Nitrogen and Silicon Contribute to Wheat Defense's to Pyrenophora tritici-repentis, but in an Independent Manner.

Nitrogen (N) and silicon (Si) are mineral elements that have shown a reduction in the damage caused by tan spot (Pyrenophora tritici-repentis (Ptr)) in wheat. However, the effects of these elements were studied separately, and the N and Si interaction effect on wheat resistance to tan spot remains elusive. Histocytological and biochemical defense responses against Ptr in wheat leaves treated with Si (+Si) at low (LN) and high N (HN) inputs were investigated. Soil amendment with Si reduced the tan spot severity in 18% due to the increase in the leaf Si concentration (around 30%), but it was affected by the N level used. The superoxide dismutase (SOD) activity was higher in +Si plants and inoculated with Ptr, leading to early and higher H2O2 and callose accumulation in wheat leaf. Interestedly, phenylalanine ammonia-lyase (PAL) activity was induced by the Si supplying, being negatively affected by the HN rate. Meanwhile, catalase (CAT), and peroxidase (POX) activities showed differential response patterns according to the Si and N rates used. Tan spot severity was reduced by both elements, but their interaction does not evidence synergic effects in this disease's control. Wheat plants from -Si and HN and +Si and LN treatments recorded lower tan spot severity.

Priming with Small Molecule-Based Biostimulants to Improve Abiotic Stress Tolerance in Arabidopsis thaliana.

Biostimulants became a hotspot in the fight to alleviate the consequences of abiotic stresses in crops. Due to their complex nature, it is challenging to obtain stable and reproducible final products and more challenging to define their mechanism of action. As an alternative, small molecule-based biostimulants, such as polyamines have promoted plant growth and improved stress tolerance. However, profound research about their mechanisms of action is still missing. To go further, we tested the effect of putrescine (Put) and its precursor ornithine (Orn) and degradation product 1,3-diaminopropane (DAP) at two different concentrations (0.1 and 1 mM) as a seed priming on in vitro Arabidopsis seedlings grown under optimal growth conditions, osmotic or salt stress. None of the primings affected the growth of the seedlings in optimal conditions but altered the metabolism of the plants. Under stress conditions, almost all primed plants grew better and improved their greenness. Only Orn-primed plants showed different plant responses. Interestingly, the metabolic analysis revealed the implication of the N- acetylornithine and Orn and polyamine conjugation as the leading player regulating growth and development under control and stress conditions. We corroborated polyamines as very powerful small molecule-based biostimulants to alleviate the adverse abiotic stress effects.

Optimizing growing conditions for hydroponic farming of selected medicinal and aromatic plants.

This work presents a pipeline for optimizing semi-hydroponic growth conditions and analyzes the impact on the growth and metabolism in three Mentha species (M. arvensis, M. x piperita, or M. spicata) and three Ocimum basilicum genotypes (́Chládek cervená́, ́Litrá, or ́Mánes). The plant growth and the content- of nitrogen-containing compounds, phenolics, and terpenoids were determined under different nitrate concentrations and salt stress. Different responses were observed among genotypes for both species. ́Chládek cervená́ had the best growth under low nitrate, with lower histamine and higher flavonoid levels. Mentha x piperita was the best mint species performing under low nitrate and salt stress. Altogether, we demonstrate that a combination of phenomics and metabolomics is ideal to identify the optimal growth conditions for these plants and the chemical markers associated with these conditions. Besides, we showed that both primary and secondary metabolites can be good markers for classifying both species.

How do wheat plants cope with Pyricularia oryzae infection? A physiological and metabolic approach.

MAIN CONCLUSION: The infection of wheat leaves by Pyricularia oryzae induced remarkable reprogramming of the primary metabolism (amino acids, sugars, and organic acids) in favor of a successful fungal infection and certain changes were conserved among cultivars regardless of their level of resistance to blast. Wheat blast, caused by Pyricularia oryzae, has become one of the major threats for food security worldwide. Here, we investigated the behavior of three wheat cultivars (BR-18, Embrapa-16, and BRS-Guamirim), differing in their level of resistance to blast, by analyzing changes in cellular damage, antioxidative metabolism, and defense compounds as well as their photosynthetic performance and metabolite profile. Blast severity was lower by 45 and 33% in Embrapa-16 and BR-18 cultivars (moderately resistant), respectively, at 120 h after inoculation in comparison to BRS-Guamirim cultivar (susceptible). Cellular damage caused by P. oryzae infection was great in BRS-Guamirim compared to BR-18. The photosynthetic performance of infected plants was altered due to diffusional and biochemical limitations for CO2 fixation. At the beginning of the infection process, dramatic changes in both carbohydrate metabolism and on the levels of amino acids, intermediate compounds of the tricarboxylic acid cycle, and polyamines were noticed regardless of cultivar suggesting an extensive metabolic reprogramming of the plants following fungal infection. Nevertheless, Embrapa-16 plants displayed a more robust and efficient antioxidant metabolism, higher phenylalanine ammonia-lyase and polyphenoloxidase activities and higher concentrations of phenolics and lignin, which, altogether, helped them to counteract more efficiently the infection by P. oryzae. Our results demonstrated that P. oryzae infection significantly modified the metabolism of wheat plants and different types of metabolic defence may act both additively and synergistically to provide additional plant protection to blast.

Picolinic acid spray stimulates the antioxidative metabolism and minimizes impairments on photosynthesis on wheat leaves infected by Pyricularia oryzae.

Fungal pathogens produce toxins that are important for their pathogenesis and/or aggressiveness towards their hosts. Picolinic acid (PA), a non-host selective toxin, causes lesions on rice leaves resembling those originated from Pyricularia oryzae infection. Considering that non-host selective toxins can be useful for plant diseases control, this study investigated whether the foliar spray with PA on wheat (Triticum aestivum L.) plants, in a non-phytotoxic concentration, could increase their resistance to blast, stimulate the anti-oxidative metabolism, and minimize alterations in photosynthesis. The PA spray at concentrations greater than 0.1 mg ml-1 caused foliar lesions, compromised the photosynthesis and was linked with greater accumulation of hydrogen peroxide (H2 O2 ) and superoxide anion radical (O2 •- ). Fungal mycelial growth, conidia production and germination decreased by PA at 0.3 mg ml-1 . Blast severity was significantly reduced by 59 and 23%, respectively, at 72 and 96 h after inoculation for plants sprayed with PA (0.1 mg ml-1 ) at 24 h before fungal inoculation compared to non-sprayed plants. Reduction on blast symptoms was linked with increases on ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), glutathione peroxidase (EC 1.11.1.9), glutathione reductase (EC 1.8.1.7), glutathione-S-transferase (EC 2.5.1.18), peroxidase (EC 1.11.1.7), and superoxide dismutase (EC 1.15.1.1) activities, lower H2 O2 and O2 •- accumulation, reduced malondialdehyde production as well as less impairments to the photosynthetic apparatus. A more efficient antioxidative metabolism that rapidly scavenges the reactive oxygen species generated during P. oryzae infection, without dramatically decreasing the photosynthetic performance, was a remarkable effect obtained with PA spray.

Wheat blast: from its origins in South America to its emergence as a global threat.

Wheat blast was first reported in Brazil in 1985. It spread rapidly across the wheat cropping areas of Brazil to become the most important biotic constraint on wheat production in the region. The alarming appearance of wheat blast in Bangladesh in 2016 greatly increased the urgency to understand this disease, including its causes and consequences. Here, we summarize the current state of knowledge of wheat blast and aim to identify the most important gaps in our understanding of the disease. We also propose a research agenda that aims to improve the management of wheat blast and limit its threat to global wheat production.

Photosynthesis impairments and excitation energy dissipation on wheat plants supplied with silicon and infected with Pyricularia oryzae.

Considering the effect of silicon (Si) in reducing the blast symptoms on wheat in a scenario where the losses in the photosynthetic capacity of the infected plants is lowered, this study investigated the ability of using the incident light, the chloroplastidic pigments (chlorophylls and carotenoids) alterations and the possible role of carotenoids on the process of light dissipation on wheat plants non-supplied (-Si) or supplied (+Si) with Si and inoculated or not with Pyricularia oryzae. For + Si plants, blast severity was reduced compared to -Si plants. Reductions in the concentration of photosynthetic pigments (total chlorophyll, violanxanthin + antheraxanthin + zeaxanthin, ß-carotene and lutein) were greater for inoculated -Si plants than for inoculated + Si ones. The α-carotene concentration increased for inoculated -Si and +Si plants in comparison to non-inoculated plants limiting, therefore, lutein production. Higher functional damage to the photosystem II (PSII) was noticed for inoculated -Si plants with reductions in the values of maximum quantum quenching, photochemical yield of PSII and electron transport rate, but higher values for quenching non-photochemical. This finding also contributed to reductions in the values of light saturated rate photosynthesis and light saturation point for -Si plants which was attenuated for inoculated + Si plants. Increase in dark respiration values occurred for inoculated plants than for non-inoculated ones. The Si supply to wheat plants, besides reducing blast severity, contributed to their better photosynthetic performance. Moreover, inoculated + Si plants coped with drastic losses of light energy dissipation processes (fluorescence and heat) by increasing the concentration of carotenoids which helped to maintain the structural and functional viability of the photosynthetic machinery minimizing, therefore, lipid peroxidation and the production of reactive oxygen species.