Facilitative and competitive interactions between mycorrhizal and nonmycorrhizal plants in an extremely phosphorus-impoverished environment: role of ectomycorrhizal fungi and native oomycete pathogens in shaping species coexistence.

Nonmycorrhizal cluster root-forming species enhance the phosphorus (P) acquisition of mycorrhizal neighbours in P-impoverished megadiverse systems. However, whether mycorrhizal plants facilitate the defence of nonmycorrhizal plants against soil-borne pathogens, in return and via their symbiosis, remains unknown. We characterised growth and defence-related compounds in Banksia menziesii (nonmycorrhizal) and Eucalyptus todtiana (ectomycorrhizal, ECM) seedlings grown either in monoculture or mixture in a multifactorial glasshouse experiment involving ECM fungi and native oomycete pathogens. Roots of B. menziesii had higher levels of phytohormones (salicylic and jasmonic acids, jasmonoyl-isoleucine and 12-oxo-phytodienoic acid) than E. todtiana which further activated a salicylic acid-mediated defence response in roots of B. menziesii, but only in the presence of ECM fungi. We also found that B. menziesii induced a shift in the defence strategy of E. todtiana, from defence-related secondary metabolites (phenolic and flavonoid) towards induced phytohormone response pathways. We conclude that ECM fungi play a vital role in the interactions between mycorrhizal and nonmycorrhizal plants in a severely P-impoverished environment, by introducing a competitive component within the facilitation interaction between the two plant species with contrasting nutrient-acquisition strategies. This study sheds light on the interplay between beneficial and detrimental soil microbes that shape plant-plant interaction in severely nutrient-impoverished ecosystems.

Grapevine Stimulation: A Multidisciplinary Approach to Investigate the Effects of Biostimulants and a Plant Defense Stimulator.

The increasing use of plant defense stimulators (PDS) and biostimulants (BS) to make agriculture more sustainable has led to questions about their action on plants. A new PhysBioGen approach is proposed with complementary tools: PHYSiological (root weight); BIOchemical and BIOlogical (secondary metabolite quantification and Plasmopara viticola development) and expressions of 161 GENes involved in metabolic plant functions. The proposed approach investigated the effects of three phytostimulants on Vitis vinifera: one PDS (ASM) and one BS chelated (CH) and another enriched with seaweed (SW). Distinct responses were obtained between the PDS and the two BS. In particular, we observed the persistence of anti-mildew efficacy over time, correlated with differentiated expressions of defense genes (VvROMT, VvSAMT, VvPR8). As expected, the two BS displayed more similarities to each other than to the PDS (flavonols, anthocyanins, free salicylic acid). However, the two BS revealed differences in the modulation of genes involved in defense and primary metabolism and some genes were identified as potential markers of their action (VvWRKY1, VvLOX9, VvPOD, VvPDV1, VvXIP1, VVDnaJ). Our results highlight the common and the specific effects of the two BS and the PDS. These new tools could help in understanding the mode of action of phytostimulants in order to achieve better quality and production yield and/or as a way to limit chemical inputs in the vineyard.

Vineyard evaluation of stilbenoid-rich grape cane extracts against downy mildew: a large-scale study.

BACKGROUND: Plasmopara viticola control in organic viticulture requires copper-based fungicides with harmful effects on health and the environment. Plant extracts represent a biorational eco-friendly alternative to copper. The aim of this study was to evaluate the potential of stilbenoid-rich grape cane extract (GCE) against downy mildew on three cultivars over 3 years following natural downy mildew infection. RESULTS: Over all field trials, GCE treatments showed an average reduction in disease incidence of -35% and -38% on leaves and clusters, respectively. The average reduction in disease severity was -35% and -43% on leaves and clusters, respectively. Under artificial downy mildew infection, GCE efficacy corresponded to 1 g L-1 of copper. Neither phytotoxicity nor adverse effects on auxiliary fauna were observed after treatment with GCE. CONCLUSION: Because few or no biocontrol agents are active alone against P. viticola, GCE is a promising alternative to copper-based fungicides. Grape canes, an abundant by-product of viticulture, have great potential for valorization as a biocontrol agent for sustainable viticulture. © 2018 Society of Chemical Industry.

Control of downy mildew (Pseudoperonospora cubensis) of greenhouse grown cucumbers with alternative biological agents.

In organic cucumber production infection with downy mildew (Pseudoperonospora cubensis) is a major problem. Plant extracts from Glycyrrhiza glabra L. (licorice), a plant belonging to the family Fabaceae, and Salvia officinalis (sage) as well as cultures of the bacterium Aneurinibacillus migulanus were investigated for efficacy of disease control under commercial growing conditions. Contrary to bioassays, where sage extract and the microorganism showed highest activity, in the trials of 2008 G. glabra extract was more effective than sage extract or A. migulanus against P. cubensis. Parameters such as concentrations of the preparations or application intervals could have been the reason for this. In the following year's trial (2009) the concentration of these agents was therefore increased somewhat and plants were either treated in seven day application intervals or in ten day application intervals. In the semi-commercial trials of 2009 all alternative biological agents showed good efficacies up to around 80% against infection with downy mildew. The application interval seemed to have a marginal effect only. Again, the licorice extract tended to be the best agent.

NMR metabolic fingerprinting based identification of grapevine metabolites associated with downy mildew resistance.

Grapevine (Vitis vinifera ssp. vinifera L.) and grapes have been extensively studied due to their numerous nutritional benefits and health affecting activities. In this study, metabolite fingerprinting of crude leaf extracts, based on (1)H nuclear magnetic resonance (NMR) spectroscopy and multivariate data analyses, has been used for the metabolic characterization of six different grapevine cultivars including downy and powdery mildew resistant 'Regent' and susceptible 'Lemberger' among others. Several two-dimensional (2D)-NMR techniques were also employed leading to the identification of a number of different types of compounds. Principal component analysis (PCA), hierarchical cluster analysis (HCA), and partial least-squares-discriminant analysis (PLS-DA) of the processed (1)H NMR data revealed clear differences among the cultivars. Metabolites responsible for the discrimination in different grapevine cultivars belong to major classes, that is, organic acids, amino acids, carbohydrates, phenylpropanoids and flavonoids. A differentiation of the cultivars based on their resistance to downy mildew infection was also achieved, and metabolites associated with this trait, namely, quercetin-3-O-glucoside and a trans-feruloyl derivative, were identified. On the basis of these results, the distribution of different plant metabolites among the different grapevine cultivars is presented.

Biomarkers for the prediction of the resistance and susceptibility of grapevine leaves to downy mildew.

We examined metabolic profiles of acetone and butanol extracts obtained from the leaves of 18 seedlings of the Bulgarian wine-making cultivar Storgozia. The acetone extracts contained the components from the leaf surface, while the butanol extracts were enriched with polar components from inside the leaf tissue. The leaves displayed different degrees of resistance and susceptibility to the etiological agent downy mildew, Plasmopara viticola. Based on the statistically significant correlations (P<0.05) between the GC-MS data of the identified metabolites and the estimated leaf resistances, 10 individual components were proposed as possible biomarkers for the downy mildew resistance and susceptibility in grapevine. All were found in the butanol extracts, and can be considered to form two groups: compounds with high correlations (r=+/-0.50 to +/-1.00) - 3-hydroxybutanoic acid, 2,3,4-trihydroxybutanoic acid, 2,3,4-trihydroxybutanoic acid (isomer), hexadecanoic acid, 3-hydroxyhexanoic acid and myo-inositol, and compounds with moderate correlations (r=+/-0.30 to +/-0.49) hydroxybutanedioic acid, alanine, glutamine, arabinoic acid and aldohexoses. Among them, the more polar compounds were related to sensitivity, and only hexadecanoic and the monohydroxycarboxylic acids were related to resistance in grapevine.

The problem of how fungal and oomycete avirulence proteins enter plant cells.

Recent advances in cloning avirulence genes from a rust fungus and three oomycete species have provided the novel insight that these eukaryotic plant pathogens deliver small proteins into the host cell cytoplasm where they are recognized by resistance proteins. Anne Rehmany et al. have recently identified a potential host-targeting signal in oomycete avirulence proteins from Hyaloperonospora parasitica, Phytophthora sojae and Phytophthora infestans that might be involved in transporting proteins into the host cell. This signal is surprisingly similar to the host targeting signal used by the malaria pathogen Plasmodium fulciparum to target virulence proteins to the mammalian host cell.

Suppression of damping-off disease in host plants by the rhizoplane bacterium Lysobacter sp. strain SB-K88 is linked to plant colonization and antibiosis against soilborne Peronosporomycetes.

We previously demonstrated that xanthobaccin A from the rhizoplane bacterium Lysobacter sp. strain SB-K88 suppresses damping-off disease caused by Pythium sp. in sugar beet. In this study we focused on modes of Lysobacter sp. strain SB-K88 root colonization and antibiosis of the bacterium against Aphanomyces cochlioides, a pathogen of damping-off disease. Scanning electron microscopic analysis of 2-week-old sugar beet seedlings from seeds previously inoculated with SB-K88 revealed dense colonization on the root surfaces and a characteristic perpendicular pattern of Lysobacter colonization possibly generated via development of polar, brush-like fimbriae. In colonized regions a semitransparent film apparently enveloping the root and microcolonies were observed on the root surface. This Lysobacter strain also efficiently colonized the roots of several plants, including spinach, tomato, Arabidopsis thaliana, and Amaranthus gangeticus. Plants grown from both sugar beet and spinach seeds that were previously treated with Lysobacter sp. strain SB-K88 displayed significant resistance to the damping-off disease triggered by A. cochlioides. Interestingly, zoospores of A. cochlioides became immotile within 1 min after exposure to a SB-K88 cell suspension, a cell-free supernatant of SB-K88, or pure xanthobaccin A (MIC, 0.01 microg/ml). In all cases, lysis followed within 30 min in the presence of the inhibiting factor(s). Our data indicate that Lysobacter sp. strain SB-K88 has a direct inhibitory effect on A. cochlioides, suppressing damping-off disease. Furthermore, this inhibitory effect of Lysobacter sp. strain SB-K88 is likely due to a combination of antibiosis and characteristic biofilm formation at the rhizoplane of the host plant.

Nicotinamide and structurally related compounds show halting activity against zoospores of the phytopathogenic fungus Aphanomyces cochlioides.

In a survey of plant secondary metabolites regulating the behavior of phytopathogenic Aphanomyces cochlioides zoospores, we found that leaf extracts of Amaranthus gangeticus and cotyledon extracts of pea (Pisum sativum) remarkably halted the motility of zoospores. Bioassay-directed fractionation of A. gangeticus and pea constituents revealed that the halting activity was dependent on a single chemical factor (halting factor). The active principle was identified as nicotinamide (1) by comparing its biological activity and spectroscopic properties with those of the authentic compound. Nicotinamide (1) showed potent halting activity toward the zoospores of A. cochlioides and A. euteiches, but it exhibited very less activity against other Oomycetes, Pythium aphanidermatum and Phytophthora infestans zoospores. Interestingly, the zoospores halted by nicotinamide (1) encysted within 10-15 min and then the resulting cystospores regenerated zoospores instead of germination. Nicotinamide (1) and related compounds were subjected to the halting activity bioassay to elucidate the structure-activity relationships. These bioassays revealed that part structures of (A) the aromatic ring containing at least one nitrogen atom, (B) carbonyl-like group adjacent to the aromatic ring and (C) hydrogen atoms on the amide group are responsible for the strong activity. So far, this is the first report of halting activity of nicotinamide (1) against fungal zoospores.

A Saprolegnia parasitica challenge system for rainbow trout: assessment of Pyceze as an anti-fungal agent for both fish and ova.

A reproducible Saprolegnia parasitica spore delivery system was developed and demonstrated to be effective in providing a sustained spore challenge for up to 10 d. Treatment of rainbow trout with slow-release intraperitoneal implants containing cortisol resulted in chronically elevated blood cortisol levels and rendered the fish susceptible to infection by S. parasitica when exposed to the spore challenge. Sham-implanted fish were not susceptible to infection. Bronopol (2-bromo-2-nitro-propane-1,3-diol), formulated as Pyceze, was effective in protecting predisposed fish from infection by S. parasitica when administered as a daily bath/flush treatment at concentrations of 15 mg l-1 and greater. Pyceze was also demonstrated to protect fertilised rainbow trout ova from S. parasitica challenge when administered as a daily bath/flush treatment at concentrations of between 30 and 100 mg l-1. Pyceze appears to qualify as a safe and effective replacement for malachite green and formalin in the prevention of fungal infections in the aquaculture environment.

Geographical spread of bacterial and fungal diseases of crustaceans.

The author discusses the way in which bacterial and fungal diseases of crustaceans can be and have been transmitted via commercial movements of stocks. Two classic examples of such diseases are presented, namely gaffkaemia (a bacterial disease of marine lobsters) and crayfish plague (a fungal disease of freshwater crayfish). In both cases, there is ample evidence that much of the disease spread can be linked to the commercial movement of infected animals caught from infected wild stocks and transported over large distances for wholesale and retail. In the case of crayfish plague, much of the relentless spread of this disease through Europe for nearly 140 years can also be liked to the movement of contaminated fishing equipment without disinfection.