Characterization of field isolates of Trichoderma antagonistic towards Rhizoctonia solani

National audienceRhizoctonia solani AG 2-2 is a phytopathogenic fungus causing damping off and root rot in sugar beet. The disease occurs in the form of patches. In monoculture, these patches are highly mobile and never occur at the same place where they were observed the previous year. The soil from within patches was found more suppressive towards the disease than soil from healthy area. Comparison of the microbial genetic structures between the different soil samples suggested that Trichoderma spp. were involved in the increased suppressiveness. Trichoderma spp. are well known for their antagonistic activities. The aim of the present study was to characterize sixteen Trichoderma isolates isolated from within and outside the patches of disease, their antagonistic abilities, and the mechanisms involved both in vitro and in vivo against R. solani AG 2-2. Mycoparasitism, production of soluble antibiotics, production of volatile inhibitors and induced suppressiveness were investigated. The isolates were identified using both molecular and morphological techniques. Molecular identification was based on sequencing of the internal transcribed spacers (ITS1 and ITS2) of the ribosomal RNA gene cluster and of the long (4th) intron of the translation elongation factor 1-alpha. Morphological identification was based on microscopic measurements of the fungal structures, and their growth rates at different temperatures on different media. It was observed that the isolates within the patches were more antagonistic than those isolated from outside the patches. Different mechanisms were evident for different strains, including direct interaction, induced suppressiveness, production of soluble antibiotics and production of volatile inhibitors. The most antagonistic strains were identified as T. gamsii. The antagonistic activity was not a characteristic of a species but a characteristic of a population. Finding the marker controlling the expression of the genes involved in the antagonistic activities can be a future perspective

Functional characterization of trichoderma isolates antagonistic against rhizoctonia solani

International audienc

Characterization of field isolates of Trichoderma antagonistic against Rhizoctonia solani

International audienceThe aim of the present study was to characterize sixteen isolates of Trichoderma originating from a field of sugar beet where disease patches caused by Rhizoctonia solani were observed. Use of both molecular and morphological characteristics gave consistent identification of the isolates. Production of water-soluble and volatile inhibitors, mycoparasitism and induced systemic resistance in plant host were investigated using in vitro and in vivo tests in both sterilized and natural soils. This functional approach revealed the intra-specific diversity as well as biocontrol potential of the different isolates. Different antagonistic mechanisms were evident for different strains. The most antagonistic strain, T30 was identified as Trichoderma gamsii. This is the first report of an efficient antagonistic strain of T. gamsii being able to reduce the disease in different conditions. The ability to produce water-soluble inhibitors or coil around the hyphae of the pathogen in vitro was not related to the disease reduction in vivo. Additionally, the strains collected from the high disease areas in the field were better antagonists. The antagonistic activity was not characteristic of a species but that of a population

Caractérisation moléculaire, phénotypique et fonctionnelle d'isolats de <em>Trichoderma sp.</em> antagonistes de <em>Rhizoctonia solani</em>

National audienceThe aim of the present study was to characterize sixteen isolates of Trichoderma originating from a field of sugar beet where disease patches caused by Rhizoctonia solani were observed. The isolates were identified using both molecular and morphological characters and both approaches were found complementary. Production of water-soluble and volatile inhibitors, mycoparasitism and induced systemic resistance in plant host were investigated using in vitro and in vivo tests in disinfested and non-disinfested soils. This functional approach revealed the intraspecific diversity as well as biocontrol potential of the different isolates. Different antagonistic mechanisms were evident for different strains. The most antagonistic strain, T30 was identified as T. gamsii. This is the first report of an efficient antagonistic strain of T. gamsii being able to reduce the disease in different conditions. The ability to produce water-soluble inhibitors or coil around the hyphae of the pathogen in vitro was not related to the disease reduction in vivo. Additionally, the strains collected from the high disease areas in the field were better antagonists. The antagonistic activity was not characteristic of a species but that of a population of strains

Préface

<p>Effect of combinations of chitosan (DP_n 206) or CHOS (DP_n 30) and Signum on cumulative <i>Botrytis cinerea</i> infection of detached chickpea leaves.</p

Inhibition of germination of <i>Botrytis cinerea</i> by chitosan (DP_n 206) and synthetic fungicides, alone and in combination.

<p>Germination was recorded 24 hours after inoculation.</p>a<p>All data are the mean of three experiments ± standard deviation</p>b<p>An E_obs/E_exp ratio of 1 indicates additivity; ratios >1 indicate synergy.</p

Effect of combinations of chitosan (DP_n 206) or chito-oligosaccharides (CHOS DP_n30) and Switch on <i>Botrytis cinerea</i> infection of detached chickpea leaves.

<p>Disease development was scored daily up to eight days after inoculation.</p>a<p>All data are the mean of three replicates (each replicate contained three compound leaves with 6 inoculated leaflets) ± standard deviation.</p>b<p>The AUDPC was used to calculate the protection index.</p>c<p>E_obs/E_exp 1 indicates additivity; E_obs/E_exp>1 indicates synergy.</p>d<p>Conidia in sterile water.</p>e<p>Recommended dose.</p

Combined anti-fungal effects of CHOS and synthetic fungicides.

<p>The pictures illustrate the inhibitory effects of combinations of a synthetic fungicide (Teldor, Switch, Amistar or Signum, at 15, 5, 10 and 10 μg mL⁻¹, respectively) and CHOS (DP_n 23, 10 μg mL⁻¹) on disease caused by <i>Botrytis cinerea</i> applied to detached strawberry flowers, six days after inoculation. The flowers were considered 100% infected when all three inoculation points displayed necrotic signs. All treatments included 18 flowers, but only nine flowers are shown. Control flowers were inoculated with conidia in sterile water.</p

Effect of chitosan (DP_n 206) or CHOS obtained by hydrolysis of chitosan with ScCsn46A on germination of <i>Botrytis cinerea</i> (measured 24 hours after inoculation).

<p>The data points are the mean of three experiments with standard deviation.</p

Dose-response relationships for the inhibitory effect of CHOS (DP_n 37) on germination of <i>Botrytis cinerea</i>, <i>Alternaria brassicicola</i> and <i>Mucor piriformis</i> (measured 24 hours after inoculation).

<p>Dose-response relationships for the inhibitory effect of CHOS (DP_n 37) on germination of <i>Botrytis cinerea</i>, <i>Alternaria brassicicola</i> and <i>Mucor piriformis</i> (measured 24 hours after inoculation).</p