Improve Plant Health Research Articles

Trichoderma Species: Versatile Plant Symbionts.

Because of the need to provide food for the growing population, agricultural activity is faced with the huge challenge of counteracting the negative effects generated by adverse environmental factors and diseases caused by pathogens on crops, while avoiding environmental pollution due to the excessive use of agrochemicals. The exploitation of biological systems that naturally increase plant vigor, preparing them against biotic and abiotic stressors that also promote their growth and productivity represents a useful and viable strategy to help face these challenges. Fungi from the genus Trichoderma have been widely used in agriculture as biocontrol agents because of their mycoparasitic capacity and ability to improve plant health and protection against phytopathogens, which makes it an excellent plant symbiont. The mechanisms employed by Trichoderma include secretion of effector molecules and secondary metabolites that mediate the beneficial interaction of Trichoderma with plants, providing tolerance to biotic and abiotic stresses. Here we discuss the most recent advances in understanding the mechanisms employed by this opportunistic plant symbiont as biocontrol agent and plant growth promoter. In addition, through genome mining we approached a less explored factor that Trichoderma could be using to become successful plant symbionts, the production of phytohormones-auxins, cytokinins, abscisic acid, gibberellins, among others. This approach allowed us to detect sets of genes encoding proteins potentially involved in phytohormone biosynthesis and signaling. We discuss the implications of these findings in the physiology of the fungus and in the establishment of its interaction with plants.

A Genome-Wide Screen Identifies Genes in Rhizosphere-Associated Pseudomonas Required to Evade Plant Defenses.

Pseudomonas fluorescens and related plant root ("rhizosphere")-associated species contribute to plant health by modulating defenses and facilitating nutrient uptake. To identify bacterial fitness determinants in the rhizosphere of the model plant Arabidopsis thaliana, we performed a high-throughput transposon sequencing (Tn-Seq) screen using the biocontrol and growth-promoting strain Pseudomonas sp. WCS365. The screen, which was performed in parallel on wild-type and immunocompromised Arabidopsis plants, identified 231 genes that increased fitness in the rhizosphere of wild-type plants. A subset of these genes decreased fitness in the rhizosphere of immunocompromised plants. We hypothesized that these genes might be involved in avoiding plant defenses and verified 7 Pseudomonas sp. WCS365 candidate genes by generating clean deletions. We found that two of these deletion mutants, ΔmorA (encoding a putative diguanylate cyclase/phosphodiesterase) and ΔspuC (encoding a putrescine aminotransferase), formed enhanced biofilms and inhibited plant growth. We found that mutants ΔspuC and ΔmorA induced pattern-triggered immunity (PTI) as measured by induction of an Arabidopsis PTI reporter and FLS2/BAK1-dependent inhibition of plant growth. We show that MorA acts as a phosphodiesterase to inhibit biofilm formation, suggesting a possible role in biofilm dispersal. We found that both putrescine and its precursor arginine promote biofilm formation that is enhanced in the ΔspuC mutant, which cannot break down putrescine, suggesting that putrescine might serve as a signaling molecule in the rhizosphere. Collectively, this work identified novel bacterial factors required to evade plant defenses in the rhizosphere.IMPORTANCE While rhizosphere bacteria hold the potential to improve plant health and fitness, little is known about the bacterial genes required to evade host immunity. Using a model system consisting of Arabidopsis and a beneficial Pseudomonas sp. isolate, we identified bacterial genes required for both rhizosphere fitness and for evading host immune responses. This work advances our understanding of how evasion of host defenses contributes to survival in the rhizosphere.

Changes in Root Exudates and Root Proteins in Groundnut–Pseudomonas sp. Interaction Contribute to Root Colonization by Bacteria and Defense Response of the Host

Selection and application of rhizobacteria, for improved plant health will benefit from a complete understanding of the plant–bacteria interaction. Root exudates (REs) are known to contain signal molecules that facilitate beneficial association of plants with microbes. We have selected a tentatively identified Pseudomonas sp. (RP2), from 126 groundnut (Arachis hypogaea L.)-associated bacterial isolates that significantly promoted growth of groundnut and also induced resistance against the stem rot pathogen Sclerotium rolfsii. REs were collected from 12 to 24 days grown RP2-bacterized and non-bacterized plants and analyzed through gas chromatography coupled with mass spectrometer. Several organic acids, fatty acids, sugars, hydrocarbons, and alcohols were detected. In the untargeted multivariate analysis of the REs, relative content of eight compounds varied significantly on RP2 bacterization. Among these eight compounds, myristic acid, stearic acid, and palmitic acid, positively influenced the root colonization by RP2. Benzoic acid and salicylic acid, increased in RP2-bacterized REs, showed the highest growth inhibition of S. rolfsii. In root proteomics, 11 differentially expressed proteins were identified by 2D-gel electrophoresis followed by matrix-assisted laser desorption ionization-time of flight. Chitinase, thaumatin-like protein, ascorbate peroxidase, and glutathione S-transferase, known to have a role in plant defense against phytopathogens, were upregulated in RP2 interaction. Similarly, upregulation of enolase in roots is likely to improve plant growth in RP2-bacterized groundnut. We conclude that colonization of groundnut roots by RP2 resulted in exudation of metabolites that facilitated root colonization, suppressed fungal growth, promoted plant growth, and also increased the expression of defense-related proteins in the roots.

Inoculation of Sinorhizobium saheli YH1 Leads to Reduced Metal Uptake for Leucaena leucocephala Grown in Mine Tailings and Metal-Polluted Soils

Metalliferous mine tailings have a negative impact on the soil environment near mining areas and render cultivable lands infertile. Phytoremediation involving the synergism of legume and rhizobia provides a useful technique in tackling this issue with cost-effective, environmentally friendly, and easy-to-use features under adverse soil conditions. Leucaena leucocephala has been found to build symbiotic relationships with native rhizobia in the iron-vanadium-titanium oxide (V-Ti magnetite) mine tailing soil. Rhizobia YH1, isolated from the root nodules of L. leucocephala, was classified as Sinorhizobium saheli according to similarity and phylogenetic analyses of 16S rRNA, housekeeping and nitrogen fixation genes. Besides nitrogen fixation, S. saheli YH1 also showed capabilities to produce indole-acetic acid (IAA) (166.77 ± 2.03 mg l−1) and solubilize phosphate (104.41 ± 7.48 mg l−1). Pot culture experiments showed that strain YH1 increased the biomass, plant height and root length of L. leucocephala by 67.2, 39.5 and 27.2% respectively. There was also an average increase in plant N (10.0%), P (112.2%) and K (25.0%) contents compared to inoculation-free control. The inoculation of YH1 not only reduced the uptake of all metals by L. leucocephala in the mine tailings, but also resulted in decreased uptake of Cd by up to 79.9% and Mn by up to 67.6% for plants grown in soils contaminated with Cd/Mn. It was concluded that S. saheli YH1 possessed multiple beneficial effects on L. leucocephala grown in metalliferous soils. Our findings highlight the role of S. saheli YH1 in improving plant health of L. leucocephala by reducing metal uptake by plants grown in heavy metal-polluted soils. We also suggest the idea of using L. leucocephala-S. saheli association for phytoremediation and revegetation of V-Ti mine tailings and soils polluted with Cd or Mn.

EFFECT OF BACTERIAL ENDOPHYTES ISOLATED FROM THE CITRUS ON THE PHYSICAL PARAMETER OF BITTER GOURD (Momordica charantia L.)

Bacterial endophytes have a symbiotic relationship between different parts of the plant and could play an important role to improve plant health. The effects of endophytic bacterial communities in bitter gourd have not been studied yet in Pakistan. In the present study, ten different bacteria that belong to class Alpha, beta and gamma Proteobacteria as well as bacilli were injected into bitter gourd seedlings under glass house conditions and five weeks after physical parameters (SL, RL, leaf area, leaf number, wet and dry weight of plant, root and shoot ratio) were studied. According to results Azomonas agilis and Ensifer adhaerens give good results as compared to control for all parameters studied. These inoculants could be used as bio fertilizer for sustainable crop production system.

Rhizosphere pseudomonads as probiotics improving plant health.

Many root-colonizing microbes are multifaceted in traits that improve plant health. Although isolates designated as biological control agents directly reduce pathogen growth, many exert additional beneficial features that parallel changes induced in animal and other hosts by health-promoting microbes termed probiotics. Both animal and plant probiotics cause direct antagonism of pathogens and induce systemic immunity in the host to pathogens and other stresses. They also alter host development and improve host nutrition. The probiotic root-colonizing pseudomonads are generalists in terms of plant hosts, soil habitats and the array of stress responses that are ameliorated in the plant. This article illustrates how the probiotic pseudomonads, nurtured by the carbon (C) and nitrogen (N) sources released by the plant in root exudates, form protective biofilms on the root surface and produce the metabolites or enzymes to boost plant health. The findings reveal the multifunctional nature of many of the microbial metabolites in the plant-probiotic interplay. The beneficial effects of probiotics on plant function can contribute to sustainable yield and quality in agricultural production.

Bacterial Production of Indole Related Compounds Reveals Their Role in Association Between Duckweeds and Endophytes.

Duckweed farming can be a sustainable practice for biofuel production, animal feed supplement, and wastewater treatment, although large scale production remains a challenge. Plant growth promoting bacteria (PGPB) have been shown to improve plant health by producing phytohormones such as auxin. While some of the mechanisms for plant growth promotion have been characterized in soil epiphytes, more work is necessary to understand how plants may select for bacterial endophytes that have the ability to provide an exogenous source of phytohormones such as auxin. We have isolated and characterized forty-seven potentially endophytic bacteria from surface-sterilized duckweed tissues and screened these bacterial strains for production of indole related compounds using the Salkowski colorimetric assay. Indole-3-acetic acid (IAA), indole-3-lactic acid (ILA), and indole produced by various bacterial isolates were verified by mass spectrometry. Using the Salkowski reagent, we found that 79% of the isolated bacterial strains from our collection may be capable of producing indole related compounds to various extents during in vitro growth. Of these bacteria that are producing indole related compounds, 19% are additionally producing indole. There is an apparent correlation between the type of indole related compound produced by a particular bacteria and the duckweed genus from which the bacterial strain is derived. These results suggest the possible association between different duckweed genera and endophytes that are producing distinct types of secondary metabolites. Understanding the role of indole related compounds during interaction between endophytes and the plant host may be useful to help design synthetic bacterial communities that could target specific or multiple species of duckweed in the future to sustainably enhance plant growth.

Revisiting bacterial volatile-mediated plant growth promotion: lessons from the past and objectives for the future.

BackgroundBacterial volatile compounds (BVCs) are important mediators of beneficial plant–bacteria interactions. BVCs promote above-ground plant growth by stimulating photosynthesis and sugar accumulation and by modulating phytohormone signalling. These compounds also improve below-ground mineral uptake and modify root system architecture.ScopeWe review advances in our understanding of the mode of action and practical applications of BVCs since the discovery of BVC-mediated plant growth promotion in 2003. We also discuss unanswered questions about the identity of plant receptors, the effectiveness of combination of two or more BVCs on plant growth, and the potential side effects of these compounds for human and animal health.ConclusionBVCs have good potential for use as biostimulants and protectants to improve plant health. Further advances in the development of suitable technologies and preparing standards and guidelines will help in the application of BVCs in crop protection and health.

Evaluation of Trichoderma harzianum as a potential bio-control option for fungal root disease of Seabuckthorn

Biocontrol involves harnessing disease suppressive micro-organisms to improve plant health. Owing to the shortage of available fungicides for economic management of soil borne diseases, alternative techniques such as biological control are increasingly being sought for disease management. The present work was carried out to study the potential of Trichoderma harzianum isolate screened from the rhizospheric soil of seabuckthorn growing areas in Uttarakhand. Antagonistic activity of isolate was observed against Fusarium oxysporum causing damping off disease in seabuckthorn. Under in vitro conditions Trichoderma harzianum significantly reduced the growth of pathogenic Fusarium oxysporum.

Natural Ecosystem Surrounding a Conventional Banana Crop Improves Plant Health and Fruit Quality.

Natural ecosystems near agricultural landscapes may provide rich environments for growing crops. However, the effect of a natural ecosystem on crop health and fruit quality is poorly understood. In the present study, it was investigated whether the presence of a natural ecosystem surrounding a crop area influences banana plant health and fruit postharvest behavior. Plants from two conventional banana crop areas with identical planting time and cultural practices were used; the only difference between banana crop areas is that one area was surrounded by a natural forest (Atlantic forest) fragment (Near-NF), while the other area was inserted at the center of a conventional banana crop (Distant-NF). Results showed that bananas harvested from Near-NF showed higher greenlife and a more homogeneous profile during ripening compared to fruits harvested from Distant-NF. Differences in quality parameters including greenlife, carbohydrate profile, and pulp firmness between fruits harvested from Near-NF and Distant-NF are explained, at least partly, by differences in the balance of plant growth regulators (indole-3-acetic acid and abscisic acid) in bananas during ripening. Furthermore, plants from Near-NF showed a lower severity index of black leaf streak disease (BLSD) and higher levels of phenolic compounds in leaves compared to plants from Distant-NF. Together, the results provide additional evidence on how the maintenance of natural ecosystems near conventional crop areas could be a promising tool to improve plant health and fruit quality.

Effects of different humic substances concentrations on root anatomy and Cd accumulation in seedlings of Avicennia germinans (black mangrove)

Mangrove areas are among most threatened tropical ecosystems worldwide. Among polluting agents Cadmium is often found in high concentrations in mangrove sediments. Humic substances, complex biomolecules formed in soil and sediments during animal and plant residuals decomposition, have a known biostimulant activity and can be adopted to counteract various plant stresses. This study explores, in controlled conditions, the effect of humic substances on Avicennia germinans seedlings, with or without cadmium contamination. Humic compounds significantly changed plant root architecture, and, when coupled with cadmium, root anatomy and Cortex to Vascular Cylinder diameter ratio. These modifications led to lower Cd uptake by humic substances-treated plants. Humic substances amendment could be effective, depending on their concentrations, on improving plant health in mangrove areas, for forest recuperation and/or dredged sediments phytoremediation purposes.

Beyond Chemical Triggers: Evidence for Sound-Evoked Physiological Reactions in Plants.

Sound is ubiquitous in nature. Recent evidence supports the notion that naturally occurring and artificially generated sound waves contribute to plant robustness. New information is emerging about the responses of plants to sound and the associated downstream signaling pathways. Here, beyond chemical triggers which can improve plant health by enhancing plant growth and resistance, we provide an overview of the latest findings, limitations, and potential applications of sound wave treatment as a physical trigger to modulate physiological traits and to confer an adaptive advantage in plants. We believe that sound wave treatment is a new trigger to help protect plants against unfavorable conditions and to maintain plant fitness.

The interactive effects of arbuscular mycorrhiza and plant growth-promoting rhizobacteria synergistically enhance host plant defences against pathogens

Belowground interactions between plant roots, mycorrhizal fungi and plant growth-promoting rhizobacteria (PGPR) can improve plant health via enhanced nutrient acquisition and priming of the plant immune system. Two wheat cultivars differing in their ability to form mycorrhiza were (co)inoculated with the mycorrhizal fungus Rhizophagus irregularis and the rhizobacterial strain Pseudomonas putida KT2440. The cultivar with high mycorrhizal compatibility supported higher levels of rhizobacterial colonization than the low compatibility cultivar. Those levels were augmented by mycorrhizal infection. Conversely, rhizobacterial colonization of the low compatibility cultivar was reduced by mycorrhizal arbuscule formation. Single inoculations with R. irregularis or P. putida had differential growth effects on both cultivars. Furthermore, while both cultivars developed systemic priming of chitosan-induced callose after single inoculations with R. irregularis or P. putida, only the cultivar with high mycorrhizal compatibility showed a synergistic increase in callose responsiveness following co-inoculation with both microbes. Our results show that multilateral interactions between roots, mycorrhizal fungi and PGPR can have synergistic effects on growth and systemic priming of wheat.

Microbial communities in soils with different population densities of soybean cyst nematode

The relationship of abiotic factors with soybean cyst nematode (SCN), the most damaging pathogen of soybean, has been studied extensively, but characterization of microbial communities in infested soils and on soybean roots under field conditions remains unknown. This study investigated the relationship of different SCN population density levels with soil physical, chemical and microbial properties in soils and on soybean roots. A commercial soybean field with different levels of SCN densities (low, medium, high) was sampled, and microbial communities were characterized using both dilution plating assays and molecular approaches. Population densities of species of Trichoderma, actinomycetes, Pseudomonas and other bacteria were significantly higher (P ≤ 0.05) in soils with low SCN (SCN-C) compared with high (SCN-A) and medium levels (SCN-B). Diversity indices of Trichoderma communities on roots based on denaturing gradient gel electrophoresis (DGGE) were significantly higher in soils with SCN-C compared with SCN-A and SCN-B. Cluster analyses and canonical correspondence analysis (CCA) generally separated microbial communities into three groups based on different SCN levels, and CCA showed that low SCN population levels were positively correlated with high levels of nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), cation exchange capacity (CEC), base saturation (BS), the populations of Trichoderma and bacteria. Moreover, diverse Trichoderma, Pseudomonas, Bacillus and actinomycetes were found on roots in SCN-C soils based on dilution plating and DGGE, suggesting that the presence of these microbes on soybean roots might be associated with improved plant health and reduction of SCN.

Combined Field Inoculations of Pseudomonas Bacteria, Arbuscular Mycorrhizal Fungi, and Entomopathogenic Nematodes and their Effects on Wheat Performance.

In agricultural ecosystems, pest insects, pathogens, and reduced soil fertility pose major challenges to crop productivity and are responsible for significant yield losses worldwide. Management of belowground pests and diseases remains particularly challenging due to the complex nature of the soil and the limited reach of conventional agrochemicals. Boosting the presence of beneficial rhizosphere organisms is a potentially sustainable alternative and may help to optimize crop health and productivity. Field application of single beneficial soil organisms has shown satisfactory results under optimal conditions. This might be further enhanced by combining multiple beneficial soil organisms, but this remains poorly investigated. Here, we inoculated wheat plots with combinations of three beneficial soil organisms that have different rhizosphere functions and studied their effects on crop performance. Plant beneficial Pseudomonas bacteria, arbuscular mycorrhizal fungi (AMF), and entomopathogenic nematodes (EPN), were inoculated individually or in combinations at seeding, and their effects on plant performance were evaluated throughout the season. We used traditional and molecular identification tools to monitor their persistence over the cropping season in augmented and control treatments, and to estimate the possible displacement of native populations. In three separate trials, beneficial soil organisms were successfully introduced into the native populations and readily survived the field conditions. Various Pseudomonas, mycorrhiza, and nematode treatments improved plant health and productivity, while their combinations provided no significant additive or synergistic benefits compared to when applied alone. EPN application temporarily displaced some of the native EPN, but had no significant long-term effect on the associated food web. The strongest positive effect on wheat survival was observed for Pseudomonas and AMF during a season with heavy natural infestation by the frit fly, Oscinella frit, a major pest of cereals. Hence, beneficial impacts differed between the beneficial soil organisms and were most evident for plants under biotic stress. Overall, our findings indicate that in wheat production under the test conditions the three beneficial soil organisms can establish nicely and are compatible, but their combined application provides no additional benefits. Further studies are required, also in other cropping systems, to fine-tune the functional interactions among beneficial soil organisms, crops, and the environment.

Identifying the Active Microbiome Associated with Roots and Rhizosphere Soil of Oilseed Rape.

RNA stable isotope probing and high-throughput sequencing were used to characterize the active microbiomes of bacteria and fungi colonizing the roots and rhizosphere soil of oilseed rape to identify taxa assimilating plant-derived carbon following 13CO2 labeling. Root- and rhizosphere soil-associated communities of both bacteria and fungi differed from each other, and there were highly significant differences between their DNA- and RNA-based community profiles. Verrucomicrobia, Proteobacteria, Planctomycetes, Acidobacteria, Gemmatimonadetes, Actinobacteria, and Chloroflexi were the most active bacterial phyla in the rhizosphere soil. Bacteroidetes were more active in roots. The most abundant bacterial genera were well represented in both the 13C- and 12C-RNA fractions, while the fungal taxa were more differentiated. Streptomyces, Rhizobium, and Flavobacterium were dominant in roots, whereas Rhodoplanes and Sphingomonas (Kaistobacter) were dominant in rhizosphere soil. "Candidatus Nitrososphaera" was enriched in 13C in rhizosphere soil. Olpidium and Dendryphion were abundant in the 12C-RNA fraction of roots; Clonostachys was abundant in both roots and rhizosphere soil and heavily 13C enriched. Cryptococcus was dominant in rhizosphere soil and less abundant, but was 13C enriched in roots. The patterns of colonization and C acquisition revealed in this study assist in identifying microbial taxa that may be superior competitors for plant-derived carbon in the rhizosphere of Brassica napusIMPORTANCE This microbiome study characterizes the active bacteria and fungi colonizing the roots and rhizosphere soil of Brassica napus using high-throughput sequencing and RNA-stable isotope probing. It identifies taxa assimilating plant-derived carbon following 13CO2 labeling and compares these with other less active groups not incorporating a plant assimilate. Brassica napus is an economically and globally important oilseed crop, cultivated for edible oil, biofuel production, and phytoextraction of heavy metals; however, it is susceptible to several diseases. The identification of the fungal and bacterial species successfully competing for plant-derived carbon, enabling them to colonize the roots and rhizosphere soil of this plant, should enable the identification of microorganisms that can be evaluated in more detailed functional studies and ultimately be used to improve plant health and productivity in sustainable agriculture.

Induction of Systemic Resistance against Insect Herbivores in Plants by Beneficial Soil Microbes.

Soil microorganisms with growth-promoting activities in plants, including rhizobacteria and rhizofungi, can improve plant health in a variety of different ways. These beneficial microbes may confer broad-spectrum resistance to insect herbivores. Here, we provide evidence that beneficial microbes modulate plant defenses against insect herbivores. Beneficial soil microorganisms can regulate hormone signaling including the jasmonic acid, ethylene and salicylic acid pathways, thereby leading to gene expression, biosynthesis of secondary metabolites, plant defensive proteins and different enzymes and volatile compounds, that may induce defenses against leaf-chewing as well as phloem-feeding insects. In this review, we discuss how beneficial microbes trigger induced systemic resistance against insects by promoting plant growth and highlight changes in plant molecular mechanisms and biochemical profiles.

DORMANCY BREAKING OF SOUR ALMOND SEEDS AND EVALUATION OF BIOTIC AND ABIOTIC ELICITORS FOR INDUCING SYSTEMIC RESISTANCE AGAINST ROOT-KNOT NEMATODES (MELOIDOGYNE SP.) IN RELEASED SEEDLINGS

In a Green –House experiments the effect of gibberellic acid at different concentrations on sour almond (Prunus amygdalus Batsch.) rootstock concerning percentage of radicle protrusion; stratification period; plant height; number of leaves and plant diameter were determined during 2014 and 2015 seasons. Also, the plant growth promoting rhizobacteria Serratia marcescens and the alga Spirulina platensis {as biotic elicitors} compared with, Trafose K (1) and white willow Salix alba extracts {as abiotic elicitors} soil treatments were tested for induction of systemic resistance (SR) in sour almond plants against root knot nematodes. In relation with nematodes population as juveniles in the soil; galls in roots; females; egg masses in roots were counted. Growth parameters plant, such as heights, fresh weight of roots and shoot were recorded. Also, some chemicals components in the plant, such as phenolic; proline ; Salicylic acid and catalase and peroxidase activity were determined. Results indicated that GA3 at 1000 p.p.m. achieved the best effect on percentage of radicle protrusion. Data revealed that using S. marcescens recorded 40%, 58.3% and 75% reduction in numbers of Meloidogyne sp. juveniles in the soil, number of galls and number of females in root respectively in season 2014. While application of S. platensis caused 55.6 %, 62.5% and 33.3% reduction of Meloidogyne sp. respectively in season 2015. Using S. marcescens, S. platensis, Trafose K (1) and Salix extract resulted in 60%, 40%, 80% and 20% reduction in the number of development stages, respectively in season 2014, 75%, 50%, 25% and 25% reduction in numbers of development stages, respectively in season 2015. S. marcescens inoculants and Salix extract improved plant health by increasing vegetative growth parameters similar to control values. The beneficial effects of these treatments extended to increasing not only total phenol and free proline but also the activities of catalase and peroxidase enzymes in comparison with control plants. All tested elicitors showed significant increasing Salicylic acid (SA) levels when being compared with control. It can be recommended that using GA3 at 1000 ppm before stratification is necessary to breaking seed dormancy and enhancing radicle protrusion of sour almond rootstock. Also, using (S. marcescens, S. platensis, as biotic inducers or white willow extracts as natural inducers) as soil treatments increased the induction of systemic acquired resistance (SAR) in the roots of infected with Meloidogyne sp. sour almond rootstock.

Identification and validation of reference genes for RT‐qPCR analysis in banana (Musa spp.) under Fusarium wilt resistance induction conditions

AbstractBanana (Musa spp.) is severely damaged by Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc). Biocontrol by inducing systemic resistance has been considered as one of the most important strategies to improve plant health. Very few studies have investigated appropriate reference gene selection for RT‐qPCR (quantitative real‐time polymerase chain reaction) analysis suitable for conditions of systemic activated resistance. In this study, we assessed over a time‐course the expression of seven candidate reference genes (EF1, TUB, ACT1, ACT2, L2, RPS2 and RAN) for Cavendish cultivar Brazilian (Musa spp. AAA) and dwarf banana cultivar Guangfen No. 1 (Musa spp. ABB) that were inoculated by Bacillus subtilis strain TR21 and Foc. We choose these plants because they are commonly planted in Southern China. Expression stability of the candidate genes was evaluated using various software packages (GeNorm, NormFinder and BestKeeper). L2 and TUB genes displayed maximum stability in Guangfen No. 1. In Brazilian, ACT1 and TUB were the most stable genes. To further validate the suitability of the reference genes identified in this study, the expression of pathogenesis‐related 1 (PR1) gene under TR21 and Foc strains Foc004/Foc009 treatments was also studied. Identified reference genes in this work that are most suitable for normalizing gene expression data in banana under Fusarium wilt resistance induction conditions will contribute to the understanding of disease resistance mechanisms induced by biocontrol strains in banana.

High soil phosphorus levels overrule the potential benefits of organic farming on arbuscular mycorrhizal diversity in northern vineyards

Organic farming is a key approach to reconcile food production, biodiversity conservation and environmental sustainability. Due to reduced inputs of agrochemicals, the success of organic farming is heavily dependent on the ecosystem services provided by the soil microbial community, and in particular by arbuscular mycorrhizal fungi (AMF). Numerous studies have already shown that also grapevines (Vitis vinifera) depend on AMF for normal growth and development. To what extent organic agriculture benefits the AMF communities on vines at regional scales, however, is still poorly understood. Here, we first quantified the relative importance of organic management, soil chemical characteristics, and geography on vineyard AMF diversity and community composition. Second, we tested whether soil nutrients fundamentally change the host-AMF community dynamics through changing universality of dissimilarity overlap curves. To identify AMF communities, we used high-throughput pyrosequencing on 170 root samples from grapevines originating from 18 conventionally and 16 organically managed Belgian and Dutch vineyards. We found no differences in AMF diversity between conventionally and organically managed vineyards. Soil phosphorus content and soil acidity, however, was strongly negatively associated with AMF diversity. Together with management type (organic vs. conventional), these two soil variables did also explain most of the variation in AMF community composition. The observed accumulation of soil copper, used to control fungal diseases, especially in organically managed vineyards, did not affect AMF communities. We observed, however, that copper concentration in the soil increased with vineyard age, indicating copper accumulation in the soil over time. AMF communities showed a regularity in interactions among taxa and their host. Under high soil P availability, however, interactions became more irregular. The potential benefits of organic vineyard management in terms of a high diversity of AMF are highly compromised by elevated soil phosphorus levels which may jeopardize the role of these symbionts in improving plant health and soil fertility. Decreasing nutrient inputs, even organic, is a key step in developing diverse AMF communities in vineyards.