Search

Nature management residues (i.e., biomass generated from the management of nature reserves) are promising peat alternatives for horticultural substrates and may have a positive effect on disease suppression because of their microbiological characteristics. Moreover, addition of fertilizer may also affect the rhizosphere microbiome and, accordingly, disease suppression. In this study, we determined the effect of two management residues in horticultural substrates (i.e., chopped heath and acidified soft rush) and two fertilization regimes (i.e., pure nitrogen fertilizer and compound fertilizer) on the suppression of Phytophthora spp. on Chamaecyparis lawsoniana. The bacterial and fungal rhizosphere community was characterized using 16S ribosomal RNA and internal transcribed spacer 2 gene metabarcoding. Soft rush with a compound fertilizer (R2) and chopped heath with a pure nitrogen fertilizer (H1) showed a disease-suppressive effect and showed the largest shifts in microbial community composition compared with peat-based substrates. The disease-suppressive treatments showed differences in their microbial communities. Different genera associated with described biocontrol agents for Phytophthora spp. were found in higher amounts in those treatments. Aspergillus and Trichoderma spp. were highly abundant in H1, while Actinomadura and Bacillus spp. had a high abundance in R2. In addition, the relative abundances of 24 bacterial and 9 fungal genera were negatively correlated with disease severity. Several of those genera, including Bacillus, Chaetomium, and Actinomadura, were significantly more abundant in one of the disease-suppressive treatments. This study shows that disease suppressiveness in sustainable horticultural substrates is dependent on fertilization and can be linked to changes in the microbial rhizosphere communities. This study was supported by Flanders Innovation & Entrepreneurship grant HBC.2017.0815 and Research Foundation Flanders grant 12S9418N.

With nematicides progressively being banned due to their environmental impact, an urgent need for novel and sustainable control strategies has arisen. Stimulation of plant immunity, a phenomenon referred to as “induced resistance” (IR), is a promising option. In this study, Cucurbitaceae COld Peeling Extracts (CCOPEs) were shown to protect rice (Oryza sativa) and tomato (Solanum lycopersicum) against the root-knot nematodes Meloidogyne graminicola and Meloidogyne incognita, respectively. Focusing on CCOPE derived from peels of melon (Cucumis melo var. cantalupensis; mCOPE), we unveiled that this extract combines an IR-triggering capacity with direct nematicidal effects. Under lab conditions, the observed resistance was comparable to the protection obtained by commercially available IR stimuli or nematicides. Via mRNA sequencing and confirmatory biochemical assays, it was proven that mCOPE-IR in rice is associated with systemic effects on ethylene accumulation, reactive oxygen species (ROS) metabolism and cell wall-related modifications. While no negative trade-offs were detected with respect to plant growth or plant susceptibility to necrotrophic pests or pathogens, additional infection experiments indicated that mCOPE may have a predominant activity toward biotrophs. In summary, the presented data illustrate a propitious potential for these extracts, which can be derived from agro-industrial waste streams.

The EFSA Panel on Plant Health was requested to prepare and deliver risk assessments for commodities listed in the relevant Implementing Acts as 'High risk plants, plant products and other objects' [Commission Implementing Regulation (EU) 2018/2019 establishing a provisional list of high risk plants, plant products or other objects, within the meaning of Article 42 of Regulation (EU) 2016/2031]. The current Scientific Opinion covers all plant health risks posed by bare rooted plants for planting of Robinia pseudoacacia (1 year old with a stem diameter of less than 2.5 cm) imported from Israel, taking into account the available scientific information, including the technical information provided by Israel by 26 December 2019. The relevance of an EU-quarantine pest for this opinion was based on evidence that: (i) the pest is present in Israel; (ii) R. pseudoacacia is a host of the pest, and (iii) the pest can be associated with the commodity. The relevance of this opinion for other non EU-regulated pests was based on evidence that: (i) the pest is present in Israel (ii) the pest is absent in the EU; (iii) R. pseudoacacia is a host of the pest; (iv) the pest can be associated with the commodity and (v) the pest may have an impact and can pose a potential risk for the EU territory. Two pests (one insect and one fungus, Euwallacea fornicatus and Fusarium euwallaceae) that fulfilled all criteria were selected for further evaluation. For the two selected pests, the risk mitigation measures proposed in the technical dossier from Israel were evaluated. Limiting factors in the effectiveness of the measures were documented. For the selected pests an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment, therefore the Panel is 95% sure that 9,950 or more plants per 10,000 will be free from these two pests.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation EU/2018/2019 as ‘High risk plants, plant products and other objects’. This Scientific Opinion covers plant health risks posed by bare rooted and potted plants of Nerium oleander that are imported from Turkey, taking into account the available scientific information, including the technical information provided by the Turkish NPPO. The relevance of any pest for this opinion was based on evidence following defined criteria. One species, the EU non‐regulated pest Phenacoccus solenopsis, fulfilled all relevant criteria and was selected for further evaluation. For this pest, the risk mitigation measures proposed in the technical dossier from Turkey were evaluated taking into account the possible limiting factors. For this pest, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9,719 and 10,000 plants per 10,000 would be free of P. solenopsis.

Biochar has been reported to play a positive role in disease suppression against airborne pathogens in plants. The mechanisms behind this positive trait are not well-understood. In this study, we hypothesized that the attraction of plant growth-promoting rhizobacteria (PGPR) or fungi (PGPF) underlies the mechanism of biochar in plant protection. The attraction of PGPR and PGPF may either activate the innate immune system of plants or help the plants with nutrient uptake. We studied the effect of biochar in peat substrate (PS) on the susceptibility of strawberry, both on leaves and fruits, against the airborne fungal pathogen Botrytis cinerea. Biochar had a positive impact on the resistance of strawberry fruits but not the plant leaves. On leaves, the infection was more severe compared with plants without biochar in the PS. The different effects on fruits and plant leaves may indicate a trade-off between plant parts. Future studies should focus on monitoring gene expression and metabolites of strawberry fruits to investigate this potential trade-off effect. A change in the microbial community in the rhizosphere was also observed, with increased fungal diversity and higher abundances of amplicon sequence variants classified into Granulicella, Mucilaginibacter, and Byssochlamys surrounding the plant root, where the latter two were reported as biocontrol agents. The change in the microbial community was not correlated with a change in nutrient uptake by the plant in either the leaves or the fruits. A decrease in the defense gene expression in the leaves was observed. In conclusion, the decreased infection of B. cinerea in strawberry fruits mediated by the addition of biochar in the PS is most likely regulated by the changes in the microbial community.

While many phenylpropanoid pathway-derived molecules act as physical and chemical barriers to pests and pathogens, comparatively little is known about their role in regulating plant immunity. To explore this research field, we transiently perturbed the phenylpropanoid pathway through application of the CINNAMIC ACID-4-HYDROXYLASE (C4H) inhibitor piperonylic acid (PA). Using bioassays involving diverse pests and pathogens, we show that transient C4H inhibition triggers systemic, broad-spectrum resistance in higher plant without affecting growth. PA treatment enhances tomato (Solanum lycopersicum) resistance in field and laboratory conditions, thereby illustrating the potential of phenylpropanoid pathway perturbation in crop protection. At the molecular level, transcriptome and metabolome analyses reveal that transient C4H inhibition in tomato reprograms phenylpropanoid and flavonoid metabolism, systemically induces immune signaling and pathogenesis-related genes, and locally affects reactive oxygen species metabolism. Furthermore, C4H inhibition primes cell wall modification and phenolic compound accumulation in response to root-knot nematode infection. Although PA treatment induces local accumulation of the phytohormone salicylic acid, the PA resistance phenotype is preserved in tomato plants expressing the salicylic acid-degrading NahG construct. Together, our results demonstrate that transient phenylpropanoid pathway perturbation is a conserved inducer of plant resistance and thus highlight the crucial regulatory role of this pathway in plant immunity.

Biochar has been reported to play a positive role in disease suppression against airborne pathogens in plants. The mechanisms behind this positive trait are not well-understood. In this study, we hypothesized that the attraction of plant growth-promoting rhizobacteria (PGPR) or fungi (PGPF) underlies the mechanism of biochar in plant protection. The attraction of PGPR and PGPF may either activate the innate immune system of plants or help the plants with nutrient uptake. We studied the effect of biochar in peat substrate (PS) on the susceptibility of strawberry, both on leaves and fruits, against the airborne fungal pathogen Botrytis cinerea. Biochar had a positive impact on the resistance of strawberry fruits but not the plant leaves. On leaves, the infection was more severe compared with plants without biochar in the PS. The different effects on fruits and plant leaves may indicate a trade-off between plant parts. Future studies should focus on monitoring gene expression and metabolites of strawberry fruits to investigate this potential trade-off effect. A change in the microbial community in the rhizosphere was also observed, with increased fungal diversity and higher abundances of amplicon sequence variants classified into Granulicella, Mucilaginibacter, and Byssochlamys surrounding the plant root, where the latter two were reported as biocontrol agents. The change in the microbial community was not correlated with a change in nutrient uptake by the plant in either the leaves or the fruits. A decrease in the defense gene expression in the leaves was observed. In conclusion, the decreased infection of B. cinerea in strawberry fruits mediated by the addition of biochar in the PS is most likely regulated by the changes in the microbial community.

The EFSA Panel on Plant Health was requested to prepare and deliver risk assessments for commodities listed in the relevant Implementing Acts as ‘High risk plants, plant products and other objects’ [Commission Implementing Regulation (EU) 2018/2019 establishing a provisional list of high risk plants, plant products or other objects, within the meaning of Article 42 of Regulation (EU) 2016/2031]. The current Scientific Opinion covers all plant health risks posed by bare rooted plants for planting of Robinia pseudoacacia (1 year old with a stem diameter of less than 2.5 cm) imported from Israel, taking into account the available scientific information, including the technical information provided by Israel by 26 December 2019. The relevance of an EU-quarantine pest for this opinion was based on evidence that: (i) the pest is present in Israel; (ii) R. pseudoacacia is a host of the pest, and (iii) the pest can be associated with the commodity. The relevance of this opinion for other non EU-regulated pests was based on evidence that: (i) the pest is present in Israel (ii) the pest is absent in the EU; (iii) R. pseudoacacia is a host of the pest; (iv) the pest can be associated with the commodity and (v) the pest may have an impact and can pose a potential risk for the EU territory. Two pests (one insect and one fungus, Euwallacea fornicatus and Fusarium euwallaceae) that fulfilled all criteria were selected for further evaluation. For the two selected pests, the risk mitigation measures proposed in the technical dossier from Israel were evaluated. Limiting factors in the effectiveness of the measures were documented. For the selected pests an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment, therefore the Panel is 95% sure that 9,950 or more plants per 10,000 will be free from these two pests.

Peat replacement by compost in growing media can increase the sustainability of soilless cultivation. Compost, when mixed into growing media, is a source of fiber, i.e., a rooting medium, as well as an important source of nitrogen (N), phosphorus (P) and potassium (K). Physical properties as well as nutrient levels in growing media are known to affect plant growth and health. Therefore we monitored the evolution of nutrient release in compost-amended growing media for strawberry in greenhouse culture with drip fertigation for a double cropping system of cv. Elsanta, i.e., autumn culture with continued culture in spring. Compost amended and other alternative growing media for strawberry production were tested during four years of trials at full-scale level in a professional greenhouse growing system, in order to optimize the new cropping system with alternative substrates. Compost amended substrates contained 20–100% (v/v) compost, with different compost types tested. We assessed effects on yield and nutrients, i.e. nutrient availability in the substrate, uptake in the plants, and losses with the drainage water, as well as effect on diseases and pests (infection by powdery mildew (Podosphaera aphanis), aphids (Chaetosiphon fragefolii), and the anthracnose pathogen (Colletotrichum acutatum)). Adding compost to growing media has potential to increase the sustainability of soilless strawberry culture. Results show that growing strawberries on alternative substrates is feasible, but the substrate mixtures containing compost required adjusted fertigation due to nutrients supplied by the compost. This study revealed that strawberry plants made highly efficient use of the P and K in the compost when P and K input by fertigation was reduced, and that compost addition results in reduced export and potential losses of nutrients with the drain water and spent growing media. In general, the compost-amended substrates with lower N fertigation performed well as a growing medium during the autumn culture, but in the continued spring culture, these substrates needed an adapted fertigation regime for N, P and K. The N supply by the tested composts during the autumn culture allowed for significant reductions in N supplied by fertigation, i.e., 50% reduction when 100% (v/v) compost was used, and 10% reduction when 20% (v/v) compost was used. Degree of infection with powdery mildew and aphids was strongly positively correlated with the N status of the crop, pointing at the risks of high N supply for the crop. At the end of the autumn culture, no significant positive or negative effect of the compost treatments on the latent survival of C. acutatum on the strawberry leaves was found.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation EU/2018/2019 as ‘High risk plants, plant products and other objects’. This Scientific Opinion covers all plant health risks posed by unrooted cuttings of Jasminum polyanthum produced in a protected environment (greenhouse) that are imported from Israel, taking into account the available scientific information, including the technical information provided by the NPPO of Israel by 15 March 2020. The relevance of an EU quarantine pest for this opinion was based on evidence that: (i) the pest is present in Israel; (ii) Jasminum is a host of the pest; and (iii) the pest can be associated with the commodity. The relevance of any other pest, not regulated in the EU, was based on evidence that: (i) the pest is present in Israel; (ii) the pest is absent in the EU; (iii) Jasminum is a host of the pest; (iv) the pest can be associated with the commodity and (v) the pest may have an impact and can pose a potential risk for the EU territory. Six species, the EU‐quarantine pest Scirtothrips dorsalis, and the EU non‐regulated pests Aonidiella orientalis,Milviscutulus mangiferae,Paracoccus marginatus,Pulvinaria psidii and Colletotrichum siamense fulfilled all relevant criteria and were selected for further evaluation. For these pests, the risk mitigation measures proposed in the technical dossier from Israel were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The estimated degree of pest freedom varies among the pests evaluated, with S. dorsalis being the pest most frequently expected on the imported plants. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9,958 and 10,000 bags per 10,000 would be free of S. dorsalis.

The EFSA Panel on Plant Health was requested to prepare and deliver risk assessments for commodities listed in the relevant Implementing Acts as ‘High risk plants, plant products and other objects’ [Commission Implementing Regulation (EU) 2018/2019 establishing a provisional list of high‐risk plants, plant products or other objects, within the meaning of Article 42 of Regulation (EU) 2016/2031]. The current Scientific Opinion covers all plant health risks posed by Albizia julibrissin imported from Israel, taking into account the available scientific information, including the technical information provided by Israel. The relevance of an EU‐regulated pest for this opinion was based on evidence that: (i) the pest is present in Israel; (ii) A. julibrissin is a host of the pest and (iii) the pest can be associated with the commodity. The relevance of this opinion for other non EU‐regulated pests was based on evidence that (i) the pest is present in Israel; (ii) the pest is absent in the EU; (iii) A. julibrissin is a host of the pest; (iv) the pest can be associated with the commodity and (v) the pest may have an impact and can pose a potential risk for the EU territory. Three pests (two insects, Aonidiella orientalis and Euwallacea fornicatus; one fungus, Fusarium euwallaceae) that fulfilled all criteria were selected for further evaluation. For the three selected pests, the risk mitigation measures proposed in the technical dossier were evaluated. Limiting factors on the effectiveness of the measures were documented. For the selected pests, an expert judgement on the likelihood of pest freedom is given taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The Panel is 95% sure that 9,950 or more units per 10,000 will be pest free from these three pests.

Peat based growing media are not ecologically sustainable and often fail to support biological control. Miscanthus straw was (1) tested to partially replace peat; and (2) pre-colonized with a Trichoderma strain to increase the biological control capacity of the growing media. In two strawberry pot trials (denoted as experiment I & II), extruded and non-extruded miscanthus straw, with or without pre-colonization with T. harzianum T22, was used to partially (20% v/v) replace peat. We tested the performance of each mixture by monitoring strawberry plant development, nutrient content in the leaves and growing media, sensitivity of the fruit to the fungal pathogen Botrytis cinerea, rhizosphere community and strawberry defense responses. N immobilization by miscanthus straw reduced strawberry growth and yield in experiment II but not in I. The pre-colonization of the straw with Trichoderma increased the post-harvest disease suppressiveness against B. cinerea and changed the rhizosphere fungal microbiome in both experiments. In addition, defense-related genes were induced in experiment II. The use of miscanthus straw in growing media will reduce the demand for peat and close resource loops. Successful pre-colonization of this straw with biological control fungi will optimize crop cultivation, requiring fewer pesticide applications, which will benefit the environment and human health.

Potato cyst nematodes (PCN), Globodera rostochiensis and G. pallida, are major constraints to potato production. They are distributed passively with soil adhering to farm machinery and harvested tubers, but also by waste soil from trading and processing plants. Inundation is considered an environmentally save method for disinfestation of waste soil. We investigated if agro-industrial waste products accelerate this disinfestation process by studying PCN survival, hatching and infectivity over time. Experiments were conducted in 2-L containers filled with 1.5 L non-amended soil, soil amended with steamed or fresh potato peels, calcium sulphate, steamed potato peels mixed with calcium sulphate, or leek leaves. In each container, cysts of G. rostochiensis or G. pallida were buried in the soil in retrievable bags and 400 ml water was added. Non-amended and non-inundated soils were the controls. It took 8 weeks of inundation of non-amended soil to reduce nematode survival by 72 %, while in amended soils survival was reduced up to 99.9 % after 4 weeks. After 1 week, fewer second-stage juveniles (J2) hatched and infected roots in inundated amended soil than in inundated non-amended soil. Host finding ability of surviving J2 was not affected. To understand mechanisms of nematode suppression, concentrations of short chain fatty acids (SCFA), gases (O2, CO2, H2S, CH4, and N2) and phospholipid fatty acids (PLFAs) were determined. Higher concentrations of SCFA and carbon dioxide and lower levels of oxygen were detected in amended treatments. H2S was occasionally detected in the leek-amended soil. The microbial biomass changed significantly in potato peels-amended soils.

Anthracnose, caused by Colletotrichum acutatum (species complex), has become a troublesome problem in strawberry production worldwide. This paper reports (i) an optimized sampling method combined with a real-time PCR technique to detect the latent presence of C. acutatum in cold-stored strawberry plants used as planting material in several European countries, and (ii) a study of the spread of C. acutatum following a point inoculation under field conditions. Screening of different parts of planting material suggested that C. acutatum is most likely to be present on runners and old petioles. In addition, in seven out of nine batches of planting material from different nurseries, latent infection by C. acutatum was detected in at least one of five replicate samples. Field experiments in 2009 and 2010 showed extensive latent within-field spread of the pathogen on strawberry leaves, with a within-row dispersal distance up to at least 1·75 m in 1 week. A straw ground cover between the rows did not decrease C. acutatum spread, probably because introduced (and/or subsequent) inoculum was confined to the plant bed (within the row) and was not present between the beds. Moreover, the number of C. acutatum spores on the symptomless leaves, as estimated using a real-time PCR method, was significantly (P

Wet sieving of soil samples, followed by plating on semi-selective medium and microscopic analysis, is the most commonly used technique to quantify microsclerotia-forming Verticillium species in soil. However, the method is restricted to small samples, does not allow easy differentiation between species, and takes several weeks to complete. This study describes an alternative method to test 100-g soil samples for three Verticillium species (V. tricorpus, V. dahliae, and V. longisporum) using density flotation-based extraction of microsclerotia followed by new real-time polymerase chain reaction (PCR) assays. Primers for these real-time PCR assays were designed to the ribosomal DNA internal transcribed spacer for V. tricorpus and the β-tubulin gene for V. dahliae + V. longisporum and V. longisporum. Tests with artificially and naturally infested soils showed that the new method is reproducible and sensitive (0.1 to 0.5 microsclerotia/g soil), allows differentiation among the three species, and can be completed in one day. The results of the new method and the wet-sieving method were highly correlated for V. tricorpus (R2 = 0.78), but not for V. dahliae/V. longisporum, probably due to the loss of germinability of V. dahliae/V. longisporum microsclerotia during prolonged dry storage of the soil.

Fusarium foetens is a recently described aggressive vascular pathogen of Begonia x hiemalis. Since 2004, it has caused severe losses for Begonia growers in Northern Europe and North America. F. foetens is likely to be of exotic origin. Little is known about the accumulation of the fungus in Begonia plants before and during symptom expression and about its host range. We have optimised a molecular detection method for F. foetens by only using the plant part containing the largest amount of the pathogen and by optimising the tissue maceration and DNA extraction techniques. This allowed a reliable detection limit of 2310 spore equivalents per plant and a theoretical detection limit of as low as 84 to 167 spore equivalents per plant. Using this method, we demonstrated exponential accumulation of F. foetens DNA in Begonia roots, resulting in symptoms at a threshold of approximately 107 spore equivalents and levelling off at 109 spore equivalents per plant. The observed rate of accumulation and the amount of pathogen DNA in non-symptomatic plants can be combined to determine whether the cuttings were infected after delivery at the Begonia nursery and to calculate the estimated timing of symptom development. To test the host range, we applied the optimised molecular detection technique. During these tests, only Begonia x hiemalis plants became symptomatic, but many other plant species supported growth of the pathogen. This information can be used to aid pathogen control and has implications for pest risk assessment.

Colletotrichum isolates (457) were collected from strawberry plant tissues with and without typical anthracnose symptoms and from symptomless weeds in 19 Belgian strawberry fields. The isolates were characterized based on genetic, morphological and pathological features. Isolates were classified according to rDNA-ITS sequencing: 97% of 211 representative isolates were C. acutatum, 2%C. gloeosporioides and 1%C. coccodes. The C. acutatum isolates belonged to the intraspecific groups A2 (33%), A3 (5%), A4 (50%), A5 (3%) and A7 (6%). Differences in spore morphology, growth rate and colony colour of a selection of 146 isolates confirmed the genetic grouping. Multiple Colletotrichum genotypes were detected in the same field. There was no association between the most common genotypes and geographic origin, presence or absence of symptoms, nor plant species or plant part. Representative Belgian Colletotrichum isolates were used in pathogenicity tests, together with European and American reference isolates. The C. acutatum A2 and the Belgian C. gloeosporioides isolates were the most aggressive on fruits, followed by C. acutatum A3, A4, A5, A7 and C. coccodes isolates. When inoculated into crowns, C. acutatum A2, A5 and American C. gloeosporioides isolates were the most aggressive, followed by C. acutatum A3 isolates. The A4 and A7 isolates and all European C. gloeosporioides isolates were non-pathogenic on crowns. These data indicate that an unusually diverse Colletotrichum population is present in Belgium. The traditional differentiation between C. acutatum and C. gloeosporioides as causal agents of fruit and crown rot, respectively, proved not to be valid in Belgian strawberry fields.

Real-time PCR assays for Colletotrichum acutatum, one of the most important pathogens of strawberry worldwide, were developed using primers designed to the ribosomal DNA internal transcribed spacer 1 (rDNA ITS1) and the β-tubulin 2 gene. Using TaqMan technology, the ITS-based assay could reliably detect as little as 50 fg genomic DNA, 100 copies of target DNA, or 25 conidia. The β-tubulin-based assay was c. 66 times less sensitive, and therefore less suitable for detection purposes. The TaqMan-ITS assay recognized all C. acutatum isolates tested from various intraspecific molecular groups, while no amplification was observed with several other Colletotrichum species or other strawberry pathogens, indicating the specificity of this assay. Detection and quantification of C. acutatum was demonstrated in artificially and naturally infected strawberry leaves. First, C. acutatum was detected in plant mixes of which only 0·001% of the tissue was infected by C. acutatum. Secondly, real-time PCR analysis of leaf samples taken at various times after inoculation indicated that the assay allowed monitoring of growth progression of C. acutatum. This real-time PCR-mediated monitoring of the pathogen was well-correlated with microscopic data, and confirmed that leaf age may play a role in the extent of C. acutatum infection. Finally, the assay allowed detection of C. acutatum in naturally infected and symptomless strawberry leaves collected from production fields and planting material.

Basal rot is a common disease in lettuce greenhouses. A 3-year study on the diversity of pathogens associated with basal rot in Belgium was carried out. A total of 150 isolates were collected originating from 56 greenhouses. Four pathogens appeared to be involved. Rhizoctonia solani was found to be the causal agent at 23 locations, Sclerotinia spp. at 14, Botrytis cinerea at 17 and Pythium spp. at seven. The isolates of R. solani were further characterised to anastomosis groups and subgroups using morphological characteristics, pectic zymogram and PCR-RFLP. Five anastomosis groups could be distinguished: AG1-1B, AG4 HGI, AG10, AG2-1, AG2-1 Nt and AG3, with isolates of AG4 HGI and AG1-1B being the most prevalent and the most aggressive. Sclerotinia sclerotiorum was found at 13 locations, while S. minor was found at only one location. Based on ITS-sequencing Pythium isolates were assigned to three different species. At 20°C, isolates of all pathogens were able to cause lesions on detached lettuce leaves, except isolates of R. solani AG3 and AG2-1 Nt. A correlation could be found between the occurrence of the pathogens and the growing season. Botrytis cinerea was the most common pathogen in winter, whereas R. solani was most frequently isolated in summer. Sclerotinia spp. and Pythium spp. were isolated in spring, summer and autumn. The information obtained in this study will be most useful in the development of an alternative control strategy for causal agents of basal rot.

Background: Biochar is a solid coproduct of biomass pyrolysis, and soil amended with biochar has been shown to enhance the productivity of various crops and induce systemic plant resistance to fungal pathogens. The aim of this study was to explore the ability of wood biochar to induce resistance to the root-knot nematode (RKN) Meloidogyne graminicola in rice (Oryza sativa cv. Nipponbare) and examine its histochemical and molecular impact on plant defense mechanisms. Results: A 1.2 % concentration of biochar added to the potting medium of rice was found to be the most effective at reducing nematode development in rice roots, whereas direct toxic effects of biochar exudates on nematode viability, infectivity or development were not observed. The increased plant resistance was associated with biochar-primed H2O2 accumulation as well as with the transcriptional enhancement of genes involved in the ethylene (ET) signaling pathway. The increased susceptibility of the Ein2b-RNAi line, which is deficient in ET signaling, further confirmed that biochar-induced priming acts at least partly through ET signaling. Conclusion: These results suggest that biochar amendments protect rice plants challenged by nematodes. This priming effect partially depends on the ET signaling pathway and enhanced H2O2 accumulation.

The response of 13 European cauliflower cultivars to Verticillium longisporum was evaluated using two greenhouse tests and one in vitro inoculation test. The greenhouse tests involved dipping roots of 3-week-old seedlings in a conidial suspension or inoculating the soil of 3-week-old seedlings with Verticillium microsclerotia. The in vitro test involved the inoculation of 9-day-old seedlings with Verticillium conidia. Useful disease parameters were the area under disease progress curve and plant growth reduction for the greenhouse tests and fresh weight reduction for the in vitro test. Significant correlations were found among the three inoculation methods. Irrespective of the inoculation method used, cultivar Sernio was most resistant to V. longisporum, while Minaret was the most susceptible cultivar. The pathogen could be re-isolated from the hypocotyls and from the stem of Minaret 4 and 49 days after inoculation respectively, whereas V. longisporum could never be re-isolated from Sernio. These results suggest that the more resistant cauliflower cultivar Sernio can suppress the ascent and the proliferation of V. longisporum into the plant.

In April 2010, pink-orange spore masses that later turned brown were observed on 7 to 50% of the transplant lots during a routine screening of Belgian strawberry (Fragaria × ananassa, cv. Elsanta) for the latent presence of Colletotrichum acutatum using the petiole freeze method (4). These spore masses contained hyaline, canoe-shaped to allantoid conidia (mean size 7.5 × 1.8 μm), which is not consistent with C. acutatum spore morphology. Subsequently, a spore mass was transferred onto potato dextrose agar (PDA) and a gray-to-brown colony with whitish, aerial mycelium was produced, which is also not consistent with C. acutatum isolates. To identify the fungus, the ITS1-5.8S-ITS2 rDNA region was amplified by PCR and sequenced. The 485-bp region was 100% identical to that of Pilidium concavum specimen voucher BPI 1107275 (GenBank Accession No. AY487094). P. concavum (Desm.) Höhn. (synanamorph Hainesia lythri; teleomorph Discohainesia oenotherae) is a pathogen of strawberry causing tan-brown rot of fruit and is a common secondary invader of roots and dead strawberry plant parts (3). A recent strain of P. concavum from strawberry, isolate UPL 50, obtained from Brazil (L. Zambolim, Univ. Fed. de Viçosa, personal communication) showed similar colony, microscopic (mean spore size of 6.8 × 1.8 μm), and molecular (ITS sequence 98% identical to that of P. concavum specimen voucher BPI 1107275) features as the Belgian isolate. Pathogenicity tests were conducted on mature strawberry fruits by submerging 15 fruits per isolate for 3 min in a conidial suspension (2 × 106 conidia ml–1 of water) obtained from a 2-week-old colony on PDA. Controls were submerged in sterile distilled water. The inoculated fruits were incubated in a moist chamber at 25°C. Sunken, yellowish brown lesions with pink and later orange-brown spore masses were observed starting 3 days after inoculation on 88 and 94% of the fruit for the Brazilian and Belgian isolate, respectively. The control fruits remained healthy. The fungal isolates were reisolated from symptomatic fruits and their identity was confirmed based on morphological features. During a strawberry field survey in July 2010 in Sint-Truiden (Belgium), lesions typical of those described above were observed on eight strawberry fruits (cv. Elsanta). The fungus was isolated from the symptomatic tissue of two fruits and characterized as described above. Since P. concavum was latently present on strawberry transplants and caused disease on the fruits in the field, we conclude that P. concavum is a potential threat for Belgian strawberry production. Moreover, no strawberry cultivars with resistance to the pathogen have been reported. The disease has previously been reported on strawberry in South America and Poland (1,2), but to our knowledge, this is the first report of P. concavum on strawberry in Belgium. Although the spore and colony morphology of P. concavum is different from C. acutatum, the spore masses of P. concavum can easily be confused with the spore masses of C. acutatum when using the freeze method. This suggests the need for microscopic analysis of these spore masses during routine analyses. References: (1) L. Cedeno et al. Interciencia 26:113, 2001. (2) U. P. Lopes et al. New Dis. Rep. 21:7, 2010. (3) J. L. Maas. Compendium of Strawberry Diseases. The American Phytopathological Society St. Paul, MN, 1998. (4) J. C. Mertely and D. E. Legard. Plant Dis. 88:407, 2004.