Seaweed-Based Compounds and Products for Sustainable Protection against Plant Pathogens

Abstract

Sustainable agricultural practices increasingly demand novel, environmentally friendly compounds which induce plant immunity against pathogens. Stimulating plant immunity using seaweed extracts is a highly viable strategy, as these formulations contain many bio-elicitors (phyco-elicitors) which can significantly boost natural plant immunity. Certain bioactive elicitors present in a multitude of extracts of seaweeds (both commercially available and bench-scale laboratory formulations) activate pathogen-associated molecular patterns (PAMPs) due to their structural similarity (i.e., analogous structure) with pathogen-derived molecules. This is achieved via the priming and/or elicitation of the defense responses of the induced systemic resistance (ISR) and systemic acquired resistance (SAR) pathways. Knowledge accumulated over the past few decades is reviewed here, aiming to explain why certain seaweed-derived bioactives have such tremendous potential to elicit plant defense responses with considerable economic significance, particularly with increasing biotic stress impacts due to climate change and the concomitant move to sustainable agriculture and away from synthetic chemistry and environmental damage. Various extracts of seaweeds display remarkably different modes of action(s) which can manipulate the plant defense responses when applied. This review focuses on both the similarities and differences amongst the modes of actions of several different seaweed extracts, as well as their individual components. Novel biotechnological approaches for the development of new commercial products for crop protection, in a sustainable manner, are also suggested.

Recent Advances in the Molecular Effects of Biostimulants in Plants: An Overview

“…Several macroscopic algae are used in the production of biostimulants, although in recent times, particular attention has been placed on the species Ascophyllum nodosum, Ecklonia maxima and Kappaphycus alvarezii, as well as the genera Gracilaria spp. [106].…”

Seaweed Extract-Stimulated Priming in Arabidopsis thaliana and Solanum lycopersicum

“…For example, Ghaderiardakani et al [8] found that extracts from Ulva species contained a range of hormones that had both inhibitory and stimulatory effects on plant growth and development. It is well recognised that extracts from various major groups of macroalgae, including the two species used in the current study, contain a wide range of biologically active compounds including plant hormones such as cytokinins [9], laminarins, alginates, phenolics, ulvans, and carrageenans [6,10,11]. However, the mechanisms that underly the effect of seaweed extracts on plants remains unclear.…”

“…Seaweed extracts are compositionally diverse and complex in nature [3]. Recent reviews [6,7] confirm the great diversity in extracts derived from macroalgae and the wide variety of physiological responses to specific components of the extracts. For example, Ghaderiardakani et al [8] found that extracts from Ulva species contained a range of hormones that had both inhibitory and stimulatory effects on plant growth and development.…”

Ulva intestinalis Extract Acts as Biostimulant and Modulates Metabolites and Hormone Balance in Basil (Ocimum basilicum L.) and Parsley (Petroselinum crispum L.)

“…Ulvan is able to reduce the disease severity in different host-pathogen biosystems [ 7 ], by stimulation of specific enzymatic activities, salicylic acid production, and increase in phenolic compounds [ 15 , 26 ], as well as being involved in the jasmonic acid signaling pathway in leaves of Arabidopsis thaliana (L.) [ 7 ]. Ulvan induced an activation of the plant immune system through the expression of the defense-related marker gene PR10 up to 15 days in Medicago young plants [ 10 ].…”

“…Ulvan bioactivity is, thus, multi-faceted, as it prepares the plant to better respond to stress (priming effect), it acts on plant genes involved in the immune response, as well as on enzymatic activities in the biosynthetic pathways of stress-protective metabolites. On the basis of the induced resistance against pathogenic fungi, recently, the ulvan seaweed extract has been selected as new sustainable and highly viable strategy for the stimulation of plant immunity [ 26 ].…”