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Rice is essential to feed the world's population, being the most important staple food in several countries. Crop production has been directly impacted by climate change. Plants can mitigate an increase in atmospheric CO2 concentration through photosynthetic conversion into carbohydrates. However, the potential for this conversion and plant responses to climate change remain unclear. The study was conducted from the cultivation of plants in open-top chambers (OTCs) with two concentrations of CO2, 400 ppm (ambient – a[CO2]) and 700 ppm (enhanced – e[CO2])). We used rice plants of the cultivar IRGA 424 RI. Evaluations occurred in the vegetative (V5 and V11) and reproductive (R2 and R7) stages. As for gas exchange, plants grown under e[CO2] showed increased net CO2 assimilation rate, greater water use efficiency, and higher intercellular CO2 concentration. On the other hand, the lowest values for stomatal conductance, chlorophyll index, nitrogen balance index, percentage of nitrogen in the leaves, and thousand-grain weight were found for this treatment. In addition, there was an increase in the activity of the glutamine synthetase and nitrate reductase enzymes in leaves and roots under e[CO2], as well as a higher content of nitrate, starch, water-soluble polysaccharides and total soluble sugars in leaves in the first evaluated phenological stage. These results showed us that the reductions in chlorophyll levels added to the stimulation of the photosynthetic machinery elevated the nutritional demand. Due to these impacts, nitrogen and carbon metabolism were reduced, negatively reflecting on the yield components of rice plants. [ABSTRACT FROM AUTHOR]

Since sugarcane is semi-perennial, it has no escape from water stresses in the Brazilian Cerrado, and consequently, drought impacts plant growth and industrial quality. The objective of this study was to evaluate the morphophysiology and quality of the first ratoon of two sugarcane varieties submitted to irrigated and stressed treatments under field conditions. For the biometric characteristics, in general, significant decreases were observed under the stressed treatment for all periods, and only minor differences were detected between the studied cultivars. Physiological parameters decreased under stressed conditions, but to a different extent between the varieties. RB855536 was able to maintain a greater rate of transpiration. Productivity was reduced by 103 t ha−1 for variety RB855536 and 121 t ha−1 for RB867515, compared to plants with full irrigation during the dry period, but cane quality was similar in both genotypes. Measurements of physiological and morphological parameters may prove useful in the rapid identification of genotypes with greater tolerance to abiotic stress. [ABSTRACT FROM AUTHOR]

The objectives of this study were to estimate the residual and half-life of [imazapic + imazapyr] and to infer on the impact of these residuals over time. The first experiment comprised the application of [imazapic + imazapyr] to Clearfield® rice. On the following summer cropping season (365 days later), undeformed soil samples 0-5 cm depth were collected and seeds of six species or varieties were sown as bioindicators of residuals (experiment 2), being assessed plant height and dry mass 20 days after emergence start. The third experiment comprised the cultivation of the same species submitted to ten increasing herbicide doses (0-280 g ha−1) to establish standard response curves, also assessing plant height and dry mass 20 days after emergence start. About 2.1-5.8% of the applied imazapic remains in soil after one year, for the label doses. Imazapyr was considered to be at negligible doses as its half-life is short, and less than 0.0000001% of the applied dose is expected to be in soil 365 days later. The expected imazapic half-life in lowland areas of Southern Brazil is longer than for dryland, being estimated as between 63 and 77 days (95% confidence interval), contrasting to the 60 days half-life previously estimated for dryland soils. [ABSTRACT FROM AUTHOR]

Previous research demonstrated that the interval between defoliation treatments based on the leaf stage is a promising tool for the management of annual ryegrass (Lolium multiflorum L.) pasture. The use of this tool, which is based on the physiological status of the plant, could also benefit the seed production. We assessed the effects of the time of defoliation based on leaf stage on seed yield and quality of annual ryegrass cut to three residual stubble heights (RSH) (50%, 25% and 0% of plant height pre-defoliation) and a second defoliation applied to certain treatments based on the leaf stage of the plant regrowth (two or three leaves per tiller). Higher defoliation intensities (lower RSH) increased the amount of harvested forage to 4.0 t DM ha-1. Moderate defoliation (50%) undertaken at the 3-leaf stage combined with intense defoliation (25% and 0%) at the 2-leaf stage resulted in the highest seed yields (1.8 t ha-1). However, lower RSH reduced mean seed weight and physiological seed quality, which was also associated with lower seed starch and protein content. Accelerated ageing (AA) tests were used to compare seed vigour between treatments. A second defoliation at the 3-leaf stage plus intense defoliation (RSH 0%) resulted in seed lots with a high rate of lipid peroxidation after the AA test, followed by lower catalase activity, germination, and seedling growth. The combination of a second defoliation at the 3-leaf stage and the retention of higher RSH (50%) promoted a greater proportion of leaf blades in the stubble, with a strong positive correlation with seed production and vigour. Antioxidant enzyme activity after the AA test is an important marker of annual ryegrass seed quality. [ABSTRACT FROM AUTHOR]

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Abiotic stresses caused by excessive cold, iron, and salt are among the main growth and yield-limiting factors of rice. Among the metabolic processes, photosynthesis stands out for being closely related to crop yields, causing a yield decline by reduced photosynthetic capacity in plants under abiotic stresses. The purpose of this study was to evaluate the differential expression of chloroplast genes involved in photosynthesis by RNA sequencing (RNA-seq) and quantify gas exchanges in leaves of rice plants exposed to cold, iron, and salt stress for 24 h. Of all genes expressed in each stress, cold had the highest number of differentially expressed genes (DEGs) related to light and chloroplast reactions, with 535 mostly down-regulated genes. Salt and iron stress was associated with 309 and 115 genes, respectively, involved in light reactions and chloroplast. The three stresses had transcripts with GOs related to light reactions, all with more than ten different GO terms. With regard to chloroplast, cold and salt stress had 12 terms of GO, and iron stress has 9 terms of GO. For gas exchange, only the parameter net assimilation rate differed significantly between stresses, with the lowest mean under cold stress. The results showed that cold stress affects photosynthesis most drastically, both at the molecular and the physiological level, and despite decreases in the net assimilation rate, changes under iron and salt stress were minor, which may be related to the tolerance of cultivar BRS Querência. [ABSTRACT FROM AUTHOR]

Salinity is a limiting factor for growth and development, since it affects several physiological processes in plants. This trial aimed to assess the levels of photosynthetic pigments, betacyanins, lipid peroxidation and activity of antioxidant enzymes in Alternanthera philoxeroides under salt stress. Plants originated from an in vitro culture were acclimatized and irrigated with sodium chloride (0, 200 and 400 mM) for 30 d. The experimental design was completely randomized with a 3×2 factorial arrangement of treatments: three concentrations of NaCl and two plant tissues (stems and leaves). The experimental data was subjected to an analysis of variance and means where compared using Tukey test (p⩽0.05). The levels of chlorophylls a, chlorophylls b and total carotenoids presented similar responses, decreasing their values according to salt concentrations, while the chlorophyll a/b ratio of the plants that were submitted to the highest salt concentration presented a significant increase when compared to the control. Higher levels of betacyanin were observed on stems, when compared to the leaves, in the highest salt concentrations. On the leaves, there was a significant increase of lipid peroxidation and superoxide dismutase activity, whereas roots showed an increase of the enzymes catalase and ascorbate peroxidase. Salt stress caused greater degradation in the photosynthetic pigments, increment of betacyanin synthesis in stems, and damage to the cell membranes of the leaves. However, the increase of antioxidant enzymes activity stimulated the protective system against oxidative stress. It is concluded that Alternanthera philoxeroides (Mart.) Griseb. plants present reduction in levels of photosynthetic pigments, increased synthesis of betacyanins and increased activity of antioxidant enzymes in leaves and roots when exposed to salt stress. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) improve plant ability to uptake P and tolerate heavy metals. This study aimed to evaluate the effect of available P and the inoculation of Rhizophagus clarus in a Cu-contaminated soil ( i ) on the activity of acid phosphatases (soil and plant), the presence of glomalin, and ( ii ) in the biochemical and physiological status of Mucuna cinereum . A Typic Hapludalf soil artificially contaminated by adding 60 mg kg −1 Cu was used in a 3 × 2 factorial design with three replicates. Treatments consisted of three P levels: 0, 40, and 100 mg kg −1 P. Each P treatment level was inoculated (+AMF)/non-inoculated (−AMF) with 200 spores of R. clarus per pot, and plants grown for 45 days. The addition of at least 40 mg kg −1 P and the inoculation of plants with R. clarus proved to be efficient to reduce Cu phytotoxicity and increase dry matter yield. Mycorrhization and phosphate fertilization reduced the activity of enzymes regulating oxidative stress (SOD and POD), and altered the chlorophyll a fluorescence parameters, due to the lower stress caused by available Cu. These results suggest a synergism between the application of P and the inoculation with R. clarus , favoring the growth of M. cinereum in a Cu-contaminated soil. This study shows that AMF inoculation represents an interesting alternative to P fertilization to improve plant development when exposed to excess Cu. [ABSTRACT FROM AUTHOR]

The silicon (Si) reduced tan spot ( Pyrenophora tritici-repentis ) severity up to 40%, through both biochemical defense mechanisms and histo-cytological defense responses. The activities of enzymes involved in plant defense system such as superoxide dismutase, peroxidase and chitinase showed greater activity in inoculated plants supplied with Si. Histo-cytological analysis indicated that Si potentiated the accumulation of hydrogen peroxide in the beginning of infection process. Together, these defense mechanisms resulted in the reduction of cell death at the infection sites in plants supplied with Si, which in turn showed lower disease severity. Si appears to be a promising alternative control measure for use in integrated management of tan spot. [ABSTRACT FROM AUTHOR]

In high-yield irrigated rice systems, options for legume cover crops with the capacity for biological nitrogen (N) fixation in the period between harvest have been sought. However, options are limited due to excess water and low oxygen level in the soil. The persian clover (Trifolium resupinatum) is an exception as it is a promising species due to its adaptation to waterlogged soils. Thus, the objective of this work was to evaluate accumulated nitrogen in the legume, soil mineral and microbial N levels and the response of a rice hybrid established in succession to persian clover during four growing seasons in subtropical conditions in southern Brazil. The field experiment was carried out during four crop seasons in a 2 × 4 factorial, with two conditions of soil cover, fallow and legume (persian clover) under four levels of N (0, 60, 120 and 180 kg N ha−1). It was observed that the cultivation of Persian clover increased the availability of mineral and microbial N in the soil by 35% and 6.5%, respectively. There was a 14.1% reduction in the optimal nitrogen rate in the rice hybrid. The grain yield of rice grains using persian clover in winter is 7.8% higher in relation to fallow, with the greatest difference between clover and fallow at the lowest N rates (0 e 60 kg ha−1). Thus, persian clover is a promising legume to be used in the period between harvest in hydromorphic soils cultivated with irrigated rice in subtropical conditions. [Display omitted] • Persian clover increase 35% soil mineral nitrogen. • Use of legume (Persian clover) reduces nitrogen fertilization by 14.1%. • Persian clover legume increases rice grain yield by 7.8%. [ABSTRACT FROM AUTHOR]

Rice plants cultivated under 700 ppm atmospheric CO 2 concentration presented a reduction in the progress and severity of the brown spot disease (Bipolaris oryzae), through the enhancement of biochemical defense mechanisms. Plants exposed to 700 ppm of CO 2 had higher activity of the enzymes superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, polyphenoloxidase and chitinase, and increased phenolic compounds and lignin concentration, independent of the rice cultivar. Therefore, the lower severity values of the disease were related to changes in the development of the lesions as a result of the defense responses, which were stimulated in the rice plants by the increase of CO 2 concentration. • This study demonstrated that increase of atmospheric CO 2 improves rice resistance to brown spot. • Rice under enhanced atmospheric CO 2 concentration have a better attenuation of the oxidative damages. • Rice under enhanced atmospheric CO 2 concentration have the reduction on the severity of the brown spot. • Rice exposed to 700 ppm of CO 2 had higher activity of antioxidant enzymes. • Rice exposed to 700 ppm of CO 2 had higher concentration of phenolic compounds and lignin content. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the radiosensitivity of castor bean seeds after applications of different doses of Cobalt60 gamma radiation. Seeds were pre-soaked for 24 hours in distilled water and then irradiated with 50, 100, 150, and 200 Gy, except the control. Sowing was performed in trays, which contained soil as substrate and were maintained in a greenhouse. The electrical conductivity, emergence, emergence speed index, growth parameters and activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, and catalase) were evaluated in the leaves and roots of castor bean seedlings. Gamma radiation did not affect the electrical conductivity of the seeds; however, at a dose of 200 Gy, the emergence and emergence speed index of the seedlings was negatively affected. An analysis of the morphophysiological parameters revealed a reduction in seedling size as the radiation dose increased. There was a significant increase in superoxide dismutase and ascorbate peroxidase activities at higher radiation doses in the leaves, but not in roots. Thus, the analysis of all the variables suggests a response pattern as to the morphophysiological and biochemical changes of castor bean seedlings due to the increase of gamma radiation, which may serve as a tool for generating greater genetic variability.