Plant health status effects on arbuscular mycorrhizal fungi associated with Lavandula angustifolia and Lavandula intermedia infected by Phytoplasma in France.

We investigated root communities of arbuscular mycorrhizal fungi (AMF) in relation to lavender (Lavandula angustifolia) and lavandin (Lavandula intermedia) health status from organic and conventional fields affected by Phytoplasma infection. The intensity of root mycorrhizal colonization was significantly different between diseased and healthy plants and was higher in the latter regardless of agricultural practice. This difference was more pronounced in lavender. The root AMF diversity was influenced by the plant health status solely in lavender and only under the conventional practice resulting in an increase in the AMF abundance and richness. The plant health status did not influence the distribution of root AMF communities in lavandin unlike its strong impact in lavender in both agricultural practices. Finally, among the most abundant molecular operational taxonomic units (MOTUs), four different MOTUs for each plant species were significantly abundant in the roots of healthy lavender and lavandin in either agricultural practice. Our study demonstrated that the plant health status influences root colonization and can influence the diversity and distribution of root AMF communities. Its effects vary according to plant species, can be modified by agricultural practices and allow plants to establish symbiosis with specific AMF species.

[Protection by some plant methanol extracts of cherry tomatoes (Solanum lycopersicum var. Cerasiforme) from fungic infection by Alternaria alternata]. / Utilisation d'extraits méthanoliques de plantes pour la protection des cultures de tomates-cerises (Solanum lycopersicum var. cerasiforme) contre l'infection fongique par Alternaria alternata.

Cherry tomato is very susceptible to fungal infections that can cause considerable damage in crops and during storage. Alternaria infection is one of the most common and dangerous alterations for this fruit. They are caused by Alternaria alternata or some other species belonging to the same genus. In this work, we tested the antifungal activity of methanol extracts from five plants harvested in the region of Jijel (Algeria) on A. alternata. The activity was first tested in vitro and then on greenhouse cherry tomato plants: extracts were applied to healthy plants before infection in order to test their preventive action, and after infection to determine whether they are able to knock out Alternaria. Results showed that Rosmarinus officinalis and Lavandula angustifolia extracts were the most active in vitro on A. alternata. Microscopic observations of the mold indicated that these extracts inhibited the dictyospores production. The antifungal activity tested on the plants grown in greenhouse revealed that R. officinalis extract still was the most active. Extracts of L. angustifolia and Punica granatum did not protect the plants from Alternaria infection, but provided a total cure at the end of the treatment. Extracts from Quercus suber and Eucalyptus globulus were the least active. They did not bestow any protection nor complete healing of the plants. Dictyospores counting on fruits at the end of the treatment confirmed the results obtained for the greenhouse crops.

TITLE: Utilisation d'extraits méthanoliques de plantes pour la protection des cultures de tomates-cerises (Solanum lycopersicum var. cerasiforme) contre l'infection fongique par Alternaria alternata. ABSTRACT: La tomate-cerise est un fruit très sujet aux infections fongiques qui peuvent causer des dégâts considérables dans les cultures et lors de la conservation. Les alternarioses comptent parmi les altérations les plus répandues et dangereuses pour ce fruit. Elles sont causées par Alternaria alternata ou d'autres espèces appartenant au même genre. Dans ce travail, nous avons testé l'activité antifongique d'extraits méthanoliques de cinq plantes récoltées dans la région de Jijel (Algérie) sur A. alternata. L'activité a d'abord été testée in vitro, puis sur des plants de tomates-cerises cultivés sous serre : les extraits ont été appliqués sur des plants sains, avant l'infection, afin de tester leur action préventive, et après l'infection pour déterminer s'ils sont capables de traiter l'alternariose. Les résultats ont montré que les extraits de Rosmarinus officinalis et Lavandula angustifolia étaient les plus actifs in vitro sur A. alternata. L'observation microscopique de la moisissure a indiqué que ces extraits agissaient en inhibant sa production de dictyospores. L'activité antifongique testée sur les plants cultivés sous serre a révélé que l'extrait de R. officinalis était toujours le plus actif. Venaient ensuite les extraits de L. angustifolia et Punica granatum qui n'ont pas permis la protection des plants contre l'alternariose, mais qui ont néanmoins donné une guérison totale à la fin du traitement. Les extraits de Quercus suber et Eucalyptus globulus étaient les moins actifs. Ils n'ont permis ni la prévention, ni la guérison complète des plants. Le comptage des dictyospores réalisé sur les fruits à la fin du traitement a confirmé les résultats obtenus pour les cultures sous serre.

Lavender Decline in France Is Associated with Chronic Infection by Lavender-Specific Strains of "Candidatus Phytoplasma solani".

Lavender decline compromises French lavender production, and preliminary data have suggested the involvement of "Candidatus Phytoplasma solani" in the etiology of the disease. In order to evaluate the epidemiological role of "Ca Phytoplasma solani," a 3-year survey was conducted in southeastern France. "Ca Phytoplasma solani" was detected in 19 to 56% of the declining plants, depending on seasons and cultivars, and its prevalence was correlated with symptom severity. Autumn was more favorable than spring for phytoplasma detection, and "Ca Phytoplasma solani" incidence was higher in Lavandula angustifolia than in Lavandula intermedia hybrids. Detection of the phytoplasma fluctuated over months, supporting the chronicity of infection. Three "Ca Phytoplasma solani" secY genotypes, S17, S16, and S14, were the most prevalent in lavender fields and were also detected in nurseries, whereas strains detected in surrounding bindweed and wild carrots were mostly of the S1 and S4 genotypes. This suggests that lavender is the main pathogen reservoir of the epidemic. Adults and nymphs of the planthopper vector Hyalesthes obsoletus were commonly captured in lavender fields and were shown to harbor mainly the prevalent phytoplasma genotypes detected in lavenders. The "Ca Phytoplasma solani" genotype S17 was transmitted to Catharanthus roseus periwinkle by naturally infected H. obsoletus Finally, the inventory of the bacterial community of declining lavenders that tested negative for "Ca Phytoplasma solani" by 16S rRNA deep sequencing ruled out the involvement of other phloem-limited bacterial pathogens.IMPORTANCE The etiology and main pathways for the spread of lavender decline, an infectious disease affecting French lavender production since the 1960s, have remained unclear, hampering the development of efficient control strategies. An extensive survey of lavender fields led to the conclusion that "Candidatus Phytoplasma solani" was chronically infecting declining lavenders and was associated with large infectious populations of Hyalesthes obsoletus planthoppers living on the crop itself. Lavender appeared to be the main reservoir host for lavender-specific phytoplasma strains, an unusual feature for this phytoplasma, which usually propagates from reservoir weeds to various economically important crops. These results point out the necessity to protect young lavender fields from the initial phytoplasma inoculum coming from surrounding lavender fields or from infected nurseries and to promote agricultural practices that reduce the development of H. obsoletus vector populations.

Native bacteria promote plant growth under drought stress condition without impacting the rhizomicrobiome.

Inoculation of plants with beneficial plant growth-promoting bacteria (PGPB) emerges a valuable strategy for ecosystem recovery. However, drought conditions might compromise plant-microbe interactions especially in semiarid regions. This study highlights the effect of native PGPB after 1 year inoculation on autochthonous shrubs growth and rhizosphere microbial community composition and activity under drought stress conditions. We inoculated three plant species of semiarid Mediterranean zones, Thymus vulgaris, Santolina chamaecyparissus and Lavandula dentata with a Bacillus thuringiensis strain IAM 12077 and evaluated the impact on plant biomass, plant nutrient contents, arbuscular mycorrhiza fungi (AMF) colonization, soil rhizosphere microbial activity and both the bacterial and fungal communities. Inoculation with strain IAM 12077 improved the ability of all three plants species to uptake nutrients from the soil, promoted L. dentata shoot growth (>65.8%), and doubled the AMF root colonization of S. chamaecyparissus. Inoculation did not change the rhizosphere microbial community. Moreover, changes in rhizosphere microbial activity were mainly plant species-specific and strongly associated with plant nutrients. In conclusion, the strain IAM 12077 induced positive effects on plant growth and nutrient acquisition with no impact on the rhizosphere microbiome, indicating a rhizosphere microbial community resilient to native bacteria inoculation.

Streptomyces tunisialbus sp. nov., a novel Streptomyces species with antimicrobial activity.

A novel actinomycete strain designated S2T was isolated from Tunisian rhizosphere soil of Lavandula officinalis. This isolate exhibited broad spectrum antibacterial activity against several Gram-positive and Gram-negative bacteria and also antifungal activity against yeast and filamentous fungi. The isolate S2T presents morphological and chemotaxonomic characteristics typical of the members of the genus Streptomyces. Whole cell hydrolysates of S2T were found to contain LL-diaminopimelic acid. The major fatty acids were identified as C16:0, anteiso-C15:0 and iso-C16:0 whereas the predominant menaquinones were found to be MK-9(H6) and MK-9(H8). The polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside and three unidentified compounds. The G+C content of the genomic DNA was determined to be 71.8 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain S2T belongs to the genus Streptomyces and is closely related to Streptomyces netropsis DSM 40259T with 99.86% sequence similarity. Multi-locus sequence analysis (MLSA) based on four house-keeping gene alleles (gyrB, recA, trpB, rpoB) showed that isolate S2T is closely related to S. netropsis, with an MLSA distance greater than 0.007. The DNA-DNA relatedness between strain S2T and its near phylogenetic neighbour was 63.6 ± 2.3%, which is lower than the 70% threshold value for delineation of genomic prokaryotic species. This isolate was also distinguished from the type strain S. netropsis DSM 40259T, using a combination of morphological and physiological features. Based on its phenotypic and molecular properties, strain S2T is considered to represent a novel species of the genus Streptomyces, for which the name Streptomyces tunisialbus sp. nov. is proposed. The type strain is S2T (= JCM 32165T = DSM 105760T).

Native plant growth promoting bacteria Bacillus thuringiensis and mixed or individual mycorrhizal species improved drought tolerance and oxidative metabolism in Lavandula dentata plants.

This study evaluates the responses of Lavandula dentata under drought conditions to the inoculation with single autochthonous arbuscular mycorrhizal (AM) fungus (five fungal strains) or with their mixture and the effects of these inocula with a native Bacillus thuringiensis (endophytic bacteria). These microorganisms were drought tolerant and in general, increased plant growth and nutrition. Particularly, the AM fungal mixture and B. thuringiensis maximized plant biomass and compensated drought stress as values of antioxidant activities [superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase APX)] shown. The AMF-bacteria interactions highly reduced the plant oxidative damage of lipids [malondialdehyde (MDA)] and increased the mycorrhizal development (mainly arbuscular formation representative of symbiotic functionality). These microbial interactions explain the highest potential of dually inoculated plants to tolerate drought stress. B. thuringiensis "in vitro" under osmotic stress does not reduce its PGPB (plant growth promoting bacteria) abilities as indole acetic acid (IAA) and ACC deaminase production and phosphate solubilization indicating its capacity to improve plant growth under stress conditions. Each one of the autochthonous fungal strains maintained their particular interaction with B. thuringiensis reflecting the diversity, intrinsic abilities and inherent compatibility of these microorganisms. In general, autochthonous AM fungal species and particularly their mixture with B. thuringiensis demonstrated their potential for protecting plants against drought and helping plants to thrive in semiarid ecosystems.

Differential activity of autochthonous bacteria in controlling drought stress in native Lavandula and Salvia plants species under drought conditions in natural arid soil.

The effectiveness of autochthonous plant growth-promoting rhizobacteria was studied in Lavandula dentata and Salvia officinalis growing in a natural arid Mediterranean soil under drought conditions. These bacteria identified as Bacillus megaterium (Bm), Enterobacter sp. (E), Bacillus thuringiensis (Bt), and Bacillus sp. (Bsp). Each bacteria has different potential to meliorate water limitation and alleviating drought stress in these two plant species. B. thuringiensis promoted growth and drought avoidance in Lavandula by increasing K content, by depressing stomatal conductance, and it controlled shoot proline accumulation. This bacterial effect on increasing drought tolerance was related to the decrease of glutathione reductase (GR) and ascorbate peroxidase (APX) that resulted sensitive indexes of lower cellular oxidative damage involved in the adaptative drought response in B. thuringiensis-inoculated Lavandula plants. In contrast, in Salvia, having intrinsic lower shoot/root ratio, higher stomatal conductance and lower APX and GR activities than Lavandula, the bacterial effects on nutritional, physiological and antioxidant enzymatic systems were lower. The benefit of bacteria depended on intrinsic stress tolerance of plant involved. Lavadula demonstrated a greater benefit than Salvia to control drought stress when inoculated with B. thuringiensis. The bacterial drought tolerance assessed as survival, proline, and indolacetic acid production showed the potential of this bacteria to help plants to grow under drought conditions. B. thuringiensis may be used for Lavandula plant establishment in arid environments. Particular characteristic of the plant species as low shoot/root ratio and high stomatal conductance are important factors controlling the bacterial effectiveness improving nutritional, physiological, and metabolic plant activities.

Drought tolerance and antioxidant activities in lavender plants colonized by native drought-tolerant or drought-sensitive Glomus Species.

This study compared the effectiveness of four arbuscular mycorrhizal (AM) fungal isolates (two autochthonous presumably drought-tolerant Glomus sp and two allochthonous presumably drought-sensitive strains) on a drought-adapted plant (Lavandula spica) growing under drought conditions. The autochthonous AM fungal strains produced a higher lavender biomass, specially root biomass, and a more efficient N and K absorption than with the inoculation of similar allochthonous strains under drought conditions. The autochthonous strains of Glomus intraradices and Glomus mosseae increased root growth by 35% and 100%, respectively, when compared to similar allochthonous strains. These effects were concomitant with an increase in water content and a decline in antioxidant compounds: 25% glutathione, 7% ascorbate and 15% H(2)O(2) by G. intraradices, and 108% glutathione, 26% ascorbate and 43% H(2)O(2) by G. mosseae. Glutathione and ascorbate have an important role in plant protection and metabolic function under water deficit; the low cell accumulation of these compounds in plants colonized by autochthonous AM fungal strains is an indication of high drought tolerance. Non-significant differences between antioxidant activities such as glutathione reductase (GR), catalase (CAT) and superoxide dismutase (SOD) in colonized plants were found. Thus, these results do not allow the generalization that GR, CAT and SOD were correlated with the symbiotic efficiency of these AM fungi on lavender drought tolerance. Plants colonized by allochthonous G. mosseae (the less efficient strain under drought conditions) had less N and K content than those colonized by similar autochthonous strain. These ions play a key role in osmoregulation. The AM symbiosis by autochthonous adapted strains also produced the highest intraradical and arbuscular development and extraradical mycelial having the greatest fungal SDH and ALP-ase activities in the root systems. Inoculation of autochthonous drought tolerant fungal strains is an important strategy that assured the greatest tolerance water stress contributing to the best lavender growth under drought.

Bacterial colonization of the phyllosphere of mediterranean perennial species as influenced by leaf structural and chemical features.

In this study, we assessed various leaf structural and chemical features as possible predictors of the size of the phyllosphere bacterial population in the Mediterranean environment. We examined eight perennial species, naturally occurring and coexisting in the same area, in Halkidiki (northern Greece). They are Arbutus unedo, Quercus coccifera, Pistacia lentiscus, and Myrtus communis (evergreen sclerophyllous species), Lavandula stoechas and Cistus incanus (drought semi-deciduous species), and Calamintha nepeta and Melissa officinalis (non-woody perennial species). M. communis, L. stoechas, C. nepeta, and M. officinalis produce essential oil in substantial quantities. We sampled summer leaves from these species and (1) estimated the size of the bacterial population of their phyllosphere, (2) estimated the concentration of different leaf constituents, and (3) studied leaf morphological and anatomical features and expressed them in a quantitative way. The aromatic plants are on average more highly colonized than the other species, whereas the non-woody perennials are more highly colonized than the woody species. The population size of epiphytic bacteria is positively correlated with glandular and non-glandular trichome densities, and with water and phosphorus contents; it is negatively correlated with total phenolics content and the thickness of the leaf, of the mesophyll, and of the abaxial epidermis. No correlation was found with the density of stomata, the nitrogen, and the soluble sugar contents. By regression tree analysis, we found that the leaf-microbe system can be effectively described by three leaf attributes with leaf water content being the primary explanatory attribute. Leaves with water content >73% are the most highly colonized. For leaves with water content <73%, the phosphorus content, with a critical value of 1.34 mg g(-1) d.w., is the next explanatory leaf attribute, followed by the thickness of the adaxial epidermis. Leaves higher in phosphorus (>1.34 mg g(-1) d.w.) are more colonized, and leaves with the adaxial epidermis thicker than 20.77 microm are the least colonized. Although these critical attributes and values hold true only within the Mediterranean ecosystem studied and the range of observations taken, they are important because they provide a hypothesis to be tested in other Mediterranean ecosystems and other biomes. Such comparative studies may give insight as to the general properties governing the leaf-microbe system.

Temporal temperature gradient gel electrophoresis (TTGE) as a tool for the characterization of arbuscular mycorrhizal fungi.

The aim of this study was to assess the feasibility of using temporal temperature gradient electrophoresis (TTGE) of PCR-amplified 18S rDNA fragments of different Glomus species for their detection and characterization. Screening of Glomus clarum, Glomus constrictum, Glomus coronatum, Glomus intraradices, Glomus mosseae and Glomus viscosum by PCR-TGGE revealed that the NS31-AM1 region of the 18S rRNA gene contained insufficient variation to discriminate between them. In contrast, TTGE analysis of the NS31-Glo1 region, which was obtained by nested PCR of the NS31-AM1 amplicon, showed that each species was characterized by a specific TTGE fingerprint. However, isolates of the same species could not be distinguished. The nested PCR-TTGE approach developed allowed identification of the Glomus species colonising the roots of different plant species.