Combined application of Ascophyllum nodosum extract and chitosan synergistically activates host-defense of peas against powdery mildew.

BACKGROUND: Powdery mildew (PM) is an important disease of pea that reduce yield. Ascophyllum nodosum extract (ANE) and chitosan (CHT) are biostimulants used to improve plant health. Efficacy of ANE and CHT was assessed individually and in combination against pea powdery mildew. RESULTS: Combined applications of ANE and CHT had a significant inhibitory effect on pathogen development and it reduced disease severity to 35%, as compared to control (90.5%). The combination of ANE and CHT enhanced the activity of plant defense enzymes; phenylalanine ammonia lyases (PAL), peroxidase (PO) and production of reactive oxygen species (ROS) and hydrogen peroxide (H2O2). Further, the treatment increased the expression of a number of plant defense genes in jasmonic acid (JA) signaling pathway such as LOX1 and COI and salicylic acid (SA)-mediated signaling pathway such as NPR1 and PR1. Other genes involved in defense mechanisms like NADPH oxidase and C4H were also upregulated by the combination treatment. CONCLUSION: The combination of ANE and CHT suppresses pea powdery mildew largely by modulating JA and SA-mediated signaling pathways.

Changes in Soil Characteristics, Microbial Metabolic Pathways, TCA Cycle Metabolites and Crop Productivity following Frequent Application of Municipal Solid Waste Compost.

The benefit sof municipal solid waste (MSW) compost on soil health and plant productivity are well known, but not its long-term effect on soil microbial and plant metabolic pathways. A 5-year study with annual (AN), biennial (BI) and no (C, control) MSW compost application were carried out to determine the effect on soil properties, microbiome function, and plantgrowth and TCA cycle metabolites profile of green beans (Phaseolus vulgaris), lettuce (Latuca sativa) and beets (Beta vulgaris). MSW compost increased soil nutrients and organic matter leading to a significant (p < 0.05) increase in AN-soil water-holding capacity followed by BI-soil compared to C-soil. Estimated nitrogen release in the AN-soil was ca. 23% and 146% more than in BI-soil and C-soil, respectively. Approximately 44% of bacterial community due to compost. Deltaproteobacteria, Bacteroidetes Bacteroidia, and Chloroflexi Anaerolineae were overrepresented in compost amended soils compared to C-soil. A strong positive association existed between AN-soil and 18 microbial metabolic pathways out of 205. Crop yield in AN-soil were increased by 6−20% compared to the BI-soil, and by 35−717% compared to the C-soil. Plant tricarboxylic acid cycle metabolites were highly (p < 0.001) influenced by compost. Overall, microbiome function and TCA cycle metabolites and crop yield were increased in the AN-soil followed by the BI-soil and markedly less in C-soil. Therefore, MSW compost is a possible solution to increase soil health and plants production in the medium to long term. Future study must investigate rhizosphere metabolic activities.

Variation in frequency of CQA-tested municipal solid waste compost can alter metabolites in vegetables.

The use of compost to enhance plant growth and mineral nutrients composition are extensively studied but not much literature information exists on its influence on plant metabolic profiles. A study was performed to assess a 5-year variable frequency of application of Compost Quality Alliance tested municipal solid waste (MSW) compost effect on metabolic profiles of the edible portions of four different vegetable plants. The plants were lettuce (Latuca sativa cv. Grand Rapids), beets (Beta vulgaris cv. Detroit Supreme), carrot (Daucus carota cv. Nantes) and green beans (Phaseolus vulgaris cv. Golden Wax) grown under a sub-humid continental climate. The treatments were annual, biennial and no (control) applications of the MSW compost. Typically, soil fertility highly increased with the annual application of the MSW compost followed by the biennial application but declined in the control plot. The annually applied MSW compost increased total amino acids in the lettuce, carrot, beets, and green beans by ca. 323%, 109%, 94% and 18% respectively, compared to the control. Overall, total phospholipids were enhanced by the biennially applied MSW compost. Total organic acids in the lettuce, beets, and green beans were altered by the annual and biennial MSW compost applications by ca. 35% and 23%; 6% and 6.4%; and 22% and 65%, respectively compared to the control. A 2-dimension principal component analysis biplot confirmed positive association between the different frequencies of MSW compost application and soil fertility enhancement of plant metabolites. In conclusion, the annual application of MSW compost enhanced amino acids, phospholipids, acylcarnitines, amines and choline but reduced glucose in the lettuce, beets, carrot, and green beans. Further studies to elucidate the mechanisms underpinning such biofortification will be required.

Mineralization and nutrient release pattern of vermicast-sawdust mixed media with or without addition of Trichoderma viride.

A combination of vermicast and sawdust mixed medium is commonly used in horticulture, but the added benefit of microbial inoculation and mechanism of nutrient availability are unknown. This study was done to determine nutrient mineralization and nutrient release patterns of different combinations or a mix of vermicast-sawdust growing media amended with or without Trichoderma viride (105 spores/g). The mixed-media treatments were (1) 80% vermicast+20% sawdust; (2) 60% vermicast+40% sawdust; (3) 40% vermicast+60% sawdust; (4) 20% vermicast+80% sawdust; and (5) sawdust alone (control). Total dissolved solids, electric conductivity and salinity increased with each sampling time following submergence in deionized. Nutrients released from media without T. viride were significantly higher than the corresponding media with added T. viride. Overall, the starting total nitrogen of the different media did not change during the incubation period, but nitrate-nitrogen was reduced to a negligible amount by the end of day 30 of incubation. A repeated measures analysis showed a significant effect of Time*T. viride*Treatment on total dissolved solids. Redundancy analysis demonstrated a positive and strong association between media composed of ≥40% vermicast and ≤60% sawdust with or without T. viride and mineral nutrients released, electrical conductivity, total dissolved solids and salinity. These findings suggest that fast-growing plants may benefit from 40% to 60% vermicast added to 40% to 60% sawdust without T. viride while slow-growing plants can benefit from the same mixed medium combined with the addition of T. viride. Further investigation is underway to assess microbial dynamics in the mixed media and their influence on plant growth.

Plant G-protein signaling cascade and host defense.

The heterotrimeric guanine-nucleotide-binding proteins (G-proteins) play a crucial role in signal transduction and regulate plant responses against biotic and abiotic stresses. Necrotrophic pathogens trigger Gα subunit and, in contrast, sometimes Gßγ dimers. Beneficial microbes play a vital role in the activation of heterotrimeric G-proteins in plants against biotrophic and necrotrophic pathogens. The subunits of G-protein (α, ß, and γ) are activated differentially against different kinds of pathogens which in turn regulates the entry of the pathogen in a plant cell. Defense mediated by G-proteins in plants imparts resistance against several pathogens. Activation of different G-protein subunits depends on the mode of nutrition of the pathogen. The current review discussed the role of the three subunits against various pathogens. It appeared to be specific in the individual host-pathogen system as well as the role of effectors in the induction of G-proteins. We also discussed the G-protein-mediated production of reactive oxygen species (ROS), including H2O2, activation of NADPH oxidases, hypersensitive response (HR), phospholipases, and ion channels in response to microorganisms.