Alkaline extract of the seaweed Ascophyllum nodosum stimulates arbuscular mycorrhizal fungi and their endomycorrhization of plant roots

Abstract

Ascophyllum nodosum extracts (ANE) are well-established plant biostimulants that improve stress tolerance and crop vigour, while also having been shown to stimulate soil microbes. The intersection of these two stimulatory activities, and how they combine to enhance plant health, however, remains poorly understood. In the present study, we aimed to evaluate: (1) the direct effect of ANE on the arbuscular mycorrhizal fungus Rhizophagus irregularis, and (2) whether ANE influences endomycorrhization in plants. ANE enhanced development of R. irregularis in vitro, showing greater spore germination, germ tube length, and hyphal branching. Greenhouse-grown Medicago truncatula drench-treated with ANE formed mycorrhizal associations faster (3.1-fold higher mycorrhization at week 4) and grew larger (29% greater leaf area by week 8) than control plants. Foliar applications of ANE also increased root colonization and arbuscular maturity, but did not appear to enhance plant growth. Nonetheless, following either foliar or drench application, M. truncatula genes associated with establishment of mycorrhizae were expressed at significantly higher levels compared to controls. These results suggest that ANE enhances mycorrhization through both direct stimulation of arbuscular mycorrhizal fungus growth and through stimulation of the plant’s accommodation of the symbiont, together promoting the establishment of this agriculturally vital plant–microbe symbiosis.

Algae and Their Metabolites as Potential Bio-Pesticides

“…Alkaline extracts of Ascophyllum nodosum enhanced the development of the mycorrhizal fungus Rhizophagus irregularis in terms of spore germination, germ tube length, and hyphal branching. The application of the extracts improved the formation of mycorrhizal associations, increased root colonization, arbuscular maturity, and the size of greenhouse-grown Medicago truncatula plants [140]. An Ascophyllum nodosum extract significantly improved the root, shoot, and fruit biomass productivity parameters by positively influencing the rhizospheric bacterial and fungal communities that are associated with pepper and tomato plants [141].…”

Soil biological quality in rhizosphere, growth, and yield of upland rice grown on acid soil after amended biochar enriched sap of Kappaphycus alvarezii

“…The study conducted by Kuwada et al (2006) found that the extracts from red (including Gricilaria verrucosa, Gelidium amansii, and Eucheuma cottonii) and green algae (Chlorella pyrenoidosa) extracted in 25% methyl alcohol solution increased hyphal growth from AMF Gigaspora margarita and Glomus caledonium spores in vitro culture. Hines et al (2021) reported the stimulation of spore germination of the AMF Rhizophagus irregularis by extracts of seaweed Ascophyllum nodosum, which contained bioactive compounds (such as alginate-derived oligosaccharides, phlorotannins, and mannitol) in the extract. Campos-López et al ( 2022) also found that combinations of flavonoids and strigolactone with or without roots stimulated spore germination and the elongation and branching of hyphae of AMF.…”

Macroalgae biorefineries as a sustainable resource in the extraction of value-added compounds

“…Several companies such as Acadian Agritech, Agri Gro Marketing Inc., MainStream Organics, etc. have developed commercial plant growth biostimulants using A. nodosum as seaweed [105][106][107]. Kappaphycus alvarezii and Sargassum vulgare, red and brown seaweeds respectively, have also been combined in a commercial biostimulant called Reabilit Algas®, developed by Nutimax Fertilizantes company.…”