Solani AG Research Articles

Timing of Glyphosate Applications to Wheat Cover Crops to Reduce Onion Stunting Caused by Rhizoctonia solani.

Stunting caused by Rhizoctonia spp. is economically important in irrigated onion bulb crops in the semiarid Columbia Basin of Oregon and Washington, where cereal winter cover crops commonly are planted the previous fall to prevent wind erosion of soil. The cover crop is killed with herbicide application just before or shortly after onion seeding, so that the dead rows of cereal plants provide a physical barrier tall enough to protect onion seedlings against wind and sand blasting but not tall enough to shade onion seedlings. However, the cover crop also serves as a green bridge for Rhizoctonia spp. on cereal roots to colonize the onion roots, potentially resulting in severe stunting of onion seedlings. To determine the effect of timing of application of the herbicide glyphosate to reduce this green bridge effect and, subsequently, onion stunting, three herbicide application intervals preceding onion planting were evaluated in a grower's onion field in each of 2012 and 2014 in the Columbia Basin. The wheat cover crop was killed with a glyphosate application 27, 17, and 3 days before onion seeding in 2012 and 19, 10, and 3 days before seeding in 2014. As the interval between herbicide application and onion planting increased from 3 days to 19 and 27 days, the number of patches of stunted onion plants decreased by ≥55%, total area of stunted patches decreased by 54 to 63%, and patch severity index decreased by 59 to 65%. Similarly, the Rhizoctonia solani AG 8 DNA concentration in soil sampled from the dead cover crop rows declined as the interval between glyphosate application and onion seeding increased in the 2012 trial but not in the 2014 trial. R. solani AG 3 and AG 8 DNA concentrations in soil sampled from the cover crop rows were significantly positively correlated with the number of patches of stunted onion plants (r = 0.490 and 0.607 at P = 0.039 and 0.008, respectively), total area of stunted patches (r = 0.496 and 0.659 at P = 0.035 and 0.003, respectively), and patch severity index (r = 0.492 and 0.635 at P = 0.038 and 0.005, respectively) in the 2012 trial; however, these variables were only correlated significantly with R. solani AG 3 DNA concentration in the 2014 trial. Increasing the interval between herbicide application to the cover crop and onion planting provides a practical management tool for stunting in onion bulb crops.

Rhizoctonia solani AG-1 IA infects both rice and signalgrass in the Colombian Llanos

ABSTRACT Foliar blight and death of signalgrass (Urochloa spp.) pastures are caused by the Rhizoctonia solani fungus. This study aimed at determining which pathogens from the Rhizoctonia species complex are associated with leaf and sheath blight in Urochloa and rice, in the Colombian Llanos. Sympatric areas of Urochloa pastures adjacent to rice cropping areas were sampled using a linear transect system. The pathogens were identified using morphological traits, molecular detection based on specific primers and sequencing of the ITS-5.8S rDNA region. R. solani AG-1 IA predominated as the pathogen associated with foliar blight in all samples from U. brizantha cv. 'Toledo' and hybrid Urochloa cv. 'Mulato'. Besides R. solani AG-1 IA (18 % of the samples), Rhizoctonia oryzae-sativae (71 %) and Sclerotium hydrophilum (11 %) were also detected. In the cross-pathogenicity test, the R. solani AG-1 IA fungus was the most aggressive to Urochloa, while R. oryzae-sativae produced very mild infection symptoms. This is the first report of R. oryzae-sativae and S. hydrophilum associated with the complex of rice sheath blight diseases in Colombia.

Potato root infection by Rhizoctonia solani anastomosis group-3 and Colletotrichum coccodes under current and future spring weather in northern Italy

SUMMARYA study was performed in controlled conditions to reproduce cold and warm spring regimes in the east Po valley, northern Italy with a temperate subcontinental climate, to evaluate whether and to what extent spring weather regimes favour the attack of Rhizoctonia solani or Colletotrichum coccodes on potato, in view of predicted climate change. The main experiment, preceded by a controlled chamber set of tests to quantify response to temperatures of R. solani anastomosis group (AG)-3 and C. coccodes strains, showed that limit temperatures (minimum, maximum and optimum of colony radial growth) of R. solani AG-3 are 6 °C lower than those of C. coccodes. Then, a trial to reproduce early growth stages of potato was performed in phytotrons with sprouts of cvar Hermes to simulate cold and warm spring regimes with two different relative soil moisture contents. That simulation was carried out on native non-sterilized soil samples which were co-inoculated artificially with R. solani AG-3 and C. coccodes. Species-abundance findings of fungal root colonization in potato roots and molecular quantification (quantitative polymerase chain reaction) of C. coccodes and R. solani AG-3 inoculum growth in soil showed that: (i) C. coccodes is more competitive than R. solani AG-3 in colonizing potato root both in warm and cold spring regimes; (ii) R. solani AG-3 infected potato roots only in the coldest spring regimes regardless of soil moisture content; (iii) soil temperature is the greatest factor that influences root colonization of C. coccodes and R. solani as well as that of soil inhabiting fungi including some potential antagonists; (iv) R. solani AG-3 and C. coccodes seem to greatly increase in soil under the relative driest and warmest spring weather regimes expected according to the mean scenarios of climate changing in northern Italy; (v) binucleate Rhizoctonia AG-A, a common non-pathogenic fungus indigenous to agricultural soil of that area, appears to be antagonistic towards root fungal pathogens of potato.

Screening Brassicaceous Plants as Biofumigants for Management of Rhizoctonia solani AG1-IA.

Brassicaceae plants rich in glucosinolates have been used as biofumigants for management of Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) and other soilborne pathogens. Efficacy of brassica plant tissue has mainly been attributed to toxic isothiocyanates released upon hydrolysis of glucosinolates. Management of R. solani AG 1-IA, the causal agent of sheath blight in rice (Oryza sativa), using biofumigation, is promising but needs more validation. Biofumigation activity of nine Brassicaceae plants and two other related species were evaluated in vitro with soils from Texas, Arkansas, or Mississippi. All plants evaluated significantly suppressed the mycelium growth of R. solani AG 1-IA. Mustard (Brassica juncea) cultivars ('Brand 199', 'Ruby Streak', 'Florida Broadleaf', and 'Green Wave') consistently provided the greatest (>90%) mycelial inhibition, while sunn hemp (Crotalaria juncea) and Chinese cabbage (B. rapa) had the least suppressive effect. B. juncea 'Red Giant' and 'Sheali Hong', turnip (B. rapa), kale (B. oleracea), and arugula (Eruca sativa) showed intermediate efficacy or were inconsistent. Effects of soil pasteurization and plant tissue amendment rates were examined with B. juncea Brand 199 and Texas soil. Inhibition of mycelial growth became greater with increasing plant amendment rates up to 3.2% (wt/wt) in the soil. Soil pasteurization almost completely suppressed the release of allyl isothiocyanate (AITC). The nonpasteurized soil amended with 0.5% (wt/wt) of the plant material released 96% more AITC than the soil amended with 0.25% (wt/wt) of the plant material. The highest levels of AITC release were observed at 12 and 24 h after soil amendment, with 0.25 and 0.5% (wt/wt) of the plant material, respectively. Antifungal effects of B. juncea are attributed to dose-dependent production of volatile AITC and could be used for managing rice sheath blight caused by R. solani AG 1-IA.

RSIADB, a collective resource for genome and transcriptome analyses in Rhizoctonia solani AG1 IA.

Rice [Oryza sativa (L.)] feeds more than half of the world’s population. Rhizoctonia solani is a major fungal pathogen of rice causing extreme crop losses in all rice-growing regions of the world. R. solani AG1 IA is a major cause of sheath blight in rice. In this study, we constructed a comprehensive and user-friendly web-based database, RSIADB, to analyse its draft genome and transcriptome. The database was built using the genome sequence (10 489 genes) and annotation information for R. solani AG1 IA. A total of six RNAseq samples of R. solani AG1 IA were also analysed, corresponding to 10, 18, 24, 32, 48 and 72 h after infection of rice leaves.The RSIADB database enables users to search, browse, and download gene sequences for R. solani AG1 IA, and mine the data using BLAST, Sequence Extractor, Browse and Construction Diagram tools that were integrated into the database. RSIADB is an important genomic resource for scientists working with R. solani AG1 IA and will assist researchers in analysing the annotated genome and transcriptome of this pathogen. This resource will facilitate studies on gene function, pathogenesis factors and secreted proteins, as well as provide an avenue for comparative analyses of genes expressed during different stages of infection.Database URL: http://genedenovoweb.ticp.net:81/rsia/index.php

잔디 근권에서 분리된 Actinomycetes균주의 생리학적 특성

Total 443 isolates of actinomycetes were isolated from turfgrass rhizosphere as potential biological control agents. The two isolates (S11 and S4) showed highest cellulase activity with compared to the other isolates that exhibited a clear zone of 1.2 mm around the colony on cellulose agar medium. S12 strain appeared the most active chitin degrading, which exhibited a 1.2 mm of clear zone. The highest proteolytic activity on skim milk agar was which exhibited a 7.5 mm of clear zone by S2 strain. S1 strain from the soli showed siderophore production ability, which exhibited a 0.6 mm of large clear zone on chrome azurol S agar. The antifungal activity of the volatile compound producing by 4 selected actinomycetes was investigated that inhibition rate against Rhizoctonia solani AG2-2 and Sclerotinia homoeocarpa. Growth inhibition effect of S8 isolate against S. homoeocarpa was appeared to 94.8%, S2 to 76.9%, S5 to 46.1% and S12 to 43.5%. The significant inhibition effects on mycelial growth of S. homoeocarpa were shown on media with four strains. The inhibition effect was the highest with S8 strain treatment at 94.8%.

Development of a Rhizoctonia solani AG1-IB Specific Gene Model Enables Comparative Genome Analyses between Phytopathogenic R. solani AG1-IA, AG1-IB, AG3 and AG8 Isolates.

Rhizoctonia solani, a soil-born plant pathogenic basidiomycetous fungus, affects various economically important agricultural and horticultural crops. The draft genome sequence for the R. solani AG1-IB isolate 7/3/14 as well as a corresponding transcriptome dataset (Expressed Sequence Tags—ESTs) were established previously. Development of a specific R. solani AG1-IB gene model based on GMAP transcript mapping within the eukaryotic gene prediction platform AUGUSTUS allowed detection of new genes and provided insights into the gene structure of this fungus. In total, 12,616 genes were recognized in the genome of the AG1-IB isolate. Analysis of predicted genes by means of different bioinformatics tools revealed new genes whose products potentially are involved in degradation of plant cell wall components, melanin formation and synthesis of secondary metabolites. Comparative genome analyses between members of different R. solani anastomosis groups, namely AG1-IA, AG3 and AG8 and the newly annotated R. solani AG1-IB genome were performed within the comparative genomics platform EDGAR. It appeared that only 21 to 28% of all genes encoded in the draft genomes of the different strains were identified as core genes. Based on Average Nucleotide Identity (ANI) and Average Amino-acid Identity (AAI) analyses, considerable sequence differences between isolates representing different anastomosis groups were identified. However, R. solani isolates form a distinct cluster in relation to other fungi of the phylum Basidiomycota. The isolate representing AG1-IB encodes significant more genes featuring predictable functions in secondary metabolite production compared to other completely sequenced R. solani strains. The newly established R. solani AG1-IB 7/3/14 gene layout now provides a reliable basis for post-genomics studies.

Rapid Quantitative Assessment of Rhizoctonia Resistance in Roots of Selected Wheat and Barley Genotypes

Rhizoctonia solani AG8, causal agent of Rhizoctonia root rot and bare patch in dryland cereal production systems of the Pacific Northwest United States and Australia, reduces yields in a wide range of crops. Disease is not consistently controlled by available management practices, so genetic resistance would be a desirable resource for growers. In this report, we describe three rapid and low-cost assays for R. solani AG8 resistance in wheat and barley, with the view of facilitating screens for genetic resistance in these hosts. The first assay uses 50-ml conical centrifuge tubes containing soil infested with R. solani AG8 on a substrate of ground oats. The second assay uses roots of 3-day-old seedlings directly coated with infested ground oats, followed by incubation in plastic dishes. The third assay, suitable for barley, uses whole infested oat kernels in 50-ml tubes. Symptoms are quantified on the bases of root fresh weight and total root length at 7 and 3 days for the tube and coating assays, respectively. Each of the assays show the same disease differential between susceptible and partially resistant wheat genotypes. The assays can be conducted in the laboratory, growth chamber, or greenhouse.

Utility of fungicides for controlling Rhizoctonia solani on sugar beet

Rhizoctonia solani is the most serious problem on sugar beet Beta vulgaris L. grown in North Dakota and Minnesota. Picoxystrobin, a quinone outside inhibitor, and penthiopyrad, a succinate dehydrogenase inhibitor, were used alone and in combinations for controlling R. solani AG 2-2 IIIB on sugar beet under greenhouse conditions of 22 ± 2 °C and a 12-h photoperiod. Fungicides were applied in-furrow at planting, followed by inoculation with R. solani grown on barley seeds. The experimental design was a randomized complete block with four replicates and the experiment was repeated three times. Stand counts were taken and roots were evaluated for symptoms using a 0 to 7 scale 21 days after inoculation. Analysis of variance was conducted by the SAS general linear model, and Fisher’s protected least significant difference at α = 0.05 was used to compare treatment means. Fungicides used alone and in mixtures provided effective control of R. solani, which had significantly greater percent survivors than the inoculated check. This research demonstrated that picoxystrobin and penthiopyrad have the potential to be used for providing control of R. solani on sugar beet.

Controlling Rhizoctonia Damping-off of Chinese Mustard by Using Endomycorrhizal Rhizoctonia spp. Isolated from Orchid Mycorrhizae

Inoculation of hypovirulent Rhizoctonia spp. has been recognized as an effective strategy for protecting plants against damping-off caused by pathogenic Rhizoctonia spp. In this study, endomycorrhizal Rhizoctonia spp. isolated from fungal pelotons in orchid plants were used for controlling Rhizoctonia damping-off of Chinese mustard. According to phylogenetic analysis and anastomosis group (AG) determination, the virulence of three isolates of multinucleate Rhizoctonia solani in AG-6; eight isolates of binucleate Rhizoctonia in AG-A, AG-B, AG-G, AG-P, and AG-R; and two isolates of binucleate R. repens were evaluated using test plants. All isolates, except that in AG-R, caused low disease severity in 10-day-old radish (0.10 to 0.61), cucumber (0.28 to 0.54), and Chinese mustard (0.18 to 0.65). By contrast, pathogenic isolates in AG-4 killed almost all test plants with symptoms of collapsed hypocotyl and wilted leaves (0.88 to 0.96). Of the 13 endomycorrhizal Rhizoctonia isolates assessed, AG-P isolates Cno10-3 and CalS1-2 provided 91 and 100% protection, respectively, against R. solani AG-4 in 26-day-old Chinese mustard. This study revealed that endomycorrhizal Rhizoctonia spp. in orchid have the potential to biologically control damping-off of Chinese mustard.

The Urochloa Foliar Blight and Collar Rot Pathogen Rhizoctonia solani AG-1 IA Emerged in South America Via a Host Shift from Rice.

The fungus Rhizoctonia solani anastomosis group (AG)-1 IA emerged in the early 1990s as an important pathogen causing foliar blight and collar rot on pastures of the genus Urochloa (signalgrass) in South America. We tested the hypothesis that this pathogen emerged following a host shift or jump as a result of geographical overlapping of host species. The genetic structure of host and regional populations of R. solani AG-1 IA infecting signalgrass, rice, and soybean in Colombia and Brazil was analyzed using nine microsatellite loci in 350 isolates to measure population differentiation and infer the pathogen reproductive system. Phylogeographical analyses based on the microsatellite loci and on three DNA sequence loci were used to infer historical migration patterns and test hypotheses about the origin of the current pathogen populations. Cross pathogenicity assays were conducted to measure the degree of host specialization in populations sampled from different hosts. The combined analyses indicate that the pathogen populations currently infecting Urochloa in Colombia and Brazil most likely originated from a population that originally infected rice. R. solani AG-1 IA populations infecting Urochloa exhibit a mixed reproductive system including both sexual reproduction and long-distance dispersal of adapted clones, most likely on infected seed. The pathogen population on Urochloa has a genetic structure consistent with a high evolutionary potential and showed evidence for host specialization.

Mid-Infrared (MIR) and Near-Infrared (NIR) Detection of Rhizoctonia solani AG 2-2 IIIB on Barley-Based Artificial Inoculum.

The amount of Rhizoctonia solani in the soil and how much must be present to cause disease in sugar beet (Beta vulgaris L.) is relatively unknown. This is mostly because of the usually low inoculum densities found naturally in soil and the low sensitivity of traditional serial dilution assays. We investigated the usefulness of Fourier transform mid-infrared (MIR) and near-infrared (NIR) spectroscopic properties in identifying the artificial colonization of barley grains with R. solani AG 2-2 IIIB and in detecting R. solani populations in plant tissues and inoculants. The objectives of this study were to compare the ability of traditional plating assays to NIR and MIR spectroscopies to identify R. solani in different-size fractions of colonized ground barley (used as an artificial inoculum) and to differentiate colonized from non-inoculated barley. We found that NIR and MIR spectroscopies were sensitive in resolving different barley particle sizes, with particles that were <0.25 and 0.25-0.5 mm having different spectral properties than coarser particles. Moreover, we found that barley colonized with R. solani had different MIR spectral properties than the non-inoculated samples for the larger fractions (0.5-1.0, 1.0-2.0, and >2.0 mm) of the ground barley. This colonization was confirmed using traditional plating assays. Comparisons with the spectra from pure fungal cultures and non-inoculated barley suggest that the MIR spectrum of colonized barley is different because of the consumption of C substrates by the fungus rather than because of the presence of fungal bands in the spectra of the colonized samples. We found that MIR was better than NIR spectroscopy in differentiating the colonized from the control samples.

Complete genome sequence of Bacillus thuringiensis strain HD521.

Bacillus thuringiensis is the most widely used biological pesticide in the world. It belongs to the Bacillus cereus sensu lato group, which contains six species. Among these six species, B. thuringiensis, B. anthracis, and B. cereus have a low genetic diversity. B. thuringiensis strain HD521 shows maroon colony which is different from most of the B. thuringiensis strains. Strain HD521 also displays an ability to inhibit plant sheath blight disease pathogen (Rhizoctonia solani AG1 IB) growth and can form bipyramidal parasporal crystals consisting of three cry7 genes. These crystals have an insecticidal activity against Henosepilachna vigintioctomaculata larva (Coleoptera). Here we report the complete genome sequence of strain HD521, which has one chromosome and six circular plasmids.

식물 성장 촉진에 사용에 있어 Bacillus mojavensis KJS-3의 특징

Scientists have recently shown an interest in the characteristics of Bacillus mojavensis strains because of their increasing use in plants as a defense against diseases and mycotoxins. We have shown here that B. mojavensis KJS-3 possesses the typical characteristics of B. mojavensis strains including a strong resistance to high temperatures (≤50°C), tolerance to high salt concentrations (7% NaCl), ethanol tolerance (40% ethanol), and pH range for growth (pH 5-9). B. mojavensis KJS-3 has been used for the production of cyclic lipopeptides including important antifungal substances such as surfactin, iturin, and fengycin. Polymerase chain reaction analysis in this study showed that B. mojavensis KJS-3 can be used for the production of fengycin and the findings of LC-MS/MS analyses suggest that B. mojavensis KJS-3 can be used to produce iturin and surfactin. Antifungal activity analys is confirmed that B. mojavensis KJS-3 has antifungal effects on Botrytis cinerea, Rhizoctonia solani AG-4, Sclerotinia sclerotiorum, and Colletotricum goeosporioides. A microscopy assessment of the roots of wild ginseng plants planted together with B. mojavensis KJS-3 revealed that the roots contained B. mojavensis KJS-3, confirming the bacteria to be a plant growth promoting endophyte (PGPE) which acts against plant diseases and mycotoxins. Our findings lead us to conclude that B. mojavensis KJS-3 can be produced at an industrial level as a microbial pesticide or microbial fertilizer.

Rhizoctonia blight of turnip green caused by Rhizoctonia solani AG-4 HG-III

Severe wilt was found on seedlings of turnip green (Brassica rapa L., perviridis group) in Ibaraki Prefecture, Japan, from May to September 2013. A fungus repeatedly isolated from diseased plants was identified as Rhizoctonia solani AG-4 HG-III based on culture morphology, anastomosis and sequencing of the internal transcribed spacer region on ribosomal DNA (rDNA-ITS region). Pathogenicity of this isolate to turnip green was confirmed based on inoculation test. Because Rhizoctonia blight of turnip green by AG-4 HG-III has not been reported so far, we propose including it as one of the pathogens causing this disease.

Transcriptomic changes in the plant pathogenic fungus Rhizoctonia solani AG-3 in response to the antagonistic bacteria Serratia proteamaculans and Serratia plymuthica.

BackgroundImproved understanding of bacterial-fungal interactions in the rhizosphere should assist in the successful application of bacteria as biological control agents against fungal pathogens of plants, providing alternatives to chemicals in sustainable agriculture. Rhizoctonia solani is an important soil-associated fungal pathogen and its chemical treatment is not feasible or economic. The genomes of the plant-associated bacteria Serratia proteamaculans S4 and Serratia plymuthica AS13 have been sequenced, revealing genetic traits that may explain their diverse plant growth promoting activities and antagonistic interactions with R. solani. To understand the functional response of this pathogen to different bacteria and to elucidate whether the molecular mechanisms that the fungus exploits involve general stress or more specific responses, we performed a global transcriptome profiling of R. solani Rhs1AP anastomosis group 3 (AG-3) during interaction with the S4 and AS13 species of Serratia using RNA-seq.ResultsApproximately 104,504 million clean 75-100 bp paired-end reads were obtained from three libraries, each in triplicate (AG3-Control, AG3-S4 and AG3-AS13). Transcriptome analysis revealed that approximately 10 % of the fungal transcriptome was differentially expressed during challenge with Serratia. The numbers of S4- and AS13-specific differentially expressed genes (DEG) were 866 and 292 respectively, while there were 1035 common DEGs in the two treatment groups. Four hundred and sixty and 242 genes respectively had values of log2 fold-change > 3 and for further analyses this cut-off value was used. Functional classification of DEGs based on Gene Ontology enrichment analysis and on KEGG pathway annotations revealed a general shift in fungal gene expression in which genes related to xenobiotic degradation, toxin and antioxidant production, energy, carbohydrate and lipid metabolism and hyphal rearrangements were subjected to transcriptional regulation.ConclusionsThis RNA-seq profiling generated a novel dataset describing the functional response of the phytopathogen R. solani AG3 to the plant-associated Serratia bacteria S4 and AS13. Most genes were regulated in the same way in the presence of both bacterial isolates, but there were also some strain-specific responses. The findings in this study will be beneficial for further research on biological control and in depth exploration of bacterial-fungal interactions in the rhizosphere.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1758-z) contains supplementary material, which is available to authorized users.

Interplay between orfamides, sessilins and phenazines in the control of Rhizoctonia diseases by Pseudomonas sp. CMR12a.

We investigated the role of phenazines and cyclic lipopeptides (CLPs) (orfamides and sessilins), antagonistic metabolites produced by Pseudomonas sp. CMR12a, in the biological control of damping-off disease on Chinese cabbage (Brassica chinensis) caused by Rhizoctonia solani AG 2-1 and root rot disease on bean (Phaseolus vulgaris L.) caused by R. solani AG 4-HGI. A Pseudomonas mutant that only produced phenazines suppressed damping-off disease on Chinese cabbage to the same extent as CMR12a, while its efficacy to reduce root rot on bean was strongly impaired. In both pathosystems, the phenazine mutant that produced both CLPs was equally effective, but mutants that produced only one CLP lost biocontrol activity. In vitro microscopic assays revealed that mutants that only produced sessilins or orfamides inhibited mycelial growth of R. solani when applied together, while they were ineffective on their own. Phenazine-1-carboxamide suppressed mycelial growth of R. solani AG 2-1 but had no effect on AG 4-HGI. Orfamide B suppressed mycelial growth of both R. solani anastomosis groups in a dose-dependent way. Our results point to an additive interaction between both CLPs. Moreover, phenazines alone are sufficient to suppress Rhizoctonia disease on Chinese cabbage, while they need to work in tandem with the CLPs on bean.

Predicting Cereal Root Disease in Western Australia Using Soil DNA and Environmental Parameters.

Root diseases have long been prevalent in Australian grain-growing regions, and most management decisions to reduce the risk of yield loss need to be implemented before the crop is sown. The levels of pathogens that cause the major root diseases can be measured using DNA-based services such as PreDicta B. Although these pathogens are often studied individually, in the field they often occur as mixed populations and their combined effect on crop production is likely to vary across diverse cropping environments. A 3-year survey was conducted covering most cropping regions in Western Australia, utilizing PreDicta B to determine soilborne pathogen levels and visual assessments to score root health and incidence of individual crop root diseases caused by the major root pathogens, including Rhizoctonia solani (anastomosis group [AG]-8), Gaeumannomyces graminis var. tritici (take-all), Fusarium pseudograminearum, and Pratylenchus spp. (root-lesion nematodes) on wheat roots for 115, 50, and 94 fields during 2010, 2011, and 2012, respectively. A predictive model was developed for root health utilizing autumn and summer rainfall and soil temperature parameters. The model showed that pathogen DNA explained 16, 5, and 2% of the variation in root health whereas environmental parameters explained 22, 11, and 1% of the variation in 2010, 2011, and 2012, respectively. Results showed that R. solani AG-8 soil pathogen DNA, environmental soil temperature, and rainfall parameters explained most of the variation in the root health. This research shows that interactions between environment and pathogen levels before seeding can be utilized in predictive models to improve assessment of risk from root diseases to assist growers to plan more profitable cropping programs.

Effects of damping-off caused by Rhizoctonia solani anastomosis group 2-1 on roots of wheat and oil seed rape quantified using X-ray Computed Tomography and real-time PCR.

Rhizoctonia solani is a plant pathogenic fungus that causes significant establishment and yield losses to several important food crops globally. This is the first application of high resolution X-ray micro Computed Tomography (X-ray μCT) and real-time PCR to study host–pathogen interactions in situ and elucidate the mechanism of Rhizoctonia damping-off disease over a 6-day period caused by R. solani, anastomosis group (AG) 2-1 in wheat (Triticum aestivum cv. Gallant) and oil seed rape (OSR, Brassica napus cv. Marinka). Temporal, non-destructive analysis of root system architectures was performed using RooTrak and validated by the destructive method of root washing. Disease was assessed visually and related to pathogen DNA quantification in soil using real-time PCR. R. solani AG2-1 at similar initial DNA concentrations in soil was capable of causing significant damage to the developing root systems of both wheat and OSR. Disease caused reductions in primary root number, root volume, root surface area, and convex hull which were affected less in the monocotyledonous host. Wheat was more tolerant to the pathogen, exhibited fewer symptoms and developed more complex root systems. In contrast, R. solani caused earlier damage and maceration of the taproot of the dicot, OSR. Disease severity was related to pathogen DNA accumulation in soil only for OSR, however, reductions in root traits were significantly associated with both disease and pathogen DNA. The method offers the first steps in advancing current understanding of soil-borne pathogen behavior in situ at the pore scale, which may lead to the development of mitigation measures to combat disease influence in the field.

Anti-phytopathogenic activity of Syzygium cumini essential oil, hydrocarbon fractions and its novel constituents

Current study aims to explore natural anti-phytopathogenic compounds for plant disease management. Syzygium cumini essential oil and its isolated compounds were screened for their antifungal assay against two phytopathogenic fungi, Rhizoctonia solani AG 4HG-III and Choanephora cucurbitarum. The chemical composition of oil the isolated oil was identified by gas chromatography and gas chromatography/mass spectrometry.Compounds such as 7-hydroxycalamenene, 7-acetoxycalamenene, 1-epi-cubenol, and α-terpineol showed an inhibition, ca. 95%, 80%, 76%, and 82%, respectively, against R. solani whereas 95%, 70%, 92%, and 100% against C. cucurbitarum in contact phase. In addition, high ocimene rich column fractions showed 70% and 87% inhibition against R. solani and C. cucurbitarum, respectively, in volatile phase.The findings of the present study suggest that the isolated 7-hydroxycalamenene, 7-acetoxycalamenene, 1-epi-cubenol, α-terpineol, and (Z)-β- & (E)-β-ocimene have a potential to be used as antifungal agents for the effective control of fungal diseases in medicinal plants. We report 7-acetoxycalamenene as novel compound from natural source for first time.