Phytoalexins in defense against pathogens

Chitosan as a potential natural compound to control pre and postharvest diseases of horticultural commodities

Chitin and chitosan are naturally-occurring compounds that have potential in agriculture with regard to controlling plant diseases. These molecules were shown to display toxicity and inhibit fungal growth and development. They were reported to be active against viruses, bacteria and other pests. Fragments from chitin and chitosan are known to have eliciting activities leading to a variety of defense responses in host plants in response to microbial infections, including the accumulation of phytoalexins, pathogen-related (PR) proteins and proteinase inhibitors, lignin synthesis, and callose formation. Based on these and other proprieties that help strengthen host plant defenses, interest has been growing in using them in agricultural systems to reduce the negative impact of diseases on yield and quality of crops. This review recapitulates the properties and uses of chitin, chitosan, and their derivatives, and will focus on their applications and mechanisms of action during plant-pathogen interactions.

https://www.mdpi.com/1660-3397/8/4/968/pdf

Chitosan in plant protection

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 mM) and high (50 mM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.

/pdf/in-posidonia-oceanica-cadmium-induces-changes-in-dna-3cu7uj83mr.pdf

In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

Plant pathogens are the main threat for profitable agricultural productivity. Currently, chemical-based pesticides are thought to be an effective and reliable agricultural management measure for controlling pests. Chemical pesticides are highly effective and convenient to use but they are a potential threat for the environment and all kinds of life on earth. Therefore, the use of biological control agents for the management of plant pathogens is considered as a safer and sustainable strategy for safe and profitable agricultural productivity. Bacillus-based biocontrol agents play a fundamental role in the field of biopesticides. Many Bacillus species have proved to be effective against a broad range of plant pathogens. They have been reported as plant growth promoter, systemic resistance inducer, and used for production of a broad range of antimicrobial compounds (lipopeptides, antibiotics and enzymes) and competitors for growth factors (space and nutrients) with other pathogenic microorganisms thr...

https://tandfonline.com/doi/pdf/10.1080/13102818.2017.1286950

Bacillus species as versatile weapons for plant pathogens: a review

Summary
• Fusaric acid (FA) is a toxin produced by Fusarium species. Most studies on FA have reported toxic effects (for example, alteration of cell growth, mitochondrial activity and membrane permeability) at concentrations greater than 10−5 m. FA participates in fungal pathogenicity by decreasing plant cell viability. However, FA is also produced by nonpathogenic Fusarii, potential biocontrol agents of vascular wilt fusaria. The aim of this study was to determine whether FA, at nontoxic concentrations, could induce plant defence responses.
• Nontoxic concentrations of FA were determined from cell-growth and O2-uptake measurements on suspensions of Arabidopsis thaliana cells. Ion flux variations were analysed from electrophysiological and pH measurements. H2O2 and cytosolic calcium were quantified by luminescence techniques.
• FA at nontoxic concentrations (i.e. below 10−6 m) was able to induce the synthesis of phytoalexin, a classic delayed plant response to pathogen. FA could also induce rapid responses putatively involved in signal transduction, such as the production of reactive oxygen species, and an increase in cytosolic calcium and ion channel current modulations.
• FA can thus act as an elicitor at nanomolar concentrations.

Early physiological responses of Arabidopsis thaliana cells to fusaric acid: toxic and signalling effects

/pdf/physico-chemical-characterization-and-effects-of-olive-oil-3mbq3lws4c.pdf

Physico-chemical Characterization and Effects of Olive Oil Mill Wastewaters Fertirrigation on the Growth of Some Mediterranean Crops

Treatment of chickpea with Rhizobium isolates enhances the expression of phenylpropanoid defense-related genes in response to infection by Fusarium oxysporum f. sp. ciceris.

The effect of chitosan on the growth and morphology of Fusarium oxysporum f. sp. albedinis (Foa), the 
causal agent of Bayoud disease, and its ability to elicit a defence reaction against this fungus in date palm roots were 
investigated. Chitosan at 1 mg ml-1 reduced the growth of Foa on potato dextrose agar medium by an average of 75%, 
while mycelial growth was totally inhibited in a liquid medium. When added to a solid medium, chitosan caused 
morphological changes in Foa mycelium. In addition, when injected into roots at three concentrations (0.1, 0.5 and 1 
mg ml-1), chitosan elicited peroxidase (PO) and polyphenoloxidase (PPO) activity and, particularly at the concentration 
of 1 mg ml-1, increased the level of phenolic compounds. Concerning phenolics, chitosan led to an accumulation of 
non-constitutive hydroxycinnamic acid derivatives, known to be of great importance in date palm resistance to Bayoud. 
The accumulation of hydroxycinnamic acid derivatives was greater in cv. BSTN than in cv. JHL. Chitosan could be 
used to protect date palm against this vascular disease.

Chitosan, antifungal product against Fusarium oxysporum f. sp. albedinis and elicitor of defence reactions in date palm roots [Phoenix dactylifera L.; Morocco]

I. El Hadrami

Papers

Early physiological responses of Arabidopsis thaliana cells to fusaric acid: toxic and signalling effects

Physico-chemical Characterization and Effects of Olive Oil Mill Wastewaters Fertirrigation on the Growth of Some Mediterranean Crops

Treatment of chickpea with Rhizobium isolates enhances the expression of phenylpropanoid defense-related genes in response to infection by Fusarium oxysporum f. sp. ciceris.

Chitosan, antifungal product against Fusarium oxysporum f. sp. albedinis and elicitor of defence reactions in date palm roots [Phoenix dactylifera L.; Morocco]

Elicitation of soluble phenolics in date palm (Phoenix dactylifera) callus by Fusarium oxysporum f. sp. albedinis culture medium