, 150, 200 and 400 chlamydospores/kg soil) and found that Plant height, Root length, Dry weight of root and shoot, NPK content, per cent mycorrhizal colonization and sporocarp number were maximum when 400 spores were used for inoculation and minimum were found in untreated plants. SPAD chlorophyll content was highest at 90 DAT among all the observation periods.

Effect of Different Levels of Mycorrhization on the Growth Parameters and Nutrient Content of Chilli

Aim: To evaluate the effect of different levels of Glomus mosseae on plant growth parameters chlorophyll content, mycorrhizal colonization (%), sporocarp number and nutrient content of chilli.
 Study Design: The experiment was conducted using a complete randomized design (CRD).
 Study Area: To study the mycorrhizal effect on the chilli plants, observations were documented in Sceenhouse and laboratory conditions. Plant Pathology Laboratory, CCS HAU, Hisar was use for the laboratory work. The experiment was undertaken during crop season 2018
 Methodology: Mycorrhizal fungi was raised and maintained on wheat and pearl millet in earthen pots. Further experiment was conducted and Plant height, Root length, Dry weight of root and shoot, Mycorrhizal colonization, Sporocarp number, SPAD chlorophyll content and NPK content was observed.
 Results: Mycorrhiza is a symbiotic association between a fungus and the root system of vascular plants. Mycorrhizal associations help the host plants to thrive in adverse soil conditions and drought situations by increasing the root surface area and nutrient uptake efficiency. In the present study Glomus mosseae was tested on chilli plant with different inoculum levels (100, 150, 200 and 400 chlamydospores/kg soil) and found that Plant height, Root length, Dry weight of root and shoot, SPAD chlorophyll content, per cent mycorrhizal colonization and sporocarp number were maximum when 400 spores were used for inoculation and minimum were found in untreated plants. Among all the four observation period i.e. 30, 45, 60 and 90 days after transplanting maximum NPK content was observed at 90 days after transplanting.
 Conclusion: Among All the inoculum levels (100, 150, 200 and 400 chlamydospores/kg soil) maximum plant growth parameters, NPK content and chlorophyll content was observed when 400 chlamydospores/kg soil were used.

The first member of Exserohilum rostratum beneficial for promoting growth and yield of sunchoke (Helianthus tuberosus L.)

Helianthus tuberosus L. (sunchoke or Jerusalem artichoke) has been widely applied in food and industrial products. Due to its economical benefits, sunchoke has been of great interest in many areas. Therefore, the aims of this study were to isolate fungal endophytes from sunchoke and screen for their ability to produce IAA, GA3 and other plant growth-promoting (PGP) agents. Among a total of 126 isolates, 4 most effective PGP strains were identified as C. gloeosporioides CPS3/5, G. cingulate NMS1.4, E. rostratum NMS1.5 and Xylariaceae sp. KKL3. In the pot experiments, several plant growth parameters such as plant height, diameter of stem, SPAD chlorophyll content, plant biomass, plant root growth, the number of tubers and tuber inulin content in sunchoke inoculated with these fungal endophytes were significantly higher than those of the uninoculated controls. Outstandingly, E. rostratum NMS1.5 exhibited the best performance on promoting growth and yield of sunchoke. Interestingly, strain NMS1.5 is the first member of E. rostratum that is beneficial to plant growth without causing any negative effects. This study suggested that our fungal endophytes can be effective plant growth promoters for use as biofertilizers for sunchoke production.

Development and Characterization of Near-Isogenic Lines Revealing Candidate Genes for a Major 7AL QTL Responsible for Heat Tolerance in Wheat.

Wheat is one of the most important food crops in the world, but as a cool-season crop, it is more prone to heat stress, which severely affects crop production and grain quality. Heat tolerance in wheat is a quantitative trait, and the genes underlying reported quantitative trait loci (QTL) have rarely been identified. Near-isogenic lines (NILs) with a common genetic background but differing at a particular locus could turn quantitative traits into a Mendelian factor; therefore, they are suitable material for identifying candidate genes for targeted locus/loci. In this study, we developed and characterized NILs from two populations Cascades × Tevere and Cascades × W156 targeting a major 7AL QTL responsible for heat tolerance. Molecular marker screening and phenotyping for SPAD chlorophyll content and grain-yield-related traits confirmed four pairs of wheat NILs that contrasted for heat-stress responses. Genotyping the NILs using a 90K Infinium iSelect SNP array revealed five single nucleotide polymorphism (SNP) markers within the QTL interval that were distinguishable between the isolines. Seven candidate genes linked to the SNPs were identified as related to heat tolerance, and involved in important processes and pathways in response to heat stress. The confirmed multiple pairs of NILs and identified candidate genes in this study are valuable resources and information for further fine-mapping to clone major genes for heat tolerance.

Effect of Panchagavya foliar spray on the plant metabolism and grain yield of Tenai under rainfed condition

The crop growth and development are constantly influenced by environmental conditions such as stresses which are the most important yield reducing factors in the world. Millets cultivation is the most important agricultural operation in the country, not only in terms of food security, but also in creating better livelihoods, opportunities for rural population. Water stress and other abiotic stresses can dramatically limit and reduce the plant growth and productivity. In the frame of physiological window, mild drought induces regulation of water loss and uptake in plants allowing maintenance of their leaf relative water content within the limits where the photosynthetic capacity shows no or little changes. But severe drought induces unfavourable changes in plants, leading to inhibition of photosynthesis and growth. The use of bioregulators is the quickest and surest way of boosting crop production under rainfed condition. Panchagavya is an organic product blended from five different cow products, commonly applied to crop plants in organic farming. It is used as foliar spray, soil application and seed treatment. It can act as growth promoter and immunity booster. The organic Panchagavya foliar spray significantly influenced various physiological and biochemical parameters. A field experiment was conducted at Centre of Excellence in Millets, Athiyandal, Tiruvannamalai, during Kharif, 2017 to study the effect of Panchagavya foliar spray for enhancing the productivity of tenai under rainfed situation. In a water shortage conditions, application of enriched FYM +Recommended dose of fertilizer + 3%Panchagavya foliar spray improves plant height, no. of tillers per plant, total dry matter partitioning, SPAD chlorophyll content and highest grain yield (1739.0 kg ha-1) of tenai under rainfed condition.

Increased Prediction Accuracy Using Combined Genomic Information and Physiological Traits in A Soft Wheat Panel Evaluated in Multi-Environments

An integration of field-based phenotypic and genomic data can potentially increase the genetic gain in wheat breeding for complex traits such as grain and biomass yield. To validate this hypothesis in empirical field experiments, we compared the prediction accuracy between multi-kernel physiological and genomic best linear unbiased prediction (BLUP) model to a single-kernel physiological or genomic BLUP model for grain yield (GY) using a soft wheat population that was evaluated in four environments. The physiological data including canopy temperature (CT), SPAD chlorophyll content (SPAD), membrane thermostability (MT), rate of senescence (RS), stay green trait (SGT), and NDVI values were collected at four environments (2016, 2017, and 2018 at Citra, FL; 2017 at Quincy, FL). Using a genotyping-by-sequencing (GBS) approach, a total of 19,353 SNPs were generated and used to estimate prediction model accuracy. Prediction accuracies of grain yield evaluated in four environments improved when physiological traits and/or interaction effects (genotype × environment or physiology × environment) were included in the model compared to models with only genomic data. The proposed multi-kernel models that combined physiological and genomic data showed 35 to 169% increase in prediction accuracy compared to models with only genomic data included when heading date was used as a covariate. In general, higher response to selection was captured by the model combing effects of physiological and genotype × environment interaction compared to other models. The results of this study support the integration of field-based physiological data into GY prediction to improve genetic gain from selection in soft wheat under a multi-environment context.

In Vitro Bioaccessibility of Carotenoids and Chlorophylls in a Diverse Collection of Spinach Accessions and Commercial Cultivars.

Spinach, a nutrient-dense, green-leafy vegetable, is a rich source of carotenoid and chlorophyll bioactives. While the content of bioactives is known to vary with the genotype, variation in bioaccessibility is unknown. Bioaccessibility was explored in 71 greenhouse-grown spinach genotypes in fall and spring 2018/2019. Spinach was phenotyped for its greenness, leaf texture, leaf shape, and SPAD chlorophyll content. Postharvest, spinach was washed, blanched, and homogenized prior to assessment of bioactive bioaccessibility using a novel high-throughput in vitro digestion model followed by high-performance liquid chromatography with a photodiode array detector analysis. There was a significant variation in the bioaccessible content for all bioactives (p < 0.05), except for chlorophyll b (p = 0.063) in spring-grown spinach. The correlation coefficients of bioaccessible contents between seasons reveal that lutein (r = 0.52) and β-carotene (r = 0.55) were correlated to a greater extent than chlorophyll a (r = 0.38) and chlorophyll b (r = 0.19). The results suggest that carotenoid and chlorophyll bioaccessible contents may vary based on spinach genotypes and may be stable across seasons.

Electrical characterization of the root system: a noninvasive approach to study plant stress responses

A pot experiment was designed to demonstrate that the parallel, single-frequency detection of electrical capacitance (CR), impedance phase angle (ΦR), and electrical conductance (GR) in root–substrate systems was an adequate method for monitoring root growth and some aspects of stress response in situ. The wheat cultivars ‘Hombar’ and ‘TC33’ were grown in a rhyolite-vermiculite mixture under control, and low, medium, and high alkaline (Na2CO3) conditions with regular measurement of electrical parameters. The photochemical efficiency (Fv/Fm) and SPAD chlorophyll content were recorded non-intrusively; the green leaf area (GLA), shoot dry mass (SDM), root dry mass (RDM), and root membrane stability index (MSI) were determined after harvest. CR progressively decreased with increasing alkalinity due to impeded root growth. Strong linear CR–RDM relationships (R2 = 0.883–0.940) were obtained for the cultivars. Stress reduced |ΦR|, presumably due to the altered membrane properties and anatomy of the roots, including primarily enhanced lignification. GR was not reduced by alkalinity, implying the increasing symplastic conductivity caused by the higher electrolyte leakage indicated by decreasing root MSI. Fv/Fm, SPAD value, GLA, and SDM showed decreasing trends with increasing alkalinity. Cultivar ‘TC33’ was comparatively sensitive to high alkalinity, as shown by the greater relative decrease in CR, SDM, and RDM under stress, and by the significantly lower MSI and higher (moderately reduced) |ΦR| compared to the values obtained for ‘Hombar’. Electrical root characterization proved to be an efficient non-intrusive technique for studying root growth and stress responses, and for assessing plant stress tolerance in pot experiments.

Optimizing cotton irrigation and nitrogen management using a soil water balance model and in-season nitrogen applications

Nitrogen (N) and irrigation can be two of the costliest management inputs in United States (U.S.) cotton (Gossypium hirsutum L.) production systems. Furthermore, input amounts are often dependent on yearly environmental conditions, making it challenging to optimize N and irrigation management. The objectives of this research were to determine optimal N and irrigation management by: (i) evaluating equally split in-season N rates applied at first square and bloom in combination with varying levels of plant available water replacement (PAWR) estimated by an ET-based soil water balance model for cotton; and (ii) evaluate the whole-plant responses to the interaction between N and water management levels. Field experiments were conducted during 2015 and 2016 at two locations in Florida (Jay and Citra), southeastern U.S. with differing soil textures consisting of a deep sand and sandy loam. Irrigation treatments consisted of: (i) 100% of PAWR (100%); (ii) a primed acclimation (PA) treatment consisting of 50% of PAWR until first bloom and then 100% of PAWR (50%PA); (iii) 50% PAWR for the entire season (50%); (iv) a rain-fed control (RF). Nitrogen treatments consisted of even application splits at first square and bloom applied at a rate of 0 (N0), 22 (N22), 34 (N34), and 45 kg N ha−1 (N45). Lint yield assessments were conducted at both locations in both years. To link yield responses to possible physiological responses, in depth crop measurements consisting of SPAD chlorophyll content, leaf area index (LAI), N uptake, and harvest index (HI) were conducted at the Citra site. Contrasting soil textures and weather conditions between research locations and years allowed for a comprehensive assessment of both N and irrigation management across varying environmental conditions. Lint yield was either increased or at least maintained during the two years of this research at the Citra location by making two split N applications at first square and bloom of N22; while the optimal N treatment at the Jay location was N34 at first square and bloom in both years of this research. Additionally, a yield reduction occurred in the dry year of 2016 at the Citra location when N45 was applied at first square and bloom. The most efficient irrigation strategy at the Citra location was the primed acclimation treatment. At the Jay location, the RF control had similar lint yields as the irrigated treatments in both years, indicating that water application was not limiting at this site. These management strategies offer ways to optimize costly inputs when growing cotton in the southeastern U.S.

Productive and morphophysiological responses of Panicum maximum Jacq. cv. BRS Zuri to timing and doses of nitrogen application and defoliation intensity

AbstractThe response of plants to nitrogen fertilization is subject to several factors, including the level of stress caused by defoliation. After defoliation, the plant needs to adjust its energy balance to meet the demands of shoot and root recovery. Our objective was to evaluate the production of forage mass and other morphophysiological responses of zurigrass (Panicum maximum cv. BRS Zuri) subjected to five nitrogen doses (0, 20, 40, 60 and 80 mg/dm3) that were applied at two stages (after the cut and after the appearance of the first leaf on the tiller) under two defoliation intensities (15 and 30 cm of residual height). The pot experiment was conducted in a greenhouse in a completely randomized design with three replications, and the forage mass, as well as other morphophysiological traits, was measured in three regrowth cycles after the first standardization cut. Moreover, to understand the effect of cutting height on the root system, the root mass and root carbohydrate content were evaluated at zero, seven and 14 days after the standardization cut. The root mass reduced after 7 days since cutting under the low residual height (15 cm), but no effects on the root carbohydrate content were observed. The dose of nitrogen had a marked effect on most of the variables analyzed, leading to a linear increase in the root mass, the SPAD chlorophyll content and the harvested forage mass, whereas the number of tillers increased quadratically in response to the nitrogen dose. An increase was observed in the harvested forage mass for plants under the 15 cm of residue treatment compared with those under the 30‐cm treatment (16.0 vs. 13.6 g/pot), but no effect was observed for the time of nitrogen application.

Identification and validation of QTL and their associated genes for pre-emergent metribuzin tolerance in hexaploid wheat (Triticum aestivum L.)

BackgroundHerbicide tolerance is an important trait that allows effective weed management in wheat crops. Genetic knowledge of metribuzin tolerance in wheat is needed to develop new cultivars for the industry. Here, we evaluated metribuzin tolerance in a recombinant inbred line (RIL) mapping population derived from Synthetic W7984 and Opata 85 over two consecutive years to identify quantitative trait loci (QTL) contributing to the trait. Herbicide tolerance was measured by two chlorophyll traits, SPAD chlorophyll content index (CCI) and visual senescence score (SNS). The markers associated with major QTL from Synthetic W7984, positively contributing to reduced phytotoxic effects under herbicide treatment were validated in two F3/4 recombinant inbred populations developed from crosses of Synthetic W7984 × Westonia and Synthetic W7984 × Lang.ResultsComposite interval mapping (CIM) identified four QTL, two on chromosome 4A and one each on chromosomes 2D and 1A. The chromosomal position of the two QTL mapped on 4A within 10 cM intervals was refined and validated by multiple interval mapping (MIM). The major QTL affecting both measures of tolerance jointly explained 42 and 45% of the phenotypic variation by percentage CCI reduction and SNS, respectively. The identified QTL have a pure additive effect. The metribuzin tolerant allele of markers, Xgwm33 and Xbarc343, conferred lower phytotoxicity and explained the maximum phenotypic variation of 28.8 and 24.5%, respectively. The approximate physical localization of the QTL revealed the presence of five candidate genes (ribulose-bisphosphate carboxylase, oxidoreductase (rbcS), glycosyltransferase, serine/threonine-specific protein kinase and phosphotransferase) with a direct role in photosynthesis and/or metabolic detoxification pathways.ConclusionMetribuzin causes photo-inhibition by interrupting electron flow in PSII. Consequently, chlorophyll traits enabled the measure of high proportion of genetic variability in the mapping population. The validated molecular markers associated with metribuzin tolerance mediating QTL may be used in marker-assisted breeding to select metribuzin tolerant lines. Alternatively, validated favourable alleles could be introgressed into elite wheat cultivars to enhance metribuzin tolerance and improve grain yield in dryland farming for sustainable wheat production.