Sint-Katelijne-Waver, Belgium
Sint-Katelijne-Waver, Belgium

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Vanachter A.,Scientia Terrae Research Institute
Acta Horticulturae | Year: 2010

The concept of plant health is far more than the opposite of plant disease, although relative freedom from disease is necessary. A healthy plant has to grow in a healthy soil, in which the absence of major (clinical) and minor (subclinical) pathogens and a balanced biotic and abiotic environment for plant growth are prerequisites for achieving a balanced system. In addition, soil health has to be sustainable, thus the soil has to maintain a certain level of suppressiveness to protect it from pathogen invasion. Soil health should be achieved with minimal disturbance of the environment and depletion of natural resources. A variety of tests can be used to assess soil health: assessment of pathogen populations, tests for microbial activity and diversity, chemical and physical analyses, biotests and remote sensing techniques. Decision-making tools can be most helpful. Soil disinfestation (alone or combined with other methods) is a very effective tool for improving soil health in pathogen-infested soils or in soil with sickness (fatigue) or replant problems. Beyond pathogen control, soil disinfestation may also improve plant health in noninfested soils. Soil disinfestation should be part of a holistic approach that includes additional means of improving crop and soil health so as not to depend on a single method of management.


Hanssen I.M.,Scientia Terrae Research Institute | Thomma B.P.H.J.,Wageningen University
Molecular Plant Pathology | Year: 2010

Taxonomy: Pepino mosaic virus (PepMV) belongs to the Potexvirus genus of the Flexiviridae family. Physical properties: PepMV virions are nonenveloped flexuous rods that contain a monopartite, positive-sense, single-stranded RNA genome of 6.4 kb with a 3′ poly-A tail. The genome contains five major open reading frames (ORFs) encoding a 164-kDa RNA-dependent RNA polymerase (RdRp), three triple gene block proteins of 26, 14 and 9 kDa, and a 25-kDa coat protein. Genome diversity: Four PepMV genotypes, with an intergenotype RNA sequence identity ranging from 78% to 95%, can be distinguished: the original Peruvian genotype (LP); the European (tomato) genotype (EU); the American genotype US1; and the Chilean genotype CH2. Transmission: PepMV is very efficiently transmitted mechanically, and a low seed transmission rate has been demonstrated. In addition, bumblebees have been associated with viral transmission. Host range: Similar to other Potexviruses, PepMV has a rather narrow host range that is thought to be largely restricted to species of the Solanaceae family. After originally being isolated from pepino (Solanum muricatum), PepMV has been identified in natural infections of the wild tomato species S. chilense, S. chmielewskii, S. parviflorum and S. peruvianum. PepMV is causing significant problems in the cultivation of the glasshouse tomato Solanum lycopersicum, and has been identified in weeds belonging to various plant families in the vicinity of tomato glasshouses. Symptomatology: PepMV symptoms can be very diverse. Fruit marbling is the most typical and economically devastating symptom. In addition, fruit discoloration, open fruit, nettle-heads, leaf blistering or bubbling, leaf chlorosis and yellow angular leaf spots, leaf mosaic and leaf or stem necrosis have been associated with PepMV. The severity of PepMV symptoms is thought to be dependent on environmental conditions, as well as on the properties of the viral isolate. Minor nucleotide sequence differences between isolates from the same genotype have been shown to lead to enhanced aggressiveness and symptomatology. Control: Prevention of infection through strict hygiene measures is currently the major strategy for the control of PepMV in tomato production. Cross-protection can be effective, but only under well-defined and well-controlled conditions, and the effectiveness depends strongly on the PepMV genotype. © 2009 Blackwell Publishing Ltd.


Jacquemyn H.,Catholic University of Leuven | Brys R.,Research Institute for Nature and Forest | Honnay O.,Catholic University of Leuven | Roldan-Ruiz I.,Belgium Institute for Agricultural and Fisheries Research | And 3 more authors.
New Phytologist | Year: 2012

• Nonrandomspecies-species associations may arise from a range of factors, including localized dispersal, intra- and interspecific interactions and heterogeneous environmental conditions. Because seed germination and establishment in orchids are critically dependent upon the availability of suitable mycorrhizal fungi, species-species associations in orchids may reflect associations with mycorrhizal fungi. • To test this hypothesis, we examined spatial association patterns, mycorrhizal associations and germination success in a hybrid zone containing three species of the genus Orchis (Orchis anthropophora, Orchis militaris and Orchis purpurea). • Hybridizationoccurred predominantly between O. purpurea and O. militaris. The spatial distribution patterns of most pure species and hybrids were independent from each other, except that of O. purpurea and its hybrids. The fungal community composition of established individuals differed significantly between pure species, but not between hybrids and O. purpurea. Seed germination experiments using pure seeds showed that the highest number of protocorms were found in regions where adult individuals were most abundant. In the case of hybrid seeds, germination was restricted to areas where the mother plant was most abundant. • Overall, these results suggest that the observed nonrandom spatial distribution of both pure and hybrid plants is dependent on the contingencies of the spatial distribution of suitable mycorrhizal fungi. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.


Bailarote B.C.,Catholic University of Leuven | Lievens B.,Scientia Terrae Research Institute | Lievens B.,Leuven University College | Jacquemyn H.,Catholic University of Leuven
American Journal of Botany | Year: 2012

• Premise of the study: Orchids rely on mycorrhizal fungi for seed germination, and many species maintain associations during later stages in their life cycle. Because of the critical dependence of orchids on fungi it has been suggested that the degree of mycorrhizal specificity may be associated with rarity and long-term survival of orchid species, especially in highly degraded or fragmented landscapes. To test this hypothesis, we compared mycorrhizal communities in two species that differed signifi- cantly in decline in Belgium and other parts of Europe. • Methods: Mycorrhizal associations were investigated in five populations of Anacamptis morio and Dactylorhiza fuchsii in Belgium. ITS-based DNA arrays were used for simultaneous detection and identification of a wide range of basidiomycetous mycorrhizal fungi. Mycorrhizal specificity, measured as phylogenetic diversity, was assessed for each population and compared between species. • Key results: For both species, the degree of phylogenetic relatedness of the mycorrhizal partners was low, and both species were associated with a large number of fungal lineages related to clades of the Tulasnellaceae family. Contrary to expectations, the species that was apparently resilient to decline was associated with fewer fungal operational taxonomical units than the declining species was, and the phylogenetic relatedness of mycorrhizal communities among populations was higher in the stable than in the declining orchid. • Conclusions: Although our results do not present detailed insights into the causes of orchid persistence, they do suggest that orchid rarity and persistence are not necessarily related to fungal diversity and that other factors may be more important in determining orchid persistence. © 2012 Botanical Society of America.


Jacquemyn H.,Catholic University of Leuven | Brys R.,Catholic University of Leuven | Lievens B.,Scientia Terrae Research Institute | Lievens B.,Campus Management | Wiegand T.,Helmholtz Center for Environmental Research
Journal of Ecology | Year: 2012

1.Understanding the many factors that affect community composition and coexistence of species in natural environments is one of the central goals in ecology. As germination and establishment of seedlings in orchids are crucially dependent on mycorrhizal availability, the diversity and spatial distribution of orchid mycorrhizal fungi are likely factors that contribute to orchid coexistence. 2.In this study, we combined molecular identification techniques with seed germination experiments and spatial point pattern analyses to investigate to what extent differences in mycorrhizal association patterns affected spatial variation in seed germination and the above-ground distribution of three co-occurring terrestrial orchid species (Anacamptis morio, Gymnadenia conopsea and Orchis mascula). 3.The three species associated with a different set of mycorrhizal fungi, except A. morio and G. conopsea, which shared one fungal associate. The number of fungal lineages detected associating with each species also differed between species, being highest in G. conopsea, which associated with five lineages, and restricted to a single lineage in O. mascula. 4.Seed germination experiments showed that below-ground seed germination was restricted to locations where orchid individuals were most abundant, and quickly declined with increasing distance from the nearest above-ground congener. Spatial point pattern analyses indicated significant fine-scale spatial clustering that was highest in O. mascula and lowest in G. conopsea. Moreover, the spatial distributions of the three species were independent from each other, except for A. morio and G. conopsea. 5.Synthesis. Our results support previous findings that co-occurring orchid species tend to use different mycorrhizal partners. Although the possibility that variation in local environmental conditions affected seed germination could not be completely ruled out, our results suggest that the presence of specific mycorrhizal fungi contributed, at least partly, to the spatial distribution and coexistence of the investigated orchid species. © 2012 The Authors. Journal of Ecology © 2012 British Ecological Society.


Jacquemyn H.,Catholic University of Leuven | Deja A.,Catholic University of Leuven | de hert K.,Catholic University of Leuven | Cachapa Bailarote B.,Catholic University of Leuven | And 2 more authors.
PLoS ONE | Year: 2012

Background: Orchid species rely on mycorrhizal symbioses with fungi to complete their life cycle. Although there is mounting evidence that orchids can associate with several fungi from different clades or families, less is known about the actual geographic distribution of these fungi and how they are distributed across different orchid species within a genus. Methodology/Principal Findings: We investigated among-population variation in mycorrhizal associations in five species of the genus Dactylorhiza (D. fuchsii, D. incarnata, D. maculata, D. majalis and D. praetermissa) using culture-independent detection and identification techniques enabling simultaneous detection of multiple fungi in a single individual. Mycorrhizal specificity, determined as the number of fungal operational taxonomic units (OTUs), and phylogenetic diversity of fungi were compared between species, whereas discriminant analysis was used to compare mycorrhizal spectra across populations and species. Based on a 95% cut-off value in internal transcribed spacer (ITS) sequence similarity, a total of ten OTUs was identified belonging to three different clades within the Tulasnellaceae. Most OTUs were found in two or more Dactylorhiza species, and some of them were common and widespread, occurring in more than 50% of all sampled populations. Each orchid species associated with at least five different OTUs, whereas most individuals also associated with two or more fungal OTUs at the same time. Phylogenetic diversity, corrected for species richness, was not significantly different between species, confirming the generality of the observed orchid mycorrhizal associations. Conclusions/Significance: We found that the investigated species of the genus Dactylorhiza associated with a wide range of fungal OTUs from the Tulasnellaceae, some of which were widespread and common. These findings challenge the idea that orchid rarity is related to mycorrhizal specificity and fungal distribution. © 2012 Jacquemyn et al.


Hanssen I.M.,Scientia Terrae Research Institute | Lapidot M.,Israel Agricultural Research Organization | Thomma B.P.H.J.,Wageningen University
Molecular Plant-Microbe Interactions | Year: 2010

Viral diseases are an important limiting factor in many crop production systems. Because antiviral products are not available, control strategies rely on genetic resistance or hygienic measures to prevent viral diseases, or on eradication of diseased crops to control such diseases. Increasing international travel and trade of plant materials enhances the risk of introducing new viruses and their vectors into production systems. In addition, changing climate conditions can contribute to a successful spread of newly introduced viruses or their vectors and establishment of these organisms in areas that were previously unfavorable. Tomato is economically the most important vegetable crop worldwide and many viruses infecting tomato have been described, while new viral diseases keep emerging. Pepino mosaic virus is a rapidly emerging virus which has established itself as one of the most important viral diseases in tomato production worldwide over recent years. Begomovirus species and other whitefly-transmitted viruses are invading into new areas, and several recently described newviruses such as Tomato torrado virus and new Tospovirus species are rapidly spreading over large geographic areas. In this article, emerging viruses of tomato crops are discussed. © 2010 The American Phytopathological Society.


Jacquemyn H.,Catholic University of Leuven | Honnay O.,Catholic University of Leuven | Cammue B.P.A.,Catholic University of Leuven | Brys R.,Research Institute for Nature and Forest | And 2 more authors.
Molecular Ecology | Year: 2010

Most orchid species rely on mycorrhizae to complete their life cycle. Despite a growing body of literature identifying orchid mycorrhizal associations, the nature and specificity of the association between orchid species and mycorrhizal fungi remains largely an open question. Nonetheless, better insights into these obligate plant-fungus associations are indispensable for understanding the biology and conservation of orchid populations. To investigate orchid mycorrhizal associations in five species of the genus Orchis (O. anthropophora, O. mascula, O. militaris, O. purpurea, and O. simia), we developed internal transcribed spacer-based DNA arrays from extensive clone library sequence data sets, enabling rapid and simultaneous detection of a wide range of basidiomycetous mycorrhizal fungi. A low degree of specificity was observed, with two orchid species associating with nine different fungal partners. Phylogenetic analysis revealed that the majority of Orchis mycorrhizal fungi are members of the Tulasnellaceae, but in some plants, members of the Thelephoraceae, Cortinariaceae and Ceratobasidiaceae were also found. In all species except one (O. mascula), individual plants associated with more than one fungus simultaneously, and in some cases, associations with ≥3 mycorrhizal fungi at the same time were identified. Nestedness analysis showed that orchid mycorrhizal associations were significantly nested, suggesting asymmetric specialization and a dense core of interactions created by symmetric interactions between generalist species. Our results add support to the growing literature that multiple associations may be common among orchids. Low specificity or preference for a widespread fungal symbiont may partly explain the wide distribution of the investigated species. © 2010 Blackwell Publishing Ltd.


Alvarez-Perez S.,CSIC - Doñana Biological Station | Lievens B.,Leuven University College | Lievens B.,Scientia Terrae Research Institute | Jacquemyn H.,Catholic University of Leuven | Herrera C.M.,CSIC - Doñana Biological Station
International Journal of Systematic and Evolutionary Microbiology | Year: 2013

The taxonomic status of 14 strains of members of the genus Acinetobacter isolated from floral nectar of wild Mediterranean insect-pollinated plants, which did not belong to any previously described species within this genus, was investigated following a polyphasic approach. Confirmation that these strains formed two separate lineages within the genus Acinetobacter was obtained from comparative analysis of the partial sequences of the 16S rRNA gene and the gene encoding the β-subunit of RNA polymerase (rpoB), DNA-DNA reassociation data, determination of the DNA G+C content and physiological tests. The names Acinetobacter nectaris sp. nov. and Acinetobacter boissieri sp. nov. are proposed. The type strain of A. nectaris sp. nov. is SAP 763.2T (=LMG 26958T=CECT8127T) and that of A. boissieri sp. nov. is SAP 284.1T (=LMG 26959T=CECT8128T). © 2013 IUMS Printed in Great Britain.


Hanssen I.M.,Scientia Terrae Research Institute | Lapidot M.,Israel Agricultural Research Organization
Advances in Virus Research | Year: 2012

Tomato (Solanum lycopersicum L.) originated in South America and was brought to Europe by the Spaniards in the sixteenth century following their colonization of Mexico. From Europe, tomato was introduced to North America in the eighteenth century. Tomato plants show a wide climatic tolerance and are grown in both tropical and temperate regions around the world. The climatic conditions in the Mediterranean basin favor tomato cultivation, where it is traditionally produced as an open-field plant. However, viral diseases are responsible for heavy yield losses and are one of the reasons that tomato production has shifted to greenhouses. The major tomato viruses endemic to the Mediterranean basin are described in this chapter. These viruses include Tomato yellow leaf curl virus, Tomato torrado virus, Tomato spotted wilt virus, Tomato infectious chlorosis virus, Tomato chlorosis virus, Pepino mosaic virus, and a few minor viruses as well. © 2012 Elsevier Inc.

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