Screening of Organic Substrates for Solid-State Fermentation, Viability and Bioefficacy of Trichoderma harzianum AS12-2, a Biocontrol Strain Against Rice Sheath Blight Disease

The present study was undertaken to find the most suitable organic substrates for the biomass production, viability and efficacy of the biocontrol strain Trichoderma harzianum AS12-2 in the solid-state fermentation system. In total, 13 inexpensive, locally available substrates (agricultural wastes or by-products) were inoculated with the antagonist, and following one month of incubation at room temperature, all colonized substrates were air dried and ground to powder. The shelf life and viability of the Trichoderma strain were assessed as colony-forming units per gram (CFUs g−1) of each substrate on a monthly basis for up to one year at room temperature (25 ± 2 °C) and in the refrigerator (4 °C). In order to find out the effect of the substrate on the bioefficacy of T. harzianum AS12-2, the biocontrol potential of the formulations was evaluated against rice sheath blight disease caused by Rhizoctonia solani. The results showed that the fungus colonized more or less all substrates after one month, although the degree of colonization and conidiation was different among the substrates, being especially high in broom sorghum grain, rice husk, rice straw, rice bran and sugar beet pulp. Analysis of variance (ANOVA) of the population in the substrates in “Month 0” showed that the effect of treatment was significant, and the means were significantly different. The maximum population was recorded for broom sorghum grain and rice straw (6.4 × 1010 and 5.3 × 1010 CFUs g−1, respectively). The population declined in all substrates after one year of incubation at room temperature. This decline was relatively smaller in broom sorghum grain, rice straw and rice husk. On the other hand, the population in the same substrate incubated in the refrigerator was decreased in a mild slope, and the final population was high. In addition, the results of greenhouse assay showed that all bioformulations were effective in controlling the disease, and there were no significant differences among the substrates. According to the results of this study, broom sorghum grain, rice husk, rice straw, sugar beet pulp and cow dung could be recommended as suitable fermentation media for the industrial-scale production of T. harzianum strains

Comparison of survival and pathogenicity of Beauveria bassiana A1-1 spores produced in solid and liquid state fermentation on whitefly nymph, Trialeurodes vaporariorum

In order to use entomopathogenic fungi (EPF) as biological control agents, it is necessary to mass produce the EPF in an economical and cost-effective manner. Currently, the mass production of EPF is carried out mainly in two ways: solid-state fermentation in which the aerial conidia are produced, and liquid fermentation in which the blastospores and submerged conidia are produced. This research compares the survival of Beauveria bassiana A1-1spores from solid and liquid culture media, after 0, 3, 6 and 9 months of storage at room temperature (25 ± 5°C) and in the refrigerator (4°C). Furthermore, it compares the pathogenicity of spores immediately after production and after 9 months of storage on third nymphs of greenhouse whitefly, Trialeurodes vaporariorum. The aerial conidia and blastospores were slightly more virulent than the submerged conidia on whitefly nymphs. In laboratory bioassays, blastospores indicated more pathogenicity on nymphs than submerged conidia, even though there was no significant difference in the pathogenicity of the spores produced in liquid culture media in greenhouse bioassays. Moreover, survival of the aerial conidia at a low temperature (4°C) was higher than that kept at room temperature (25 ± 5°C). This storage temperature comparison revealed a positive effect on the stability and survival of blastospores and submerged conidia as well. Meanwhile, the survival of spores drastically decreased after 3 months of storage at room temperature

Biological control of rice sheath blight disease with formulation of indigenous Trichoderma strains under paddy field conditions

The effectiveness of indigenous Trichoderma strains in preventing sheath blight disease was evaluated during two growing seasons under paddy field conditions. Broom sorghum seeds were used for mass production of Trichoderma strains. Colonized seeds were ground to powder and mixed with talc and carboxymethyl cellulose. Suspensions were made from the bioformulations and sprayed onto rice plants. Effects of Trichoderma strains on disease incidence and severity as well as yield and other growth parameters were determined and compared with a chemical fungicide and a commercial biofungicide. A combined analysis of variance across two years was performed and a statistically significant effect of year, treatment and their interaction was reported. Results indicate that environmental factors and different biological fungicides had a strong effect on disease development under natural conditions. According to the results, propiconazole and T. harzianum AS12-2 resulted in the least disease severity and incidence. Overall, the efficacy of T. harzianum AS12-2 in reducing sheath blight development was significantly better than other Trichoderma treatments and was comparable to the conventional fungicide

Biological control of rice sheath blight disease with formulation of indigenous Trichoderma strains under paddy field conditions

The effectiveness of indigenous Trichoderma strains in preventing sheath blight disease was evaluated during two growing seasons under paddy field conditions. Broom sorghum seeds were used for mass production of Trichoderma strains. Colonized seeds were ground to powder and mixed with talc and carboxymethyl cellulose. Suspensions were made from the bioformulations and sprayed onto rice plants. Effects of Trichoderma strains on disease incidence and severity as well as yield and other growth parameters were determined and compared with a chemical fungicide and a commercial biofungicide. A combined analysis of variance across two years was performed and a statistically significant effect of year, treatment and their interaction was reported. Results indicate that environmental factors and different biological fungicides had a strong effect on disease development under natural conditions. According to the results, propiconazole and T. harzianum AS12-2 resulted in the least disease severity and incidence. Overall, the efficacy of T. harzianum AS12-2 in reducing sheath blight development was significantly better than other Trichoderma treatments and was comparable to the conventional fungicide

Biological Control of Rhizoctonia solani AG1-1A, the Causal Agent of Rice Sheath Blight with Trichoderma Strains

Sheath blight caused by Rhizoctonia solani is one of the most serious rice diseases worldwide. The disease is currently managed only by the excessive application of chemical fungicides which are toxic and not environmentally friendly. Therefore, greater emphasis should be given to biological control as being both safe and effective. Trichoderma species are ubiquitous fungi in the soil and have an antagonistic activity against several soil-borne plant pathogens including R. solani. The present study was undertaken to evaluate the potential of indigenous Trichoderma strains from Mazandaran province, Northern Iran (a Mediterranean region on the southern coast of the Caspian Sea) against R. solani AG1-IA  in vitro, and against sheath blight disease in the glasshouse, in order to find biocontrol isolates for application in the field. More than 200 Trichoderma strains were isolated from the soil, plant debris and the phyllosphere in rice felds. Strains were first screened for their antagonism to R. solani by in vitro antagonism tests including dual culture, antibiosis, the effect of Trichoderma strains on the production and viability of R. solani sclerotia, and hyperparasitism on microscopic slides. According to the in vitro experiments, several strains belonging to T. harzianum, T. virens and T. atroviride showed excellent biocontrol. These potential antagonist strains were further evaluated for their effectiveness in controlling sheath blight under glasshouse conditions. Among the 55 selected strains, seven significantly controlled the disease. T. harzianum AS12-2 was the most effective strain in controlling rice sheath blight, better even than propiconazole, the most commonly used fungicide in Iran

Biological control of rice brown spot with native isolates of three Trichoderma species

Brown spot caused by Bipolaris oryzae is an important rice disease in Southern coast of Caspian Sea, the major rice growing region in Iran. A total of 45 Trichoderma isolates were obtained from rice paddy fields in Golestan and Mazandaran provinces which belonged to Trichoderma harzianum, T. virens and T. atroviride species. Initially, they were screened against B. oryzae by antagonism tests including dual culture, volatile and nonvolatile metabolites and hyperparasitism. Results showed that Trichoderma isolates can significantly inhibit mycelium growth of pathogen in vitro by producing volatile and nonvolatile metabolites Light microscopic observations showed no evidence of mycoparasitic behaviour of the tested isolates of Trichoderma spp. such as coiling around the B. oryzae. According to in vitro experiments, Trichoderma isolates were selected in order to evaluate their efficacy in controlling brown spot in glasshouse using seed treatment and foliar spray methods. Concerning the glasshouse tests, two strains of T. harzianum significantly controlled the disease and one strain of T. atroviride increased the seedling growth. It is the first time that the biological control of rice brown spot and increase of seedling growth with Trichoderma species have been studied in Iran

Biological control of Rhizoctonia solani AG1-1A, the causal agent of rice sheath blight with Trichoderma strains

<p class="MsoNormal" style="margin: 0cm 0cm 10pt;"><span style="mso-ansi-language: EN-US;" lang="EN-US"><span style="font-size: small;"><span style="font-family: Calibri;">Sheath blight caused by <em style="mso-bidi-font-style: normal;">Rhizoctonia solani</em> is one of the most serious rice diseases worldwide. The disease is currently managed only by the excessive application of chemical fungicides which are toxic and not environmentally friendly. Therefore, greater emphasis should be given to biological control as being both safe and effective. <em style="mso-bidi-font-style: normal;">Trichoderma</em> species are ubiquitous fungi in the soil and have an antagonistic activity against several soil-borne plant pathogens including <em style="mso-bidi-font-style: normal;">R. solani</em>. The present study was undertaken to evaluate the potential of indigenous <em style="mso-bidi-font-style: normal;">Trichoderma</em> strains from Mazandaran province, Northern Iran (a Mediterranean region on the southern coast of the Caspian Sea) against <em style="mso-bidi-font-style: normal;">R. solani</em> AG1-IA<span style="mso-spacerun: yes;">&nbsp; </span>in vitro, and against sheath blight disease in the glasshouse, in order to find biocontrol isolates for application in the field. More than 200 <em style="mso-bidi-font-style: normal;">Trichoderma</em> strains were isolated from the soil, plant debris and the phyllosphere in rice felds. Strains were first screened for their antagonism to <em style="mso-bidi-font-style: normal;">R. solani</em> by in vitro antagonism tests including dual culture, antibiosis, the effect of <em style="mso-bidi-font-style: normal;">Trichoderma</em> strains on the production and viability of <em style="mso-bidi-font-style: normal;">R. solani</em> sclerotia, and hyperparasitism on microscopic slides. According to the in vitro experiments, several strains belonging to <em style="mso-bidi-font-style: normal;">T. harzianum</em>, <em style="mso-bidi-font-style: normal;">T. virens</em> and <em style="mso-bidi-font-style: normal;">T. atroviride</em> showed excellent biocontrol. These potential antagonist strains were further evaluated for their effectiveness in controlling sheath blight under glasshouse conditions. Among the 55 selected strains, seven significantly controlled the disease. <em style="mso-bidi-font-style: normal;">T. harzianum</em> AS12-2 was the most effective strain in controlling rice sheath blight, better even than propiconazole, the most commonly used fungicide in Iran.</span></span></span></p

Perception of Biocontrol Potential of Bacillus inaquosorum KR2-7 against Tomato Fusarium Wilt through Merging Genome Mining with Chemical Analysis

Tomato Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (Fol), is a destructive disease that threatens the agricultural production of tomatoes. In the present study, the biocontrol potential of strain KR2-7 against Fol was investigated through integrated genome mining and chemical analysis. Strain KR2-7 was identified as B. inaquosorum based on phylogenetic analysis. Through the genome mining of strain KR2-7, we identified nine antifungal and antibacterial compound biosynthetic gene clusters (BGCs) including fengycin, surfactin and Bacillomycin F, bacillaene, macrolactin, sporulation killing factor (skf), subtilosin A, bacilysin, and bacillibactin. The corresponding compounds were confirmed through MALDI-TOF-MS chemical analysis. The gene/gene clusters involved in plant colonization, plant growth promotion, and induced systemic resistance were also identified in the KR2-7 genome, and their related secondary metabolites were detected. In light of these results, the biocontrol potential of strain KR2-7 against tomato Fusarium wilt was identified. This study highlights the potential to use strain KR2-7 as a plant-growth promotion agent