Molecular Approaches to Improve Salt Resistance in Crops: Facts and Perspectives

SUMMARY

Because of the expansion of agriculture into marginal environments, enhancement of crop resistance to soil salinity is becoming a frequent objective for breeders. The tools offered by molecular biology to transfer a single or a few genes provide a major hope to reduce the negative impact of broad gene transfer that takes place in wide-cross hybridizations. Due to the presence of osmotic and toxic components in the growth response of plants to salt stress, any attempt to improve plant performance in saline environments should ensure the maintenance of an adequate flux of water into plant tissues, and also avoid the build up of ions into the cell compartments where they can exert toxic effects. Besides, reduction of injury effects due to salinity on plant tissues is a highly desirable objective. Transgenic plants overexpressing ion transporters able to exclude Na⁺ into vacuoles, the enzymes required for the biosynthesis of several osmocompatible, organic solutes, or the enzymes participating in detoxification pathways, have been obtained. Some of these transgenic plants display an enhanced growth relative to their wild type parents in saline environments, although the way in which this resistance is achieved remains essentially unknown. A fourth and promising way to engineer salt resistance in plants is the attempt to manipulate gene regulatory pathways. The extent to which these experiences, mainly with model plants, could be extrapolated to crop plants growing in the field is discussed. It is proposed that a combination of different molecular approaches could be helpful to achieve enhanced salt resistance in crop plants.     

菌肥与腐熟秸秆对盐碱地燕麦渗透生理特性及产量的影响

为明确菌肥和腐熟秸秆对盐碱地燕麦渗透生理及产量的调节作用,以燕麦品种白燕2号和草莜1号为材料,分析了菌肥(F)、腐熟秸秆(S)及二者配施(FS)对燕麦不同生育时期植株K⁺、Na⁺、可溶性糖、有机酸含量及株高和产量的影响。结果表明,苗期和拔节期燕麦各器官K⁺和Na⁺积累量较高,且茎和叶的K⁺、Na⁺积累量均明显高于根部。与空白对照(CK)相比,S和FS处理均显著提高各时期燕麦根、茎、叶K⁺含量,显著降低Na⁺含量。F、S和FS处理对各时期两个燕麦品种植株可溶性糖含量也有显著影响。F处理显著增加了抽穗期和灌浆期两个品种植株总有机酸含量,尤其是草酸、乙酸、柠檬酸比例提高;S和FS处理下抽穗期燕麦植株总有机酸含量在第一年较CK显著提高,而第二年显著降低,主要是由草酸变化引起。F、S及FS处理在第二年均显著提高两个品种的籽粒、鲜草和干草产量,其中FS处理的增产效果最好。这说明腐熟秸秆配施菌肥有助于增强盐碱地燕麦植株的渗透调...     

Evaluation of salt-tolerant genotypes of durum wheat derived from in vitro and field experiments

The performance of selected salt-tolerant genotypes of durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.], derived from field and in vitro assessment methods, was evaluated under greenhouse and field conditions. Eight durum wheat genotypes comprising three salt-tolerant genotypes and one salt-sensitive genotype selected from each of the methods were used. This study was conducted under both saline and non-saline field conditions as well as under greenhouse condition with salinized solution culture at 0 mM (control), 75 and 150 mM NaCl (concentrations) using supplemental Ca²⁺. Days to heading, days to maturity, plant height, number of grains per spike, grain weight per spike, 1000 grain weight, number of spikes per m², grain yield and harvest index were recorded in the field experiments. Plant dry weight, Na⁺, K⁺ and Ca²⁺ accumulated in the hydroponically grown seedlings were measured 20 days after salinity treatments. In spite of the smaller range of genotypes used by the in vitro screening method, tolerant genotypes screened by the in vitro method (ITGs) performed comparably with those of the field-derived tolerant genotypes (FTGs) for grain yield under saline field conditions. Field salinity significantly reduced (P < 0.01) means of all traits averaged on eight tested genotypes. In vitro salt-tolerant genotypes Dipper-6 and Prion-1 produced the highest dry weight and K⁺/Na⁺ ratio under salt stress conditions (150 mM NaCl) in the greenhouse. Although dry matter correlated with the grain yield (R² = 0.37), the regression coefficient was higher for shoot K⁺/Na⁺ ratio (R² = 0.44). Dipper-6 (ITG) and Prion-1 (ITG) genotypes have been ranked superior while Massara-1 (ISG) was inferior for salt tolerance in the regression analysis. However, based on grain yield reduction Ajaia/Hora/Jro/3/Gan (FTG) and PI40100 (ITG) were the most tolerant having 58% and 60% reduction, respectively.     

Vertical Distribution of Sodium in Roots of Rice Plants Exposed to Salinity as Analyzed by Cryo Time-of-Flight Secondary Ion Mass Spectrometry

Abstract

Distribution of Na⁺ along the root axis under salinity stress was analyzed in two rice (Oryza sativa L.) cultivars with different salt resistance (salt-sensitive IR 24 and salt-resistant Pokkali). Rice plants were grown hydroponically and NaCl was applied with nutrient solution at concentrations of 0, 25 and 50 mM for 7 d after germination. The distribution of Na⁺ in roots under salinity was analyzed by the cryo time-of-flight secondary ion mass spectrometry (cryo TOF-SIMS). The Na⁺ content in the root was higher in salt-sensitive IR 24 than in salt-resistant Pokkali under NaCl stress. The content was highest at the root tip and was decreased basipetally along the root axis. The difference in Na⁺ content between the cultivars was apparent in all regions from the root tip.     

Differential Sensitivity of Rice Cultivars to Salinity and Its Relation to Ion Accumulation and Root Tip Structure

Abstract

Effects of NaCl on the growth, ion content, root cap structure and Casparian band development were examined in four rice (Oryza sativa L.) cultivars with different salt resistance (salt-sensitive indica-type IR 24 and japonica-type Nipponbare and salt-resistant indica-type Nona Bokra and Pokkali). Experiments were conducted to find the differences in salinity resistance during early seedling and developed seedling stages among the cultivars. For salinity treatment, sodium chloride (NaCl) was added to nutrient solution at concentrations of 0, 25 and 50 mM for 7 days from germination to the 7th day (early seedling stage) or from the 7th day to 14th day (developed seedling stage). Growth inhibition by salinity was more prominent in the early seedling stage than in the developed seedling stage. Based on the growth, the order of the sensitivity was IR24 > Nipponbare > Nona Bokra > Pokkali. The growth of NaCl-treated rice cultivars relative to control was significantly and negatively correlated with the Na⁺ content and Na⁺/K⁺ ratio in roots and shoots in both stages. Scanning electron microscopic observation revealed that the root cap tissues proliferated and extended to the basal part of the root tip by salinity. The length of root cap was, however, reduced by 50 mM NaCl in sensitive cultivars due to peeling off. An endodermal Casparian band was formed in the basal region of the root tip. Development of the Casparian band was more prominent in sensitive cultivars than in tolerant cultivars. Root cap proliferation might be related to NaCl resistance in rice seedlings, but the Casparian band may not function efficiently in Na⁺ exclusion. Essentially the present results suggest that exclusion of Na⁺ from roots plays a critical role in expression of Na⁺ resistance in rice seedlings and the root cap is important for Na⁺ exclusion.     

Antioxidant Capacity and Damages Caused by Salinity Stress in Apical and Basal Regions of Rice Leaf

Abstract

We investigated the mechanisms of increased sensitivity to Na⁺ in the apical and basal regions of the rice leaf under salinity. Three-week-old plants were treated with 200 mM NaCl in hydroponic culture for 3 d. Segments 6 cm in length were obtained from the apical and basal regions of the fully expanded uppermost leaves (6th leaf blades) as old and young tissues, respectively. In the plants exposed to 200 mM NaCl, Nitro blue tetrazolium (NBT) reducing activity, and H₂O₂ and Malondialdehyde (MDA) contents significantly increased, accompanied by the swelling of thylakoids and destruction of thylakoid membranes in the apical regions. However, no indication of oxidative damages was observed in the basal region, even though the Na⁺ content in the basal region was comparable to that in the apical region. In the apical region, the capacity to scavenge H₂O₂ was lower than that in the basal region due to decrease in the constitutive levels of ascorbate peroxidase and guaiacol peroxidase. In addition, the activities of antioxidant enzymes except superoxide dismutase and guaiacol peroxidase decreased drastically after 48 hr of exposure to NaCl. By contrast, the activities of catalase and glutathione reductase in the basal region increased compared with those in the control, and other antioxidant enzymes did not decrease under salinity during the experimental period. These results suggest that the capacity to scavenge reactive oxygen species decreased with age, and thus the apical region of the leaf blade suffered severer damage by Na⁺ than the basal region.     

Na+/K+-ATPase Activation by cAMP in the Midgut of Lutzomyia longipalpis (Lutz & Neiva, 1912; Diptera: Psychodidae)

Lutzomyia longipalpis (Lutz & Neiva, 1912) females have been intensively studied regarding the regulation of midgut pH. The mechanisms involved in pH regulation are complex, and some aspects remain to be clarified. Here, we investigated the role of the Na⁺/K⁺-ATPase pump as an electrochemical potential generator and its modulation by the second messenger cAMP in the midgut of female L. longipalpis. Our results suggest that not only may Na⁺/K⁺-ATPase be the main generator of an electrochemical potential across membranes in the midgut of female L. longipalpis, but also its activity is positively regulated by cAMP. cAMP-mediated Na⁺/K⁺-ATPase pump activity might be necessary to maintain the transport of the nutrients produced during blood digestion.     

Differences in the Vegetative Growth between Common and Tartary Buckwheat in Saline Hydroponic Culture

Abstract

Common buckwheat (Fagopyrum esculentum Moench cv. Tsushima) and Tartary buckwheat (F. tataricum (L.) Gaertn. cv. Pontivy) were grown in a nutrient solution with or without added NaCl to investigate interspecific differences in their responses to salinity, based on their dry-matter production. The mechanism of salt tolerance was also studied. Addition of 100 mM NaCl to the culture solution (salt treatment) lowered the plant growth rate to 48% and 16% of the control in Tsushima and Pontivy, respectively, and decreased the net assimilation rate and mean leaf area of Pontivy more severely than in Tsushima. The salt treatment decreased the leaf growth rate and leaf area per leaf to 30% and 72% of the control, respectively, in Tsushima, and to 12% and 52%, respectively, in Pontivy. It decreased the photosynthetic rate to 67% and 35% of the control, and stomatal conductance to 25% and 15% of the control in Tsushima and Pontivy, respectively. It also decreased the transpiration rate to 41% and 30% of the control in Tsushima and Pontivy, respectively, and increased the wateruse efficiency 1.6 times in Tsushima, but did not influence the wateruse efficiency in Pontivy. In the saline solution, the accumulation of Na⁺ in leaves and stem was greater in Pontivy than in Tsushima, but that in the roots, was greater in Tsushima than in Pontivy. In both species, Na⁺ accumulated rapidly in the leaves after removal of the roots in the saline solution. We conclude that the difference in salt tolerance between common and Tartary buckwheat may result from the difference in accumulation of Na⁺ in leaves and absorption of Na⁺ by the roots.     

Lesquerella growth and selenium uptake affected by saline irrigation water composition

A greenhouse study was conducted to determine the effects of waters differing in salt composition on growth and selenium (Se) accumulation by lesquerella (Lesquerella fendleri Gray S. Wats.). Plants were established by direct seeding into sand cultures and irrigated with solutions containing either (a) Cl⁻ as the dominant anion or (b) a mixture of salts of SO₄²⁻ and Cl⁻. Four treatments of each salinity type were imposed. Electrical conductivities of the irrigation waters were 1.7, 4, 8, and 13 dS m⁻¹. Two months after salinization, Se (l mg l⁻¹, 12.7 μM) was added to all solutions as Na₂SeO₄. Shoot growth was significantly reduced by increasing Cl-salinity. Regardless of salinity type, concentrations of Ca²⁺, Mg²⁺, Cl⁻, total-S, and Se were higher in the leaves than the stems, whereas K⁺ and Na⁺ were higher in the stem. Leaf-Se concentrations were not significantly affected by Cl-based irrigation waters, averaging 503 mg Se kg⁻¹ dry wt across salinity levels, whereas leaf-Se decreased consistently and significantly from 218 to 13 mg kg⁻¹ as mixed salt salinity increased. The dramatic reduction in Se was attributed to SO₄²⁻:SeO₄²⁻ competition during plant uptake. The strong Se-accumulating ability of lesquerella suggests that the crop should be further evaluated as a potentially valuable phytoremediator of Se-contaminated soils and waters of low to moderate salinity in areas where the dominant anion in the substrate is Cl⁻.     

磷对NaCl胁迫下玉米幼苗渗透调节能力的影响

研究不同供磷水平对NaCl胁迫下玉米幼苗有机渗透调节物质和离子含量的影响。结果表明,盐胁迫下低磷处理玉米幼苗叶片中可溶性糖和游离氨基酸增加,根系中显著降低;增加供磷水平,叶片中可溶性糖和游离氨基酸含量下降,根系中含量上升,同时叶片和根系中可溶性蛋白含量增加。磷可降低盐胁迫下玉米幼苗各器官中的Na~+含量,同时增加各器官的K~+、Ca~(2+)和Mg~(2+)含量,降低Na~+/K~+与Na~+/Ca~(2+)比值。磷有助于维持植株的碳氮代谢平衡,促进有机渗透调节物质的运输与分配,改善各器官的离子平衡,增强植株的渗透调节能力,从而缓解盐胁迫带来的伤害。     

Long-Term Reuse of Drainage Waters of Varying Salinities for Crop Irrigation in a Cotton-Safflower Rotation System in the San Joaquin Valley of California—A Nine Year Study: I. Cotton (Gossypium hirsutum L.)

Summary

Use of saline drainage water for crop irrigation was evaluated as a means of decreasing its volume. Results of a nine-year crop rotation (cotton-cotton-safflower, × 3) in which only the cotton was irrigated with drainage water of 400, 1,500, 3,000, 4,500, 6,000, and 9,000 ppm total dissolved salts are presented. The different salinity levels of irrigation waters were achieved by mixing nonsaline canal water (400 ppm) and saline drainage water. Cotton lint yields were not affected by increased salinity level of the irrigation water for the first two years. Detrimental effects became evident in the third cotton crop with increasing severity in later years. In the fifth year of cotton (seventh year of the study), lint yields were adversely affected by waters of salinity greater than 3,000 ppm. However, fiber quality remained unaffected at all levels of irrigation water salinity. The reductions in lint yield appeared to be a function of time and the salinity level of applied water. Shoot height and biomass were reduced by the irrigation water salinity before lint yields. Stand establishment appeared to be the most sensitive to salinity and was perhaps the main reason for yield reduction. Increase in irrigation water salinity increased Na⁺ content of leaf blades and petioles and decreased K⁺/Na⁺ ratio of leaf blades and petioles. The study showed that irrigation waters of up to 3,000 ppm salinity may be used for four years without any yield reductions, as long as some leaching occurs through preplant irrigations with low salinity water. Data on crop growth and development and ionic content collected over the nine year period are presented.     

Genome duplication improves rice root resistance to salt stress

Background

Salinity is a stressful environmental factor that limits the productivity of crop plants, and roots form the major interface between plants and various abiotic stresses. Rice is a salt-sensitive crop and its polyploid shows advantages in terms of stress resistance. The objective of this study was to investigate the effects of genome duplication on rice root resistance to salt stress.

Results

Both diploid rice (HN2026-2x and Nipponbare-2x) and their corresponding tetraploid rice (HN2026-4x and Nipponbare-4x) were cultured in half-strength Murashige and Skoog medium with 150 mM NaCl for 3 and 5 days. Accumulations of proline, soluble sugar, malondialdehyde (MDA), Na⁺ content, H⁺ (proton) flux at root tips, and the microstructure and ultrastructure in rice roots were examined. We found that tetraploid rice showed less root growth inhibition, accumulated higher proline content and lower MDA content, and exhibited a higher frequency of normal epidermal cells than diploid rice. In addition, a protective gap appeared between the cortex and pericycle cells in tetraploid rice. Next, ultrastructural analysis showed that genome duplication improved membrane, organelle, and nuclei stability. Furthermore, Na⁺ in tetraploid rice roots significantly decreased while root tip H⁺ efflux in tetraploid rice significantly increased.

Conclusions

Our results suggest that genome duplication improves root resistance to salt stress, and that enhanced proton transport to the root surface may play a role in reducing Na⁺ entrance into the roots.     

Chemical properties of Niger floodplain soils,eastern Nigeria,in relation to mineralogy

The agricultural potentials of the floodplain soils of river Niger have been less exploited due to lack of information on their chemical and mineralogical characteristics. We studied five soil profiles within the floodplain to determine the levels of plant nutrients and relate them to their clay mineralogy and total element. The soils flooded for eight months of the year are low in pH and plant available nutrients while the dominant clay mineral is kaolinite. Kaolinite and interlayered vermiculite were negatively correlated with all the exchangeable bases, CEC and available P, indicating the negative contribution of these clay minerals to the plant nutrient reserve of these soils. Illite correlated positively with Na⁺ and K⁺ (r=0.51; 0.50), while smectite correlated significantly with Na, K, Ca and CEC. Also positive significant correlation existed between illite/smectite and Na⁺, K⁺, Mg²⁺, CEC and base saturation thus confirming the positive role of smectite and illite to the plant nutrient reserve in the soils. Kaolinite and CaO could be used for the prediction of exchangeable K (R²=0.62, 0.78 respectively). Although the level of nutrient cations are low, the depositional effect of the river and traditional cultivation practices can boost crop yield especially paddy rice.     

Characterizing the Saltol Quantitative Trait Locus for Salinity Tolerance in Rice

This study characterized Pokkali-derived quantitative trait loci (QTLs) for seedling stage salinity tolerance in preparation for use in marker-assisted breeding. An analysis of 100 SSR markers on 140 IR29/Pokkali recombinant inbred lines (RILs) confirmed the location of the Saltol QTL on chromosome 1 and identified additional QTLs associated with tolerance. Analysis of a series of backcross lines and near-isogenic lines (NILs) developed to better characterize the effect of the Saltol locus revealed that Saltol mainly acted to control shoot Na⁺/K⁺ homeostasis. Multiple QTLs were required to acquire a high level of tolerance. Unexpectedly, multiple Pokkali alleles at Saltol were detected within the RIL population and between backcross lines, and representative lines were compared with seven Pokkali accessions to better characterize this allelic variation. Thus, while the Saltol locus presents a complex scenario, it provides an opportunity for marker-assisted backcrossing to improve salt tolerance of popular varieties followed by targeting multiple loci through QTL pyramiding for areas with higher salt stress.     

玉米耐盐基因ZmHKT1;5在烟草中的功能验证

HKT类基因是与植物耐盐性密切相关的一类基因。在作物中HKT蛋白可通过排出Na+来维持植物体内的Na~+/K~+平衡,从而影响植物耐盐性。通过在烟草中过表达玉米ZmHKT1;5基因,验证该基因具有提高植物耐盐性的作用。结果表明,过表达ZmHKT1;5基因的T0代材料即显示出叶片耐盐能力的明显提高;T2代转基因株系种子在含盐培养基上的发芽能力明显强于野生型材料,T2代转基因株系幼苗阶段的耐盐能力也得到了明显的提高。通过比较在盐胁迫后2月龄的转基因材料和野生型材料的生理指标,发现野生型材料中MDA和H_2O_2的含量相较转基因材料发生了更为明显的上升,说明转基因材料中过表达ZmHKT1;5基因有效降低了盐胁迫引起的过氧化物积累。综合转基因验证的结果,证明ZmHKT1;5基因具有提高植物耐盐性的作用。     

Comparative effects of salt and alkali stresses on organic acid accumulation and ionic balance of seabuckthorn (Hippophae rhamnoides L.)

Seabuckthorn (Hippophae rhamnoides L.) is uniquely capable of growing well under various extreme environmental conditions, such as water deficit, salt stress, low temperature, and high altitude. It is of economic value and its berries are used in cosmetics and pharmaceutical products. In this study, we compared the effects of salt stresses (9:1 molar ratio of NaCl to Na₂SO₄, pH 6.48–6.65) and alkali stresses (9:1 molar ratio of NaHCO₃ to Na₂CO₃, pH 8.70–8.88) on the levels of inorganic ions and organic acids in H. rhamnoides L. to elucidate the physiological mechanism by which it tolerates salt or alkali stress (high pH). The results showed that, in leaves and stems under alkali stress, the Na⁺ content increased to a much greater extent than under salt stress. Neither salt nor alkali stress decreased the K⁺ content in leaves and stems; however, in roots, the K⁺ content decreased sharply with increasing alkali stress, whereas it remained relatively unchanged with increasing salt stress. This revealed a specific mechanism of absorption or transport for Na⁺ and K⁺ that was affected strongly by alkali stress. The results indicated that accumulation of organic acid (OA) was a central adaptive mechanism by which H. rhamnoides maintained intracellular ionic balance under alkali stress. OA may play different roles in different organs during adaptation to alkali stress, and its percentage contribution to total negative charge was higher in leaf than in stem. H. rhamnoides accumulated mainly malate, oxalate, and citrate in leaves and stems; however, in roots, less malate and citrate was accumulated, and acetate accumulation was enhanced significantly, which indicated that roots and shoots use different mechanisms to modulate OA metabolism.     

外源硅对NaCl胁迫下玉米幼苗渗透调节物质含量影响

采用水培法研究外源硅对盐胁迫下玉米幼苗可溶性糖、游离氨基酸等渗透调节物质含量的影响。结果表明,盐胁迫下适量的增加硅供应能增加叶片和根系中渗透调节物质含量,其中根系中游离氨基酸、可溶性蛋白和可溶性糖含量的增加幅度大于叶片;同时能增加玉米幼苗各器官K+的含量,降低不同部位Na+含量,维持玉米幼苗体内的离子平衡。研究表明,硅参与盐胁迫下渗透调节物质在植物中的运输和分配,适宜浓度的硅能提高玉米耐盐性。     

The effects of nitrogen rate and the ratio of NO3:NH4 on Bemisia tabaci populations in hydroponic tomato crops

Nitrogen fertilization is one of the factors that influences Bemisia tabaci (Gennadius) population density. The aim of this study was to determine the effects of three N application rates (75, 205 and 335 mg/l) and three ratios of NO₃⁻:NH₄⁺ ions (92:8, 75:25 and 55:45) in standard nutrient solution (205 mg/l N) on the population density of B. tabaci. The experiments were conducted on spring-summer hydroponic crops of tomato. The effect of plant stratum on the whitefly population was also determined. The aggregation of B. tabaci adults as well as their oviposition rate was higher at 205 and 335 mg/l N than on plants grown at 75 mg/l N. By the end of the experiment (60 d after infestation), the number of nymphs on plants at 205 mg/l N was higher than on plants at 75 mg/l N. The number of pupae was lowest on plants supplied with 75 mg/l N. An increase in NH₄⁺ percentage in standard nutrient solution (from 25% to 45% of the total N) reduced adult population density and oviposition rate. The density of nymphs and pupae, at 60 d after infestation, was lower on the tomato plants grown at 75:25 and 55:45 NO₃⁻:NH₄⁺ ratios compared to the 92:8 ratio. The 75:25 and 55:45 NO₃⁻:NH₄⁺ ratios resulted in a higher incidence of blossom-end rot of tomato fruit, with a lower incidence of disorder at 75:25 than at the 55:45 ratio. Plant stratum influenced adult whitefly distribution in two years of the study. Middle stratum leaves were more attractive to adults in both years. The results demonstrate the effects of N fertilization (N rate and the ratio of NO₃⁻:NH₄⁺) and plant stratum on B. tabaci population density.     

Tolerance of Amaranthus palmeri populations from California to postemergence herbicides at various growth stages

In recent years, poor control of Amarathus palmeri S. Wats. plants with glyphosate in many agricultural and non-crop has been observed in the San Joaquin Valley (SJV), California, USA. Studies were conducted to assess if these were glyphosate-resistant (GR) populations. Populations from 23 different locations of the SJV were exposed to glyphosate application of 840 g ae ha⁻¹ at the 5 to 8 leaf stage of the plant and compared against a known GR and glyphosate-susceptible (GS) population from New Mexico, USA. None of the plants from the SJV survived the glyphosate application suggesting that they were GS. Plant mortality following application of glyphosate (840 g ae ha⁻¹), glufosinate (490 g ai ha⁻¹), paraquat dichloride (660 g ai ha⁻¹), saflufenacil (50 g ai ha⁻¹), rimsulfuron (70 g ai ha⁻¹⁾, and a tank-mix of glyphosate (840 g ae ha⁻¹) + saflufenacil (50 g ai ha⁻¹) applied at the 4 to 6, 8 to 10, and 12 to 16 leaf stages of A. palmeri was determined on potted plants grown outdoors. Complete control was obtained with all the treatments applied at the 4 to 6 leaf stage but control was reduced to less than 70% and 20% with glyphosate and glufosinate, respectively at the later stages. The other treatments provided 100% control at all growth stages. Combinations of saflufenacil + glyphosate, saflufenacil + glufosinate, saflufenacil + dicamba, rimsulfuron + glyphosate, tembotrione + glyphosate, flumioxazin + pyroxasulfone + glyphosate, flumioxazin + pyroxasulfone + glyphosate, dicamba + paraquat dichloride, and glyphosate + glufosinate were also tested on 8 to 10 leaf stage A. palmeri plants and all the combinations provided 100% control.