The other side of the coin: systemic effects of Serendipita indica root colonization on development of sedentary plant-parasitic nematodes in Arabidopsis thaliana.

MAIN CONCLUSION: Upon systemic S. indica colonization in split-root system cyst and root-knot nematodes benefit from endophyte-triggered carbon allocation and altered defense responses what significantly facilitates their development in A. thaliana. Serendipita indica is an endophytic fungus that establishes mutualistic relationships with different plants including Arabidopsis thaliana. It enhances host's growth and resistance to different abiotic and biotic stresses such as infestation by the cyst nematode Heterodera schachtii (CN). In this work, we show that S. indica also triggers similar direct reduction in development of the root-knot nematode Meloidogyne javanica (RKN) in A. thaliana. Further, to mimick the natural situation occurring frequently in soil where roots are unequally colonized by endophytes we used an in vitro split-root system with one half of A. thaliana root inoculated with S. indica and the other half infected with CN or RKN, respectively. Interestingly, in contrast to direct effects, systemic effects led to an increase in number of both nematodes. To elucidate this phenomenon, we focused on sugar metabolism and defense responses in systemic non-colonized roots of plants colonized by S. indica. We analyzed the expression of several SUSs and INVs as well as defense-related genes and measured sugar pools. The results show a significant downregulation of PDF1.2 as well as slightly increased sucrose levels in the non-colonized half of the root in three-chamber dish. Thus, we speculate that, in contrast to direct effects, both nematode species benefit from endophyte-triggered carbon allocation and altered defense responses in the systemic part of the root, which promotes their development. With this work, we highlight the complexity of this multilayered tripartite relationship and deliver new insights into sugar metabolism and plant defense responses during S. indica-nematode-plant interaction.

Efficiency of inorganic fungicides against the formation of Erysiphe necator chasmothecia in vineyards.

BACKGROUND: A reduction in chasmothecia, an important inoculum of grape powdery mildew (Erysiphe necator Schwein.), is essential for disease control in vineyards; the use of fungicides during the formation of chasmothecia on vine leaves, late in the growing season, may accomplish this. Inorganic fungicides, such as sulphur, copper, and potassium bicarbonate, are very useful for this purpose because of their multisite mode of action. The aim of this study was to evaluate chasmothecia reduction using different fungicide applications late in the growing season in commercially managed vineyards and in an exact application trial. RESULTS: Chasmothecia on vine leaves were reduced in commercial vineyards by four copper (P = 0.01) and five potassium bicarbonate (P = 0.026) applications. The positive effect of potassium bicarbonate was also confirmed in the application trial, where two applications showed lower chasmothecia numbers than the control (P = 0.002). CONCLUSION: The application of inorganic fungicides reduced the amount of chasmothecia as the primary inoculum source. Potassium bicarbonate and copper are of further interest for disease control as these fungicides can be used by organic and conventional wine growers. The application of these fungicides should be carried out as late as possible before harvest to reduce chasmothecia formation and, consequently, the potential for powdery mildew infestation in the subsequent season. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Improvement in the sensitivity of viroid detection by adapting the reverse transcription step in one-step RT-qPCR assays.

Over the course of developing and applying a new real-time PCR assay for the detection of the newly described apple chlorotic fruit spot viroid (ACFSVd), slight modifications of the reverse transcription (RT) step were found to improve significantly the detection limit of the assay. To prove this hypothesis, three different one-step RT-qPCR kits for the detection of three plant viroids and three plant viruses were compared. The results showed both extension of the RT reaction time from 10 or 15 min-30 min or the increase in reaction temperature from 49 to 52 °C for the cDNA synthesis step results in a 10 times higher sensitivity for potato spindle tuber viroid and apple scar skin viroid one-step RT-qPCR assay and 45 higher sensitivity for ACFSVd one-step RT-qPCR assay. No variation in the detection limit was observed when the modifications were tested on tomato brown rugose fruit virus, plum pox virus and tomato ringspot virus assays. This finding is highly valuable for the investigation of viroids in general and could contribute to enhance sensitivity in their detection and to benefit regulatory outcomes for national plant protection organisations.

Serendipita indica changes host sugar and defense status in Arabidopsis thaliana: cooperation or exploitation?

MAIN CONCLUSION: Manipulation of sugar metabolism upon S. indica root colonization triggers changes in sugar pools and defense responses in A. thaliana. Serendipita indica is an endophytic fungus that establishes mutualistic relationships with many different plants including important crops as well as the model plant A. thaliana. Successful root colonization typically results in growth promotion and enhanced tolerance against various biotic and abiotic stresses. The fungus delivers phosphorus to the host and receives in exchange carbohydrates. There are hints that S. indica prefers hexoses, glucose, and fructose, products of saccharose cleavage driven by invertases (INVs) and sucrose synthases (SUSs). Carbohydrate metabolism in this interaction, however, remains still widely unexplored. Therefore, in this work, the sugar pools as well as the expression of SUSs and cytosolic INVs in plants colonized by S. indica were analyzed. Using sus1/2/3/4 and cinv1/2 mutants the importance of these genes for the induction of growth promotion and proper root colonization was demonstrated. Furthermore, the expression of several defense-related marker genes in both multiple mutants in comparison to the wild-type plants was determined. Our results show that in colonized A. thaliana plants S. indica manipulates the sugar metabolism by altering the expression of host's INV and SUS and modulates both the sugar pools and plant defense in its favor. We conclude that the interaction A. thaliana-S. indica is a balancing act between cooperation and exploitation, in which sugar metabolism plays a crucial role. Small changes in this mechanism can lead to severe disruption resulting in the lack of growth promotion or altered colonization rate.

Proteomic Analysis Reveals the Importance of Exudates on Sclerotial Development in Sclerotinia sclerotiorum.

Sclerotinia sclerotiorum is a ubiquitous necrotrophic pathogenic fungus causing significant losses in a broad range of plant species. Sclerotia formed by S. sclerotiorum play important roles in both the fungal life cycle and the disease development cycle. Sclerotial exudation during sclerotial development is a characteristic feature of this fungus. In this study, a proteome-level investigation of proteins present in sclerotial exudates was conducted by high-throughput LC-MS/MS analysis. A total of 258 proteins were identified, in which 193 were annotated by GO annotation and 54 were classified by KEGG analysis. Four proteins related to plant cell wall degradation were further validated by measuring the corresponding enzymatic activity of the sclerotial exudates and/or by assessing the gene expression during sclerotial development. Results indicated that the proteins identified in sclerotial exudates help in the development of sclerotia and contribute to host cell necrosis caused by S. sclerotiorum. Furthermore, we proposed that sclerotial exudates can degrade plant cell walls to release carbohydrates that provide nutrition for fungal growth and possibly facilitate fungal cell wall assembly in developing sclerotia. This study also provides new insights on the morphogenesis and pathogenicity of other sclerotia-forming fungi.

The Fungal Endophyte Serendipita williamsii Does Not Affect Phosphorus Status but Carbon and Nitrogen Dynamics in Arbuscular Mycorrhizal Tomato Plants.

Some members of the root endophytic Serendipitaceae were observed to frequently coexist with arbuscular mycorrhizal fungi (AMF), but their interactions and potential synergistic effects in plants have not yet been well elucidated. Here, we inoculated three-week-old tomato seedlings with Serendipita indica or Serendipita williamsii alone or in combination with the arbuscular mycorrhizal fungus Funneliformis mosseae and cultivated the plants in a greenhouse until the late vegetative stage. Our data show that the simultaneous presence of Serendipita spp. did not affect root colonization by AMF, proving the feasibility of their combination for future agronomic uses. The photosynthetic performance was enhanced in AM tomato plants, although growth remained unresponsive following single or dual inoculation with Serendipita spp. and AMF. With regard to nutrient status under dual inoculation, AMF-induced phosphorus increases remained unaffected, but nitrogen and carbon dynamics were highly altered. Specifically, the application of S. williamsii to mycorrhizal tomato plants significantly enhanced nitrogen concentration in the shoots, but this effect was also compensated with a carbon cost. Our findings indicate that S. williamsii performs differently from S. indica when co-inoculated with AMF, and this suggests an unknown mechanism that needs more detailed investigation.

Correction to: Transmission studies of the newly described apple chlorotic fruit spot viroid using a combined RT-qPCR and droplet digital PCR approach.

Authors would like to update the given name and family name of authors which were incorrect in the original version.

Transmission studies of the newly described apple chlorotic fruit spot viroid using a combined RT-qPCR and droplet digital PCR approach.

The transmission of the apscaviroid tentatively named apple chlorotic fruit spot viroid (ACFSVd) was investigated using a one-step reverse-transcription (RT) droplet digital PCR assay for absolute quantification of the viroid, followed by quantification of relative standard curves by RT-qPCR. Our results indicate that ACFSVd is effectively transmitted by grafting, budding and seeds. No transmission has yet been observed to the viroid-inoculated pome fruit species Pyrus sp. and Cydonia sp. ACFSVd was detected in viruliferous aphids (Myzus persicae, Dysaphis plantaginea) and in codling moths (Cydia pomonella). The viroid was also detected systemically in the infected hemiparasitic plant Viscum album subsp. album (mistletoe).

Identification and characterization of Colletotrichum destructivum causing anthracnose on sunflower.

Sunflower is one of the most economically important oil crops. Recently, sunflower anthracnose caused by Colletotrichum destructivum was reported and suggested to be a potential threat to the quality of oil and edible seeds derived from sunflower in the field and even on the ornamentals in the residential gardens. Colletotrichum destructivum, as the causal agent of sunflower anthracnose, has been rarely studied. In this study, the vegetative growth and sporulation of this fungal species were investigated by assessing the requirements of nutrition and other environmental conditions, such as temperature, ambient pH, and lightness regime. Additionally, the sensitivity of C. destructivum to several fungicides was assessed. The results will provide a baseline for better understanding of the biology and etiology of C. destructivum. This study will be the first reference for a sustainable management strategy according to the occurrence and prevalence of the sunflower anthracnose.

Serendipita Species Trigger Cultivar-Specific Responses to Fusarium Wilt in Tomato.

The endophytic fungi Serendipita indica and S. vermifera have recently gained increasing attention due to their beneficial effects on plant growth and plant health. Little is known about other species, such as S. williamsii and S. herbamans. To test their biocontrol and growth-promoting potential, susceptible and tolerant tomato cultivars (Kremser Perle and Micro-Tom, respectively) were inoculated with S. williamsii, S. herbamans, S. indica, or S. vermifera and challenged with the soilborne pathogen Fusarium oxysporum f. sp. lycopersici (Fol) in greenhouse experiments. Furthermore, in vitro assays on the direct inhibitory effects of Serendipita spp. against Fol were performed. Negative effects of Fol on phenological growth in the susceptible cultivar were alleviated by all four applied Serendipita spp. Apart from these similar effects on biometric parameters, disease incidence was only reduced by S. herbamans and S. vermifera. In the tolerant cultivar, disease parameters remained unaffected although shoot dry mass was negatively affected by S. vermifera. Direct effects of Serendipita spp. against Fol were not evident in the in vitro assays indicating an indirect effect via the host plant. Our results highlight the importance of identifying cultivar-specific effects in pathogen-endophyte-plant interactions to determine the most beneficial combinations.

Apple chlorotic fruit spot viroid: a putative new pathogenic viroid on apple characterized by next-generation sequencing.

Viroid-like symptoms were observed in 2016 on apple fruits of the cultivar "Ilzer Rose" in southern Burgenland, Austria. Preliminary molecular biological investigations indicated that the symptoms were caused by a new unknown viroid. Therefore, new primers were designed, and the whole genome sequence of the viroid (354 nt) was determined by next-generation amplicon sequencing using the Illumina MiSeq® platform (San Diego, California, USA). The viroid secondary structure has a rod-like conformation and contains conserved regions (the TCR, CCR upper strand, and CCR lower strand) that are characteristic of members of the genus Apscaviroid. Based on our results and the demarcation criteria for viroids, the tentatively named "apple chlorotic fruit spot viroid" should be considered a putative new member of the genus Apscaviroid.

Arbuscular mycorrhizal fungi and their response to pesticides.

Arbuscular mycorrhizal fungi (AMF) form symbioses with the majority of plant species and can provide multiple benefits to the host plant. In agro-ecosystems, the abundance and community structure of AMF are affected by agricultural management practices. This review describes and discusses current knowledge on the effects of inorganic and organic chemical pesticides on AMF in the conflicting area between agricultural use and environmental concerns. Variable effects have been reported following chemical pesticide use, ranging from neutral to positive and negative. Moreover, a species-specific reaction has been documented. The reported effects of pesticides on arbuscular mycorrhizal symbiosis are very diverse, and even when the same substance is investigated, the results are often contradictory. These effects depend on many parameters, such as the active substance, the mode of action, the mode of application and the dosage. In the field, determinants such as the physico-chemical behavior of the active substances, the soil type and other soil microorganisms contribute to the fate of pesticides and thus the amount of active substances to which AMF are exposed. This review highlights that the fate of AMF following pesticide use needs to be addressed in a broader agro-ecosystem context. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Deficiency of the melanin biosynthesis genes SCD1 and THR1 affects sclerotial development and vegetative growth, but not pathogenicity, in Sclerotinia sclerotiorum.

The fungus Sclerotinia sclerotiorum is a necrotrophic plant pathogen causing significant damage on a broad range of crops. This fungus produces sclerotia that serve as the long-term survival structures in the life cycle and the primary inoculum in the disease cycle. Melanin plays an important role in protecting mycelia and sclerotia from ultraviolet radiation and other adverse environmental conditions. In this study, two genes, SCD1 encoding a scytalone dehydratase and THR1 encoding a trihydroxynaphthalene reductase, were disrupted by target gene replacement, and their roles in mycelial growth, sclerotial development and fungal pathogenicity were investigated. Phylogenetic analyses indicated that the deduced amino acid sequences of SCD1 and THR1 were similar to the orthologues of Botrytis cinerea. Expression of SCD1 was at higher levels in sclerotia relative to mycelia. THR1 was expressed at similar levels in mycelia and sclerotia at early stages, but was up-regulated in sclerotia at the maturation stage. Disruption of SCD1 or THR1 did not change the pathogenicity of the fungus, but resulted in slower radial growth, less biomass, wider angled hyphal branches, impaired sclerotial development and decreased resistance to ultraviolet light.

Compost and biochar alter mycorrhization, tomato root exudation, and development of Fusarium oxysporum f. sp. lycopersici.

Soil amendments like compost and biochar are known to affect soil properties, plant growth as well as soil borne plant pathogens. Complex interactions based on microbial activity and abiotic characteristics are supposed to be responsible for suppressive properties of certain substrates, however, the specific mechanisms of action are still widely unknown. In the present study, the main focus was on the development of the soil borne pathogen, Fusarium oxysporum f.sp. lycopersici (Fol) in tomato (Solanum lycopersicum L.) and changes in root exudates of tomato plants grown in different soil substrate compositions, such as compost (Comp) alone at application rate of 20% (v/v), and in combination with wood biochar (WB; made from beech wood chips) or green waste biochar (GWB; made from garden waste residues) at application rate of 3% (v/v), and/or with additional arbuscular mycorrhizal fungi (AMF). The association of GWB and AMF had a positive effect on tomato plants growth unlike to the plants grown in WB containing a soil substrate. The AMF root colonization was not enhanced by the addition of WB or GWB in the soil substrate, though a bio-protective effect of mycorrhization was evident in both biochar amended treatments against Fol. Compost and biochars altered root exudates differently, which is evident from variable response of in vitro growth and development of Fol. The microconidia germination was highest in root exudates from plants grown in the soil containing compost and GWB, whereas root exudates of plants from a substrate containing WB suppressed the mycelial growth and development of Fol. In conclusion, the plant growth response and disease suppression in biochar containing substrates with additional AMF was affected by the feedstock type. Moreover, application of compost and biochars in the soil influence the quality and composition of root exudates with respect to their effects on soil-dwelling fungi.

The intercropping partner affects arbuscular mycorrhizal fungi and Fusarium oxysporum f. sp. lycopersici interactions in tomato.

Arbuscular mycorrhizal fungi (AMF) and their bioprotective aspects are of great interest in the context of sustainable agriculture. Combining the benefits of AMF with the utilisation of plant species diversity shows great promise for the management of plant diseases in environmentally compatible agriculture. In the present study, AMF were tested against Fusarium oxysporum f. sp. lycopersici with tomato intercropped with either leek, cucumber, basil, fennel or tomato itself. Arbuscular mycorrhizal (AM) root colonisation of tomato was clearly affected by its intercropping partners. Tomato intercropped with leek showed even a 20 % higher AM colonisation rate than tomato intercropped with tomato. Positive effects of AMF expressed as an increase of tomato biomass compared to the untreated control treatment could be observed in root as well as in shoot weights. A compensation of negative effects of F. oxysporum f. sp. lycopersici on tomato biomass by AMF was observed in the tomato/leek combination. The intercropping partners leek, cucumber, basil and tomato had no effect on F. oxysporum f. sp. lycopersici disease incidence or disease severity indicating no allelopathic suppression; however, tomato co-cultivated with tomato clearly showed a negative effect on one plant/pot with regard to biomass and disease severity of F. oxysporum f. sp. lycopersici. Nonetheless, bioprotective effects of AMF resulting in the decrease of F. oxysporum f. sp. lycopersici disease severity were evident in treatments with AMF and F. oxysporum f. sp. lycopersici co-inoculation. However, these bioprotective effects depended on the intercropping partner since these effects were only observed in the tomato/leek and tomato/basil combination and for the better developed plant of tomato/tomato. In conclusion, the effects of the intercropping partner on AMF colonisation of tomato are of great interest for crop plant communities and for the influences on each other. The outcome of the bioprotective effects of AMF resulting in the decrease on F. oxysporum f. sp. lycopersici disease severity and/or compensation of plant biomass does not depend on the degree of AM colonisation but more on the intercropping partner.

A comparison of wild-type, old and modern tomato cultivars in the interaction with the arbuscular mycorrhizal fungus Glomus mosseae and the tomato pathogen Fusarium oxysporum f. sp. lycopersici.

The effect of the arbuscular mycorrhizal symbiosis (AM) varies in plant cultivars. In the present study, we tested whether wild-type, old and modern tomato cultivars differ in the parameters of the AM interaction. Moreover, the bioprotective effect of AM against the soilborne tomato pathogen Fusarium oxysporum f. sp. lycopersici (Fol) was tested in the different cultivars. Ten tomato cultivars were inoculated with the arbuscular mycorrhizal fungus (AMF) Glomus mosseae alone or in combination with Fol. At the end of the experiment, AM root colonization, Fusarium infection, and the plant fresh weight was determined. The tomato cultivars differed in their susceptibility to AMF and Fol, but these differences were not cultivar age dependent. In all the cultivars affected by Fol, mycorrhization showed a bioprotective effect. Independent of the cultivar age, tomato cultivars differ in their susceptibility to AMF and Fol and the bioprotective effect of mycorrhization, indicating that the cultivar age does not affect the AM parameters tested in this study.

The Rhizobium sp. strain NGR234 systemically suppresses arbuscular mycorrhizal root colonization in a split-root system of barley (Hordeum vulgare).

Nitrogen-fixing bacteria (rhizobia) form a nodule symbiosis with legumes, but also induce certain effects on non-host plants. Here, we used a split-root system of barley to examine whether inoculation with Rhizobium sp. strain NGR234 on one side of a split-root system systemically affects arbuscular mycorrhizal (AM) root colonization on the other side. Mutant strains of NGR234 deficient in Nod factor production (strain NGRΔnodABC), perception of flavonoids (strain NGRΔnodD1) and secretion of type 3 effector proteins (strain NGRΩrhcN) were included in this study. Inoculation resulted in a systemic reduction of AM root colonization with all tested strains. However, the suppressive effect of strain NGRΩrhcN was less pronounced. Moreover, levels of salicylic acid, an endogenous molecule related to plant defense, were increased in roots challenged with rhizobia. These data indicate that barley roots perceived NGR234 and that a systemic regulatory mechanism of AM root colonization was activated. The suppressive effect appears to be Nod factor independent, but enhanced by type 3 effector proteins of NGR234.

Root colonization by symbiotic arbuscular mycorrhizal fungi increases sesquiterpenic acid concentrations in Valeriana officinalis L.

In some medicinal plants a specific plant-fungus association, known as arbuscular mycorrhizal (AM) symbiosis, increases the levels of secondary plant metabolites and/or plant growth. In this study, the effects of three different AM treatments on biomass and sesquiterpenic acid concentrations in two IN VITRO propagated genotypes of valerian ( VALERIANA OFFICINALIS L., Valerianaceae) were investigated. Valerenic, acetoxyvalerenic and hydroxyvalerenic acid levels were analyzed in the rhizome and in two root fractions. Two of the AM treatments significantly increased the levels of sesquiterpenic acids in the underground parts of valerian. These treatments, however, influenced the biomass of rhizomes and roots negatively. Therefore this observed increase was not accompanied by an increase in yield of sesquiterpenic acids per plant. Furthermore, one of the two genotypes had remarkably high hydroxyvalerenic acid contents and can be regarded as a hydroxyvalerenic acid chemotype.

Flavonoids and strigolactones in root exudates as signals in symbiotic and pathogenic plant-fungus interactions.

Secondary plant compounds are important signals in several symbiotic and pathogenic plant-microbe interactions. The present review is limited to two groups of secondary plant compounds, flavonoids and strigolactones, which have been reported in root exudates. Data on flavonoids as signaling compounds are available from several symbiotic and pathogenic plant-microbe interactions, whereas only recently initial data on the role of strigolactones as plant signals in the arbuscular mycorrhizal symbiosis have been reported. Data from other plant-microbe interactions and strigolactones are not available yet. In the present article we are focusing on flavonoids in plant-fungal interactions such as the arbuscular mycorrhizal (AM) association and the signaling between different Fusarium species and plants. Moreover the role of strigolactones in the AM association is discussed and new data on the effect of strigolactones on fungi, apart from arbuscular mycorrhizal fungi (AMF), are provided.

Abscisic acid determines arbuscule development and functionality in the tomato arbuscular mycorrhiza.

The role of abscisic acid (ABA) during the establishment of the arbuscular mycorrhiza (AM) was studied using ABA sitiens tomato (Lycopersicon esculentum) mutants with reduced ABA concentrations. Sitiens plants and wild-type (WT) plants were colonized by Glomus intraradices. Trypan blue and alkaline phosphatase histochemical staining procedures were used to determine both root colonization and fungal efficiency. Exogenous ABA and silver thiosulfate (STS) were applied to establish the role of ABA and putative antagonistic cross-talk between ABA and ethylene during AM formation, respectively. Sitiens plants were less susceptible to the AM fungus than WT plants. Microscopic observations and arbuscule quantification showed differences in arbuscule morphology between WT and sitiens plants. Both ABA and STS increased susceptibility to the AM fungus in WT and sitiens plants. Fungal alkaline phosphate activity in sitiens mutants was completely restored by ABA application. * The results demonstrate that ABA contributes to the susceptibility of tomato to infection by AM fungi, and that it seems to play an important role in the development of the complete arbuscule and its functionality. Ethylene perception is crucial to AM regulation, and the impairment of mycorrhiza development in ABA-deficient plants is at least partly attributable to ethylene.