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Dry rot of potato caused by Fusarium spp. affects tubers in the field and during storage and represents the primary postharvest loss. The present study aimed to assess, in a two-year trial (2021–2022) conducted in Central Italy, the effects of a sustainable and circular cultural model consisting of two conservative tillage techniques (subsoiling and spading) versus ploughing and organic fertilization by compost versus mineral fertiliser on the severity of tuber dry rot and fungal species involved. A high percentage of dry-rotted tubers was recorded in the cropping season 2022, characterized by abnormally high temperatures. In 2022, spading combined with compost fertilization led to a significant decrease in dry rot. Fusarium brachygibbosum was the predominant and most virulent pathogen isolated from symptomatic tubers, followed by F. oxysporum and F. equiseti. Fertilization with compost, particularly when combined with subsoiling, significantlu decreased the frequency of F. brachygibbosum. On symptomatic tubers, the antagonists and hyperparasites Trichoderma atroviride and T. gamsii were also isolated, more frequently on tubers from organically fertilized plots. The saprophytic and antagonistic fungus Linnemannia elongata was isolated on tubers from subsoiling. Plants grown on soil fertilized with compost significantly increased colonization by the arbuscular mycorrhizal fungus identified as Paraglomus occultum. Sustainable and circular agriculture management systems can maintain or restore soil fertility through conservative tillering and organic fertilization and minimizing losses due to diseases such as dry rot of potato tubers.

Arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in plants, whereas little is known regarding AMF contribution to sucrose and proline metabolisms under drought stress (DS). In this study, Funneliformis mosseae and Paraglomus occultum were inoculated into trifoliate orange ( Poncirus trifoliata ) under well watered and DS. Although the 71-days DS notably ( P  < 0.05) inhibited mycorrhizal colonization, AMF seedlings showed significantly ( P  < 0.05) higher plant growth performance and leaf relative water content, regardless of soil water status. AMF inoculation significantly ( P  < 0.05) increased leaf sucrose, glucose and fructose concentration under DS, accompanied with a significant increase of leaf sucrose phosphate synthase, neutral invertase, and net activity of sucrose-metabolized enzymes and a decrease in leaf acid invertase and sucrose synthase activity. AMF inoculation produced no change in leaf ornithine-δ-aminotransferase activity, but significantly ( P  < 0.05) increased leaf proline dehydrogenase activity and significantly ( P  < 0.05) decreased leaf both Δ 1 -pyrroline-5-carboxylate reductase and Δ 1 -pyrroline-5-carboxylate synthetase activity, resulting in lower proline accumulation in AMF plants under DS. Our results therefore suggest that AMF strongly altered leaf sucrose and proline metabolism through regulating sucrose- and proline-metabolized enzyme activities, which is important for osmotic adjustment of the host plant.

As beneficial microorganisms in the soil, arbuscular mycorrhizal fungi (AMF) and rhizobia (Rh) form a mutualistic symbiosis with plant roots, while it is unclear whether AMF and Rh synergistically promote root colonization, plant growth, and nitrogen (N) acquisition during the colonization. The aim of this study was carried out to analyze the effect of inoculation with an arbuscular mycorrhizal fungus (Paraglomus occultum) and a rhizobium (Rhizobium trifolii), singly and in combination, on root mycorrhizal colonization and nodules as well as changes in plant growth, hydrogen peroxide (H2O2), and N acquisition of white clover over a period of 90 days. Double inoculation of AMF and Rh favored root AMF colonization and nodules compared to single inoculation. AMF colonized roots earlier than the formation of root nodules, with AMF colonized the root nodules after 30 days. H2O2 (a signaling molecule for plant defense against microbial infestation) was increased in roots from day 5 to day 10 following dual inoculation and single AMF inoculation, and from day 10 to day 15 following single Rh inoculation, indicating a pre-response of roots to AMF colonization during the two microbial colonization. At 20 days after inoculation, single or double inoculation of AMF and Rh showed positive effects on leaf and root biomass production and plant height, while improved effects on taproot length began at 15 days of inoculation, along with the improved magnitude most prominently with double inoculation. The earliest effect of significant improvement in leaf N appeared on day 10 of double inoculation, while the improvement in root N started 15 days later, following the prominent effect with double inoculation among three treatments. It is concluded that AMF and Rh could synergistically promote each other’s colonization in roots, thus further enhancing plant growth and N acquisition.

Arbuscular mycorrhizal fungal diversity can be altered by intercropping plant species, as well as N fertilizer applications. This study examined the effects of oat-pea intercropping and N fertilizer addition on the richness and diversity of mycorrhizal species, as well as identified the most common arbuscular mycorrhizal fungi (AMF) genera recruited for oats and peas in two growing seasons (2019 and 2020). The AMF diversity was higher in an intercropped system compared to their respective monocropping system. Under drier conditions in 2019, arbuscular mycorrhizal richness decreased with N fertilizer addition in sole peas and increased with N fertilizer addition in sole oats, but no significant change in richness was observed in oat-pea intercropping. During the wetter growing season 2020, arbuscular mycorrhizal diversity increased when oat and pea were intercropped, compared to either sole oat or sole pea. Diversispora in sole pea was a significant indicator differentiating the root associated AMF community from sole oat. Claroideoglomus richness increased in peas in 2020, thus this genus could be moisture dependent. Paraglomus richness in oat-pea intercropping was similar to sole oat in 2019, and similar to sole pea in 2020. This can suggest that Paraglomus is an indicator of plant stress under intercropping, as based on the premise that stressed plants release more exudates, and the subsequent mycorrhizal associations favor these plants with higher exudation. Future investigations can further reveal the functions and benefits of these mycorrhizal genera in annual monocrop and intercropping systems.

To test direct and indirect effects of glomalin, mycorrhizal hyphae and roots on aggregate stability, perspex pots separated by 37-μm nylon mesh in the middle were used to form root-free hyphae and root/hyphae chambers, where trifoliate orange ( Poncirus trifoliata ) seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in the root/hyphae chamber. Both fungal species induced significantly higher plant growth, root total length, easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) and mean weight diameter (an aggregate stability indicator). The Pearson correlation showed that root colonization or soil hyphal length significantly positively correlated with EE-GRSP, difficultly-extractable GRSP (DE-GRSP), T-GRSP and water-stable aggregates in 2.00–4.00, 0.50–1.00 and 0.25–0.50 mm size fractions. The path analysis indicated that in the root/hyphae chamber, aggregate stability derived from a direct effect of root colonization, EE-GRSP or DE-GRSP. Meanwhile, the direct effect was stronger by EE-GRSP or DE-GRSP than by mycorrhizal colonization. In the root-free hyphae chamber, mycorrhizal-mediated aggregate stability was due to total effect but not direct effect of soil hyphal length, EE-GRSP and T-GRSP. Our results suggest that GRSP among these tested factors may be the primary contributor to aggregate stability in the citrus rhizosphere.

Arbuscular mycorrhizal fungi (AMF) in the roots and soil surrounding their hosts are typically independently investigated and little is known of the relationships between the communities of the two compartments. We simultaneously collected root and surrounding soil samples from Cryptomeria japonica (Cj) and Chamaecyparis obtusa (Co) at three environmentally different sites. Based on molecular and morphological analyses, we characterized their associated AMF communities. Cj was more densely colonized than Co and that root colonization intensity was significantly correlated with soil AMF diversity. The communities comprised 15 AMF genera dominated by Glomus and Paraglomus and 1443 operational taxonomic units (OTUs) of which 1067 and 1170 were in roots and soil, respectively. AMF communities were significantly different among sites, and the root AMF communities were significantly different from those of soil at each site. The root and soil AMF communities responded differently to soil pH. At the genus level, Glomus and Acaulospora were abundant in roots while Paraglomus and Redeckera were abundant in soil. Our findings suggest that AMF colonizing roots are protected from environmental stresses in soil. However, the root-soil-abundant taxa have adapted to both environments and represent a model AMF symbiont. This evidence of strategic exploitation of the rhizosphere by AMF supports prior hypotheses and provides insights into community ecology.

Arbuscular mycorrhizal fungi (AMF) that establish reciprocal symbiosis with plant roots can enhance resistance to various stresses, including salt stress, but relevant mechanisms, especially at the molecular level, are scarce. The objective of this study was to analyze the effect of an arbuscular mycorrhizal fungus Paraglomus occultum on plant growth, leaf gas exchange, and expression of plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs) and salt overly sensitive (SOS) genes in tomato under salt (150 mmol/L NaCl) and non-salt stress. Salt stress for 4 weeks inhibited root colonization rate of P. occultum and soil hyphal length by 0.21- and 0.57-fold, respectively. Salt stress also inhibited plant growth performance and leaf gas exchange, while inoculation with P. occultum significantly enhanced them under salt and non-salt stress conditions. AMF showed diverse regulation of root SlPIPs and SlTIPs expression, among which under salt stress, SlPIP1;2, SlPIP1;5, SlPIP2;1, SlPIP2;6, SlPIP2;9, SlPIP2;10, SlTIP2;2, SlTIP3;2, and SlTIP5;1 were up-regulated by AMF colonization, and SlPIP1;7, SlPIP2;5, SlPIP2;8, SlPIP2;11, SlPIP2;12, SlTIP2;3, and SlTIP3;1 were down-regulated, accompanied by no change in SlPIP1;1, SlPIP1;3, SlPIP2;4, SlTIP1;1, SlTIP1;2, SlTIP1;3, SlTIP2;1, and SlTIP2;5. Interestingly, salt stress inhibited the expression of SlSOS1 and SlSOS2 in non-mycorrhizal plants, while it increased the expression of SlSOS1 and SlSOS2 in mycorrhizal plants. AMF colonization down-regulated expression of SlSOS1 and SlSOS2 under non-salt stress while up-regulated expression of SlSOS1 and SlSOS2 under salt stress. It was concluded that AMF inoculation impacted the expression of stress-responsive genes, especially SOS1 and SOS2, and enhanced salt resistance of tomato.

Glomalin released from arbuscular mycorrhizal fungi (AMF) has important roles in soil nutrient cycles, whereas contributing to glomalin-related soil protein (GRSP) fractions to soil nitrogen (N) is unknown. In this study, a two-chambered root-box that was divided into root chamber (root and mycorrhizal fungi hypha) and hypha chamber (free of the root) was used, and three AMF species including Diversispora epigaea, Paraglomus occultum, and Rhizoglomus intraradices were separately inoculated into the root chamber. Plant growth, soil total N, N content of purified GRSP fractions, and its contribution to soil total N, and leaf and root N contents were analysed. After four months, total biomass and root total length, surface area, and volume were improved by all AMF inoculations. AMF inoculations dramatically increased soil total N content in two chambers. The N content of purified easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) was 0.10 ± 0.01 mg/g and 0.16 ± 0.02 mg/g, respectively, accounted for 15.6 ± 1.6% and 18.1 ± 1.8% of soil total N, respectively. AMF inoculations stimulated the N accumulation in EE-GRSP and DE-GRSP, especially in the hypha chamber. It concluded that GRSP, especially DE-GRSP, acts as a soil N pool accounting for 33.8 ± 1.9% of soil total N in orchards.

Background and aims Variations in root-associated fungal communities contribute to the so-called 'crop rotation benefit' on soil productivity. We assessed the effects of chickpea, lentil, and pea in wheat-based rotations, as compared to wheat monoculture, on the structure of root-associated fungal communities, and described the legacy of pulses on a following wheat crop. Methods The internal transcribed spacer (ITS) and 18S rRNA gene markers, and 454 amplicon pyrosequencing were used to describe the fungal communities of crop roots and rhizosphere soil in a field experiment and agronomic data were collected. Results Pulses influenced only the structure of the nonmycorrhizal fungal community of roots. Fusarium tricinctum, Clonostachys rosea, Fusarium redolens, and Cryptococcus sp. were specific to certain crops. Despite the absence of selective effects of pulses on their associated arbuscular myconhizal (AM) fungal community, pea had a legacy effect on the structure of the AM fungal community associated with the roots of the following wheat crop, in one of the two year/sites examined. Species of Mortierella, Cryptococcus, and Paraglomus in wheat rhizosphere soil may benefit yield, whereas species of Fusarium, Davidiella, Lachnum, Sistotrema and Podospora may reduce yield. Conclusion The effect of pulse crops on root fungal communities varied with rotation crop species. Pulses had various effects on the physiology of the following wheat crop, including increased productivity.

Arbuscular mycorrhizal fungi (AMF) colonize biochar in soils, yet the processes governing their colonization and growth in biochar are not well characterized. Biochar amendment improves soil health by increasing soil carbon, decreasing bulk density, and improving soil water retention, all of which can increase yield and alleviate environmental stress on crops. Biochar is often applied with nutrient addition, impacting mycorrhizal communities. To understand how mycorrhizas explore soils containing biochar, we buried packets of non-activated biochar in root exclusion mesh bags in contrasting agricultural soils. In this greenhouse experiment, with quinoa (Chenopodium quinoa) as the host plant, we tested impacts of mineral nutrient (as manure and fertilizer) and biochar addition on mycorrhizal colonization of biochar. Paraglomus appeared to dominate the biochar packets, and the community of AMF found in the biochar was a subset (12 of 18) of the virtual taxa detected in soil communities. We saw differences in AMF community composition between soils with different edaphic properties, and while nutrient addition shifted those communities, the shifts were inconsistent between soil types and did not significantly influence the observation that Paraglomus appeared to selectively colonize biochar. This observation may reflect differences in AMF traits, with Paraglomus previously identified only in soils (not in roots) pointing to predominately soil exploratory traits. Conversely, the absence of some AMF from the biochar implies either a reduced tendency to explore soils or an ability to avoid recalcitrant nutrient sources. Our results point to a selective colonization of biochar in agricultural soils.