ADVERTISEMENT

Agronomy

Online ISSN: 2073-4395

Print ISSN: XXXX-XXXX



Publisher: MDPI
Search by keywords:
Article Download / Year
Article Published / Year

Initial Steps towards Biocontrol in Hops: Successful Colonization and Plant Growth Promotion by Four Bacterial Biocontrol Agents

Author(s):

Katja A. Maurer -- Christin Zachow -- Stefan Seefelder -- Gabriele Berg


Abstract
| Pages: 583-594
Verticillium wilt, caused by Verticillium nonalfalfae and V. dahliae, is a devastating disease in hops that can cause considerable economic crop losses. The perennial use of hops combined with the long persistence of the pathogen in soil make it difficult to suppress the disease with conventional measures. Biological control agents (BCA) are the basis of an environmentally friendly plant protection strategy that uses plant promotion and antagonistic effects of microorganisms. We evaluated the effect of four selected beneficial bacterial strains, Burkholderia terricola ZR2-12, Pseudomonas poae RE*1-1-14, Serratia plymuthica 3Re4-18, and Stenotrophomonas rhizophila DSM14405T for their use in hops. All strains were shown to be both rhizosphere and endorhiza competent, and their abundances ranged from log10 3.0 to log10 6.2 CFU g−1 root fresh weight in the endorhiza and from log10 2.9 to log10 4.7 CFU g−1 root fresh weight in the rhizosphere withB. terricola ZR2-12 showing the highest overall cell densities. Microscopic visualization of DsRed-labeled transformants with confocal laser scanning microscopy showed different colonization patterns and confirmed the rhizosphere competence. Growth promoting effects on seedlings treated with bacteria were found for S. plymuthica 3Re4-18 and S. rhizophila DSM14405T. Competent colonization and plant growth promoting effects are the most important prerequisites towards efficient biocontrol.

Bacillus simplex—A Little Known PGPB with Anti-Fungal Activity—Alters Pea Legume Root Architecture and Nodule Morphology When Coinoculated with Rhizobium leguminosarum bv. viciae

Author(s):

Allison R. Schwartz, Irma Ortiz, Maskit Maymon, Craig W. Herbold, Nancy A. Fujishige, Janahan A. Vijanderan, William Villella, Kayoko Hanamoto, Andrew Diener, Erin R. Sanders, Darleen A. DeMason an

Abstract
| Pages: 595-620
Two strains, 30N-5 and 30VD-1, identified as Bacillus simplex and B. subtilis, were isolated from the rhizospheres of two different plants, a Podocarpus and a palm, respectively, growing in the University of California, Los Angeles (UCLA) Mildred E. Mathias Botanical Garden. B. subtilis is a well-known plant-growth promoting bacterial species, but B. simplex is not. B. simplex 30N-5 was initially isolated on a nitrogen-free medium, but no evidence for nitrogen fixation was found. Nevertheless, pea plants inoculated with B. simplexshowed a change in root architecture due to the emergence of more lateral roots. When Pisum sativumcarrying a DR5::GUSA construct, an indicator for auxin response, was inoculated with either B. simplex 30N-5 or its symbiont Rhizobium leguminosarum bv. viciae 128C53, GUS expression in the roots was increased over the uninoculated controls. Moreover, when pea roots were coinoculated with either B. simplex 30N-5 or B. subtilis 30VD-1 and R. leguminosarum bv. viciae 128C53, the nodules were larger, clustered, and developed more highly branched vascular bundles. Besides producing siderophores and solubilizing phosphate, the twoBacillus spp., especially strain 30VD-1, exhibited anti-fungal activity towards Fusarium. Our data show that combining nodulating, nitrogen-fixing rhizobia with growth-promoting bacteria enhances plant development and strongly supports a coinoculation strategy to improve nitrogen fixation, increase biomass, and establish greater resistance to fungal disease.

Host Plant Specific Control of 2,4-Diacetylphloroglucinol Production in the Rhizosphere

Author(s):

Feth el Zahar Haichar -- Sylvain Fochesato -- Wafa Achouak


Abstract
| Pages: 621-631
To shed light on phytobeneficial bacterial gene expression in situ, we investigated the expression ofphlD gene involved in 2,4-diacetylphloroglucinol production. For that purpose, stable isotope probing (SIP) of DNA and mRNA approaches were used. Arabidopsis thaliana seedlings were grown under 13CO2 for 27 days, and the presence and expression of phlD gene was determined in the rhizosphere soil and on the roots of A. thaliana. Results showed that phlD was present and expressed by bacteria inhabiting rhizosphere soil and deriving nutrients from the breakdown of organic matter and from root exudates, whereas phlD gene expression seemed to be repressed on roots. These data were validated in vitro by inoculating four plant species by the phytobeneficial bacterium Pseudomonas brassicacearum. phlD gene expression was highly activated by root exudates of wheat and that of Medicago truncatula and to a lesser extent by that of Brassica napus while it was completely suppressed by root exudates of A. thaliana. Overall, these results lead us to the conclusion that the signals to down regulate phl gene expression may derive from A. thaliana root exudates.

Interaction of Ulocladium atrum, a Potential Biological Control Agent, with Botrytis cinerea and Grapevine Plantlets

Author(s):

Sébastien Ronseaux -- Christophe Clément -- Essaid Ait Barka


Abstract
| Pages: 632-647
The effectiveness of biological control agent, Ulocladium atrum (isolates U13 and U16) in protectingVitis vinifera L. cv. Chardonnay against gray mold disease caused by Botrytis cinerea, and simulation of the foliar defense responses was investigated. A degraded mycelium structure during cultural assay on potato dextrose agar revealed that U. atrum isolates U13 and U16 were both antagonistic to B. cinerea, mainly when isolates were inoculated two days before Botrytis. Under in vitro conditions, foliar application of U. atrumprotected grapevine leaves against gray mold disease. An increase in chitinase activity was induced by the presence of U. atrum isolates indicating that the biological control agents triggered plant defense mechanisms. Moreover, U13 has the potential to colonize the grapevine plantlets and to improve their growth. The ability of U. atrum isolates to exhibit an antagonistic effect against B. cinerea in addition to their aptitude to induce plant resistance and to promote grapevine growth may explain a part of their biological activity. Hence, this study suggests that U. atrum provides a suitable biocontrol agent against gray mold in grapevines.

Next-Generation Bio-Products Sowing the Seeds of Success for Sustainable Agriculture

Author(s):

Gabriele Berg -- Christin Zachow -- Henry Müller -- Jörg Philipps -- Ralf Tilcher


Abstract
| Pages: 648-656
Plants have recently been recognized as meta-organisms due to a close symbiotic relationship with their microbiome. Comparable to humans and other eukaryotic hosts, plants also harbor a “second genome” that fulfills important host functions. These advances were driven by both “omics”-technologies guided by next-generation sequencing and microscopic insights. Additionally, these new results influence applied fields such as biocontrol and stress protection in agriculture, and new tools may impact (i) the detection of new bio-resources for biocontrol and plant growth promotion, (ii) the optimization of fermentation and formulation processes for biologicals, (iii) stabilization of the biocontrol effect under field conditions, and (iv) risk assessment studies for biotechnological applications. Examples are presented and discussed for the fields mentioned above, and next-generation bio-products were found as a sustainable alternative for agriculture.

Amending Subsoil with Composted Poultry Litter-I: Effects on Soil Physical and Chemical Properties

Author(s):

Mili Mandal -- Rakesh S. Chandran -- John C. Sencindiver


Abstract
| Pages: 657-669
During construction disturbance, topsoil is often removed and turfgrasses are established in poor soils. Our study determined the effects of amending subsoil with composted poultry litter on physical and chemical properties that affect turfgrass growth attributes. To simulate typical disturbance conditions, 20 cm of topsoil was removed from a Dormont silt loam (fine-loamy, mixed, superactive, mesic Oxyaquic Hapludalfs) and composted poultry litter was incorporated at 0.1, or 0.2, or 0.4 cm/cm-soil into the exposed subsoil to a depth of 12.7 cm before growing turf. Composted plots were compared to N-fertilized (50 × 10−4 kg m−2) and control plots. Linear increases in total water content, organic matter, pH, and basic cations were observed following compost incorporation. Composted poultry litter increased total water content by 38% and decreased soil bulk density by 42%. Compost applications increased organic matter by 5.8%–6.4%, along with an increase in pH from 6.0–7.4. The cation exchange capacity increased up to 186% in compost-incorporated plots. No differences were observed between fertilized and control plots for all soil properties except for P levels, which increased in fertilized plots. Overall, compost treatments improved soil physical and chemical properties compared to conventionally fertilized and control plots.

Amending Subsoil with Composted Poultry Litter-II: Effects on Kentucky Bluegrass (Poa pratensis) Establishment, Root Growth, and Weed Populations

Author(s):

Mili Mandal -- Rakesh S. Chandran -- John A. Balasko


Abstract
| Pages: 670-684
Turfgrasses established on a soil deprived of the topsoil during construction disturbance often have low levels of density and uniformity making them susceptible to weeds. Field experiments evaluated composted poultry litter incorporation into subsoil on Kentucky bluegrass growth attributes and subsequent effects on weed populations. Top 20 cm of topsoil was removed and composted poultry litter was incorporated at 0.1, or 0.2, or 0.4 cm/cm-soil into the exposed subsoil to a depth of 12.7 cm before seeding or sodding, and was compared to N-fertilized (50 × 10−4 kg m−2) and control plots. A greenhouse experiment was also conducted to determine the effect of compost incorporation rates on turfgrass rooting depth. Turfgrass yield from seeded plots with compost incorporation rates of 0.1, 0.2, and 0.4 cm/cm-soil, were 200%, 300%, and 500% more, respectively, compared to control plots. Composted poultry litter incorporated at 0.1 cm/cm-soil resulted in at least 70 seedlings in 7.6 cm−2, which was sufficient to attain 100% turf cover. Higher incorporation rates in seeded plots maintained lower numbers of buckhorn plantain and red clover than untreated plots. Rooting depth also increased linearly with compost rates. Overall, compost treatments were able to maintain superior turf cover and quality compared to conventionally fertilized or control plots.

Identification and Characterisation of New Microbial Antagonists for Biocontrol of Monilinia laxa, the Causal Agent of Brown Rot on Stone Fruit

Author(s):

Nattawut Rungjindamai -- Xiang-Ming Xu -- Peter Jeffries


Abstract
| Pages: 685-703
Monilinia laxa is the causal agent of brown rot disease on stone fruits, and also causes blossom wilt and twig canker. The common practice used to manage this disease is through fungicide treatments. However the demand to reduce fungicide inputs has been increasing and there is a growing number of reports of M. laxa strains that are resistant to fungicides. There is an urgent need to search for an alternative strategy to control the disease. This study focused on the isolation and characterisation of biological control agents (BCAs) using indigenous isolates isolated from cherries and plums collected within the UK. A total of 192 isolates were screened against two strains of M. laxa in a series of in vitro dual culture tests. From this in vitro screen, 12 isolates were selected for a subsequent in vivo screen on detached fruits, which then narrowed these isolates down to two potential BCAs. These two strains were identified as Bacillusamyloliquefaciens/subtilis (isolate B91) and Aureobasidium pullulans (isolate Y126). The capability of these two potential BCAs to grow and survive at a range of temperatures likely to be experienced under field and storage conditions was studied in order to gain knowledge for product formulation and field application.Bacillus sp. B91 was shown to be a mesophilic bacterium that could grow at 10–25 °C but suffered significant mortality at 0 and 5 °C, while A. pullulans Y126 was both mesophilic and psychrotolerant as it grew between 0–25 °C with the optimum at 20 °C. When all nutrients were removed, Y126 was able to survive for several weeks in all test temperatures (0–25 °C) but showed significant mortality at 25 °C. The capability of B91 to survive at 20 and 25 °C was higher than at low temperatures (0–15 °C). In addition, the modes of action of the potential BCAs were studied. B91 was shown to produce soluble and volatile organic compounds that inhibited M. laxa, while A. pullulans Y126 did not produce inhibitory compounds, but appeared to inhibit the pathogen via competition for nutrients. This study shows that microbial antagonists against M. laxa can be found from indigenous sources and that they are capable of preventing brown rot disease in controlled conditions, thus demonstrating a potential to be developed into commercial products.

Introduction of Aureobasidium pullulans to the Phyllosphere of Organically Grown Strawberries with Focus on Its Establishment and Interactions with the Resident Microbiome

Author(s):

Justine Sylla -- Beatrix W. Alsanius -- Erika Krüger -- Annette Reineke -- Monika Bischoff-Schaefer -- Walter Wohanka


Abstract
| Pages: 704-731
Currently, there is little knowledge of the establishment of repeatedly applied biological control agents (BCAs) in the phyllosphere of plants and, in particular, their interactions with the resident microbiome. Under field conditions, the BCA Aureobasidium pullulans was applied as a model organism to organically grown strawberries during two subsequent years (2011, 2012), either as single strain treatment or with the co-application of the entomopathogenic fungus Beauveria bassiana. Fungal and bacterial communities of strawberry leaves were investigated by means of plate counts and 454 pyrosequencing. The establishment of the introduced A. pullulans strains considerably differed between the two years, presumably due to distinct environmental conditions. Short-term and long-term effects of BCA applications on the composition and diversity of fungal communities could be observed as a result of successful establishment of A. pullulans, in 2011, showing, for instance, reduced diversity of fungal communities by competitive displacement shortly after BCA introduction. Due to considerable dynamics in untreated resident microbial communities in the phyllosphere in general, however, we suggest that even the effects caused by the applied BCA preparations in 2011 are negligible under practical conditions.

Enhancing the Sustainability of Quinoa Production and Soil Resilience by Using Bioproducts Made with Native Microorganisms

Author(s):

Noel Ortuño -- José Antonio Castillo -- Mayra Claros -- Oscar Navia -- Marlene Angulo -- Daniel Barja -- Claudia Gutiérrez -- Violeta Angulo


Abstract
| Pages: 732-746
Microorganisms are involved in a network of interactions with plants, promoting growth and acting as biocontrol agents against diseases. In this work, we studied native microorganisms associated with quinoa plants (Chenopodium quinoa) and the application of these organisms to the organic production of quinoa in the Andean Altiplano. Quinoa is a non-cereal grain native to the Andean highlands and is highly nutritious and gluten-free. As such, the international demand for quinoa has increased substantially in recent years. We isolated native endophytic bacteria that are able to fix nitrogen, solubilize phosphate and synthesize a phytohormone and native strains of Trichoderma, a fungus typically used for increasing plant growth and tolerance to biotic and abiotic stresses. Greenhouse assays and field trials allowed for selecting promissory bacterial isolates, mostly belonging to Bacillus and Paenibacillus genera, that increased plant length, panicle weight and grain yield. Selected microbial isolates were large-scale multiplied in simple and inexpensive culture media and then formulated to obtain bioproducts that were distributed among local farmers. Thus, we developed a technology for the exploitation of beneficial microbes, offering promising and environmentally friendly strategies for the organic production of quinoa without perturbing the native microbial diversity of Andean soils and making them more resilient to the adverse effects of climatic change and the over-production of quinoa.

Identification of Water Stress in Citrus Leaves Using Sensing Technologies

Author(s):

Kaitlin Johnson -- Sindhuja Sankaran -- Reza Ehsani


Abstract
| Pages: 747-756
Water stress is a serious concern in the citrus industry due to its effect on citrus quality and yield. A sensor system for early detection will allow rapid implementation of control measures and management decisions to reduce any adverse effects. Laser-induced breakdown spectroscopy (LIBS) presents a potentially suitable technique for early stress detection through elemental profile analysis of the citrus leaves. It is anticipated that the physiological change in plants due to stress will induce changes in the element profile. The major goal of this study was to evaluate the performance of laser-induced breakdown spectroscopy as a method of water stress detection for potential use in the citrus industry. In this work, two levels of water stress were applied to Cleopatra (Cleo) mandarin, Carrizo citrange, and Shekwasha seedlings under the controlled conditions of a greenhouse. Leaves collected from the healthy and stressed plants were analyzed using LIBS, as well as with a spectroradiometer (visible-near infrared spectroscopy) and a thermal camera (thermal infrared). Statistical classification of healthy and stressed samples revealed that the LIBS data could be classified with an overall accuracy of 80% using a Naïve-Bayes and bagged decision tree-based classifiers. These accuracies were lower than the classification accuracies acquired from visible-near infrared spectra. An accuracy of 93% and higher was achieved using a bagged decision tree with visible-near infrared spectral reflectance data.

A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields

Author(s):

Russell G. Sharp


Abstract
| Pages: 757-793
 In recent decades, a greater knowledge of chitin chemistry, and the increased availability of chitin-containing waste materials from the seafood industry, have led to the testing and development of chitin-containing products for a wide variety of applications in the agriculture industry. A number of modes of action have been proposed for how chitin and its derivatives can improve crop yield. In addition to direct effects on plant nutrition and plant growth stimulation, chitin-derived products have also been shown to be toxic to plant pests and pathogens, induce plant defenses and stimulate the growth and activity of beneficial microbes. A repeating theme of the published studies is that chitin-based treatments augment and amplify the action of beneficial chitinolytic microbes. This article reviews the evidence for claims that chitin-based products can improve crop yields and the current understanding of the modes of action with a focus on plant-microbe interactions.

Catch the Best: Novel Screening Strategy to Select Stress Protecting Agents for Crop Plants

Author(s):

Christin Zachow -- Henry Müller -- Ralf Tilcher -- Christina Donat -- Gabriele Berg


Abstract
| Pages: 794-815
Climate change increases stress levels for crops and affects the economic and environmental aspects of agricultural management systems. The application of stress tolerance-mediating microorganisms is an auspicious strategy for improving crop protection, and as such, we developed a direct selection strategy to obtain cultivable microorganisms from promising bioresources using the bait plants, maize, oilseed rape, sorghum and sugar beet. Alpine mosses, lichens and primrose were selected as bioresources, as each is adapted to adverse environmental conditions. A 10% crop-specific selection was found for bait plant rhizosphere communities using cultivation-independent fingerprints, and their potential role as stress protecting agents (SPA) was evaluated following the cultivation of captured bacteria. In addition to assays identifying phytopathogen antagonism and plant growth promotion capacities, our evaluation included those that test the ability to allocate nutrients. Moreover, we developed new assays to measure tolerance in diverse stress conditions. A score scheme was applied to select SPAs with desired properties, and threePseudomonas species with pronounced antagonistic activity that showed elevated tolerance to desiccation and an improved seed germination rate were subsequently chosen. Screening for environmentally-conditioned and host-adapted microorganisms provides a novel tool for target-oriented exploitation of microbial bioresources for the management of ecofriendly crops facing biotic and abiotic stresses.

Rhodococcus erythropolis and Its γ-Lactone Catabolic Pathway: An Unusual Biocontrol System That Disrupts Pathogen Quorum Sensing Communication

Author(s):

Xavier Latour -- Corinne Barbey -- Andrea Chane -- Anne Groboillot -- Jean-François Burini


Abstract
| Pages: 816-838
Rhodococcus erythropolis is an environmental Gram-positive Actinobacterium with a versatile metabolism involved in various bioconversions and degradations. Rhodococci are best known for their great potential in numerous decontamination and industrial processes. However, they can also prevent plant disease by disrupting quorum sensing-based communication of Gram-negative soft-rot bacteria, by degradingN-acyl-homoserine lactone signaling molecules. Such biocontrol activity results partly from the action of the γ-lactone catabolic pathway. This pathway is responsible for cleaving the lactone bond of a wide range of compounds comprising a γ-butyrolactone ring coupled to an alkyl or acyl chain. The aliphatic products of this hydrolysis are then activated and enter fatty acid metabolism. This short pathway is controlled by the presence of the γ-lactone, presumably sensed by a TetR-like transcriptional regulator, rather than the presence of the pathogen or the plant-host in the environment of the Rhodococci. Both the density and biocontrol activity of R.erythropolis may be boosted in crop systems. Treatment with a cheap γ-lactone stimulator, for example, the food flavoring γ-caprolactone, induces the activity in the biocontrol agent, R. erythropolis, of the pathway degrading signaling molecules; such treatments thus promote plant protection.
ADVERTISEMENT