Different methods of silicon application attenuate salt stress in sorghum and sunflower by modifying the antioxidative defense mechanism.

Soil salinization is the most common abiotic stress limiting agricultural productivity worldwide. Recent research has suggested that the application of silicon (Si) has beneficial effects against salt stress in sorghum (Sorghum bicolor L. Moench) and sunflower (Helianthus annuus L.) by regulating the antioxidant system, mineral nutrients, and other important mechanisms. However, whether these effects can be achieved through foliar application of Si, or whether Si application affects Si-accumulating (e.g., sorghum), and intermediate-Si-accumulating (e.g., sunflower) plant species differently, remains unclear. This study investigated different methods of Si application in attenuating the detrimental effects of salt stress, based on the biological responses of two distinct species of Si accumulators, under greenhouse conditions. Two pot experiments were designed as a factorial (2 × 4), randomized complete blocks design (RCBD) with control and salt-stress groups (0 and 100 mmol.L-1 NaCl), and four Si-treatment groups: control (no Si), foliar application (28.6 mmol.L-1), root application (2 mmol.L-1), and combined foliar and root applications. Our results showed that the harmful effects of salt stress were attenuated by Si treatments in both plant species, which decreased Na+ uptake and lipid peroxidation, and increased Si and K+ uptake, relative leaf water content, antioxidant enzyme activities, leaf area, and shoot dry matter. These results were more prominent when Si was applied via nutrient solution in the sorghum plants, and the combined foliar and root applications of Si in sunflower plants. In addition, foliar application of Si alone is an efficient alternative in attenuating the effects of salinity in both plant species when Si is not available in the growth medium. These results suggest that the Si application method plays an important role in Na+ detoxification by modifying the antioxidative defense mechanism, which could actively mediate some important physiological and biochemical processes and helps to increase the shoot dry matter production in sorghum and sunflower plants under salt stress.

Exogenous silicon and salicylic acid applications improve tolerance to boron toxicity in field pea cultivars by intensifying antioxidant defence systems.

Field peas (Pisum sativum L.) are widely cultivated throughout the world as a cool season grain and forage crop. Boron (B) toxicity is caused by high B concentration in the soil or irrigation water, and is particularly problematic in medium or heavier textured soil types with moderate alkalinity and low annual rainfall. Previous studies have indicated that B-toxicity increases oxidative stress in plants, and B-tolerance has been considered an important target in field pea plant breeding programmes. Inducers of tolerance may be a promising alternative for plant breeding. Little research has been conducted on the combined use of silicon (Si) and salicylic acid (SA) to remediate B-toxicity in field peas. The present study revealed the physiological and biochemical plant responses of applying Si + SA under B-toxicity (15 mg B L-1) on two Brazilian field pea cultivars (Iapar 83 and BRS Forrageira). A semi-hydroponic experiment was conducted using a completely randomized factorial design (2 × 5): with two field pea cultivars and five treatments which were formed by individual and combined applications of Si and SA under B-toxicity plus a control (control, B, B + Si, B + SA, and B + Si + SA). Si (2 mmol L-1) was applied to plants in two forms (root and leaf), while for SA (36 µmol L-1) only foliar applications were applied. Our results demonstrated that the combined use of exogenous Si + SA in field peas increased tolerance to B-toxicity through an intensified antioxidant plant defence system, resulting in a better regulation of reactive oxygen species (ROS) production and degradation. It significantly increased total chlorophyll and carotenoids contents, the activities of major antioxidant enzymes, and reduced MDA and H2O2 contents, resulting in increased fresh shoot and total plant dry biomass. The application of Si + SA alleviated the inhibitory effects of boron toxicity in field peas, resulting in greater plant growth by preventing oxidative membrane damage through an increased tolerance to B-excess within the plant tissue. Therefore, the use of Si + SA is an important and sustainable strategy to alleviate B-toxicity in field pea cultivation.

Silicon attenuates sodium toxicity by improving nutritional efficiency in sorghum and sunflower plants.

Salt stress is known to negatively affect the fundamental processes in plants, reducing their growth and yield. The role of Silicon (Si) to protect the sorghum and sunflower plants against salinity stress was assessed. The objective of this study was to evaluate the effects of different forms of Si application on the uptake and use efficiency of macronutrients and micronutrients in sorghum and sunflower plants under salinity stress under greenhouse conditions. Two experiments were conducted using sorghum and sunflower under greenhouse conditions. Four Si levels were applied to plants: no Si application; foliar application of 28.6 mmol.L-1; root application of 2.0 mmol.L-1; and combined Si application with both via nutrient solution and foliar spraying. Each Si treatment was applied in the absence and presence of NaCl (100 mM). Thirty days after treatments, sodium (Na+) and Si accumulation, nutrient uptake and use efficiency, and the roots and total plant dry weight were measured. Salinity stress induced nutritional imbalance and decreased dry weight production in both plant species. Our results showed that Si application alleviated the salinity stress by decreased Na+ uptake and increased nutritional efficiency, thereby favoring the total plant dry weight in sorghum by 27% and sunflower by 41%. This occurred when Si was applied either via root or in combination via root and foliar application, respectively. Collectively, our findings indicate that Si application can attenuate the deleterious effects of salt stress and increase yield in sorghum and sunflower plants in a sustainable manner.

Unsuitability of indigenous South American Rutaceae as potential hosts of Diaphorina citri.

BACKGROUND: 'Candidatus Liberibacter asiaticus' is transmitted by Diaphorina citri, an insect with a wide range of hosts in Rutaceae. Species related to Citrus occur in Brazilian forests where they may serve as hosts for psyllids and infested citrus orchards. RESULTS: The suitability of plants as hosts of D. citri was classified into four groups. Group I (high suitability): Citrus × aurantium 'Valencia', 'Citrus limonia', Murraya paniculata (syn. Murraya exotica L.) (Aurantioideae: Aurantieae) and Bergera koenigii (Aurantioideae: Clauseneae). Group II (intermediate to low suitability): Citrus (Poncirus) trifoliata 'Pomeroy', Citrus wintersii, Swinglea glutinosa (Aurantieae) and Clausena lansium (Clauseneae). Group III (not suitable): Aegle marmelos, Atalantia buxifolia, Citrus ('Microcitrus') sp. (Aurantieae) and Helietta apiculata (Amyridoideae). Group IV (non-hosts): Glycosmis pentaphylla (Clauseneae), Balfourodendron riedelianum, Casimiroa edulis, Esenbeckia febrifuga, Esenbeckia leiocarpa, Metrodorea stipularis, Zanthoxylum rhoifolium (Amyridoideae) and Dictyoloma vandellianum (Cneoroideae). Insects survived longer on newly differentiated leaves compared with fully expanded soft leaves. Psyllids either did not develop or did not survive for long on most Group IV species, all of which, with the exception of G. pentaphylla, occur naturally in Brazilian forests. CONCLUSION: Citrus relatives occurring in forests near citrus orchards are not suitable hosts of D. citri and, therefore, do not contribute to huanglongbing spread. © 2018 Society of Chemical Industry.

Preliminary Studies to Characterize the Temporal Variation of Micronutrient Composition of the Above Ground Organs of Maize and Correlated Uptake Rates.

The improvement of agronomic practices and the use of high technology in field crops contributes for significant increases in maize productivity, and may have altered the dynamics of nutrient uptake and partition by the plant. Official recommendations for fertilizer applications to the maize crop in Brazil and in many countries are based on critical soil nutrient contents and are relatively outdated. Since the factors that interact in an agricultural production system are dynamic, mathematical modeling of the growth process turns out to be an appropriate tool for these studies. Agricultural modeling can expand our knowledge about the interactions prevailing in the soil-plant-atmosphere system. The objective of this study is to propose a methodology for characterizing the micronutrient composition of different organs and their extraction, and export during maize crop development, based on modeling nutrient uptake, crop potential evapotranspiration and micronutrient partitioning in the plant, considering the production environment. This preliminary characterization study (experimental growth analysis) considers the temporal variation of the micronutrient uptake rate in the aboveground organs, which defines crop needs and the critical nutrient content of the soil solution. The methodology allowed verifying that, initially, the highest fraction of dry matter, among aboveground organs, was assigned to the leaves. After the R1 growth stage, the largest part of dry matter was partitioned to the stalk, which in this growth stage is the main storage organ of the maize plant. During the reproductive phase, the highest fraction of dry matter was conferred to the reproductive organs, due to the high demand for carbohydrates for grain filling. The micronutrient (B, Cu, Fe, Mn, and Zn) content follows a power model, with higher values for the initial growth stages of development and leveling off to minimum values at the R6 growth stage. The proposed model allows to verify that fertilizer recommendations should be related to the temporal variability of micronutrient absorption rates, in contrast to the classic recommendation based on the critical soil micronutrient content. The maximum micronutrient absorption rates occur between the reproductive R4 and R5 growth stages. These evaluations allowed to predict the maximum micronutrient requirements, considered equal to respective stalk sap concentrations.

Maize dry matter production and macronutrient extraction model as a new approach for fertilizer rate estimation.

Decision support for nutrient application remains an enigma if based on soil nutrient analysis. If the crop could be used as an auxiliary indicator, the plant nutrient status during different growth stages could complement the soil test, improving the fertilizer recommendation. Nutrient absorption and partitioning in the plant are here studied and described with mathematical models. The objective of this study considers the temporal variation of the nutrient uptake rate, which should define crop needs as compared to the critical content in soil solution. A uniform maize crop was grown to observe dry matter accumulation and nutrient content in the plant. The dry matter accumulation followed a sigmoidal model and the macronutrient content a power model. The maximum nutrient absorption occurred at the R4 growth stage, for which the sap concentration was successfully calculated. It is hoped that this new approach of evaluating nutrient sap concentration will help to develop more rational ways to estimate crop fertilizer needs. This new approach has great potential for on-the-go crop sensor-based nutrient application methods and its sensitivity to soil tillage and management systems need to be examined in following studies. If mathematical model reflects management impact adequately, resources for experiments can be saved.

Maize dry matter production and macronutrient extraction model as a new approach for fertilizer rate estimation

ABSTRACT Decision support for nutrient application remains an enigma if based on soil nutrient analysis. If the crop could be used as an auxiliary indicator, the plant nutrient status during different growth stages could complement the soil test, improving the fertilizer recommendation. Nutrient absorption and partitioning in the plant are here studied and described with mathematical models. The objective of this study considers the temporal variation of the nutrient uptake rate, which should define crop needs as compared to the critical content in soil solution. A uniform maize crop was grown to observe dry matter accumulation and nutrient content in the plant. The dry matter accumulation followed a sigmoidal model and the macronutrient content a power model. The maximum nutrient absorption occurred at the R4 growth stage, for which the sap concentration was successfully calculated. It is hoped that this new approach of evaluating nutrient sap concentration will help to develop more rational ways to estimate crop fertilizer needs. This new approach has great potential for on-the-go crop sensor-based nutrient application methods and its sensitivity to soil tillage and management systems need to be examined in following studies. If mathematical model reflects management impact adequately, resources for experiments can be saved.