Soil-borne Pathogen Rhizoctonia Solani Research Articles

Identification of Quantitative Trait Loci and Development of Intermediate Breeding Parent for Rice Sheath Blight Resistance.

The soil-borne pathogen Rhizoctonia solani is one of the most devastating necrotrophic pathogens worldwide, responsible for causing rice sheath blight (RSB). This pathogen has a broad host range, affecting economically important monocots and dicots such as rice, wheat, potato, soybean, sugar beet, and cucumber. Despite extensive screening of rice germplasm, genes that confer full resistance to RSB have rarely been identified, leading to slow progress in breeding resistant varieties. To identify RSB-resistant rice cultivars in Korea, variations in quantitatively inherited resistance have been observed. We conducted a study to visually assess the RSB resistance phenotypes of 250 cultivated varieties under natural disease conditions in the field over several years. Notable candidates included P1401, which showed resistance, while Junam was susceptible. To identify the quantitative trait loci (QTLs) associated with resistance, we developed an F2 mapping population by crossing P1401 and Junam, followed by bulked segregant analysis. These QTLs were mapped to specific locations on seven of the 12 rice chromosomes. This mapping population and the resulting datasets provide valuable resources for advancing genomic research in rice, particularly for marker-assisted breeding strategies for enhancing resistance to R. solani and other important agronomic traits.

Antagonistic potential of Fusarium oxysporum as an endophyte isolated from Horse-chestnut tree in the management of Rhizoctonia solani under in-vitro conditions

Symbiotic relationships are established by endophytic microorganisms with their host, resulting in the provision of diverse advantages, such as protection against plant pathogens. Soil-borne pathogens have become a devastating source of infection in many plant species. The environmentally friendly approaches are scare in managing these soil-borne pathogens. This study was aimed to manage one soil-borne pathogen (Rhizoctonia solani) by employing another fungal endophyte (Fusarium oxysporum) via mean inhibition zone technique. The fungal endophyte was isolated from horse-chestnut tree leaves. The R. solani was extracted from the vegetable’s plants showing typical symptoms of root rot and damping off. Both endophyte and pathogen were grown on suitable culture media. The antagonistic activity of collected endophyte for soil-borne pathogen was checked via mean inhibition zone technique under in-vitro condition. The diversity indices and isolation frequency analysis revealed that this tree specie has versatile endophytic range. The results from the dual culture experiment assessing the antagonistic activity of endophyte against the soil-borne pathogen (R. solani) revealed a significant (P <0.001) impact of the endophyte, evaluation times, and the interaction between endophyte and evaluation times on the size of the pathogen colony. The endophyte exhibited a substantial decrease in pathogen development compared to the control, except between days 11 and 15 after inoculation. The data indicate that F. oxysporum contains endophytic potential, which might be investigated for potential biocontrol agents against other soil-borne diseases.

On-Farm Conversion of Cannabis Sativa Waste Biomass into an Organic Fertilizer by Microbial Digestion

Nearly 90% of the total biomass of hemp plants grown for cannabidiol (CBD) is left to rot in piles, burned, or hauled to landfills post-harvest even though these residues are nutrient-rich. Composting is an option for waste management and nutrient recovery for hemp producers. However, materials, labor costs, time, and space needed to properly construct compost piles pose significant logistic challenges to smallholder farmers who want to manage their waste on-farm. Additionally, the high lignin content of cannabis hurd is often poorly degraded if the compost fails to meet national organic standards for thermophilic conditions. A potentially more efficient and cost-effective alternative is to convert leftover cannabis waste into bio-fertilizers through a semi-anaerobic process by adding microbial inoculants that specialize in lignin degradation. Imio Technologies, Inc. (Imio) developed cannabis-specific microbial inoculants designed to optimize the conversion of hemp waste into a bio-available form. Applied as a liquid culture, Imio microbes colonize wasted stalks and produce organic acids and oxidative enzymes that decompose lignin and release plant nutrients. This study aimed to investigate the ability of Imio microbial inoculants to degrade lignin-rich material into a fertilizer substitute. At the conclusion of a 3-week digestion period, biomass was transformed into a more bioavailable form with a nutrient profile similar to finished composts. Two-week cured fertilizer generated through this process promoted greater root:shoot ratios, which suggests plant growth promotion, compared to a synthetically fertilized control group. The digested hemp fertilizer also showed a value-added property of disease suppression against the soilborne pathogen Rhizoctonia solani.

Biological control of diseases caused by Rhizoctonia solani AG-2-2 in sugar beet (Beta vulgaris L.) using plant growth-promoting rhizobacteria (PGPR)

The soil-borne pathogen Rhizoctonia solani AG-2-2 induces both root and crown rot (RCR) and damping-off in sugar beet, which considerably reduces the productivity of this industrial crop. Most often, synthetic fungicides are commonly used to control this fungus. Biological control agents have attracted interest as an alternative to chemical fungicides for controlling several plant diseases. The current study aimed at finding antagonistic bacteria that could be used for biological control against this pathogen. A set of 198 bacterial strains were screened using an in vitro dual culture test with R. solani AG-2-2. Out of these, eleven isolates with important antifungal activity against the pathogen were chosen and characterized using 16S rRNA gene sequencing. Molecular characterization demonstrated that all selected isolates clustered under the genus Bacillus (B. velezensis B. amyloliquefaciens and B. subtilis). In addition, chosen isolates of bacteria were also characterized for their potential to synthesize antifungal metabolites and for their abilities as plant growth-stimulators. Bacterial isolates differed substantially in their capability to synthesize antifungal metabolites and for their abilities as plant growth-stimulators. Bacterial isolates differed substantially in their capability to synthesize antifungal metabolites and for their abilities as plant growth-stimulators. Bacterial isolates differed substantially in their capability to synthesize lipopeptide antibiotics. A test under greenhouse conditions revealed that sugar beet seeds soaked in an individual bacterial isolate significantly decreased Rhizoctonia damping-off. Additionally, seedlings grown from soaked seeds exhibited significant increase in assessed growth parameters. Likewise, selected bacterial isolates exhibited an antagonistic effect on this pathogen, and considerably decreased the severity of RCR caused by Rhizoctonia. For sustainable agriculture, B. velezensis SS2 seems more promising as a fungal biocontrol agent against Rhizoctonia RCR and B. velezensis BM2 can be used as a bio-fertilizer.

Aerial Blight of Soybean Caused by Rhizoctonia solani AG1-IA: A Diagnostic Guide

Aerial blight is an important disease affecting soybean production in the mid-southern United States and other countries. Aerial blight is caused by the soilborne pathogen Rhizoctonia solani AG1-IA. This diagnostic guide provides details about the symptoms, host range, distribution, isolation, identification, and other characteristics of R. solani AG1-IA to aid with diagnosis and identification of aerial blight in the field.

Efficacy of Biocontrol Agent (BCA) Trichoderma spp. Against Black Scurf Disease (Rhizoctonia solani) of Potato

The current study was designed to determine the efficacy of Trichoderma against soil borne pathogen Rhizoctonia solani causing Black scurf disease in potato. Five various species of Trichoderma (Trichoderma herzianum, Trichoderma asperellum, Trichoderma viride, Trichoderma hamatum and Trichoderma helicum) were screened in vitro against Rhizoctonia solani via Dual culture technique. Amongst the antagonists Trichoderma herzianum, Trichoderma viride and Trichoderma helicum was found to be more potent in inhibiting the mycelial growth of Rhizoctonia solani. The results indicate that Trichoderma helicum and Trichoderma viride showed significant growth in suppressing the mycelial growth of Rhizoctonia solani thus a highest inhibition percentage 71.8% was attained however, the Trichoderma herzianum, Trichoderma asperellum and Trichoderma hamatum showed mycelial percentage of 71.45%, 68.2% and 64.5% respectively. It is therefore concluded that an insignificant inhibition percentage 64.5% was shown by Trichoderma hamatum and found to be least effective in reducing mycelial growth as well as sclerotia formation of the test pathogen Rhizoctonia solani. However Trichoderma is good biocontrol agent and therefore can be used against Black scurf disease of potato.

New Sources of Resistance and Identification of DNA Marker Loci for Sheath Blight Disease Caused by Rhizoctonia solani Kuhn, in Rice

Sheath blight disease caused by the necrotrophic, soilborne pathogen Rhizoctonia solani Kuhn, is the global threat to rice production. Lack of reliable stable resistance sources in rice germplasm pool for sheath blight has made resistance breeding a very difficult task. In the current study, 101 rice landraces were screened against R. solani under artificial epiphytotics and identified six moderately resistant landraces, Jigguvaratiga, Honasu, Jeer Sali, Jeeraga-2, BiliKagga, and Medini Sannabatta with relative lesion height (RLH) range of 21-30%. Landrace Jigguvaratiga with consistent and better level of resistance (21% RLH) than resistant check Tetep (RLH 28%) was used to develop mapping population. DNA markers associated with ShB resistance were identified in F2 mapping population developed from Jigguvaratiga × BPT5204 (susceptible variety) using bulk segregant analysis. Among 56 parental polymorphic markers, RM5556, RM6208, and RM7 were polymorphic between the bulks. Single marker analysis indicated the significant association of ShB with RM5556 and RM6208 with phenotypic variance (R2) of 28.29 and 20.06%, respectively. Co-segregation analysis confirmed the strong association of RM5556 and RM6208 located on chromosome 8 for ShB trait. This is the first report on association of RM6208 marker for ShB resistance. In silico analysis revealed that RM6208 loci resides the stearoyl ACP desaturases protein, which is involved in defense mechanism against plant pathogens. RM5556 loci resides a protein, with unknown function. The putative candidate genes or quantitative trait locus harbouring at the marker interval of RM5556 and RM6208 can be further used to develop ShB resistant varieties using molecular breeding approaches.

Effect of limestone dose on the incidence of Rhizoctonia root rot and soybean yield in four soil types

AbstractRhizoctonia root rot (RRR) is a disease caused by the soilborne pathogen Rhizoctonia solani, which kills soybean plants in patches over croplands. Control is difficult because the pathogen survives in the soil and has a wide host range; therefore, cultural control methods might help to diminish disease pressure. The objective of this study was to evaluate liming as a strategy to reduce the incidence of RRR in soybean grown in four soil types: acrisol (Ac), cambisol Ta (CaTa), cambisol Tb (CaTb) and nitisol (Nit). The treatments were arranged in a factorial design of four doses of limestone (0, 3, 6 and 9 t/ha) at two sites within each field (inside and outside a Rhizoctonia patch). The incidence of RRR inside the patch was on average 40.3% whereas outside it was 1.2%. The reduction in disease incidence was 3.9%, 3.7%, 3.6% and 1.8% per 1000 kg of limestone applied for the Ac, CaTa, CaTb and Nit soils, respectively. The highest soybean yield was of 4713 and 3349 kg/ha for the Ac and Nit soils with application of 6.6 and 6.2 t/ha of limestone, respectively. Soybean yield in the cambisols increased linearly with liming, with an increase in yield of 121 and 172 kg/ha in CaTa and CaTb, respectively, for each 1000 kg of limestone applied. Thus, liming reduced the incidence of RRR in all soils and promoted better soybean nutrition, increasing soybean yield. Therefore, liming is a practice that contributes to both soil fertility and disease control.

Heavy metals bio-removal potential of the isolated Klebsiella sp TIU20 strain which improves growth of economic crop plant (Vigna radiata L.) under heavy metals stress by exhibiting plant growth promoting and protecting traits

Toxic heavy metals, chemical fertilizer and fungicides are mutagenic substances that are becoming increasingly common as a result of urbanization and industrialization. Plants, animals, humans, and the environment as a whole are all affected by these. The elimination of these contaminants is become a worldwide concern. The bio-removal effectiveness of heavy metals, protection against the phytopathogen Rhizoctonia solani , and stimulation of growth in Vigna radiata L. under heavy metals stress by Klebsiella sp. strain TIU20 (KTIU20) was isolated and identified in this study. KTIU20 shows bio-removal capacity for heavy metals by biodegradation, biofilm formation, extracellular polymeric substances (EPS), bioaccumulation , and bio-sorption. The KTIU20 also exhibited in vitro antagonism against the soil-borne pathogen Rhizoctonia solani via creating volatile organic compounds (VOCs) and proteases. The insoluble phosphate solubilization (59.1 μg/ml), production of indole acetic acid (39.5 μg/ml) and ammonia (14.6 μg/ml) by KTIU20, displays plant growth boosting properties that encourage Vigna radiate L. growth when exposed to heavy metals in pot experiment. KTIU20 may be employed as an effective plant growth candidate in agricultural soil, contaminated with heavy metals and fungal pathogen near industrial area. • Heavy metals tolerant bacterium Klebsiella sp strain TIU20(KTIU20) was isolated. • It removes heavy metals by degradation, bioaccumulation, EPS and absorption. • It showed PGP traits and antagonistic role against Rhizoctonia solani ( R.solani ). • It promotes plant growth of mung bean ( Vigna radiata L.) under heavy metals stress. • KTIU20 can be used as a bioremediating agent, plant defender and growth enhancer.

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.

Biocontrol of rice sheath blight with microorganisms obtained in rice cultivated soils

Actinobacteria of the genus Streptomyces are part of the soil microbiota from rice-growing areas and along with other microorganisms, such as Trichoderma spp., combine to act as natural enemies against the destructive soil-borne pathogen Rhizoctonia solani, causal agent of rice sheath blight disease. In this study, seven actinobacteria of the genus Streptomyces and three fungi of the genera Trichoderma and Purpureocillium were isolated from soils cultivated with rice using the serial dilution method. Streptomyces spp. M2A2 was selected for its ability to significantly reduce the in vitro growth of R. solani by 52% after 96 h by antibiosis in dual culture, while in the control treatment the mycelial growth was 100%. Furthermore, biocontrol efficacy of treated plants of the susceptible cultivar Fedearroz 68 with actinobacteria was confirmed and the onset of symptoms were delayed up to 14 days, compared to the control treatment. Rice plants treated with Streptomyces spp. M2A2 showed lesions of R. solani reaching 0.7% of the plant height, the effectiveness of this treatment was similar to the difenoconazole treatment, whereas in the control treatment, the lesions covered 34% of the plant height. When compared to the antagonist fungus Trichoderma spp. M2H1, Streptomyces spp. M2A2 presented a better performance of biological control. The results clearly demonstrated that Streptomyces spp. M2A2 isolate from soils of rice growing areas has biocontrol efficiency against R. solani and therefore can be a promising biocontrol agent.

Necrotrophic lifestyle of Rhizoctonia solani AG3-PT during interaction with its host plant potato as revealed by transcriptome analysis

The soil-borne pathogen Rhizoctonia solani infects a broad range of plants worldwide and is responsible for significant crop losses. Rhizoctonia solani AG3-PT attacks germinating potato sprouts underground while molecular responses during interaction are unknown. To gain insights into processes induced in the fungus especially at early stage of interaction, transcriptional activity was compared between growth of mycelium in liquid culture and the growing fungus in interaction with potato sprouts using RNA-sequencing. Genes coding for enzymes with diverse hydrolase activities were strongly differentially expressed, however with remarkably dissimilar time response. While at 3 dpi, expression of genes coding for peptidases was predominantly induced, strongest induction was found for genes encoding hydrolases acting on cell wall components at 8 dpi. Several genes with unknown function were also differentially expressed, thus assuming putative roles as effectors to support host colonization. In summary, the presented analysis characterizes the necrotrophic lifestyle of R. solani AG3-PT during early interaction with its host.

Trichoderma virens-Tv4 enhances growth promoter and plant defense-related enzymes of mungbean (Vigna radiata) against soil-borne pathogen Rhizoctonia solani

Abstract. Inayati A, Sulistyowati L, Aini LQ, Yusnawan E. 2020. Trichoderma virens-Tv4 enhances growth promoter and plant defense-related enzymes of mungbean (Vigna radiata) against soil-borne pathogen Rhizoctonia solani. Biodiversitas 21: 2410-2419. Trichoderma virens has been studied for its ability to control various soil-borne pathogens as well as to induce plant resistance. The ability of T. virens control R. solani and its capability to induce resistance was evaluated in two different genotypes of mungbean (Vigna radiata (L.) R. Wilczek). Plant growth-promoting capability and production of plant defense-related enzymes during plant-pathogen-Trichoderma interaction were investigated. Pathogen infection caused the morphological and biochemical changes as well as increased plant defense enzymes activity such as peroxidase, polyphenol oxidase, PAL, phenolics, and flavonoid compared to control uninoculated plants. T. virens improved mungbean seedling growth in terms of increased total biomass, root weight, and root length as well as improved chlorophyll content and IAA-synthase from leaves and roots. T. virens treatment alone or in the presence of pathogen-induced mungbean defense-related enzymes indicated by the increasing of PO and PPO activity, and higher accumulation of total phenolic and flavonoid content. Although most of plant induced resistance parameters showed low and non-significant in direct single-factor comparison, Pearson’s correlation showed there was a positive correlation between plant growth promoter compounds (IAA and chlorophyll) with plant defense-related enzymes (total phenol, and flavonoid content). T. virens treatment can induce systemic defense response of mungbean seedling directly by increasing the activity of some defense-related enzymes, and indirectly by improving plant health, and promoting plant growth. In conclusion, T. virens-Tv4 has potential to be developed as bio-control agents to control R. solani as well as to induce mungbean resistance.

Fungistatic Effect of a Chicken Manure-Based Organic Fertilizer for Suppression of a Soilborne Pathogen Rhizoctonia Solani Kühn

Fungistatic Effect of a Chicken Manure-Based Organic Fertilizer for Suppression of a Soilborne Pathogen Rhizoctonia Solani Kühn

Identification of New Resistance Loci Against Sheath Blight Disease in Rice Through Genome-Wide Association Study

Sheath blight (SB) caused by the soil borne pathogen Rhizoctonia solani is one of the most serious global rice diseases. Breeding resistant cultivar is the most economical and effective strategy to control the disease. However, no rice varieties are completely resistant to SB, and only a few reliable quantitative trait loci (QTLs) linked with SB resistance have been identified to date. In this study, we conducted a genome-wide association study (GWAS) of SB resistance using 299 varieties from the rice diversity panel 1 (RDP1) that were genotyped using 44 000 high-density single nucleotide polymorphism (SNP) markers. Through artificial inoculation, we found that only 36.5% of the tested varieties displayed resistance or moderate resistance to SB. In particular, the aromatic and aus sub-populations displayed higher SB resistance than the tropical japonica (TRJ), indica and temperate japonica sub-populations. Seven varieties showed similar resistance levels to the resistant control YSBR1. GWAS identified at least 11 SNP loci significantly associated with SB resistance in the three independent trials, leading to the identification of two reliable QTLs, qSB-3 and qSB-6, on chromosomes 3 and 6. Using favorable alleles or haplotypes of significantly associated SNP loci, we estimated that both QTLs had obvious effects on reducing SB disease severity and can be used for enhancing SB resistance, especially in improving SB resistance of TRJ sub-population rice varieties. These results provided important information and genetic materials for developing SB resistant varieties through breeding.

Modulation of Tomato Response to Rhizoctonia solani by Trichoderma harzianum and Its Secondary Metabolite Harzianic Acid.

The present study investigated the transcriptomic and metabolomic changes elicited in tomato plants (Solanum lycopersicum cv. Micro-Tom) following treatments with the biocontrol agent Trichoderma harzianum strain M10 or its purified secondary metabolite harzianic acid (HA), in the presence or the absence of the soil-borne pathogen Rhizoctonia solani. Transcriptomic analysis allowed the identification of differentially expressed genes (DEGs) that play a pivotal role in resistance to biotic stress. Overall, the results support the ability of T. harzianum M10 to activate defense responses in infected tomato plants. An induction of hormone-mediated signaling was observed, as shown by the up-regulation of genes involved in the ethylene and jasmonate (ET/JA) and salicylic acid (SA)-mediated signaling pathways. Further, the protective action of T. harzianum on the host was revealed by the over-expression of genes able to detoxify cells from reactive oxygen species (ROS). On the other hand, HA treatment also stimulated tomato response to the pathogen by inducing the expression of several genes involved in defense response (including protease inhibitors, resistance proteins like CC-NBS-LRR) and hormone interplay. The accumulation of steroidal glycoalkaloids in the plant after treatments with either T. harzianum or HA, as determined by metabolomic analysis, confirmed the complexity of the plant response to beneficial microbes, demonstrating that these microorganisms are also capable of activating the chemical defenses.

Conventional farming impairsRhizoctonia solanidisease suppression by disrupting soil food web

AbstractIntensive farming in agriculture raises questions in relation to environmental sustainability and the widespread use of agrochemicals. In the present work, we compare the impact of organic and intensive farming, in connection to the soil suppressiveness against the soilborne pathogenRhizoctonia solani. Three farms were considered in the study: two practicing organic cultivation (for 10 and 20 years, respectively), and one applying conventional cultivation. Soil suppressiveness was assessed in a greenhouse bioassay with lettuce (Lactuca sativa). Soil microbiome was characterized by combining BIOLOG EcoPlates™with high‐throughput sequencing of bacterial and eukaryotic rRNA gene markers. Suppressiveness towardsR. solaniwas higher in organic than in conventional farming soil, but this property was lost after soil sterilization. Functional biodiversity was significantly higher in the two organic soils, and this parameter was predictive of the suppressiveness towardsR. solani. According to our analyses, the overall microbial taxonomic diversity was unlinked to suppressiveness. A correlation analysis, carried out at the genus level for the most abundant bacterial and eukaryotic microbialtaxa, showed that 58.7% of the genera had a statistically significant correlation with suppressiveness. In particular, the generaFlavisolibacter,Massilia,Pseudomonas,Ramlibacter,Rhizophusand the oligochaete worms belonging to the Enchytraeidae family positively correlated with the disease suppression.

Soil pathogen-aphid interactions under differences in soil organic matter and mineral fertilizer.

There is increasing evidence showing that microbes can influence plant-insect interactions. In addition, various studies have shown that aboveground pathogens can alter the interactions between plants and insects. However, little is known about the role of soil-borne pathogens in plant-insect interactions. It is also not known how environmental conditions, that steer the performance of soil-borne pathogens, might influence these microbe-plant-insect interactions. Here, we studied effects of the soil-borne pathogen Rhizoctonia solani on aphids (Sitobion avenae) using wheat (Triticum aestivum) as a host.In a greenhouse experiment, we tested how different levels of soil organic matter (SOM) and fertilizer addition influence the interactions between plants and aphids. To examine the influence of the existing soil microbiome on the pathogen effects, we used both unsterilized field soil and sterilized field soil.In unsterilized soil with low SOM content, R. solani addition had a negative effect on aphid biomass, whereas it enhanced aphid biomass in soil with high SOM content. In sterilized soil, however, aphid biomass was enhanced by R. solani addition and by high SOM content. Plant biomass was enhanced by fertilizer addition, but only when SOM content was low, or in the absence of R. solani.We conclude that belowground pathogens influence aphid performance and that the effect of soil pathogens on aphids can be more positive in the absence of a soil microbiome. This implies that experiments studying the effect of pathogens under sterile conditions might not represent realistic interactions. Moreover, pathogen-plant-aphid interactions can be more positive for aphids under high SOM conditions. We recommend that soil conditions should be taken into account in the study of microbe-plant-insect interactions.

PH and water activity in culture media affect biological control activity of Trichoderma atroviride against Rhizoctonia solani

Biological control activity of Trichoderma spp. is heavily influenced by abiotic factors. Effects of pH and water activity (aw) in culture media of Trichoderma atroviride LU132 were assessed on conidium production, germination percentage and bioactivity against a soil-borne pathogen Rhizoctonia solani in dual agar culture assays. The effects of pH and buffer capacity in media were tested on T. atroviride colonies using different proportions (50, 100, 200 and 400mM) of phosphate buffers at pHs of 3.5, 4.5, 5.5, 6.5, 7.5 or 8.5. Water activity experiments tested different aw values (0.998, 0.995, 0.985, 0.977, 0.961 and 0.948). Conidium production was reduced with increasing phosphate buffer concentrations from 50 to 400mM. Maximum germination, and inhibition activity against R. solani was measured for conidia obtained from medium at pH 7.5. Greatest conidium production occurred at aw 0.995 and the least at aw 0.948. Mean conidium germination was greatest (78%) from media at aw 0.961, and least (21%) from aw 0.985. Inhibition and overgrowth activities of Trichoderma colonies were greatest at aw 0.961 and least at aw 0.998. This study has demonstrated that manipulation of culture conditions as such may improve conidium fitness (quantity and quality). However, these factors may not have caused independently effects on the fungus. Effects of physical growth conditions (besides nutritional requirements) are likely to be important for optimum production of biocontrol agents based on T. atroviride LU132, and other similar biocontrol agents.

Effects of Bacillus amyloliquefaciens FZB42 on lettuce growth and health under pathogen pressure and its impact on the rhizosphere bacterial community.

The soil-borne pathogen Rhizoctonia solani is responsible for crop losses on a wide range of important crops worldwide. The lack of effective control strategies and the increasing demand for organically grown food has stimulated research on biological control. The aim of the present study was to evaluate the rhizosphere competence of the commercially available inoculant Bacillus amyloliquefaciens FZB42 on lettuce growth and health together with its impact on the indigenous rhizosphere bacterial community in field and pot experiments. Results of both experiments demonstrated that FZB42 is able to effectively colonize the rhizosphere (7.45 to 6.61 Log 10 CFU g−1 root dry mass) within the growth period of lettuce in the field. The disease severity (DS) of bottom rot on lettuce was significantly reduced from severe symptoms with DS category 5 to slight symptom expression with DS category 3 on average through treatment of young plants with FZB42 before and after planting. The 16S rRNA gene based fingerprinting method terminal restriction fragment length polymorphism (T-RFLP) showed that the treatment with FZB42 did not have a major impact on the indigenous rhizosphere bacterial community. However, the bacterial community showed a clear temporal shift. The results also indicated that the pathogen R. solani AG1-IB affects the rhizosphere microbial community after inoculation. Thus, we revealed that the inoculant FZB42 could establish itself successfully in the rhizosphere without showing any durable effect on the rhizosphere bacterial community.