Seed treatment and foliar application of methyl salicylate (MeSA) as a defense mechanism in rice plants against the pathogenic bacterium, Xanthomonas oryzae pv. oryzae

Enhancement of root abscisic acid mediated osmotic regulation by macroalgal compounds promotes adaptability of rice (Oryza sativa L.) in response to progressive metal ion mediated environmental stress

Soil deterioration is a major cause of poor agricultural productivity, necessitating sufficient nutrient inputs like fertilizers and amendments for sustainable use. As one such strategy, the current study evaluates the potential of Sargassum wightii, a brown seaweed extract, as an osmopriming agent to improve seed germination, early establishment, and competent seedling performances in acidic soil. The elemental makeup of seaweed extract (BS) showed that it included major plant macro (Potassium, Nitrogen and Phosphorous), as well as micronutrients (Magnesium and Iron) and trace elements (Zinc, Copper, and Molybdenum). While seed germination was impacted by H+ ion toxicity, seeds primed with BS emerged earlier and showed a higher germination percentage (98.2%) and energy (92.4%). BS treatments enhanced seedling growth by 63% and had a positive effect on root growth (68.2%) as well as increases in root surface area (10%) and volume (67.01%). Stressed seedlings had 76.39% and 63.2% less carotenoid and chlorophyll, respectively. In seedlings treated with BS, an increase in protein and Total Soluble Sugars content of 14.56 and 7.19%, respectively, was seen. Fourier Transform-Infra Red analysis of postharvest soil indicated improved soil health with absorbance corresponding to enhanced soil water holding capacity and organic matter. Increased abscisic acid synthesis rate and associated antioxidant enzyme system (Malondialdehyde, Glutathione peroxidases and ascorbate peroxidase) activation, along with enhanced H+ adenosine triphosphate-ase and glutathione activities, help ameliorate and deport H+ ions from cells, scavenge Reactive Oxygen Species, thus protecting cells from injury. Seaweed extract successfully reduced H+-induced ion toxicities in rice by promoting their germination, physiological, metabolically, and growth parameters that could ultimately increase their productivity and yield in a sustainable and environmentally friendly manner.

Physiological and biochemical alterations in Vigna rdiate L. triggered by sesame derived elicitors as defense mechanism against Rhizoctonia and Macrophomina infestation

Improving agricultural products by the stimulation of plant growth and defense mechanisms by priming with plant extracts is needed to attain sustainability in agriculture. This study focused to consider the possible improvement in Vigna radiata L. seed germination rate, plant growth, and protection against the natural stress by increasing the defense mechanisms through the incorporation of Sesamum indicum phytochemical compounds with pre-sowing seed treatment technologies. The gas chromatography coupled with mass spectroscopy (GC-MS) analysis revealed that the methanol extract of S. indicum leaf extract contained eight major bioactive compounds, namely, 2-ethylacridine (8.24%), tert-butyl (5-isopropyl-2-methylphenoxy) dimethylsilane (13.25%), tris(tert-butyldimethylsilyloxy) arsane (10.66%), 1,1,1,3,5,5,5-heptamethyltrisiloxane (18.50%), acetamide, N-[4-(trimethylsilyl) phenyl (19.97%), 3,3-diisopropoxy-1,1,1,5,5,5-hexamethyltrisiloxane (6.78%), silicic acid, diethyl bis(trimethylsilyl) ester (17.71%) and cylotrisiloxane, hexamethyl-(4.89%). The V. radiata seeds were treated with sesame leaf extract seeds at concentrations 0, 10, 25, 50, and 100 mg/L. Sesame leaf extract at 50 and 100 mg/L concentrations was effective in increasing the germination percentage and the fresh and dry weights of roots and shoots. The increased peroxidase activity was noticed after treatment with S. indicum extract. In addition, disease percentage (< 60%) of both fungal pathogens (Rhizoctonia and Macrophomina) was significantly reduced in V. radiata plants treated with 100 mg/L of sesame leaf extract. These results revealed that physiochemical components present in S. indicum mature leaf extract significantly enhanced growth and defense mechanism in green gram plants.

Transcriptomic and proteomic profiling reveals toxicity and molecular action mechanisms of bioengineered chitosan‑iron nanocomposites against Xanthomonas oryzae pv. oryzae

Bacterial leaf blight (BLB) pathogen, Xanthomonas oryzae pv. oryzae (Xoo) is the most devastating bacterial pathogen, which jeopardizes the sustainable rice (Oryza sativa L.) production system. The use of antibiotics and conventional pesticides has become ineffective due to increased pathogen resistance and associated ecotoxicological concerns. Thus, the development of effective and sustainable antimicrobial agents for plant disease management is inevitable. Here, we investigated the toxicity and molecular action mechanisms of bioengineered chitosan‑iron nanocomposites (BNCs) against Xoo using transcriptomic and proteomic approaches. The transcriptomic and proteomics analyses revealed molecular antibacterial mechanisms of BNCs against Xoo. Transcriptomic data revealed that various processes related to cell membrane biosynthesis, antioxidant stress, DNA damage, flagellar biosynthesis and transcriptional regulator were impaired upon BNCs exposure, which clearly showing the interaction of BNCs to Xoo pathogen. Similarly, proteomic profiling showed that BNCs treatment significantly altered the levels of functional proteins involved in the integral component of the cell membrane, catalase activity, oxidation-reduction process and metabolic process in Xoo, which is consistent with the results of the transcriptomic analysis. Overall, this study suggested that BNCs has great potential to serve as an eco-friendly, sustainable, and non-toxic alternative to traditional agrichemicals to control the BLB disease in rice.

Trichoderma hamatum can act as an inter-plant communicator of foliar pathogen infections by colonizing the roots of nearby plants: A new inter-plant "wired communication"

Trichoderma is a genus of filamentous fungi widely studied and used as a biological control agent in agriculture. However, its ability to form fungal networks for inter-plant communication by means of the so-called inter-plant "wired communication" has not yet been addressed. In our study we used the model plant Arabidopsis thaliana, the fungus Trichoderma hamatum (isolated from Brassicaceae plants) and the pathogens Sclerotinia sclerotiorum and Xanthomonas campestris (necrotrophic fungus and hemibiotrophic bacteria, respectively). We performed different combinations of isolated/neighboring plants and root colonization/non-colonization by T. hamatum, as well as foliar infections with the pathogens. In this way, we were able to determine how, in the absence of T. hamatum, there is an inter-plant communication that induces systemic resistance in neighboring plants of plants infected by the pathogens. On the other hand, the plants colonized by T. hamatum roots show a greater systemic resistance against the pathogens. Regarding the role of T. hamatum as an inter-plant communicator, it is the result of an increase in foliar signaling by jasmonic acid (increased expression of LOX1 and VSP2 genes and decreased expression of ICS1 and PR-1 genes), antagonistically increasing root signaling by salicylic acid (increased expression of ICS1 and PR-1 genes and decreased expression of LOX1 and VSP2). This situation prevents root colonization by T. hamatum of the foliarly infected plant and leads to massive colonization of the neighboring plant, where jasmonic acid-mediated systemic defenses are induced.

Exogenous Application of Methyl Salicylate Induces Defence in Brassica against Peach Potato Aphid Myzus persicae

Plants use a variety of secondary metabolites to defend themselves against herbivore insects. Methyl salicylate (MeSA) is a natural plant-derived compound that has been used as a plant defence elicitor and a herbivore repellent on several crop plants. The aim of this study was to investigate the effect of MeSA treatment of Brassica rapa subsp. chinensis ('Hanakan' pak choi) on its interactions with peach potato aphids, Myzus persicae, and their natural enemy, Diaeretiella rapae. For this, we selected two concentrations of MeSA (75 mg/L and 100 mg/L). Our results showed that aphid performance was significantly reduced on plants treated with MeSA (100 mg/L). In a cage bioassay, the MeSA (100 mg/L)-treated plants showed lower adult survival and larviposition. Similarly, the MeSA (100 mg/L)-treated plants had a significantly lower aphid settlement in a settlement bioassay. In contrast, the M. persicae aphids did not show any significant difference between the MeSA (75 mg/L)-treated and control plants. In a parasitoid foraging bioassay, the parasitoid D. rapae also did not show any significant difference in the time spent on MeSA-treated and control plants. A volatile analysis showed that the MeSA treatment induced a significant change in volatile emissions, as high numbers of volatile compounds were detected from the MeSA-treated plants. Our results showed that MeSA has potential to induce defence in Brassica against M. persicae and can be utilised in developing sustainable approaches for the management of peach potato aphids.

How do plants defend themselves against pathogens-Biochemical mechanisms and genetic interventions

In agro-ecosystem, plant pathogens hamper food quality, crop yield, and global food security. Manipulation of naturally occurring defense mechanisms in host plants is an effective and sustainable approach for plant disease management. Various natural compounds, ranging from cell wall components to metabolic enzymes have been reported to protect plants from infection by pathogens and hence provide specific resistance to hosts against pathogens, termed as induced resistance. It involves various biochemical components, that play an important role in molecular and cellular signaling events occurring either before (elicitation) or after pathogen infection. The induction of reactive oxygen species, activation of defensive machinery of plants comprising of enzymatic and non-enzymatic antioxidative components, secondary metabolites, pathogenesis-related protein expression (e.g. chitinases and glucanases), phytoalexin production, modification in cell wall composition, melatonin production, carotenoids accumulation, and altered activity of polyamines are major induced changes in host plants during pathogen infection. Hence, the altered concentration of biochemical components in host plants restricts disease development. Such biochemical or metabolic markers can be harnessed for the development of "pathogen-proof" plants. Effective utilization of the key metabolites-based metabolic markers can pave the path for candidate gene identification. This present review discusses the valuable information for understanding the biochemical response mechanism of plants to cope with pathogens and genomics-metabolomics-based sustainable development of pathogen proof cultivars along with knowledge gaps and future perspectives to enhance sustainable agricultural production.

Methyl jasmonate-induced resistance to Delia platura (Diptera: Anthomyiidae) in Lupinus mutabilis

BACKGROUND

Andean lupin (Lupinus mutabilis Sweet) is an important leguminous crop from South America with a high protein content. In Ecuador, lupin yields are severely affected by the infestation of Delia platura larvae on germinating seeds. The application of elicitor molecules with activity against herbivorous insects to control D. platura infestation constitutes an unexplored and promising alternative for chemical insecticides. In this study, methyl jasmonate (MeJA), hexanoic acid, menadione sodium bisulfite, and DL-β-aminobutyric acid were evaluated for their ability to induce resistance against D. platura in three commercial lupin cultivars.

RESULTS

Only seeds pretreated with MeJA significantly impaired insect performance during choice and no-choice assays. Additionally, fitness indicators such as seed germination and growth were not affected by MeJA treatment. To investigate the molecular mechanisms behind the MeJA-mediated resistance, RT-qPCR assays were performed. First, RT-qPCR reference genes were validated, showing that LmUBC was the most stable reference gene. Next, expression analysis over time revealed that MeJA application up-regulated the activity of the jasmonic acid biosynthetic genes LmLOX2 and LmAOS, together with other jasmonate-related defense genes, such as LmTPS1, LmTPS4, LmPI2, LmMBL, LmL/ODC, LmCSD1, and LmPOD.

CONCLUSION

This study indicates that MeJA can be used as an environmentally friendly elicitor molecule to protect Andean lupin from D. platura attack without fitness cost. MeJA application induces plant defense responses to insects in Andean lupin that may be modulated by the onset of terpenoid biosynthesis, proteinase inhibitors, lectins, polyamines, and antioxidative enzymes. © 2021 Society of Chemical Industry.

Biological activity of chitosan inducing resistance efficiency of rice (Oryza sativa L.) after treatment with fungal based chitosan

Reduced pathogen resistance and management of the left-over rice stubble are among the most important challenges faced in rice cultivation. A novel and eco-friendly strategy to synthesise 'Fungal Chitosan' (FC) from Aspergillus niger using rice straw could serve as a sustainable treatment approach to improve both disease resistance and yields, while also effectively managing the rice stubble waste. The FC treatment promoted germination as well as growth parameters in rice varieties, TN1 (high yielding-susceptible) and PTB33 (low yielding-resistant) better than a commercial chitosan (PC). Treatments of exogenously applied FC to plants produced direct toxicity to Xoo, and reduced the BLB disease index by 39.9% in TN1. The capability of FC to trigger a cascade of defense pathways was evident from the measurable changes in the kinetics of defense enzymes, peroxidase (POD) and polyphenol oxidase (PPO). FC treatment increased levels of POD in TN1 by 59.4%, which was 35.3% greater than that of untreated PTB33. Therefore, the study demonstrated the effectiveness of FC treatments for use in agriculture as a potential biostimulant as well as protective agent against bacterial leaf blight, BLB, of rice (Oryza sativa) that could be produced from stubble waste and improve rice stubble management strategies.