Solani Disease Research Articles

Antifungal activity of Neowestiellopsis persica against Rhizoctonia solani in root and crown of Faba bean cultivated under modified BG-110 medium composition

Rhizoctonia solani, a fungal pathogen, affects the quality and yield of Faba bean crops and hinders plant export. Chemical fungicides effectively control fungal pathogens, but their long-term use harms the environment, soil properties, and human health. Cyanobacteria, a promising source of natural bioactive compounds, have shown efficacy against the fungal colony growth of various plant pathogens, highlighting the need for sustainable practices. As a result, this study examined the biological control of the Rhizoctonia solani disease that affects the Faba bean's root and crown. Disease assessments were then done in five groups: (1) healthy control; (2) control infected with Rhizoctonia solani and not treated with cyanobacterial extract; (3) plant infected with Rhizoctonia solani and treated with cyanobacterial extract suspension of 0.02, (4) 0.04, and (5) 0.08 g/L phosphate during 20 and 34 days. The results of the antioxidant activity by the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay showed that with increasing phosphate concentration, the activity increased significantly. The results of enzymatic activity indicated that time did not significantly impact the enzymatic activity of glutathione peroxidase (GPx), catalase (CAT), and guaiacol peroxidase (GPX), with the highest and lowest activity being related to codes 2 and control, respectively. However, time had a significant effect on superoxidase dismutase (SOD) activity, with the highest activity reported on day 35. Moreover, the results showed that increasing the concentration of the extract significantly decreased cell viability in hepatoblastoma (HepG-2) cell lines. The cyanobacterial extract treatment caused over 66 % damage to plants infected with Rhizoctonia solani. The overall results indicated that Neowestiellopsis persica, grown under higher phosphate concentrations, can be used as an effective antifungal biocontrol against Rhizoctonia solani in Faba bean roots and crowns.

Rhizoctonia solani disease suppression: addition of keratin-rich soil amendment leads to functional shifts in soil microbial communities.

Promoting soil suppressiveness against soil borne pathogens could be a promising strategy to manage crop diseases. One way to increase the suppression potential in agricultural soils is via the addition of organic amendments. This microbe-mediated phenomenon, although not fully understood, prompted our study to explore the microbial taxa and functional properties associated with Rhizoctonia solani disease suppression in sugar beet seedlings after amending soil with a keratin-rich waste stream. Soil samples were analyzed using shotgun metagenomics sequencing. Results showed that both amended soils were enriched in bacterial families found in disease suppressive soils before, indicating that the amendment of keratin-rich material can support the transformation into a suppressive soil. On a functional level, genes encoding keratinolytic enzymes were found to be abundant in the keratin-amended samples. Proteins enriched in amended soils were those potentially involved in the production of secondary metabolites/antibiotics, motility, keratin-degradation, and contractile secretion system proteins. We hypothesize these taxa contribute to the amendment-induced suppression effect due to their genomic potential to produce antibiotics, secrete effectors via the contractile secretion system, and degrade oxalate-a potential virulence factor of R. solani-while simultaneously possessing the ability to metabolize keratin.

FytoSol, a Promising Plant Defense Elicitor, Controls Early Blight (Alternaria solani) Disease in the Tomato by Inducing Host Resistance-Associated Gene Expression

Early blight (EB), caused by the necrotrophic pathogen Alternaria solani, is one of the most common and destructive diseases in the tomato (Solanum lycopersicum L.). The use of fungicides is a prominent tactic used to control EB; however, their undesirable effects on the environment and human health, as well as involvement in the development of resistant strains, have driven researchers to search for new alternatives. Plant defense elicitors are exogenous defense-triggering molecules that induce a plant’s defense system associated with extensive transcriptional- and metabolic reprogramming of the genome and do not cause direct toxicity to phytopathogens. Moreover, 2,6-dichloroisonicotinic acid (INA) was an early-identified and strong plant defense elicitor to various phytopathogens. Recently, the combination of chitosan oligomers and pectin-derived oligogalacturonides that can mimic the induction of plants by a pathogen or damaged-derived molecules (PAMP and DAMP) were characterized as defense elicitors, named FytoSol. In this study, the preventive roles of these two defense elicitors—FytoSol and INA—against EB disease and its molecular basis, were explored. According to the results, FytoSol significantly reduced disease severity by an average of 30% for almost one month with an AUDPC value of 399 compared to the control, which had an AUDPC value of 546. On the contrary, INA did not provide any protection against EB. Gene expression analyses of these two distinct plant defense elicitors indicated that the expression patterns of several SA-, JA-, or ET-pathway-related genes (Pti4, TPK1b, Pto kinase, TomloxD, PRB1-2, SABP2, WRKY33b, WRKY70, PR-5, and PR3) were induced by defense elicitors differently. FytoSol extensively upregulated gene expressions of PR3, downregulated the SA-related defense pathway, and provided remarkable protection against the necrotrophic pathogen Alternaria solani. On the contrary, INA mostly induced genes related to biotrophic and/or hemibiotrophic pathogen protection. Our results indicate that FytoSol is a promising plant defense elicitor against EB and the modes of action of the elicitors are important to characterize their effects against pathogens. Further research may extend the use of defense elicitors as alternatives to pesticides in agriculture.

Effects of silicon dioxide, zinc oxide and titanium dioxide nanoparticles on Meloidogyne incognita, Alternaria dauci and Rhizoctonia solani disease complex of carrot

Foliar spray of silicon dioxide (SiO2 NPs), zinc oxide (ZnO NPs) and titanium dioxide (TiO2 NPs) nanoparticles were used for the management of Meloidogyne incognita, Alternaria dauci and Rhizoctonia solani disease complex of carrot. Foliar spray of SiO2 NPs/ZnO NPs or TiO2 NPs increased plant growth attributes, chlorophyll and carotenoid of carrot. Foliar spray of 0.10 mg ml−1 SiO2 NPs caused the highest increase in plant growth, chlorophyll and carotenoid content of leaves followed by spray of 0.10 mg ml−1 ZnO NPs, 0.05 mg ml−1 SiO2 NPs, 0.05 mg ml−1 ZnO NPs, 0.10 mg ml−1 TiO2 NPs and 0.05 mg ml−1 TiO2 NPs. Use of SiO2 NPs caused a higher reduction in root galling, nematode multiplication and disease indices followed by ZnO NPs and TiO2 NPs. Two principal components analysis showed a total of 97.84% overall data variance in plants inoculated with single pathogen and 97.20% in plants inoculated with two or more pathogens. Therefore, foliar spray of SiO2 NPs appears interesting for the management of disease complex of carrot.

Chitin- and Keratin-Rich Soil Amendments Suppress Rhizoctonia solani Disease via Changes to the Soil Microbial Community.

Enhancing soil suppressiveness against plant pathogens or pests is a promising alternative strategy to chemical pesticides. Organic amendments have been shown to reduce crop diseases and pests, with chitin products the most efficient against fungal pathogens. To study which characteristics of organic products are correlated with disease suppression, an experiment was designed in which 10 types of organic amendments with different physicochemical properties were tested against the soilborne pathogen Rhizoctonia solani in sugar beet seedlings. Organic amendments rich in keratin or chitin reduced Rhizoctonia solani disease symptoms in sugar beet plants. The bacterial and fungal microbial communities in amended soils were distinct from the microbial communities in nonamended soil, as well as those in soils that received other nonsuppressive treatments. The Rhizoctonia-suppressive amended soils were rich in saprophytic bacteria and fungi that are known for their keratinolytic and chitinolytic properties (i.e., Oxalobacteraceae and Mortierellaceae). The microbial community in keratin- and chitin-amended soils was associated with higher zinc, copper, and selenium, respectively.IMPORTANCE Our results highlight the importance of soil microorganisms in plant disease suppression and the possibility to steer soil microbial community composition by applying organic amendments to the soil.

Effects of Pseudomonas putida and Rhizophagus irregularis alone and in combination on growth, chlorophyll, carotenoid content and disease complex of carrot

Effects of Pseudomonas putida and Rhizophagus irregularis alone and in combination were observed on Meloidogyne incognita, Alternaria dauci and Rhizoctonia solani disease complex of carrot (Daucus carota). Rhizoctonia solani caused a higher reduction in plant growth, chlorophyll and carotenoid content followed by A. dauci and M. incognita. Use of P. putida and R. irregularis alone and in combination caused a significant increase in plant growth, chlorophyll, carotenoid and reduced disease indices, galling and nematode multiplication. Application of P. putida caused a higher increase in plant growth, chlorophyll and carotenoid and reduced disease indices, galling and nematode multiplication greater than R. irregularis. Application of P. putida plus R. irregularis was best for the management of M. incognita, A. dauci and R. solani disease complex. Root colonization of R. irregularis/P. putida was high when alone but colonisation by both was increased when inoculated together. M. incognita, A. dauci and R. solani reduced root colonization caused by P. putida and R. irregularis. Disease indices were rated on 1–5 scale. Leaf blight and crown rot indices were nearly 3 when A. dauci and R. solani were inoculated respectively. Disease indices were nearly 5 when pathogens under study were inoculated in combination of 2 or 3. Application of P. putida or R. irregularis with A. dauci or R. solani reduced indices to nearly 2 while both biocontrol agents together reduced indices to nearly 1. In other treatments, disease indices were 2–4 out of 5. The principal components analysis showed significant correlations among various studied attributes with 82.10% overall data variability.

Evaluation of three doses of Trichoderma harzianum for the control of black scab (Rhizoctonia solani) of potatoes in Huari, Ancash

Objectives: To evaluate the effect of three levels of concentration of the biological agent Trichoderma harzianum (Tricho-D) in the control of Rhizoctonia solani potato cv. Yungay in Huari, Ancash. Methods: The research was carried at Tumbos farm, located in the district of Chavin de Huantar, Huari, from November 2018 to February 2019. A completely randomized block design was used, with four treatments (three levels of Tricho-D, and a control). The variables evaluated were: the degree of severity, percentage of incidence, AUDPC, control efficiency, and tuber yield per plant. Results: The dose of 0.3 kg ha-1 of Tricho-D reported less severity with a degree of 0.75 and 7.5% incidence of R. solani disease. Likewise, the dose of 0.3 kg ha-1 of Tricho-D had an effect antagonistic about the fungus R. solani obtaining a high control efficiency with 82.5%. The highest dose of 0.3 kg ha-1 of Tricho-D reported a higher yield per plant with 757.5 g plant-1 in cv. Yungay. Conclusions: The dose of 0.3 kg ha-1 of Tricho-D had an antagonistic effect with the parasitic activity of the R. solani fungus controlling the black scab in potatoes cv. Yungay under field conditions in Chavín of Huantar, Huari-Ancash.

Influence of Substrates in the Development of Bean and in Pathogenicity of Rhizoctonia solani JG Kühn

The number of plants produced in horticultural substrates has increased over the last decade. These substrates are to have some physicochemical and phytosanitary characteristics that allow for optimal growth. Rhizoctonia solani JG Kühn is one of the root and hypocotyl diseases that frequently develops in seedbeds causing severe economic losses worldwide. The aim of this work was to evaluate the substrates and additives used in bean plantlets and the R. solani disease severity. The use of vermiculite or peat did not affect bean germination percentage, but peat promoted the development of the aerial part and vermiculite improved the growth of the root system. R. solani reduced bean germination percentage and bean growth in both peat and vermiculite. The presence of additives (bentonite and/or cornmeal) in the substrates (vermiculite or peat) reduced bean germination and development, favouring the severity of R. solani. However, the addition of cornmeal improves bean dry weight of the aerial part. So, whenever it is necessary to add additives to the substrates to improve the installation and development of a biocontrol agent, such as Trichoderma harzianum, the mix of peat and cornmeal would improve the development of both bean and biocontrol agent.

Effects of Crop Rotation and Biocontrol Amendments on Rhizoctonia Disease of Potato and Soil Microbial Communities

Rotation crops and biocontrol amendments were investigated for suppression of Rhizoctonia solani on potato (Solanum tuberosum) and their interactive effects on soil microbial communities. Greenhouse trials were conducted to evaluate selected rotation crops, including barley, common and “Lemtal” ryegrass, clover, potato, and combinations of barley with ryegrass or clover, for their effects on populations of R. solani and Rhizoctonia disease. Potato and clover preceding potato resulted in higher disease severity than most other rotations, whereas ryegrass reduced stem canker severity. In addition, all ryegrass treatments resulted in substantially higher populations of R. zeae. Field trials evaluating selected biocontrol treatments in combination with different rotations were conducted at two locations in Maine. Potatoes were treated with the biocontrol organisms Laetisaria arvalis, Trichoderma virens, or Bacillus subtilis and planted following rotation crops of barley and ryegrass, barley and clover, or potato. The barley/ryegrass rotation significantly reduced incidence and severity of stem canker and increased tuber yield at one location. Efficacy of the biocontrol treatments varied by rotation and location, with L. arvalis and T. virens reducing black scurf in some rotations and increasing some aspects of tuber yield at one location. Soil microbial community characteristics differed among rotation crops and biocontrol treatments. Significant crop by biocontrol interactions were observed demonstrating the complex interactions among rotation crops, biocontrol treatments, and soil microbial communities, as well as indicating that biocontrol can be enhanced within beneficial rotations.

Use of silicon dioxide nanoparticles for the management of Meloidogyne incognita, Pectobacterium betavasculorum and Rhizoctonia solani disease complex of beetroot (Beta vulgaris L.)

Silicon dioxide nanoparticles (SiO2 NPs) were used as seed priming and foliar spray in two concentrations (100 mg L−1 and 200 mg L−1) for the management of Meloidogyne incognita, Pectobacterium betavasculorum and Rhizoctonia solani disease complex of beetroot (Beta vulgaris L) under greenhouse condition. The disease suppressive ability of SiO2 NPs was dependent on the concentration of NPs and also on the method of its application. Plants grown with SiO2 NPs primed seeds and inoculated with pathogens were found more beneficial than foliar spray in enhancing shoot and root dry weight, chlorophyll content, chlorophyll fluorescence attributes and the activities of defense enzymes in beetroot. Seed priming with SiO2 NPs at 200 mg L−1 caused the highest improvement in shoot and root dry weight, chlorophyll content, chlorophyll fluorescence characters and enhanced the activities of defense enzymes followed by seed priming with SiO2 NPs at 100 mg L−1, foliar spray of SiO2 NPs at 200 mg L-1 and foliar spray of SiO2 NPs at 100 mg L−1. SiO2 NPs seed priming as well as foliar spray caused a reduction in root galling, nematode multiplication and disease indices. Seed priming with SiO2 NPs at 200 mg L−1 resulted the highest reduction in root galling, nematode multiplication and disease indices. The principal component analysis showed significant correlations among the various studied parameters. Two principal components explained a total of 84.2 % overall data variability in plants inoculated with single pathogens and 91.9 % of overall data variability in plants inoculated with two or more pathogens. Therefore, seed priming with SiO2 NPs is expected to serve as an effective measure for the management of M. incognita, P. betavasculorum, and R. solani on beetroot.

Potential of Pseudomonas putida, Bacillus subtilis, and their mixture on the management of Meloidogyne incognita, Pectobacterium betavasculorum, and Rhizoctonia solani disease complex of beetroot (Beta vulgaris L.)

Effects of Pseudomonas putida and Bacillus subtilis alone, and in combinations for the management of Meloidogyne incognita, Pectobacterium betavasculorum, and Rhizoctonia solani disease complex of beetroot (Beta vulgaris L.), were studied. Application of P. putida or B. subtilis to plants with M. incognita or P. betavasculorum or R. solani singly or in combinations caused a significant increase in plant growth parameters and the activities of defense enzymes. A significant increase in chlorophyll fluorescence attributes, viz., Fv/Fm, ɸPSII, qP, NPQ, and ETR were recorded in plants treated with P. putida or B. subtilis over pathogen-inoculated plants. Inoculation of P. putida results in a higher reduction in galling and nematode multiplication than B. subtilis. Maximum reduction in nematode multiplication and galling occurred when a mixture of P. putida and B. subtilis was used. Soft rot and root rot indices were 3 when Pectobacterium betavasculorum and Rhizoctonia solani were inoculated alone. The disease indices were rated 5 when these pathogens and M. incognita were inoculated in combinations. Inoculation of P. putida/B. subtilis with P. betavasculorum or R. solani reduced soft rot and root rot indices to 2 out of 3, while the use of P. putida + B. subtilis reduced indices to 1. Disease indices were reduced to 2–3 out of 5, when P. putida + B. subtilis were used to plants inoculated with two or three pathogens. The principal component analysis showed significant correlations among the various studied attributes. Two principal components explained a total of 86.1 and 93.4% of the overall data variability. Therefore, the use of P. putida together with B. subtilis had the potential for successful management of disease complex of beetroot.

Antifungal action of Lippia alba essential oil in Rhizoctonia solani disease management

Plant pathogens damage agriculture sector to a large extent, resulted in poor crop yield and quality. A well followed practice to curb plant diseases are mostly involved with application of conventional fungicides (synthetic chemical). However, their continuous and uncontrolled use has emerged as big challenge for humans due to the hazardous effect to the environment. This can also leads to the development of resistance to plant pathogens. Green chemistry based approaches have revolutionized the development of new strategies to curb plant diseases. Natural products mainly essential oils have potential to minimize the use of synthetic fungicides for some extent. Therefore, current study was conducted to find out alternative of disease managements strategies against Rhizoctonia solani damping off. The rationale was to study the effect of linalool rich Lippia essential oil against two R. solani isolates infecting commercially important crops, Ocimum basilicum and Plantago ovata. Current study revealed that the use of essential oil emulsion can enhance the survivability of seedlings up to 98% and 92% in treated O. basilicum and P. ovata pots as comparison to non-treated pots 20% and 15%, respectively. Headspace-gas chromatography of treated soil samples have detected minimum oil components leading to lower exposures. Herein, we demonstrated a successful management of damping off disease on two commercially important crops for two consecutive years at nurseries. The isolates of R. solani were further characterized up to sub group level for the first time. In conclusion, Lippia essential oil could be used as biopesticide to treat damping of disease at nursery level.

The Rhizoctonia solani AG1-IB (isolate 7/3/14) transcriptome during interaction with the host plant lettuce (Lactuca sativa L.).

The necrotrophic pathogen Rhizoctonia solani is one of the most economically important soil-borne pathogens of crop plants. Isolates of R. solani AG1-IB are the major pathogens responsible for bottom-rot of lettuce (Lactuca sativa L.) and are also responsible for diseases in other plant species. Currently, there is lack of information regarding the molecular responses in R. solani during the pathogenic interaction between the necrotrophic soil-borne pathogen and its host plant. The genome of R. solani AG1-IB (isolate 7/3/14) was recently established to obtain insights into its putative pathogenicity determinants. In this study, the transcriptional activity of R. solani AG1-IB was followed during the course of its pathogenic interaction with the host plant lettuce under controlled conditions. Based on visual observations, three distinct pathogen-host interaction zones on lettuce leaves were defined which covered different phases of disease progression on tissue inoculated with the AG1-IB (isolate 7/3/14). The zones were defined as: Zone 1—symptomless, Zone 2—light brown discoloration, and Zone 3—dark brown, necrotic lesions. Differences in R. solani hyphae structure in these three zones were investigated by microscopic observation. Transcriptional activity within these three interaction zones was used to represent the course of R. solani disease progression applying high-throughput RNA sequencing (RNA-Seq) analysis of samples collected from each Zone. The resulting three transcriptome data sets were analyzed for their highest expressed genes and for differentially transcribed genes between the respective interaction zones. Among the highest expressed genes was a group of not previously described genes which were transcribed exclusively during early stages of interaction, in Zones 1 and 2. Previously described importance of up-regulation in R. solani agglutinin genes during disease progression could be further confirmed; here, the corresponding genes exhibited extremely high transcription levels. Most differentially higher expressed transcripts were found within Zone 2. In Zone 3, the zone with the strongest degree of interaction, gene transcripts indicative of apoptotic activity were highly abundant. The transcriptome data presented in this work support previous models of the disease and interaction cycle of R. solani and lettuce and may influence effective techniques for control of this pathogen.

Trichoderma virens 106 inoculation stimulates defence enzyme activities and enhances phenolic levels in tomato plants leading to lowered Rhizoctonia solani infection

ABSTRACTInteraction of tomato roots with Trichoderma virens TRS106 provided protection against Rhizoctonia solani-induced disease. In tomato, plants inoculated with R. solani disease symptoms were observed on the roots as brown, necrotic lesions. These symptoms were limited on plants treated with TRS106 and inoculated with R. solani. It was shown that TRS106 did not directly inhibit Rhizoctonia growth in in vitro test. The tested Trichoderma isolate stimulated systemic defence responses in tomato plants, by activating defence enzymes including guaiacol peroxidase (GPX), syringaldazine peroxidase (SPX) and phenylalanine ammonia lyase (PAL). Simultaneously, it enhanced accumulation of phenolics and hydrogen peroxide (H2O2) accompanied by decrease in lipid peroxidation in the leaves. HPLC analysis indicated remarkable increases in the concentrations of 22 phenolics in the leaves of Trichoderma-treated tomato, both uninoculated and inoculated with R. solani. Some of the phenolics were present in a free form, the others were accumulated in a bound form as glycosylated conjugates belonging to phenylpropanoids, hydroxybenzoic and cinnamic acid derivatives and flavonoids. Several of the detected phenolics: ferulic and salicylic acids, pyrocatechol and hesperetin were strongly toxic to R. solani in plate tests. The systemic mobilisation of phenolic metabolism might be an element of tomato defence response positively involved in biocontrol of R. solani by TRS106. Based on the results, T. virens TRS106 may have potential to develop a new biofungicide for integrated management of R. solani-induced disease.

Performance of Three Silicon Sources in Suppressing Rhizoctonia solani Diseases on Sage (Salvia officinalis L.) and in Improving Yield of Plant Herb and Essential Oil

Performance of Three Silicon Sources in Suppressing Rhizoctonia solani Diseases on Sage (Salvia officinalis L.) and in Improving Yield of Plant Herb and Essential Oil

Isolation, Purification and Characterization of Phytotoxins Produced by Rhizoctonia solani AG-3, the Cause Agent of Potato Stem Canker

Studies were conducted to isolate and characterize the phytotoxins extracted from culture filtrates of Rhizoctonia solani isolate anastomosis group 3 (AG-3) using preparative thin layer chromatography (TLC) method. The culture filtrates of R. solani contain a toxic substance that causes canker on potato stems. Eight toxin fractions were collected by column layer chromatography but only four spots were obtained in the TLC analysis. All the four toxin fractions (third, fourth, sixth and seventh fractions) were recognised to have phytotoxic activity. Fourier-transform infrared spectroscopy (FTIR), high performance liquid chromatography (HPLC) and 1H and 13C NMR spectral techniques were used to characterize the phytotoxin. The major functional groups identified from FTIR spectrum includes 2962.1 cm−1 (−CH3), 1465.6 cm−1 (−CH2−), 1727.9 cm−1 (C = O), 1729.8 cm−1 (−COOH) and 1124.3 cm−1 (−OH). Result from HPLC, 1H NMR and 13C NMR showed phytotoxic fractions of 3-methylthiopropionic acid (3-MTPA) and 3-methylthioacrylic acid (3-MTAA). The results of this investigation add to the body of evidence that multiple related compounds are involved in R. solani disease development.

Diversity and Activity of Lysobacter Species from Disease Suppressive Soils.

The genus Lysobacter includes several species that produce a range of extracellular enzymes and other metabolites with activity against bacteria, fungi, oomycetes, and nematodes. Lysobacter species were found to be more abundant in soil suppressive against the fungal root pathogen Rhizoctonia solani, but their actual role in disease suppression is still unclear. Here, the antifungal and plant growth-promoting activities of 18 Lysobacter strains, including 11 strains from Rhizoctonia-suppressive soils, were studied both in vitro and in vivo. Based on 16S rRNA sequencing, the Lysobacter strains from the Rhizoctonia-suppressive soil belonged to the four species Lysobacter antibioticus, Lysobacter capsici, Lysobacter enzymogenes, and Lysobacter gummosus. Most strains showed strong in vitro activity against R. solani and several other pathogens, including Pythium ultimum, Aspergillus niger, Fusarium oxysporum, and Xanthomonas campestris. When the Lysobacter strains were introduced into soil, however, no significant and consistent suppression of R. solani damping-off disease of sugar beet and cauliflower was observed. Subsequent bioassays further revealed that none of the Lysobacter strains was able to promote growth of sugar beet, cauliflower, onion, and Arabidopsis thaliana, either directly or via volatile compounds. The lack of in vivo activity is most likely attributed to poor colonization of the rhizosphere by the introduced Lysobacter strains. In conclusion, our results demonstrated that Lysobacter species have strong antagonistic activities against a range of pathogens, making them an important source for putative new enzymes and antimicrobial compounds. However, their potential role in R. solani disease suppressive soil could not be confirmed. In-depth omics'–based analyses will be needed to shed more light on the potential contribution of Lysobacter species to the collective activities of microbial consortia in disease suppressive soils.

Biocontrol of tomato plant diseases caused by Fusarium solani using a new isolated Aspergillus tubingensis CTM 507 glucose oxidase

The present study focuses on the potential of glucose oxidase (GOD) as a promising biocontrol agent for fungal plant pathogens. In fact, a new GOD producing fungus was isolated and identified as an Aspergillus tubingensis. GOD (125 AU) has been found to inhibit Fusarium solani growth and spore production. Indeed, GOD caused the reduction of spores, the formation of chlamydospores, the induction of mycelial cords and the vacuolization of mycelium. In vivo assays, GOD acted as a curative treatment capable of protecting the tomato plants against F. solani diseases. In fact, the incidence was null in the curative treatment with GOD and it is around 45% for the preventive treatment. The optimization of media composition and culture conditions led to a 2.6-fold enhancement in enzyme activity, reaching 81.48U/mL. This study has demonstrated that GOD is a potent antifungal agent that could be used as a new biofungicide to protect plants from diseases.

Tobacco leaf spot and root rot caused by Rhizoctonia solani Kühn

Rhizoctonia solani Kühn is a soil-borne fungal pathogen that causes disease in a wide range of plants worldwide. Strains of the fungus are traditionally grouped into genetically isolated anastomosis groups (AGs) based on hyphal anastomosis reactions. This article summarizes aspects related to the infection process, colonization of the host and molecular mechanisms employed by tobacco plants in resistance against R. solani diseases. Teleomorph: Thanatephorus cucumeris (Frank) Donk; anamorph: Rhizoctonia solani Kühn; Kingdom Fungi; Phylum Basidiomycota; Class Agaricomycetes; Order Cantharellales; Family Ceratobasidiaceae; genus Thanatephorus. Somatic hyphae in culture and hyphae colonizing a substrate or host are first hyaline, then buff to dark brown in colour when aging. Hyphae tend to form at right angles at branching points that are usually constricted. Cells lack clamp connections, but possess a complex dolipore septum with continuous parenthesomes and are multinucleate. Hyphae are variable in size, ranging from 3 to 17 µm in diameter. Although the fungus does not produce any conidial structure, ellipsoid to globose, barrel-shaped cells, named monilioid cells, 10-20 µm wide, can be produced in chains and can give rise to sclerotia. Sclerotia are irregularly shaped, up to 8-10 mm in diameter and light to dark brown in colour. Symptoms in tobacco depend on AG as well as on the tissue being colonized. Rhizoctonia solani AG-2-2 and AG-3 infect tobacco seedlings and cause damping off and stem rot. Rhizoctonia solani AG-3 causes 'sore shin' and 'target spot' in mature tobacco plants. In general, water-soaked lesions start on leaves and extend up the stem. Stem lesions vary in colour from brown to black. During late stages, diseased leaves are easily separated from the plant because of severe wilting. In seed beds, disease areas are typically in the form of circular to irregular patches of poorly growing, yellowish and/or stunted seedlings. Knowledge is scarce regarding the mechanisms associated with resistance to R. solani in tobacco. However, recent evidence suggests a complex response that involves several constitutive factors, as well as induced barriers controlled by multiple defence pathways. This fungus can survive for many years in soil as mycelium, and also by producing sclerotia, which makes the management of the disease using conventional means very difficult. Integrated pest management has been most successful; it includes timely fungicide applications, crop rotation and attention to soil moisture levels. Recent developments in biocontrol may provide other tools to control R. solani in tobacco.

Biocontrol of Rhizoctonia solani and Sclerotium rolfsii on tomato by delivering antagonistic bacteria through a drip irrigation system

In a 2-year assessment carried out on tomato crops of Central and Southern Italy, a high incidence of Rhizoctonia solani and Sclerotium rolfsii was found. These fungal pathogens attack horticultural crops and are responsible for severe crown and stem rot. Because of technical, economical and environmental issues their chemical control is an arduous task. To find alternative and eco-compatible control methods, the effectiveness of two new antagonistic bacterial isolates ( Burkholderia cepacia, T1A-2B, and Pseudomonas sp., T4B-2A), previously selected from suppressive organic amendments, were tested on tomato plants grown under both growth chamber and field conditions. The potential antagonists were compared with two commercial biofungicides, based on Bacillus subtilis (BSF4) and Trichoderma asperellum (TV1), and four synthetic fungicides (tolclofos-methyl, azoxystrobin, fosetyl-Al and fosetyl-Al + propamocarb). In 2-year field experiments carried out on tomato plants, the biocontrol bacteria as well as the other treatments were applied to the soil, proximal to the plant crowns and main roots, by means of an effective and specific system of drip irrigation. In all the experiments the novel selected biocontrol bacteria significantly reduced both incidence and severity of the diseases caused by S. rolfsii or R. solani, with results demonstrating effectiveness equal to TV1, better than BSF4 and comparable with the synthetic fungicides, except for tolclofos-methyl which was the most effective treatment. In field experiments, carried out for two consecutive years, isolate T1A-2B reduced up to 58.33% and up to 63.8% the severity of the diseases caused by S. rolfsii and R. solani respectively; whereas isolate T4B-2A gave reduction of S. rolfsii and R. solani diseases severity up to 73.2% and up to 62.7%, respectively. This investigation provided insight for the development of novel antagonistic bacterial isolates and, particularly, a suitable method for a more efficient antagonist's distribution in the field in order to better control fungal crown and root rot of horticultural crops.