SUNScholar - Browsing by Author "Roets, Francois"

Browsing by Author "Roets, Francois"

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Alien plants have greater impact than habitat fragmentation on native insect flower visitation networks
(Wiley, 2018) Hansen, Simone; Roets, Francois; Seymour, Colleen L.; Thebault, Elisa; Van Veen, F. J. Frank; Pryke, James S.
Aim: Habitat fragmentation and alien species are among the leading causes of biodiversity loss. In an attempt to reduce the impact of forestry on natural systems, networks of natural corridors and patches of natural habitat are often maintained within the afforested matrix, yet these can be subject to degradation by invasion of non-native species. Both habitat fragmentation and alien invasive species disrupt the complex interaction networks typical of native communities. This study examines whether an invasive plant and/or the fragmented nature of the forestry landscape influences natural flower visitation networks (FVNs), flower–visitor abundance and richness or flower/visitor species composition. Location: The species rich and diverse grasslands in the KwaZulu-Natal Midlands, South Africa is under threat from transformation, particularly by commercial forestry plantations, restricting much of the remaining untransformed grasslands into remnant grassland patches (RGPs). Remaining patches are under additional threat from the invasive Rubus cuneifolius Pursh (bramble). Sites were established in RGPs and in a nearby protected area (PA), with and without brambles present for both areas. Results: Flower abundance and flower area of native plant species were greater within RGP than in PA, but only in the absence of R. cuneifolius. Flower–visitor assemblages differed between invaded and uninvaded sites and also differed between PA and RGP sites. Both areas lost specialist flower–visitor species in the presence of brambles. Network modularity was greatly reduced by the presence of bramble, indicating a reduction in complexity and organization. The structure of FVNs was otherwise unaffected by presence of bramble or being located in RGPs or the PA. Main conclusions: The RPGs contribute to regional biodiversity conservation through additional compositional diversity and intact FVNs. Rubus cuneifolius reduces ecological complexity of both RGPs and PAs, however, and its removal must be prioritized to conserve FVNs.
Bark beetle mycobiome : collaboratively defined research priorities on a widespread insect-fungus symbiosis
(Springer, 2020-06-03) Hulcr, Jiri; Barnes, Irene; De Beer, Wilhelm; Duong, Tuan A.; Gazis, Romina; Johnson, Andrew J.; Jusino, Michelle A.; Kasson, Matthew T.; Li, You; Lynch, Shannon; Mayers, Chase; Musvuugwa, Tendai; Roets, Francois; Seltmann, Katja C.; Six, Diana; Vanderpool, Dan; Villari, Caterina
One of the main threats to forests in the Anthropocene are novel or altered interactions among trees, insects and fungi. To critically assess the contemporary research on bark beetles, their associated fungi, and their relationships with trees, the international Bark Beetle Mycobiome research coordination network has been formed. The network comprises 22 researchers from 17 institutions. This forward-looking review summarizes the group’s assessment of the current status of the bark beetle mycobiome research field and priorities for its advancement. Priorities include data mobility and standards, the adoption of new technologies for the study of these symbioses, reconciliation of conflicting paradigms, and practices for robust inference of symbiosis and tree epidemiology. The Net work proposes contemporary communication strategies to interact with the global community of researchers studying symbioses and natural resource managers. We conclude with a call to the broader scientific community to participate in the network and contribute their perspectives.
Diversity and ecology of ophiostomatoid fungi and arthropods associated with proteaceae infructescences
(Stellenbosch : Stellenbosch University, 2002-12) Roets, Francois; Dreyer, L. L.; Crous, P. W.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Five new species of ophiostomatoid fungi, colon ising the infructescences of serotinous Protea species, have recently been discovered in South Africa. Prior to this, ophostomatoid fungi were thought to be restricted to the Northern Hemisphere. The discovery of these five species thus extensively expanded the known geographical range of these fungi, now also to include the Southern Hemisphere. Since this discovery, few studies have focused on the interesting ecology of this group, which is uniquely adapted for spore dispersal by arthropods. Studies focussed on ophiostomatoid fungi provide an unique opportunity to study inter-organism interactions between fungi, their host plants and the arthropods responsible for their spore dispersal. Very few similar studies have been undertaken, particularly in the Fynbos Biome, to which most of our economically important Protea species are confined. The current study provides insight into some ecological aspects of these complex interactions. The seasonal distribution of the ophiostomatoid fungi associated with the infructescences of members of the Proteaceae was investigated. Definite seasonal patterns were observed, with peak fungal colonisation occurring during the wetter winter months. While determining the host specificity of these fungi, a new Protea host for Ophiostoma splendens was identified, and a new species of Rhyncomeliola was discovered. All ophiostomatoid species native to Fynbos in the Stellenbosch region are exclusively associated with the infructescences of species in the plant genus Protea. By employing a multiplex Polymerase Chain Reaction (PCR), a set of group specific primers was developed for the identification of South African Ophiostoma and Gondwanamyces fungal DNA. This newly developed method was used to scan arthropods collected from the infructescences of P. repens for the presence of 0. splendens and G. proteae spores. By using these group-specific primers, three insects possibly responsible for long range dispersal of fungal spores were identified. Three further insect species, possibly contributing to the short-range dispersal of ophiostomatoid spores, were also implicated through this method. All arthropods associated with the fruiting structures of selected members of the Proteaceae were also investigated. A total of 62 pseudospecies (ca. 7500 individuals), belonging to 45 different arthropod families, were collected. Proteaceae species with larger fruiting structures housed more arthropod species and higher numbers of individuals than Proteaceae taxa with smaller fruiting structures. Some plant species housed similar arthropod communities, while others housed unique suites of arthropods. Seasonal patterns in arthropod numbers were observed, and it was found that, in most instances, arthropod numbers peaked during the autumn and winter months. Twenty-five fungal taxa were isolated from various Proteaceae arthropods, many of which are genera known to include Proteaceae pathogenic species. Ophiostomatoid fungi have a saprophytic relationship with their Protea hosts, and may deter some of these potentially harmful fungi from colon ising the infrutescences. Some fungi showed a high degree of specificity towards potential vectors, while others were found on a diverse range of arthropods. This study highlights the existence of complex inter-organismal interactions within the Fynbos Biome, a study area where the interactions between plants, fungi and insects have been grossly neglected. The few studies that have been conducted in this field have mostly focussed on a limited number of organisms, and no wide-scale attempts, such as presented here, have been published. It is important to obtain a holistic view in any ecological study that focuses on interactions between different suites of organisms. Ultimately this will aid in the development of better conservation strategies. This study thus provides a muchneeded start in studies on multi-organismal interactions in the Fynbos Biome.
Ecology and systematics of South African Protea-associated Ophiostoma species
(Stellenbosch : University of Stellenbosch, 2006-12) Roets, Francois; Dreyer, L. L.; Crous, P. W.; Wingfield, M. J.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.
The well-known, and often phytopathogenic, ophiostomatoid fungi are represented in South Africa by the two phylogenetically distantly related genera Ophiostoma (Ophiostomatales) and Gondwanamyces (Microascales). They are commonly associated with the fruiting structures (infructescences) of serotinous members of the African endemic plant genus Protea. The species O. splendens, O. africanum, O. protearum, G. proteae and G. capensis have been collected from various Protea spp. in South Africa where, like other ophiostomatoid fungi, they are thought to be transported by arthropod vectors. The present study set out to identify the vector organisms of Protea-associated members of mainly Ophiostoma species, using both molecular and direct isolation methods. A polymerase chain reaction (PCR) and taxon specific primers for the two Protea-associated ophiostomatoid genera were developed. Implementation of these newly developed methods revealed the presence of Ophiostoma and Gondwanamyces DNA on three insect species. They included a beetle (Genuchus hottentottus), a bug (Oxycarenus maculates) and a psocopteran species. It was, however, curious that the frequency of these insects that tested positive for ophiostomatoid DNA was very low, despite the fact that ophiostomatoid fungi are known to colonise more than 50% of Protea infructescences. Subsequent direct isolation methods revealed the presence of reproductive propagules of Ophiostoma spp. on four Protea-associated mite species (Oodinychus sp., two Tarsonemus spp. and Proctolaelaps vandenbergi). These mites are numerous within Protea infructescences and Ophiostoma spp. were isolated from a high frequency of these individuals. The Oodinychus sp. mite was found to vector most of the Protea-associated Ophiostoma species. It was thus postulated that the mites (in particular the Oodinychus sp.) act as primary vectors of the Protea-associated Ophiostoma species. The association between Oodinychus mites collected from P. repens and O. splendens proved to be mutualistic. Mites feeding on this fungus showed significantly higher population growth than mites feeding on any of the other fungal species tested. The short- and long-distance dispersal methods of these mites were also investigated. Firstly the ability of mites to move from drying infructescences to moist and sheltered areas such as provided by intact infructescences on the same plant was investigated experimentally. Significantly more mites were found to actively disperse from drying infructescences to artificially manufactured infructescences containing moistened filter paper shreds than to artificially manufactured infructescences containing dry filter paper shreds. The frequent fires associated with the habitat of these mites would, however, require movement over larger areas than what would be possible through self-dispersal. Dispersal of mites via air currents was thus investigated using sticky traps, but no Ophiostoma-vectoring mites were captured in this way. Self-dispersal aided by air currents could thus be ruled out, and our investigations shifted to vectored dispersal. Numerous insects emerging from Ophiostoma-containing P. repens and P. neriifolia infructescences were collected using specially designed emergence cages. Scanning electron microscopy and stereo-microscopy revealed that all three Ophiostoma-vectoring mite genera were phoretic on the beetle G. hottentottus. Tarsonemus spp. and P. vandenbergi were also phoretic on the beetles Trichostetha fascicularis and T. capensis associated with P. repens and P. neriifolia flowers. Mites collected from the surface of these beetles were found to vector reproductive propagules of various Ophiostoma spp. This thus seems to be the only method of long-distance dispersal of these mites and subsequently also the Protea-associated Ophiostoma species. Molecular phylogenetic reconstruction based on large subunit, ITS and beta-tubulin DNA sequence data suggests a polyphyletic origin for the Protea-associated members of Ophiostoma, which proposes multiple invasions of this unusual niche by these fungi. These studies also revealed the presence of four new species of Ophiostoma associated with Protea spp. The new species O. palmiculminatum, O. phasma, O. gemellus and Sporothrix variecibatus were thus described. Ophiostoma palmiculminatum is associated with P. repens infructescences and the Oodinychus mites collected from them. Ophiostoma phasma was collected from various Protea and mite species. Ophiostoma gemellus and Sporothrix variecibatus were initially only isolated from mites, but have subsequently also been isolated from Protea spp. The present study clarifies many aspects pertaining to the phylogeny and ecology of the interesting members of Ophiostoma associated with Protea hosts. As such this study will form the platform for further studies on the co-evolution of these insect / mite / fungi / plant associations.
Genome sequences of Knoxdaviesia capensis and K. proteae (Fungi: Ascomycota) from Protea trees in South Africa
(BioMed Central, 2016) Aylward, Janneke; Steenkamp, Emma T.; Dreyer, Leanne L.; Roets, Francois; Wingfield, Brenda D.; Wingfield, Michael J.
Two closely related ophiostomatoid fungi, Knoxdaviesia capensis and K. proteae, inhabit the fruiting structures of certain Protea species indigenous to southern Africa. Although K. capensis occurs in several Protea hosts, K. proteae is confined to P. repens. In this study, the genomes of K. capensis CBS139037 and K. proteae CBS140089 are determined. The genome of K. capensis consists of 35,537,816 bp assembled into 29 scaffolds and 7940 predicted protein-coding genes of which 6192 (77.98 %) could be functionally classified. K. proteae has a similar genome size of 35,489,142 bp that is comprised of 133 scaffolds. A total of 8173 protein-coding genes were predicted for K. proteae and 6093 (74.55 %) of these have functional annotations. The GC-content of both genomes is 52.8 %.
IMA Genome-F 11: Draft genome sequences of Fusarium xylarioides, Teratosphaeria gauchensis and T. zuluensis and genome annotation for Ceratocystis fimbriata
(BMC (part of Springer Nature), 2019-09-13) Wingfield, Brenda D.; Fourie, Arista; Simpson, Melissa C.; Bushula-Njah, Vuyiswa S.; Aylward, Janneke; Barnes, Irene; Coetzee, Martin P. A.; Dreyer, Leanne L.; Duong, Tuan A.; Geiser, David M.; Roets, Francois; Steenkamp, E. T.; Van Der Nest, Magriet A.; van Heerden, Carel J.; Wingfield, Michael J.
ENGLISH ABSTRACT: Draft genomes of the fungal species Fusarium xylarioides, Teratosphaeria gauchensis and T. zuluensis are presented. In addition an annotation of the genome of Ceratocystis fimbriata is presented. Overall these genomes provide a valuable resource for understanding the molecular processes underlying pathogenicity and potential management strategies of these economically important fungi.
Interactions among predators and plant specificity protect herbivores from top predators
(Ecological Society of America, 2018) Bosc, Christopher; Roets, Francois; Hui, Cang; Pauw, Anton
The worldwide loss of top predators from natural and agricultural systems has heightened the need to understand how important they are in controlling herbivore abundance. The effect of top predators on herbivore species is likely to depend on (1) the importance of the consumption of intermediate predators by top predators (intra‐guild predation; IGP), but also on (2) plant specificity by herbivores, because specialists may defend themselves better (enemy‐free space; EFS). Insectivorous birds, as top predators, are generally known to effectively control herbivorous insects, despite also consuming intermediate predators such as spiders, but how this effect varies among herbivore species in relation to the cascading effects of IGP and EFS is not known. To explore this, we excluded birds from natural fynbos vegetation in South Africa using large netted cages and recorded changes in abundance relative to control plots for 199 plant‐dwelling intermediate predator and 341 herbivore morpho‐species that varied in their estimated plant specificity. We found a strong negative effect of birds on the total abundance of all intermediate predators, with especially clear effects on spiders (strong IGP). In contrast with previous studies, which document a negative effect of birds on herbivores, we found an overall neutral effect of birds on herbivore abundance, but the effect varied among species: some species were negatively affected by birds, suggesting that they were mainly consumed by birds, whereas others, likely released from spiders by IGP, were positively affected. Some species were also effectively neutrally affected by birds. These tended to be more specialized to plants compared to the other species, which may imply that some plant specialists benefited from protection provided by EFS from both birds and spiders. These results suggest that the response of herbivore species to top predators may depend on cascading effects of interactions among predators and on their degree of plant specificity.
Knoxdaviesia proteae is not the only Knoxdaviesia-symbiont of Protea repens
(International Mycological Association, 2015-11-10) Aylward, Janneke; Dreyer, Leanne L.; Steenkamp, Emma T.; Wingfield, Michael J.; Roets, Francois
Two polyphyletic genera of ophiostomatoid fungi are symbionts of Proteaceae in southern Africa. One of these, Knoxdaviesia, includes two closely related species, K. proteae and K. capensis, that have overlapping geographical distributions, but are not known to share Protea host species. Knoxdaviesia capensis appears to be a generalist that occupies numerous hosts, but has never been found in P. repens, the only known host of K. proteae. In this study, extensive collections were made from P. repens and isolates were identified using DNA sequence comparisons. This led to the surprising discovery of K. capensis from P. repens for the first time. The fungus was encountered at a low frequency, suggesting that P. repens is not its preferred host, which may explain why it has not previously been found on this plant. The basis for the specialisation of K. proteae and K. capensis on different Protea species remains unknown.
Lessons from a major pest invasion : the polyphagous shot hole borer in South Africa
(ASSAf, 2020-11-26) Paap, Trudy; Wingfield, Michael J.; De Beer, Z. Wilhelm; Roets, Francois
The arrival and establishment of invasive forest pests can cause devastating environmental damage and great economic impact. For example, the cost over the past decade of dealing with the arrival of a single invasive beetle in the USA, the emerald ash borer (Agrilus planipennis), is estimated at more than USD10 billion.1 Originating from Asia, this beetle has killed hundreds of millions of native ash trees since it became established in the USA. However, this beetle is but one of hundreds of invasive insect pests that impact forests in the USA, and that contribute to a global tree health crisis caused by invasive insects and pathogenic microorganisms.2-4 South Africa is no different from other countries and is experiencing an increasing rate of introductions of damaging forest pests.5,6 These invasions are largely unintentional and are a by-product of globalisation and increasing global trade.7,8 The movement of living plants and plant products, including untreated wood packaging materials (i.e. pallets, dunnage and crating), is known to be a major pathway for these pests.9,10 For clarification, in this commentary we use the terms ‘insect’ and ‘pathogen’ to distinguish between the two types of organisms, although we also use the general term ‘pest’ to refer to both groups. The term ‘invasive pest’ is used for introduced species that, in addition to maintaining a self-sustaining population, show evidence of spread and impact.
Nitrogen-fixing bacteria and Oxalis – evidence for a vertically inherited bacterial symbiosis
(BMC (part of Springer Nature), 2019-10-23) Jooste, Michelle; Roets, Francois; Midgley, Guy F.; Oberlander, Kenneth C.; Dreyer, Leanne L.
Background: Plant-endophyte symbioses often revolve around nitrogen metabolism, and involve varying degrees of intimacy. Although evidence for vertical inheritance of nitrogen-fixing endophytic bacteria is increasing, it is confined mostly to crop plants, and to date no such system has been reported for geophytes. Methods: Bacterial endophytes associated with Oxalis, the most species-rich geophytic genus form the Cape Flora in southern Africa was studied. Culturable endophytes were isolated from surface-sterilized vegetative and reproductive plant organs for six host species at three locations. Colonies of microbes on various artificial media were morphotyped, enumerated and identified using sequence data. Filter exclusion experiments were conducted to determine if endophytes were vertically transmitted to seeds, determine if mucilage plays a role to actively attract microbes from the soil and to assess microbial richness isolated from the mucilage of Oxalis seedlings. Fluorescent microscopy was implemented in order to visualize endophytic bacteria in cryo-sectioned seeds. Results: Evidence for a novel, vertically transmitted symbiosis was reported. Communities of nitrogen-fixing and plant growth-promoting Bacillus endophytes were found to associate with selected Oxalis hosts from nitrogen-deficient environments of the Cape. Bacillus endophytes were ubiquitous and diverse across species and plant bodies, and were prominent in seeds. Three common nitrogen-fixing Bacillus have known oxalotrophic properties and appear to be housed inside specialised cavities (containing oxalates) within the plant body and seeds. Conclusions: The discovery of vertical transmission and potential benefits to both host and endophyte suggest a particularly tight mutualism in the Oxalis-endophyte system. This discovery suggests unexpected ways in which geophytes might avoid nitrogen deficiency, and suggest that such symbioses are more common than previously expected.
Panmixia defines the genetic diversity of a unique arthropod-dispersed fungus specific to Protea flowers
(Wiley Open Access, 2014-09) Aylward, Janneke; Dreyer, Leanne L.; Steenkamp, Emma T.; Wingfield, Michael J.; Roets, Francois
Knoxdaviesia proteae, a fungus specific to the floral structures of the iconic Cape Floral Kingdom plant, Protea repens, is dispersed by mites phoretic on beetles that pollinate these flowers. Although the vectors of K. proteae have been identified, little is known regarding its patterns of distribution. Seed bearing infructescences of P. repens were sampled from current and previous flowering seasons, from which K. proteae individuals were isolated and cultured. The genotypes of K. proteae isolates were determined using 12 microsatellite markers specific to this species. Genetic diversity indices showed a high level of similarity between K. proteae isolates from the two different infructescence age classes. The heterozygosity of the population was high (0.74 +- 0.04), and exceptional genotypic diversity was encountered (^G = 97.87%). Population differentiation was negligible, owing to the numerous migrants between the infructescence age classes (Nm = 47.83) and between P. repens trees (Nm = 2.96). Parsimony analysis revealed interconnected genotypes, indicative of recombination and homoplasies, and the index of linkage disequilibrium confirmed that outcrossing is prevalent in K. proteae (rd = 0.0067; P = 0.132). The high diversity and panmixia in this population is likely a result of regular gene flow and an outcrossing reproductive strategy. The lack of genetic cohesion between individuals from a single P. repens tree suggests that K. proteae dispersal does not primarily occur over short distances via mites as hypothesized, but rather that longdistance dispersal by beetles plays an important part in the biology of these intriguing fungi.
A plant pathology perspective of fungal genome sequencing
(International Mycological Association, 2017) Aylward, Janneke; Steenkamp, Emma T.; Dreyer, Leanne L.; Roets, Francois; Wingfield, Brenda D.; Wingfield, Michael J.
The majority of plant pathogens are fungi and many of these adversely affect food security. This minireview aims to provide an analysis of the plant pathogenic fungi for which genome sequences are publically available, to assess their general genome characteristics, and to consider how genomics has impacted plant pathology. A list of sequenced fungal species was assembled, the taxonomy of all species verified, and the potential reason for sequencing each of the species considered. The genomes of 1090 fungal species are currently (October 2016) in the public domain and this number is rapidly rising. Pathogenic species comprised the largest category (35.5 %) and, amongst these, plant pathogens are predominant. Of the 191 plant pathogenic fungal species with available genomes, 61.3 % cause diseases on food crops, more than half of which are staple crops. The genomes of plant pathogens are slightly larger than those of other fungal species sequenced to date and they contain fewer coding sequences in relation to their genome size. Both of these factors can be attributed to the expansion of repeat elements. Sequenced genomes of plant pathogens provide blueprints from which potential virulence factors were identified and from which genes associated with different pathogenic strategies could be predicted. Genome sequences have also made it possible to evaluate adaptability of pathogen genomes and genomic regions that experience selection pressures. Some genomic patterns, however, remain poorly understood and plant pathogen genomes alone are not sufficient to unravel complex pathogen-host interactions. Genomes, therefore, cannot replace experimental studies that can be complex and tedious. Ultimately, the most promising application lies in using fungal plant pathogen genomics to inform disease management and risk assessment strategies. This will ultimately minimize the risks of future disease outbreaks and assist in preparation for emerging pathogen outbreaks.
Teratosphaeria stem canker of Eucalyptus : two pathogens, one devastating disease
(British Society for Plant Pathology, 2018) Aylward, Janneke; Roets, Francois; Dreyer, Leanne L.; Wingfield, Michael J.
Background: Teratosphaeria gauchensis and T. zuluensis are closely related fungi that cause Teratosphaeria (previously Coniothyrium) stem canker disease on Eucalyptus species propagated in plantations for commercial purposes. This disease is present in many countries in which Eucalyptus trees are planted, and continues to spread with the international trade of infected plant germplasm. Taxonomy: Fungi, Ascomycota, Pezizomycotina, Dothideomycetes, Dothideomycetidae, Capnodiales, Teratosphaeriaceae, Teratosphaeria. Identification: The causal agents form dark masses of pycnidia that are visible on the surface of distinct stem cankers that typically form on young green stem tissues. Accurate diagnosis of the causal agents requires DNA sequence data. Host range: Nine species of Eucalyptus are known to be affected. Of these, E. grandis and its hybrids, which include some of the most important planting stock globally, appear to be particularly vulnerable. Disease symptoms: Small necrotic lesions develop on young green stem tissue. These lesions coalesce to form large cankers that exude gum. Epicormic shoots develop below the girdling canker and, in severe cases, trees die.
Wild herbivore grazing enhances insect diversity over livestock grazing in an African grassland system
(Public Library of Science, 2016) Pryke, James S.; Roets, Francois; Samways, Michael J.
Southern Africa’s grassland biodiversity is threatened by habitat transformation such as commercial forestry. Ecological networks (ENs) have been investigated to alleviate the pressure of habitat transformation on local biodiversity. ENs are large scale webs of corridors and patches of natural vegetation criss-crossing production landscapes that can simulate conditions in protected areas (PAs). Many ENs have lost many native large mammal species, which have been replaced by domestic livestock to retain natural grazing dynamics, which could have an impact on the long-term value of ENs for insects. Here we compared dung beetle, butterfly and grasshopper diversity in ENs across a landscape mosaic of timber plantations, where 1) wild megaherbivores were maintained, 2) in ENs where these herbivores were replaced by livestock and, 3) in a nearby World Heritage PA which retained its natural complement of megaherbivores. Sites in the PA far from any plantation were similar in composition to those in the wild grazed EN. Presence of the wild grazers improved the alpha- and beta-diversity of all focal insect taxa when compared to domestic grazing. Furthermore, species composition shows significant differences between the two grazing systems indicating that an assemblage of native large mammals facilitates insect diversity conservation. We support the maintenance or introduction of large native mammals in ENs or similar conservation areas in production landscapes to simulate the ecological conditions and natural heterogeneity in nearby PAs.

Browsing by Author "Roets, Francois"

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