Pyrenochaeta Lycopersici Research Articles

A Quantitative PCR Method to Detect the Tomato Corky Root Rot Pathogens, Pseudopyrenochaeta lycopersici and P. terrestris.

Corky root rot is an important disease in tomato production systems and is caused by Pseudopyrenochaeta terrestris and P. lycopersici (formerly Pyrenochaeta lycopersici Types 1 and 2, respectively). The corky root rot pathogens are slow growing and difficult to isolate and quantify in soil and plant tissue. A multiplex hydrolysis probe-based qPCR assay was designed to allow for simultaneous detection and quantification of P. lycopersici and P. terrestris with a competitive internal control to indicate if qPCR inhibitors are present. Single species and multiplex assays for Pseudopyrenochaeta spp. detected DNA levels above 0.013 pg of DNA per reaction. These highly specific assays had no nontarget amplification of other fungal and oomycete pathogens or rhizosphere-associated fungi of tomatoes that were tested. This assay can be used to quantify Pseudopyrenochaeta populations in roots and soils in tomato production systems to better determine the impacts of disease management strategies on Pseudopyrenochaeta spp. and provides a tool to study the biology of Pseudopyrenochaeta spp.

Tomato Crop Health, Yield, and Greenhouse Soil Conditions after 17 Years of Repeated Treatments of Biofumigation and Solarization

The combination of biofumigation and solarization is known as bio-solarization. An experiment was performed from 2003 to 2019 in a greenhouse at INTA San Pedro, Buenos Aires province, Argentina (33°44'12.7"S 59°47'58.2"W). Treatments (TRAT) were applied every two years. TRAT evaluated were: 1=Control; 2= Solarization, 3= Biorot, a succession of organic amendments (chicken manure, broccoli, chicken manure, broccoli, tomato, and pepper crop debris, mustard, tomato crop debris, broccoli, tomato crop debris), 4=Biobras based only on the use of brassicas (rapeseed, broccoli, mustard, and Brassica campestris). Treatments were carried out in spring or summer so that a late-season tomato crop could be grown after them. The tomato hybrid planted was Superman (Petoseed), except for the last season where the hybrid used was Rodeo (BHN). Fungal pathogens controlled were Pyrenochaeta lycopersici, Fusarium solani, Sclerotium rolfsii, and Sclerotinia sclerotiorum, and nematodes like Nacobbus aberrans, Helicotylenchus and Criconemella. Fungi of Aspergillus genera were observed growing on death sclerotia of Sclerotinia sclerotiorum and Sclerotium rolfsii in Biobras and Biorot. Tomato plants in control showed a higher percentage of dead plants, root rots, and lower root dry matter at the end of each crop. Solarization alone without adding organic matter reduced this parameter in the soil and showed more death plants and less yield than Biobras and Biorot. Tomato and pepper crop debris used as biofumigants produced high yield values and adequate pathogen control. Biofumigation in combination with solarization is an effective technique for managing soil-borne pathogens in greenhouses and is being adopted by horticultural growers in Argentina.

On-Farm Evaluations of Anaerobic Soil Disinfestation and Grafting for Management of a Widespread Soilborne Disease Complex in Protected Culture Tomato Production.

Tomato production in Ohio protected culture systems is hindered by a soilborne disease complex consisting of corky root rot (Pyrenochaeta lycopersici), black dot root rot (Colletotrichum coccodes), Verticillium wilt (Verticillium dahliae), and root-knot (Meloidogyne hapla and M. incognita). In a survey of 71 high tunnels, C. coccodes was detected in 90% of high tunnels, and P. lycopersici (46%), V. dahliae (48%), and Meloidogyne spp. (45%) were found in nearly half of high tunnels. Anaerobic soil disinfestation (ASD) with wheat bran (20.2 Mg/ha) plus molasses (10.1 Mg/ha) and grafting onto 'Maxifort' or 'Estamino' rootstocks were evaluated in high tunnels on five farms. In post-ASD bioassays of trial soils, root and taproot rot severity were significantly reduced after ASD, and root-knot galling was also reduced by ASD. Soilborne pathogenic fungi were isolated less frequently from bioassay plants grown in ASD-treated soils than control soils. Similar results were observed in tomato plants grown in high tunnels. Root rot was significantly reduced by ASD in nearly all trials. Corky root rot severity was highest in nongrafted plants grown in nontreated soils, and the lowest levels of corky root rot were observed in 'Maxifort'-grafted plants. Black dot root rot severity was higher or equivalent in grafted plants compared with nongrafted plants. Root-knot severity was lower in plants grown in ASD-treated soils in high tunnels compared with plants grown in control soils, but grafting did not significantly decrease root-knot severity. However, soil treatment did not significantly affect yield, and grafting led to inconsistent impacts on yield.

Evaluation of Agricultural Byproducts and Cover Crops as Anaerobic Soil Disinfestation Carbon Sources for Managing a Soilborne Disease Complex in High Tunnel Tomatoes

Anaerobic soil disinfestation (ASD) is a viable option for disease management in tomato production and reduces damage due to a soilborne disease complex consisting of Pyrenochaeta lycopersici, Colletotrichum coccodes, Verticillium dahliae, and Meloidogyne spp. There are plentiful options for ASD carbon sources using byproducts of Midwestern United States agriculture or cover crops, yet these carbon sources have not been evaluated for use in Midwestern settings. Low (10.1 Mg/ha) and high (20.2 Mg/ha) rates of corn gluten meal, distillers dried grains, soybean meal, wheat bran, and dry sweet whey were evaluated as ASD carbon sources in growth chamber and greenhouse bioassays. Cover crops including buckwheat, cowpea, crimson clover, mustard, oilseed radish, sorghum-sudangrass, white clover, and winter rye were evaluated in similar bioassays with one amendment rate (20.2 Mg/ha). Reducing conditions developed in soils regardless of carbon source or rate. Use of high rates of corn gluten meal, distillers dried grains, soybean meal, and wheat bran led to the lowest levels of root rot severity compared to non-treated controls. The higher rate of any byproduct carbon source was always more effective than the lower rate in reducing root rot severity. Use of both rates of soybean meal or corn gluten meal and the high rate of distillers dried grains or dry sweet whey led to significant increases in dry root and shoot biomass compared to controls. For cover crops, ASD with crimson clover, sorghum-sudangrass, white clover, or winter rye amendments reduced root rot severity relative to the aerobic control, but not relative to the anaerobic control. Use of cover crops did not significantly impact plant biomass. A subset of three ASD carbon sources [distillers dried grains, soybean meal, and wheat middlings (midds), all 20.2 Mg/ha] were evaluated in five on-farm ASD trials in high tunnels. Soil temperatures were low during the application period, limiting treatment efficacy. Reducing conditions developed in all soils during ASD treatment, and a moderate but significant reduction in root rot severity was observed following ASD with the soybean meal or wheat midds compared to ASD with distillers dried grains. Tomato yield was not significantly affected by ASD treatment.

Effectiveness of Olive Fruit Polyphenol Extract Combined with Aqueous Extracts of Solid Wastes of Pomegranate or/ and Orange Juice Against Important Plant Pathogens - Part 2 (in vivo studies)

Olive fruit extracts, combined with pomegranate and orange waste extracts, isolated using microwave assisted extraction technique, were used as a potential alternative crop protection method against Verticillium dahliae, Rhizoctonia solani, Botrytis cinerea and Pyrenochaeta lycopersici on tomato plants. For the evaluation of the antimicrobial activity, various mixtures of the extracts were applied on 15 days old tomato plants, variety

Grafting eggplant as a control method of soilborne pathogens and nematodes

Soil borne pathogens and nematodes are very destructive in vegetable crops and one of the most limiting factors to farmer's income. Soil fumigation has been an essential component of greenhouse crops since the 1960s, but according to the Montreal Protocol (1997), methyl bromide, as an ozone-depleting compound, is banned for plant protection (fumigation applications) in Romania, starting January 2005. Growing vegetables without soil fumigants has remained a challenge, in part because commercially acceptable eggplant cultivars produced through conventional breeding lack resistance to many soil borne plant pathogens. Grafting cultivars with high quality and productivity on rootstocks that are resistant to the soil pests and diseases is a method known for many years, but which was improved and quickly spread in the last years. Therefore, the objective of the research was to evaluate the performance of the eggplant grafting on some rootstocks, in greenhouse conditions. The study was carried out in the experimental greenhouse of the Horting Institute from Bucharest. Data obtained in the combinations scion/rootstock were compared with data recorded from plants not grafted. Disease incidence, disease severity and the attack degree of soilborne disease and pest were determined and calculated in the experimental variants. The grafting process led to significant reduction in the incidence of attack produced by soil borne disease (Fusarium oxysporum f. sp. melongenae, Pyrenochaeta lycopersici) and nematodes (Meloidogyne incognita).

First Report of Black Dot Root Rot, Caused by Colletotrichum coccodes, on Tomato in Kentucky High Tunnels

As the most profitable vegetable crop grown in Kentucky (KY) high tunnels, tomato (Solanum lycopersicum L.) is often produced without crop rotation. In November 2016, ‘Mountain Fresh Plus’ tomato samples were received by the University of Kentucky Plant Disease Diagnostic Lab from Nelson County, KY. The high tunnel had an extended history of tomato production, and 100% of plants were affected. Common late-season symptoms of plant dieback and fruit decay were reported. Brown discoloration with dry, cracked cankers and microsclerotia were observed on primary and secondary sample roots, respectively. Symptomatic root sections (4 to 6 mm) were sterilized with 1% NaOCl and then placed on acidified potato dextrose agar (aPDA). Hyphal tips of the cultured fungus were aseptically transferred to fresh aPDA, and then mycelium was aseptically transferred to potato dextrose broth. DNA was extracted from 3-day-old broth culture (Li et al. 2008). Polymerase chain reaction (PCR) amplicons using ITS1/ITS4 (White et al. 1990) were generated, using protocols modified from Gardes and Bruns (1993) and Matsuda et al. (2005). Modifications included 35 total cycles, 30 s annealing step, and final extension for 10 min. Additional PCR products were amplified using partial actin (ACT; Prihastuti et al. 2009) and glyceraldehyde-3-phosphate dehydrogenase primers (GPDH; Berbee et al. 1999). ExoSap-IT (Affymetrix, Cleveland, OH) was used for PCR product cleanup, and then bidirectional Sanger sequence (Eurofin Genomics, Louisville, KY) was generated for each housekeeping gene. The internal transcribed spacer sequence was submitted to GenBank (MG544880) and matched 100% on identity and coverage with multiple Colletotrichum coccodes accessions, including KY364640. ACT and GPDH sequences were used in phylogenetic trees, which further supported identification as C. coccodes. The original isolate was grown on quarter-strength PDA at 23°C. Microsclerotia developed after 7 days within sparse, white mycelium. Conidia were dislodged from 4-week-old plates flooded with sterile deionized water using a sterile micropestle and then filtered through two layers of cheesecloth. Conidia were 18 to 22 μm long and 3 to 5 μm wide and were cylindrical, aseptate, and hyaline, with cylindrical conidiophores. Acervuli on tomato roots were circular with approximately 100-μm-long setae. Two-week-old ‘Sunstart’ tomatoes were used for Koch’s postulates. Eight plants were each drenched with 25 ml of 5 × 10⁵ conidia/ml (Vrisman et al. 2017). Eight plants drenched with 25 ml of sterile deionized water were noninoculated controls. After 11 weeks, root discoloration was observed, with black acervuli with setae visible on 50× magnified root surfaces; control plants were asymptomatic and lacked fungal growth. Symptomatic root cuttings were submerged in 0.6% NaOCl for 30 s and then plated on quarter-strength PDA. Mycelium was macroscopically visible after 1 week at ambient temperature. Microscopic examination indicated the fungus was morphologically indistinguishable from mycelium, conidiophores, and conidia of the original isolate, confirming Koch’s postulates. This experiment was repeated with the same results. Although C. coccodes and Pyrenochaeta lycopersici were recently reported to cause brown root rot complex in high tunnel tomato (Vrisman et al. 2017), P. lycopersici was not found here. This first report of black dot root rot in intensive high tunnel tomato production in KY reiterates the need for aggressive sanitation prior to disease development, because severe pathogen pressure in soil may necessitate relocation of the high tunnel.

Comparative transcriptome profiling of the response to Pyrenochaeta lycopersici in resistant tomato cultivar Mogeor and its background genotype—susceptible Moneymaker

Breeding for resistance is the most effective tool for controlling the corky root disease of tomato caused by Pyrenochaeta lycopersici. A comparative RNA-Seq-based transcriptomic analysis was conducted at 96 hpi (hours post infection) on two tomato cultivars: resistant Mogeor and its genetic background, and susceptible Moneymaker to investigate the differences in their transcriptomic response and identify the molecular bases of this plant-pathogen interaction. The number of differentially expressed genes (DEGs) identified was much higher in the susceptible than in the resistant genotype; however, the proportion of upregulated genes was higher in Mogeor (70.81%) than in Moneymaker (52.95%). Gene Ontology (GO) analysis enabled identification of 24 terms shared by the two cultivars that were consistent with responses to external stimulus, such as fungal infection. On the other hand, as many as 54 GO were enriched solely in Moneymaker, including terms related to defense response and cell wall metabolism. Our results could support the previous observations in other pathosystems, that susceptibility and resistance have overlapping signaling pathways and responses, suggesting that the P. lycopersici resistance gene pyl might be a recessive allele at a susceptibility locus, for which different candidate genes were identified based on the differences in induction or expression levels, observed between the resistant and susceptible genotype. MapMan analysis highlighted a complex hormone and transcription factors interplay where SA- and JA-induced pathways are modulated in a similar way in both genotypes and thus take part in a common response while the ethylene signaling pathways, induced mainly in susceptible Moneymaker, seem putatively contribute to its susceptibility.

First Report of Corky Root Rot of Tomato Caused by Pyrenochaeta lycopersici in Africa

First Report of Corky Root Rot of Tomato Caused by <i>Pyrenochaeta lycopersici</i> in Africa

The genome assembly of the fungal pathogen Pyrenochaeta lycopersici from Single-Molecule Real-Time sequencing sheds new light on its biological complexity.

The first draft genome sequencing of the non-model fungal pathogen Pyrenochaeta lycopersici showed an expansion of gene families associated with heterokaryon incompatibility and lacking of mating-type genes, providing insights into the genetic basis of this “imperfect” fungus which lost the ability to produce the sexual stage. However, due to the Illumina short-read technology, the draft genome was too fragmented to allow a comprehensive characterization of the genome, especially of the repetitive sequence fraction. In this work, the sequencing of another P. lycopersici isolate using long-read Single Molecule Real-Time sequencing technology was performed with the aim of obtaining a gapless genome. Indeed, a gapless genome assembly of 62.7 Mb was obtained, with a fraction of repetitive sequences representing 30% of the total bases. The gene content of the two P. lycopersici isolates was very similar, and the large difference in genome size (about 8 Mb) might be attributable to the high fraction of repetitive sequences detected for the new sequenced isolate. The role of repetitive elements, including transposable elements, in modulating virulence effectors is well established in fungal plant pathogens. Moreover, transposable elements are of fundamental importance in creating and re-modelling genes, especially in imperfect fungi. Their abundance in P. lycopersici, together with the large expansion of heterokaryon incompatibility genes in both sequenced isolates, suggest the presence of possible mechanisms alternative to gene re-assorting mediated by sexual recombination. A quite large fraction (~9%) of repetitive elements in P. lycopersici, has no homology with known classes, strengthening this hypothesis. The availability of a gapless genome of P. lycopersici allowed the in-depth analysis of its genome content, by annotating functional genes and TEs. This goal will be an important resource for shedding light on the evolution of the reproductive and pathogenic behaviour of this soilborne pathogen and the onset of a possible speciation within this species.

Carbon Source and Soil Origin Shape Soil Microbiomes and Tomato Soilborne Pathogen Populations During Anaerobic Soil Disinfestation

Soilborne disease complexes are an emerging constraint in protected culture tomato production systems in the Midwestern United States. Diseases in these complexes include Verticillium wilt (Verticillium dahliae), black dot root rot (Colletotrichum coccodes), corky root rot (Pyrenochaeta lycopersici), and root knot (Meloidogyne spp.). Anaerobic soil disinfestation (ASD) may be a viable, environmentally benign strategy for managing these complexes. Soils from two farms in Ohio were used to determine the impacts of ASD, using wheat bran, molasses, or ethanol as carbon sources, on soilborne diseases and soil bacterial communities. ASD with wheat bran or ethanol amendments led to significantly reduced tomato root rot severity, while nematode galling damage was significantly reduced following ASD with any carbon source compared with nontreated controls. When ethanol was used as a carbon source in ASD, the colonization of tomato roots by P. lycopersici and C. coccodes was observed less frequently than in control roots. A high throughput sequencing approach was used to characterize soil bacterial communities following ASD. Carbon source and soil origin influenced the composition of bacterial communities in soils treated with ASD. Bacterial community diversity decreased following ASD with wheat bran in all soils tested and following ASD with ethanol in soils from one farm. The abundance of bacteria in the phylum Firmicutes generally increased significantly following ASD, while the abundance of those in the phyla Acidobacteria, Actinobacteria, Chloroflexi, and Plantomycetes generally decreased following ASD. These findings provide insight into the impacts of ASD on microbial communities and soilborne diseases and will be used to optimize ASD as a tool for Midwestern vegetable growers.

Efficacy of Anaerobic Soil Disinfestation with Sugar-containing Diatomite in Controlling Tomato Corky Root Caused by Pyrenochaeta lycopersici in Hokkaido

Efficacy of Anaerobic Soil Disinfestation with Sugar-containing Diatomite in Controlling Tomato Corky Root Caused by <i>Pyrenochaeta lycopersici</i> in Hokkaido

First Report of Tomato Brown Root Rot Complex Caused by Colletotrichum coccodes and Pyrenochaeta lycopersici in Ohio

First Report of Tomato Brown Root Rot Complex Caused by <i>Colletotrichum coccodes</i> and <i>Pyrenochaeta lycopersici</i> in Ohio

Frequent Applications of Organic Matter to Agricultural Soil Increase Fungistasis

Soil–borne plant pathogens are among the most important limiting factors for the productivity of agro–ecosystems. Fungistasis is the natural capability of soils to inhibit the germination and growth of soil–borne fungi in the presence of optimal abiotic conditions. The objective of this study was to assess the effects of different soil managements, in terms of soil amendment types and frequency of application, on fungistasis. For this purpose, a microcosm experiment was performed by conditioning a soil with frequent applications of organic matter with contrasting biochemical quality (i. e., glucose, alfalfa straw and wheat straw). Thereafter, the fungistasis response was assessed on four fungi (Aspergillus niger, Botrytis cinerea, Pyrenochaeta lycopersici and Trichoderma harzianum). Conditioned soils were characterized by measuring microbial activity (soil respiration) and functional diversity using the BIOLOG EcoPlatesTM method. Results showed that irrespective of the fungal species and amendment types, frequent applications of organic matter reduced fungistasis relief and shortened the time required for fungistasis restoration. The frequent addition of easily decomposable organic compounds enhanced soil respiration and its specific catabolic capabilities. This study demonstrated that frequent applications of organic matter affected soil fungistasis likely as a result of higher microbial activity and functional diversity.

Effect of repeated cycles of soil solarization and biosolarization on corky root, weeds and fruit yield in screen-house tomatoes under subtropical climate conditions in the Canary Islands

Soil solarization is a non-chemical soil disinfestation method proven effective against soil-borne pathogens and weeds. However, it should be assessed under local cropping conditions before it can be implemented in commercial crops, since the process is highly dependent on climate conditions, among other factors. Soil biosolarization combines biofumigation with solarization to improve its effectiveness but knowledge about its use on tomato crops is still rather scarce and limited to nematode control. We have tested the effectiveness of soil solarization, biosolarization and fumigation with metam sodium over three tomato cropping seasons, to control corky root caused by Pyrenochaeta lycopersici and weeds under screen-house conditions in the Canary Islands (Spain). During the three seasons, maximum soil temperatures at 10 cm depth in solarized and biosolarized plots were about 10 °C higher than in controls, rising up to 41.4–43.3 °C in solarization and 43.0–44.7 °C in biosolarization, with an accumulated number of hours exceeding 40 °C of 48.8–138.2 and 92.3–204.7 h in solarized and biosolarized plots, respectively. The most effective treatment was biosolarization, which significantly increased tomato yield by 12.4% in 2001–02; 22.8% in 2002–03 and 22.2% in 2003–04, and reduced corky root severity in the last two seasons. Corky root was also significantly reduced by solarization in 2003–04, whereas there was no difference between metam sodium and control plots in any season. Weed infestation was evaluated in 2002–03 and 2003–04, in which weed density in biosolarized plots was significantly lower than in controls (88.8% and 50.6% reduction at 45 and 165 days after tomato transplanting in 2002–03; and 69.6% after 120 days in 2003–04). In contrast, weeds were not controlled by solarization, and inconsistent results were obtained with metam sodium. Here we show that soil biosolarization is clearly a way to improve the effectiveness of soil solarization under less favorable environmental conditions, like those prevailing in tomato screen-houses in the Canaries, and a feasible alternative to chemical fumigation for the control of corky root and weeds.

Specific detection of Type 1 and Type 2 isolates of Pyrenochaeta lycopersici by loop-mediated isothermal amplification reaction

ABSTRACTPyrenochaeta lycopersici is the causal agent of corky root, an important soilborne disease of tomato (Lycopersicon esculentum) and other solanaceous crops. P. lycopersici isolates are classified into Types 1 and 2 on the basis of several physiological and molecular features. In this study, we aimed to establish a loop-mediated isothermal amplification (LAMP) method to identify Types 1 and 2 isolates. Using specific LAMP primer sets for Types 1 and 2, both types were easily identified within 35 min. The LAMP method demonstrated equal sensitivity to the polymerase chain reaction in molecular identification of the pathogen in cultured mycelia, infested plant roots, and their surrounding soil. The LAMP technology will contribute to the detection and identification of the pathogen, crop protection, and thorough understanding about the ecology of corky root disease of tomato.

Genetic structure of Italian populations ofPyrenochaeta lycopersici, the causal agent of corky root rot of tomato

Pyrenochaeta lycopersici is the causal agent of corky root rot, which is a serious disease worldwide that attacks the roots of tomato. A total of 139 isolates were sampled from eight locations in Italy and Israel and assigned to two molecular types (type 1 and type 2) based on internal transcribed spacer (ITS) sequences. These isolates were genotyped using amplified fragment length polymorphisms (AFLPs) to decipher the population structure. Based on this population structure analysis, three groups of P. lycopersici were identified. One group correlated to ITS type 1, while the other two correlated to ITS type 2. AMOVA indicated high genetic divergence (FST = 0� 40) between the Italian types 1 and 2. These data support the view that the two ITS types represent significant evolutionary entities, although there might be incomplete lineage sorting present. Some isolates of different ITS type were observed to have very similar multilocus AFLP profiles, and some genotypes were intermediate between the two ITS types. This suggests that parasexual hybridization between the two types has had a significant role in shaping the population structure of P. lycopersici. Finally, the average divergence among the populations within the ITS types was very high (FSC = 0� 710, P < 10 � 5 ), probably

Genetic transformation of the tomato pathogen Pyrenochaeta lycopersici allowed gene knockout using a split-marker approach

Pyrenochaeta lycopersici, as other soil-transmitted fungal pathogens, generally received little attention compared to the pathogens affecting the aerial parts of the plants, although causing stunt and important fruit yield reduction of agronomic relevant crops. The scope of this study was to develop a system allowing to investigate the functional role of P. lycopersici genes putatively involved in the corky root rot of tomato. A genetic transformation system based on a split-marker approach was developed and tested to knock out a P. lycopersici gene encoding for a lytic polysaccharide monooxygenase (Plegl1) induced during the disease development. The regions flanking Plegl1 gene were fused with the overlapping parts of hygromycin marker gene, to favour homologous recombination. We were able to obtain four mutants not expressing the Plegl1 gene though, when tested on a susceptible tomato cultivar, Plegl1 mutants showed unaltered virulence, compared with the wild-type strain. The strategy illustrated in the present work demonstrated for the first time that homologous recombination occurs in P. lycopersici. Moreover, a transformation system mediated by Agrobacterium tumefaciens was established and stable genetic transformants have been obtained. The transformation systems developed represent important tools for investigating both the role of genes putatively involved in P. lycopersici interaction with host plant and the function of other physiological traits which emerged to be genetically expanded from the recent genome sequencing of this fungus.

Evaluation of Streptomyces spp. for the biological control of corky root of tomato and Verticillium wilt of eggplant

The effects of Streptomyces spp. isolates in the biological control of corky root of tomato and Verticillium wilt of eggplant was determined in in vitro, greenhouse and field trials. Twenty-six Streptomyces spp. isolates were obtained from the rhizospheres of different vegetable crops in southern Italy. In in vitro dual culture tests, mycelial radial growth of Pyrenochaeta lycopersici and Verticillium dahliae was reduced up to 18.6% and 30.1%, respectively. Radial growth of seven other fungal pathogens was variably reduced as well. The isolates StB-3, StB-6, StB-11 and StB-12 showed a good antagonistic effect against both P. lycopersici and V. dahliae, while the rest of isolates eventually showed antagonism against only one pathogen.In pot-experiments in the greenhouse three of the four above-mentioned Streptomyces spp. isolates significantly reduced corky root up to 64.9% (StB-11), and all four isolates reduced foliar symptoms of Verticillium wilt (AUDPC) up to 48.3%, but none of them reduced the severity of vascular browning. In naturally infested field trials, StB-11 significantly reduced corky root severity in tomato by 48.2%, StB-12 by 35% and StB-6 by 32.6%, but none of the isolates were effective in controlling Verticillium wilt of eggplant. The effectiveness of the streptomycete AtB-42, successfully used in previous researches, was here confirmed as it reduced corky root of tomato in the field by 33.6%. In conclusion, our research demonstrates that under field conditions corky root of tomato, but not Verticillium wilt of eggplant, can be effectively controlled by the Streptomyces spp. isolates used in this study.

Impact of shortened crop rotation of oilseed rape on soil and rhizosphere microbial diversity in relation to yield decline.

Oilseed rape (OSR) grown in monoculture shows a decline in yield relative to virgin OSR of up to 25%, but the mechanisms responsible are unknown. A long term field experiment of OSR grown in a range of rotations with wheat was used to determine whether shifts in fungal and bacterial populations of the rhizosphere and bulk soil were associated with the development of OSR yield decline. The communities of fungi and bacteria in the rhizosphere and bulk soil from the field experiment were profiled using terminal restriction fragment length polymorphism (TRFLP) and sequencing of cloned internal transcribed spacer regions and 16S rRNA genes, respectively. OSR cropping frequency had no effect on rhizosphere bacterial communities. However, the rhizosphere fungal communities from continuously grown OSR were significantly different to those from other rotations. This was due primarily to an increase in abundance of two fungi which showed 100% and 95% DNA identity to the plant pathogens Olpidium brassicae and Pyrenochaeta lycopersici, respectively. Real-time PCR confirmed that there was significantly more of these fungi in the continuously grown OSR than the other rotations. These two fungi were isolated from the field and used to inoculate OSR and Brassica oleracea grown under controlled conditions in a glasshouse to determine their effect on yield. At high doses, Olpidium brassicae reduced top growth and root biomass in seedlings and reduced branching and subsequent pod and seed production. Pyrenochaeta sp. formed lesions on the roots of seedlings, and at high doses delayed flowering and had a negative impact on seed quantity and quality.