1,721,051 research outputs found
STREPTOMYCETES AS BIOLOGICAL CONTROL AGENTS AND PLANT GROWTH-PROMOTING BACTERIA
Full text linkDeveloping no-chemical strategies for the control of soil borne pathogens is one of the major issues for the cultivation of leafy vegetables. The application of Biological Control Agents (BCAs) represents a valuable approach and nowadays some biocontrol products are available on the market for greenhouse and field applications. However, these products often show lack of consistency and variable results mainly due to the poor knowledge about their biology and modes of applications and how the agroecosystem components modulate their efficacy.
Streptomycetes are soil inhabitants and have an important ecological role in the turn-over of organic matter; they can also establish beneficial relationships with plant roots enhancing host growth and protection against pathogens through the production of bioactive compounds, lytic enzymes, phytohormones and siderophores.
This PhD project aimed to study streptomycetes as BCA and Plant Growth Promoting Bacteria for their use to manage soil borne fungal epidemics in horticulture.
A collection of 200 endophytic streptomycete strains isolated from roots was used in this work. To be able to compare the activity of every strain against the pathogens, the dual culture assay was optimized for some representative fungal pathogens based on mycelium radial growth rate in vitro. Subsequently, the optimized method was applied to screen the collection. Some strains showed strong inhibitory activity, but it was specific for one target pathogen and in few cases comprised more than one pathogen. Based on the promising results obtained from the in vitro assays for Sclerotinia sclerotiorum, further studies were focused on the activity of ten strains used for biological control of lettuce drop in different conditions. In particular, it was studied the effect of the application timing of the antagonist and the pathogen, and the amount of the streptomycete used to improve lettuce drop protection. The survival analysis applied to the data of the growth chamber experiments showed that when lettuce was sown one week after the growth substrate inoculation with the pathogen and antagonists, disease control improved, and Streptomyces spp. FT05W, SW06W and SW29W reduced the risk of disease incidence by 42%. On the contrary, no beneficial effect was observed when lettuce was sown the same day of the growth substrate inoculation. Streptomycetes spore concentration significantly influenced lettuce drop protection, but this effect was strain-dependent.
Based on these results we planned appropriate field experiment to confirm the results obtained, however, in the field we did not observed significant differences in lettuce protection. Therefore we
speculated that moving from controlled to a more complex agroecosystem environment the streptomycete antagonistic activity could fade away probably due to unfavorable interaction in a more complex microflora.
Indole-3-acetic acid and the siderophore production were observed for Streptomyces spp. CVM02R and SW29W in in vitro assays, but in field experiments no significant PGP effect on lettuce was obtained at harvest assessing the head weights of plants.
The colonization of lettuce rhizosphere and root tissues was investigated using the EGFP labelled strain Streptomyces sp. ZEA17I. This strain showed both rhizospheric and endophytic competences, characters necessary for its successful use for biological control. In addition we showed that applying the strains as spore suspension in the growth substrate resulted in significantly higher roots and rhizosphere colonization than when delivered as seed coating.
In conclusion, the results obtained in this study showed that bacteria of the genus Streptomycetes appear valuable candidates for the biological control of soil borne fungal pathogens. However, the complex interactions among the host plant, the antagonist and the pathogen occurring in the agroecosystem are mostly unknown and could generate contradictory results for different environments. Therefore, we think that further studies on simplified models are necessary in order to understand the mechanism on which biological control is based, in order to improve streptomycete activity as BCA for the management of fungal soil borne epidemics
Indagini micologiche sulla componente eumicetica del deperimento della quercia in Lombardia
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Sensibilità ai fungicidi di Anthostoma decipiens ed Endothiella sp., responsabili della moria del carpino
No full textCompetence of two Streptomyces strains to colonize lettuce seeds, roots and rhizosphere
No full textBeneficial microorganisms with positive activity on plant growth and health offer an attractive alternative to conventional
agriculture. However, the successful application of biological control agents (BCAs) in agriculture has been hindered by
insufficient knowledge of mechanisms by which BCAs interact with the host plants and other microorganisms. Colonization of
the plant roots and development of rhizosphere competence are widely considered as crucial steps through which BCAs
could create useful interactions with plants, and also protect them against soil borne pathogens. Recently, Streptomyces
species are gaining increased interest as BCAs due to their different mechanisms to inhibit plant pathogens. We evaluated one of these mechanisms, the abilities of two Streptomyces spp. strains, ZEA17I, and SW06W, to colonize lettuce seeds,
rhizosphere, and roots. By conjugation, the strains were tagged with enhanced green fluorescent protein and apramycin
resistance genes to study the lettuce colonization dynamics in sterilized sand. The preliminary results showed that both
strains could successfully colonize the lettuce seeds in a very short time, and then develop rhizosphere competence up to six
weeks. Endophytic colonization of the root tissue was also detected after six weeks. The seed, rhizospheric, and endophytic
colonization ability of the two Streptomyces strains may contribute to their biocontrol activities against lettuce soil borne
fungal pathogens
Streptomycetes as biological control agents against basal drop
No full textBasal drop caused by the soil borne pathogen Sclerotinia sclerotiorum is one of the most common and serious diseases of horticultural crops worldwide. The disease can be managed with biological control agents (BCAs) such as Coniothyrium minitans or streptomycetes. The aim of this work was to select new Streptomyces strains to widen the range of BCAs. Two hundred streptomycetes were first tested for their ability to inhibit S. sclerotiorum mycelial growth by dual culture plate assay. 69 strains showed inhibition activity ranging from 60 to 90%. In greenhouse, the amount of S. sclerotiorum inoculum needed to cause about 50% disease incidence was determined in a preliminary test. Ten of the in vitro most active streptomycetes were assessed in vivo by adding their spore suspension to S. sclerotiorum inoculated soil. When BCAs were applied 7 days prior sowing, all streptomycetes and the commercial product were more effective on reducing the lettuce drop incidence than when applied at sowing, and three strains had efficacy similar to C. minitans. These strains were also evaluated on chicory in the field. Plants treated with strains FT05W and ZEA17I produced heavier heads than those treated with CVM02R, suggesting their possible plant growth promoting activity
Cross-resistance studies of metrafenone resistant isolates of Erysiphe necator
No full textErysiphe necator is one of the major fungal diseases of cultivated grapevine worldwide and it is managed almost exclusively by fungicides. It has already developed resistance to several fungicide groups including quinone outside inhibitors (QoI) and sterol biosynthesis inhibitors (SBI). Metrafenone is a fungicide belonging to benzophenones (FRAC group U8), and it is used specifically to control powdery mildews. Although its exact mode of action is not known, it is different from other fungicides used in powdery mildew management and is therefore a valuable choice in fungicide rotation programs.
Recently, we have described metrafenone resistance in a population of E. necator in northern Italy. Thirteen strains were obtained from Franciacorta area and analyzed for their sensitivity to metrafenone in terms of mycelium growth and sporulation. All isolates grew abundantly on control plants; after 14 days of growth their average colony area was 89.4 mm2 (standard deviation, SD 39.9) and they produced on average 2212.1 spores/cm2 (SD. 1668.8). Two strains were sensitive, and they did not grow at the metrafenone concentration used in field (125 mg/l a.i.). The resistant strains grew and sporulated similarly to control at metrafenone field concentration, and even at metrafenone concentration of 1250 mg/l.
Moreover, we studied the cross-resistance of E. necator metrafenone-resistant strains to pyriofenone, which belongs to the same FRAC group and two fungicides representative of QoI and SBI groups, azoxystrobin and myclobutanil. The leaf surface of pyriofenone-treated plants was 100% colonized by metrafenone-resistant strains, confirming cross-resistance between metrafenone and pyriofenone, whereas they were fully inhibited by azoxystrobin and myclobutanil, indicating absence of cross-resistance with QoI and SBI
BIOCONTROL OF SOIL-BORNE PATHOGENS BY STREPTOMYCETES
No full textSoil-borne pathogens such as Pythium, Fusarium, Rhizoctonia or Sclerotinia spp. cause
severe epidemics and extensive crop losses. Disease management employs cultivation of
resistant varieties and use of fungicides. However, these strategies meet serious problems,
such as evolution of virulent pathogen strains, environmental pollution or decreased diversity
of non-target organisms. Furthermore, recent legislation restricts the use of synthetic
chemicals and favors the use of biological control products. Until now, only a small number of
microorganisms have been formulated as biocontrol agents.
Streptomycetes are common inhabitants of rhizosphere. They have been exploited in
farmaceutical industry for the production of antibiotics, but very little is known about their
potential in agrobiology applications as plant growth promoters or biocontrol agents.
In our study, Streptomyces spp. strains isolated from diverse plant species were studied for
their plant growth promoting and biocontrol potential against selected fungal pathogens.
Strains were selected based on their in vitro antagonism against several pathogenic agents
of root rot. These strains were successively tested for their plant growth promoting activity in
vitro and in vivo, with particular reference to tomato, lettuce, corn salad, rocket and onion.
Five strains were identified in in vitro antagonistic assay, that showed inhibitory effects
against at least five diverse pathogens. The ability of selected strains to colonize seed coats
was confirmed by SEM. They were further studied in vitro for their effects on seed
germination and radicle and hypocotyl growth. The activity of individual strains depended on
plant species used in the test and according to their performance the best combinations of
strain-plant species were identified. 3 Streptomyces strains were investigated also in vivo to
evaluate their promoting activity on seedling emergence and plant growth. All three strains
improved substantially seed germination of three selected plant species. The strains were reisolated
from surface-sterilized plant roots to confirm their ability to colonize root tissues. The
ability of these strains to control plant diseases in vivo will be determined successively by
greenhouse pathogenicity tests
Resistance of erysiphe necator to metrafenone in Northern Italy
No full textErysiphe necator is one of the major fungal diseases of cultivated grapevine worldwide. Its management relies almost exclusively on the use of fungicides. However, it has already developed resistance to several fungicide groups, including quinone outside inhibitors and sterol biosynthesis inhibitors. Metrafenone, belonging to benzophenones (FRAC group U8), is a fungicide used to specifically control powdery mildews. It was registered in Europe in 2006 and since then it has been extensively used on grapevine, cereals and cucurbits. Although its exact mode of action is not known, it is different from other fungicides used in powdery mildew management and therefore it represents a valuable choice in fungicide rotation programs [1]. So far, resistance to metrafenone was reported in wheat powdery mildew [2]. In the presented work we investigated metrafenone resistance in the population of E. necator in northern Italy.
The dynamics of grapevine powdery mildew epidemics and metrafenone efficacy were monitored in field in three consecutive years. While 2011 was not favorable for disease development, in 2012 and 2013, almost 100% of grape clusters were infected in the control plots by mid-July, with the disease severity higher than 50%. Metrafenone protected well treated plants in the first two years, where it demonstrated the protection of grape clusters especially in terms of disease severity by more than 80%. On the contrary, no difference from control plots was observed in 2013, neither on leaves nor grape clusters.
Due to the low efficacy of metrafenone in field in 2013, thirteen monoconidial strains were obtained from Franciacorta area and analyzed for their sensitivity to metrafenone in terms of mycelium growth and sporulation. All isolates grew abundantly on control plants; after 14 days of growth their average colony area was 89.4 mm2 (standard deviation, SD 39.9) and they produced on average 2212.1 spores/cm2 (SD. 1668.8). Two strains were sensitive, and they did not grow at the metrafenone concentration used in field (125 mg/l a.i.). The remaining strains showed variable response to metrafenone, and four of them grew and sporulated equally to control even at the metrafenone concentration of 1250 mg/l. Moreover, two additional resistant strains were isolated from the experimental field in 2014, after metrafenone was discontinued and the vineyard changed to biological management.
To our knowledge, this is the first study reporting metrafenone resistance in Erysiphe necator. Our identification of metrafenone resistant strains will be valuable for getting an insight into its mode of action. Further studies are needed to understand its implications for the use of metrafenone in the integrated disease management of grapevine powdery mildew in vineyards, and to determine the impact of resistance on changes in the pathogen population structure, fitness and spread of the resistant strains.
1 Opalski KS, Tresch S, Kogel K-H, Grossmann K, Köhle H, Hückelhoven R. Metrafenone: studies on the mode of action of a novel cereal powdery mildew fungicide. Pest Manag Sci 2006; 62: 393–401.
2 Felsenstein F, Semar M, Stammler G. Sensitivity of wheat powdery mildew (Blumeria graminis f.sp. tritici) towards metrafenone. Gesunde Pflanz 2010; 62: 29–33
- …
