Interconnectedness, length and viability of arbuscular mycorrhizal mycelium as affected by selected herbicides and fungicides

Abstract

Arbuscular mycorrhizal fungi (AMF) play a key role in plant nutrition and in the maintenance of soil fertility in agroecosystems, but their survival can be affected by different agricultural practices, including the use of pesticides. In this work, we assessed the impact of chemicals with herbicidal and fungicidal activity on mycelial growth and structure of the worldwide distributed AMF Funneliformis mosseae. Results showed that mycelial growth and interconnectedness of three different F. mosseae lineages were affected by the chemicals tested at concentrations lower than those indicated for agricultural use. Indeed, benomyl reduced mycelial growth in one lineage and fenhexamid negatively affected germlings growth in the three lineages, while both fungicides significantly affected mycelial viability and induced abnormal hyphal branching. The three F. mosseae lineages showed sensitivity to herbicides, with significant growth and viability decreases in the presence of the active ingredient glufosinate ammonium and a low viability at increasing concentrations of dicamba. Anastomosis rates were reduced by the two fungicides and by very low levels of the herbicide glufosinate, whose impact on AMF networks should be further investigated, given its wide use in agriculture. Our results suggest that the use of some pesticides in agroecosystems may lead to growth reduction and disruption of AMF mycelial structural traits, even in AMF species able to tolerate soil disturbance, posing serious threats to AMF symbiotic performance and to the maintenance of soil mycorrhizal potential.

Fungicides With Contrasting Mode of Action Differentially Affect Hyphal Healing Mechanism in Gigaspora sp. and Rhizophagus irregularis

“…Thirdly, the GHTs elongate and grow toward each other and in most cases enter into contact. Fourthly, fusion is observed between GHTs with re-establishment of cytoplasmic/protoplasmic flow (de la Providencia et al, 2005). Importantly, the HHM differ between Glomeraceae and Gigasporaceae.…”

“…Keeping the integrity of this belowground network is thus essential, not only for the survival of these fungi but also for their manifold benefits to plants. Mechanisms such as anastomosis and healing are pivotal for the spread and maintenance/survival of AM fungal colonies (de la Providencia et al, 2005). Both mechanisms drastically differ between genera (de la Providencia et al, 2005;Voets et al, 2006) and could be affected by agricultural practices such as plowing (Brito et al, 2012) or application of pesticides (de Novais et al, 2019b;Hage-Ahmed et al, 2019).…”

“…Anastomosis, that is the process of fusion between branches of the same or different hyphae to constitute a mycelial network (Kirk et al, 2008), has been abundantly reported in the fungal kingdom (Glass et al, 2000) and described in intact two-dimensional (Giovannetti et al, 2004) as well as three-dimensional (de la Providencia et al, 2005) ERM networks of AM fungi. It indistinctly concern intact and damaged hyphae, the latter being described as a hyphal healing mechanism (HHM) (de la Providencia et al, 2007). The HHM has been described in four successive events.…”

Arbuscular Mycorrhizal Fungi and Associated Microbiota as Plant Biostimulants: Research Strategies for the Selection of the Best Performing Inocula

“…Specifically, AMF isolates showing a high anastomosing ability are able to tolerate soil disturbance, such as tillage, by producing large mycorrhizal networks capable of re-establish interconnections after disruption [54][55][56][57]. ERM length and structure may be affected by pesticides, as reported by a recent work performed using a whole-plant experimental system, i.e., in F. mosseae, ERM length and density decreased in the presence of the herbicides dicamba and glufosinolate and the fungicides benomyl and fenhexamid, while ERM length and density increased in the presence of two mycorrhizospheric bacteria, Ensifer meliloti (formerly Sinorhizobium meliloti) and Enterobacter ludwigii [58]. Such recent novel data stress the need for further studies to evaluate the impact of agrochemicals and biocontrol agents on ERM structure and activity in a large number of AMF taxa in order to detect the most resilient isolates able to maintain a high mycorrhizal inoculum potential in soil.…”

Mycorrhizal Interventions for Sustainable Potato Production in Africa

“…The malfunctioning of these enzymes affects AM survival as well as P supply to the plant. Fungicides also induce abnormal hyphal branching, reduce the hyphal length and diminish anastomosis, which is pivotal in the life cycle of AM fungi, and consequentially AM fungal -plant symbiosis (de Novais et al, 2019). In experiments involving pesticides against Rhizotonia solani, azoxystrobin affected AM fungal extraradical development and spore formation whilst flutolanil affected arbuscular formation (Buysens et al, 2015).…”