A survey of diseases of exotic trees in plantations was undertaken in southern and southwestern E... more A survey of diseases of exotic trees in plantations was undertaken in southern and southwestern Ethiopia during 2000 and 2001. Our aim was to ascertain the occurrence and distribution of diseases of major plantation species and to provide a basis for further research. Root, stem and leaf samples were collected from both plantations and trees growing near farms and homesteads in and around Wondo Genet, Munessa Shashemene, Jima, Bedele, Mizan and Menagesha. Armillaria root rot was the most common disease, associated mainly with Pinus patula , but also found on Acacia abyssinica, Cordia alliodoral/ig and Cedrela odorata . Stem cankers associated with ligBotryosphaerial/ig species were common on Eucalyptus globulus, E. salignal/ig and E. citriodora . Stem canker disease associated with a ligConiothyriuml/ig species was commonly observed on E. camaldulensis . Leaf blotch associated with ligMycosphaerellal/ig species was common on E. globulusl/ig in most areas where this species is plante...
Little is known regarding the fungi, especially fungal pathogens, associated with mangroves in Af... more Little is known regarding the fungi, especially fungal pathogens, associated with mangroves in Africa. This includes fungi in the Botryosphaeriaceae that comprise numerous opportunistic, stress-associated pathogens often associated with trees affected by environmental and anthropogenically generated stresses, such as those affecting mangroves. We investigated the occurrence of endophytic Botryosphaeriaceae along the entire distribution of mangroves in South Africa. Asymptomatic branches were collected from ten localities and six mangrove species. Isolates resembling species of Botryosphaeriaceae were identified based on multi-gene sequence data of the internal transcribed spacer regions (ITS), including the 5.8S nrRNA, the beta-tubulin (tub2), partial translation elongation factor 1-alpha (tef1-α), and DNA-directed RNA polymerase II second largest subunit (rpb2) gene regions. Inoculation trials were conducted on healthy branches of Avicennia marina and Bruguiera gymnorrhiza to evalu...
Mangrove trees are continuously under stress due to environmental and/or anthropogenic pressures,... more Mangrove trees are continuously under stress due to environmental and/or anthropogenic pressures, which expose them to attack by pathogens, compromising their survival. Ophiostomatoid fungi cause sap stain and diseases of a wide spectrum of tree species globally. These fungi infect trees through natural, insect, animal and/or human made wounds. During routine surveys of mangrove trees in South Africa, wounds on branches and stems of Avicennia marina were regularly monitored for the presence of ophiostomatoid fungi at ten study sites in the country. The stems of four mangrove species, A. marina, Bruguiera gymnorrhiza, Rhizophora mucronata and Barringtonia racemosa were also wounded and evaluated for the appearance of these fungi. Ophiostomatoid fungi were obtained from the mangrove associate B. racemosa, but not from any of the true mangroves. Analyses of DNA sequence data for the internal transcribed spacer, β-tubulin, calmodulin and translation elongation factor gene regions reveal...
Armillaria root-rot is one of the most serious root diseases of perennial tree crops in tropical ... more Armillaria root-rot is one of the most serious root diseases of perennial tree crops in tropical Africa. The disease was first reported on cacao in Ghana during 1927. It was initially referred to as 'collar crack' due to typical longitudinal cracks that are formed in the bark at the tree collar, as a result of mechanical pressure from fungal fans colonizing the cambium. These fungal fans are typical of species in the genus Armillaria. The pathogen associated with the disease was identified as A. mellea (Valh Ex. Fr.). However, A. mellea is a taxonomic complex that currently includes a number of morphologically indistinguishable species, the true identity of the species causing root-rot on cacao in Africa is thus uncertain. More recent studies have shown that DNA sequence comparisons can effectively differentiate among Armillaria species from Africa with uniform morphologies. In this study we applied a molecular approach to characterize Armillaria isolates associated with roo...
Thielaviopsis ethacetica was recently reinstated as a distinct taxon using DNA phylogenies. It is... more Thielaviopsis ethacetica was recently reinstated as a distinct taxon using DNA phylogenies. It is widespread affecting several crop plants of global economic importance. In this study, microsatellite markers were developed and used in conjunction with sequence data to investigate the genetic diversity and structure of Th. ethacetica in Cameroon. A collection of 71 isolates from cacao, oil palm, and pineapple, supplemented with nine isolates from other countries were analysed. Four genetic groups were identified. Two of these were associated with oil palm in Cameroon and showed high genetic diversity, suggesting that they might represent an indigenous population of the pathogen. In contrast, the remaining two groups, associated with cacao and pineapple, had low genetic diversity and, most likely, represent introduced populations. There was no evidence of gene flow between these groups. Phylogenetic analyses based on sequences of the tef1-a as well as the combined flanking regions of six microsatellite loci were consistent with population genetic analyses and suggested that Th. ethacetica is comprised of two divergent genetic lineages.
Knowledge of the diversity and ecology of plant pathogenic fungi in cacao agroforests and surroun... more Knowledge of the diversity and ecology of plant pathogenic fungi in cacao agroforests and surrounding natural ecosystems can inform the development of sustainable management strategies for new cacao disease outbreaks. In this study, we investigated the occurrence of fungi related to the Ceratocystisdaceae and their nitidulid beetle vectors in cacao agroforests in Cameroon, under diverse agroecological conditions. The fungi and their vectors were collected 1 from artificially induced stem wounds on cacao and associated shade trees. Collections were also made from abandoned cacao pod husks and other tree wounds within and around plantations. Fungal isolates were identified using DNA sequence-based phylogenies and morphological comparisons, and two representatives of each species were evaluated for pathogenicity on cacao. Five species of Ceratocystidaceae were recovered, including Huntiella chlamydoformis sp. nov., H. pycnanthi sp. nov. and H. moniliformis, as well as Thielaviopsis cerberus and Th. ethacetica. The incidence of these fungi appeared to be influenced by the prevailing agroecological conditions. Nitidulid beetles in the genus Brachypeplus were found to be their most common insect associates on cacao. Both Th. ethacetica and H. pycnanthi produced extensive lesions after inoculation on branches of mature cacao trees, while Th. ethacetica also caused pod rot. Although their impact remains unknown, fungi in the Ceratocystidaceae and their nitidulid beetle vectors are common and likely contribute to the parasitic pressure in Cameroonian cacao agrosystems.
Southern Forests: a Journal of Forest Science, 2015
Zimbabwe embarked on planting Eucalyptus species in the early 1900's. Based on a robust breeding ... more Zimbabwe embarked on planting Eucalyptus species in the early 1900's. Based on a robust breeding programme, it has become a major source of seed for other countries in and outside Africa. Tree health surveys conducted on Eucalyptus in some east and southern Africa countries over the past two decades have revealed several important fungal diseases that were previously not known in the region, but little is known regarding these problems in Zimbabwe. The aim of this study was to identify important eucalypt diseases across Zimbabwe's agro-climatic regions. Morphological characteristics and DNA sequence data were used to identify pathogens collected to species level. Widespread stem canker diseases, caused by species belonging to the Botryosphaeriaceae and Teratosphaeriaceae, and leaf spot diseases caused by fungi in the Capnodiales, were identified. Armillaria root and stem rot was restricted to a single site in the Eastern Highlands. Fungi that could cause canker or blue stain of timber were isolated from recently harvested stumps and included species of Ceratocystis and Ophiostoma. This study is the first to identify Eucalyptus pathogens to species level in Zimbabwe and we report for the first time the presence of the stem canker pathogen T. 1 gauchensis in southern Africa. The results will provide a foundation for the formulation of future disease management strategies in the country.
During routine surveys for possible fungal pathogens in the rapidly expanding plantations of Euca... more During routine surveys for possible fungal pathogens in the rapidly expanding plantations of Eucalyptus and Cunninghamia lanceolata in China, numerous isolates of unknown species in the genus Ceratocystis (Microascales) were obtained from tree wounds. In this study we identified the Ceratocystis isolates from Eucalyptus and Cunninghamia in the GuangDong, GuangXi, FuJian and HaiNan Provinces of South China based on morphology and through comparisons of DNA sequence data for the ITS, partial β-tubulin and TEF-1α gene regions. Morphological and DNA sequence comparisons revealed two previously unknown species residing in the Indo-Pacific Clade. These are described here as Ceratocystis cercfabiensis sp. nov. and Ceratocystis collisensis sp. nov. Isolates of Ceratocystis cercfabiensis showed intragenomic variation in their ITS sequences and four strains were selected for cloning of the ITS gene region. Twelve ITS haplotypes were obtained from 17 clones selected for sequencing, differing i...
Identification of fungi and the International Code of Nomenclature underpinning this process, res... more Identification of fungi and the International Code of Nomenclature underpinning this process, rests strongly on the characterisation of morphological structures. Yet, the value of these characters to define species in many groups has become questionable or even superfluous. This has emerged as DNA-based techniques have increasingly revealed cryptic species and species complexes. This problem is vividly illustrated in the present study where 105 isolates of the Botryosphaeriales were recovered from both healthy and diseased woody tissues of native Acacia spp. in Namibia and South Africa. Thirteen phylogenetically distinct groups were identified based on Internal Transcribed Spacer (ITS) rDNA PCR-RFLP and translation elongation factor 1-α (TEF1-α) sequence data, two loci that are known to be reliable markers to distinguish species in the Botryosphaeriales. Four of these groups could be linked reliably to sequence data for formerly described species, including Botryosphaeria dothidea, ...
The Ceratocystis paradoxa complex accommodates a group of fungal pathogens that have become speci... more The Ceratocystis paradoxa complex accommodates a group of fungal pathogens that have become specialized to infect mostly monocotyledonous plants. Four species currently are recognized in this group, including C. paradoxa, which has a widespread distribution and broad host range. In this study, multigene phylogenetic analyses involving sequences of the ITS, β-tubulin and TEF-1α gene loci, in combination with phenotypic and mating studies, were used to characterize purported C. paradoxa isolates from Cameroon and to compare them with isolates from elsewhere, including protologs and type specimens of known species. We show that the C. paradoxa complex comprises substantially greater species diversity than previously recognized. One new species in this group is described from Cameroon as Ceratocystis cerberus, while C. paradoxa sensu stricto (s. str.) and four other species are redefined. Lectotypes are designated for C. ethacetica and Endoconidium fragrans (synonym of C. ethacetica), w...
ABSTRACT Kirramyces stem canker, caused by species of Raederiella (previously Coniothyrium) is on... more ABSTRACT Kirramyces stem canker, caused by species of Raederiella (previously Coniothyrium) is one of the most important eucalypt stem diseases in the southern hemisphere. During a disease survey conducted in Zimbabwe, symptoms of the disease, characterised by discrete dark brown sunken lesions, kino exudation and pockets in the wood, were observed in four sites on E. grandis, E. camaldulensis, E. grandis-X-camaldulensis hybrid clone and E. propingua. The ITS region, exons 3 through 6 of the β-tubulin gene and the intron of the translation elongation factor 1-α gene were sequenced to identify the causal pathogen. Representative isolates from Zimbabwe were compared with authenticated isolates of T. zuluensis and T. gauchensis. Sequence comparisons identified the pathogens as T. gauchensis. This study is the first to confirm the presence of Kirramyces stem canker on eucalypts in Zimbabwe. Furthermore, it is the first to report T. gauchensis in Southern Africa.
In a survey for Cryphonectria and Chrysoporthe species on Myrtales in South Africa, a fungus rese... more In a survey for Cryphonectria and Chrysoporthe species on Myrtales in South Africa, a fungus resembling the stem canker pathogen Chrysoporthe austroafricana was collected from native Syzygium cordatum near Tzaneen (Limpopo Province), Heteropyxis canescens near Lydenburg (Mpumalanga Province) and exotic Tibouchina granulosa in Durban (KwaZulu-Natal Province). The fungus was associated with dying branches and stems on S. cordatum, H. canescens and T. granulosa. However, morphological differences were detected between the unknown fungus from these three hosts and known species of Chrysoporthe. The aim of this study was to characterise the fungus using DNA sequence comparisons and morphological features. Pathogenicity tests were also conducted to assess its virulence on Eucalyptus (ZG 14 clones), H. natalensis and T. granulosa. Plants of H. canescens were not available for inoculation. Results showed distinct morphological differences between the unknown fungus and Chrysoporthe spp. Phylogenetic analysis showed that isolates reside in a clade separate from Chrysoporthe and other related genera. Celoporthe dispersa gen. et sp. nov. is, therefore, described to accommodate this fungus. Pathogenicity tests showed that C. dispersa is not pathogenic to H. natalensis, but that it is a potential pathogen of Eucalyptus and Tibouchina spp.
Species of Ceratocystis are well-known wound related pathogens of many tree species, including co... more Species of Ceratocystis are well-known wound related pathogens of many tree species, including commercially planted Acacia spp. Recently, several Ceratocystis isolates were collected from wilting A. mangium in plantations in Indonesia. The aim of this study was to identify these Ceratocystis isolates and to investigate their ability to cause disease on two plantation-grown Acacia spp. using greenhouse and field inoculation experiments. For identification, morphological characteristics and comparisons of DNA sequence data for the ITS, β-tubulin and TEF 1-α gene regions, was used. Ceratocystis isolates were identified as C. manginecans, a serious pathogen of mango trees in Oman and Pakistan and a previously undescribed species, described here as C. acaciivora sp. nov. Both fungi produced significant lesions in inoculation experiments on A. mangium and A. crassicarpa, however, C. acaciivora was most pathogenic suggesting that this fungus is the primary cause of the death of trees under natural conditions.
The Botryosphaeriaceae is a species-rich family that includes pathogens of a wide variety of tree... more The Botryosphaeriaceae is a species-rich family that includes pathogens of a wide variety of trees, including Eucalyptus species. Symptoms typical of infection by the Botryosphaeriaceae have recently been observed in Eucalyptus plantations in South China. The aim of this study was to identify the Botryosphaeriaceae associated with these symptoms. Isolates were collected from branch cankers and senescent twigs of different Eucalyptus spp. All isolates resembling Botryosphaeriaceae were separated into groups based on conidial morphology. Initial identifications were made using PCR-RFLP fingerprinting, by digesting the ITS region of the rDNA operon with the restriction enzymes CfoI and KspI. Furthermore, to distinguish isolates in the Neofusicoccum parvum/N. ribis complex, a locus (BotF15) previously shown to define these species, was amplified and restricted with CfoI. Selected isolates were then identified using comparisons of DNA sequence data for the ITS rDNA and translation elongation factor 1-alpha (TEF-1α) gene regions. Based on anamorph morphology and DNA sequence comparisons, five species were identified: Lasiodiplodia pseudotheobromae, L. theobromae, Neofusicoccum parvum, N. ribis sensu lato and one undescribed taxon, for which the name Fusicoccum fabicercianum sp. nov. is provided. Isolates of all species gave rise to lesions on the stems of an E. grandis clone in a glasshouse inoculation trial and on the stems of five Eucalyptus genotypes inoculated in the field, where L. pseudotheobromae and L. theobromae were most pathogenic. The five Eucalyptus genotypes differed in their susceptibility to the Botryosphaeriaceae species suggesting that breeding and selection offers opportunity for disease avoidance in the future.
Recent disease surveys in the Western Cape province of South Africa have revealed a previously un... more Recent disease surveys in the Western Cape province of South Africa have revealed a previously unknown and serious stem canker disease on native Rapanea melanophloeos (Myrsinaceae, Ericales) trees. Cankers commonly result in the death of branches or entire stems. Fruiting structures typical of fungi in the Cryphonectriaceae were observed on the surfaces of cankers. In this study, the fungus was identified and its pathogenicity to R. melanophloeos was tested. Multigene phylogenetic analyses based on DNA sequences of the partial LSU gene, ITS region of the nuclear ribosomal DNA gene and two regions of the b-tubulin (BT) gene, showed that the fungus represents a formerly undescribed genus and species in the Cryphonectriaceae. The fungus was also morphologically distinct from other genera in this family. Inoculation trials showed that the fungus described here as Immersiporthe knoxdaviesiana gen. et sp. nov. is an aggressive pathogen of R. melanophloeos trees.
The genus Ceratocystis includes many important tree pathogens and agents of sap stain. These fung... more The genus Ceratocystis includes many important tree pathogens and agents of sap stain. These fungi have a global distribution and commonly infect wounds on trees. During a survey of woundinfecting pathogens in the genus Ceratocystis on plantation-grown Acacia mangium trees in Indonesia, several isolates resembling Ceratocystis moniliformis sensu lato (s.l.) were obtained. The aim of this study was to identify these isolates and to test their pathogenicity on commercially grown Acacia spp. in the country. Use was made of morphology and comparisons of DNA sequence data for the ITS, β-tubulin, and transcription elongation factor 1-α gene regions to identify the isolates. Three previously undescribed species in the C. moniliformis s.l. species complex were identified and are described here as C. inquinans sp. nov., C. sumatrana sp. nov., and C. microbasis sp. nov. Pathogenicity trials on Acacia mangium and A. crassicarpa in the greenhouse and in the field indicated that all three species have the potential to infect A. mangium and A. crassicarpa, although they are not considered important pathogens.
The emergence of wattle wilt disease on non-native Acacia mearnsii trees in Africa, caused by the... more The emergence of wattle wilt disease on non-native Acacia mearnsii trees in Africa, caused by the indigenous fungus Ceratocystis albifundus, has highlighted a need to better understand the diversity, ecology and distribution of Ceratocystis species in natural African environments. In this study we applied phylogenetic inference to identify and characterize isolates of Ceratocystis collected in a natural savanna ecosystem in South Africa. Three new species were recognized and are described as C. cryptoformis sp. nov. in the C. moniliformis complex, as well as C. thulamelensis sp. nov. and C. zambeziensis sp. nov., both residing in the C. fimbriata complex. Incorporating the new species into global phylogenies of Ceratocystis provided insights into the patterns of evolution and biogeography of this group of fungi. Notably, the African continent was identified as an important centre of diversification of Ceratocystis spp., from which several lineages of these fungi were shown to have radiated. A vivid illustration of the consequences associated with the adoption of wild plant pathogens in cultivated plant systems is found in the Wattle Wilt Disease (WWD) system affecting forest plantations based on Australian Acacia species in Africa. The WWD is caused by the fungus Ceratocystis albifundus M. J. Wingf., De Beer & M. J. Morris (Wingfield et al. 1996). The disease was first discovered in South Africa on A. mearnsii De Wild. (Morris et al. 1993). It is now known to be distributed, at least, across southern and eastern Africa (Roux et al. 2001b, 2005; Heath et al. 2009) and may affect other non-native Acacia species (Morris et al. 1993). Interestingly, C. albifundus has been found colonizing wounds on several native African trees in natural ecosystems, in the absence of disease (Roux et al. 2007; Kamgam et al. 2008). This, in addition to supporting evidence from population genetic studies (Roux et al. 2001a; Barnes et al. 2005), has led to the view that the wattle wilt pathogen is native to Africa. The WWD is the most serious Ceratocystis disease affecting plantation forestry using A. mearnsii in Africa (Roux and Wingfield 2009), and as an emerging "new encounter disease" (Parker and Gilbert 2004), could result in terrible ecological consequences if it were to be introduced into the natural range of wattle trees in Australia (Roux and Wingfield 2013). Ceratocystis species are ascomycete fungi residing in the order Microascales (Schoch et al. 2009; Réblová et al. 2011). Their morphological characteristics typically combine bulbous ascomatal bases with extended necks in their sexual states and deep-seated, tubular phialides in their asexual states (Nag Raj and Kendrick 1975, Upadhyay 1981). DNA sequence data and molecular phylogenetics have profoundly impacted on the taxonomy of this group of fungi, starting with the recognition of C. albifundus as a novel species, distinct from C. fimbriata Ellis & Halst. (Wingfield et al. 1996). This group is now recognized, based on DNA sequence comparison, morphology and ecology, to include very distinct evolutionary lineages and species complexes for which discrete genera will be established (Wingfield et al. 2013). One of these will accommodate species in the C. fimbriata complex that includes C. albifundus and many other, mainly pathogenic species (Baker et al. 2003; Johnson et al. 2005; Van Wyk et al. 2013). However, taxonomic studies of Ceratocystis spp. are still compounded by the lack of distinctive morphological characters between closely related species and the limited resolution of molecular markers available (Van Wyk et al. 2010, 2011a, b, 2012; Kamgan Nkuekam et al. 2012a, b), limiting quick and accurate identification of these pathogens. One of the first studies to consider the identity of Ceratocystis spp. in natural woody ecosystems in South Africa resulted in the discovery of C. savannae Kamgan & Jol. Roux in the savanna dominated Kruger National Park (KNP) and C. tsitsikammensis Kamgan & Jol. Roux in the Garden Route National Park 2.3. Species delineation and primary identification Consensus sequences were assembled from forward and reverse sequencing reads using MEGA version 5 (Tamura et al. 2011). Multiple sequence alignments were constructed using MAFFT (http://www.align.bmr.kyushu-u.ac.jp/mafft/online/server/) version 6 (Katoh et al. 2005) and edited manually in MEGA. The ITS sequence dataset was used for species delineation in the C. fimbriata s.l. and T. thielavioides s.l. groups, while the β-tubulin dataset was used for the C. moniliformis s.l. group. For this purpose, we applied the General Mixed Yule Coalescent (GMYC) model statistical approach developed by Pons et al. (2006). The GMYC model uses branching patterns in an ultrametric phylogenetic tree to C. acaciivora CMW22562 EU588655 EU588635 EU588645 Acacia mangium Indonesia M. Tarigan Tarigan et al. (2010a) C. acaciivora CMW22563 EU588656 EU588636 EU588646 Acacia mangium Indonesia M. Tarigan Tarigan et al. (2010a) C. albifundus CMW5329 AF388947 DQ371649 EF070401 Acacia mearnsii Uganda J. Roux Roux et al.(2001b) C. albifundus CMW23825 CBS119681 EU245010 EU244982 EU244942 Acacia mearnsii South Africa R.N. Heath Heath et al. (2009) C. albifundus CMW37312 KC691452 KC691476 KC691500 Terminalia sericea South Africa M. Mbenoun & J. Roux Present study C. albifundus CMW37313 KC691453 KC691477 KC691501 Combretum zeyheri South Africa M. Mbenoun & J. Roux Present study C. atrox CMW19383 CBS 120517 EF070414 EF070430 EF070402
Species in the Botryosphaeriaceae represent some of the most important fungal pathogens of woody ... more Species in the Botryosphaeriaceae represent some of the most important fungal pathogens of woody plants. Although these fungi have been relatively well studied on economically important crops, hardly anything is known regarding their taxonomy or ecology on native or non-commercial tree species. The aim of this study was to compare the diversity and distribution of the Botryosphaeriaceae on Terminalia catappa, a tropical tree of Asian origin planted as an ornamental in Cameroon, Madagascar and South Africa. A total of 83 trees were sampled, yielding 79 Botryosphaeriaceae isolates. Isolates were initially grouped based on morphology of cultures and conidia. Representatives of the different morphological groups were then further characterised using sequence data for the ITS, tef 1-alpha, rpb2, BOTF15 and beta-tubulin gene regions. Five species of the Botryosphaeriaceae were identified, including Neofusicoccum parvum, N. batangarum sp. nov., Lasiodiplodia pseudotheobromae, L. theobromae and L. mahajangana sp. nov. Lasiodiplodia pseudotheobromae and L. theobromae, were the most commonly isolated species (62%), and were found at all the sites. Neofusicoccum parvum and N. batangarum were found in South Africa and Cameroon, respectively, whereas L. mahajangana was found only in Madagascar. Greenhouse inoculation trials performed on young T. catappa trees showed variation among isolates tested, with L. pseudotheobromae being the most pathogenic. The Botryosphaeriaceae infecting T. catappa appear to be dominated by generalist species that also occur on various other hosts in tropical and subtropical climates.
A survey of diseases of exotic trees in plantations was undertaken in southern and southwestern E... more A survey of diseases of exotic trees in plantations was undertaken in southern and southwestern Ethiopia during 2000 and 2001. Our aim was to ascertain the occurrence and distribution of diseases of major plantation species and to provide a basis for further research. Root, stem and leaf samples were collected from both plantations and trees growing near farms and homesteads in and around Wondo Genet, Munessa Shashemene, Jima, Bedele, Mizan and Menagesha. Armillaria root rot was the most common disease, associated mainly with Pinus patula , but also found on Acacia abyssinica, Cordia alliodoral/ig and Cedrela odorata . Stem cankers associated with ligBotryosphaerial/ig species were common on Eucalyptus globulus, E. salignal/ig and E. citriodora . Stem canker disease associated with a ligConiothyriuml/ig species was commonly observed on E. camaldulensis . Leaf blotch associated with ligMycosphaerellal/ig species was common on E. globulusl/ig in most areas where this species is plante...
Little is known regarding the fungi, especially fungal pathogens, associated with mangroves in Af... more Little is known regarding the fungi, especially fungal pathogens, associated with mangroves in Africa. This includes fungi in the Botryosphaeriaceae that comprise numerous opportunistic, stress-associated pathogens often associated with trees affected by environmental and anthropogenically generated stresses, such as those affecting mangroves. We investigated the occurrence of endophytic Botryosphaeriaceae along the entire distribution of mangroves in South Africa. Asymptomatic branches were collected from ten localities and six mangrove species. Isolates resembling species of Botryosphaeriaceae were identified based on multi-gene sequence data of the internal transcribed spacer regions (ITS), including the 5.8S nrRNA, the beta-tubulin (tub2), partial translation elongation factor 1-alpha (tef1-α), and DNA-directed RNA polymerase II second largest subunit (rpb2) gene regions. Inoculation trials were conducted on healthy branches of Avicennia marina and Bruguiera gymnorrhiza to evalu...
Mangrove trees are continuously under stress due to environmental and/or anthropogenic pressures,... more Mangrove trees are continuously under stress due to environmental and/or anthropogenic pressures, which expose them to attack by pathogens, compromising their survival. Ophiostomatoid fungi cause sap stain and diseases of a wide spectrum of tree species globally. These fungi infect trees through natural, insect, animal and/or human made wounds. During routine surveys of mangrove trees in South Africa, wounds on branches and stems of Avicennia marina were regularly monitored for the presence of ophiostomatoid fungi at ten study sites in the country. The stems of four mangrove species, A. marina, Bruguiera gymnorrhiza, Rhizophora mucronata and Barringtonia racemosa were also wounded and evaluated for the appearance of these fungi. Ophiostomatoid fungi were obtained from the mangrove associate B. racemosa, but not from any of the true mangroves. Analyses of DNA sequence data for the internal transcribed spacer, β-tubulin, calmodulin and translation elongation factor gene regions reveal...
Armillaria root-rot is one of the most serious root diseases of perennial tree crops in tropical ... more Armillaria root-rot is one of the most serious root diseases of perennial tree crops in tropical Africa. The disease was first reported on cacao in Ghana during 1927. It was initially referred to as 'collar crack' due to typical longitudinal cracks that are formed in the bark at the tree collar, as a result of mechanical pressure from fungal fans colonizing the cambium. These fungal fans are typical of species in the genus Armillaria. The pathogen associated with the disease was identified as A. mellea (Valh Ex. Fr.). However, A. mellea is a taxonomic complex that currently includes a number of morphologically indistinguishable species, the true identity of the species causing root-rot on cacao in Africa is thus uncertain. More recent studies have shown that DNA sequence comparisons can effectively differentiate among Armillaria species from Africa with uniform morphologies. In this study we applied a molecular approach to characterize Armillaria isolates associated with roo...
Thielaviopsis ethacetica was recently reinstated as a distinct taxon using DNA phylogenies. It is... more Thielaviopsis ethacetica was recently reinstated as a distinct taxon using DNA phylogenies. It is widespread affecting several crop plants of global economic importance. In this study, microsatellite markers were developed and used in conjunction with sequence data to investigate the genetic diversity and structure of Th. ethacetica in Cameroon. A collection of 71 isolates from cacao, oil palm, and pineapple, supplemented with nine isolates from other countries were analysed. Four genetic groups were identified. Two of these were associated with oil palm in Cameroon and showed high genetic diversity, suggesting that they might represent an indigenous population of the pathogen. In contrast, the remaining two groups, associated with cacao and pineapple, had low genetic diversity and, most likely, represent introduced populations. There was no evidence of gene flow between these groups. Phylogenetic analyses based on sequences of the tef1-a as well as the combined flanking regions of six microsatellite loci were consistent with population genetic analyses and suggested that Th. ethacetica is comprised of two divergent genetic lineages.
Knowledge of the diversity and ecology of plant pathogenic fungi in cacao agroforests and surroun... more Knowledge of the diversity and ecology of plant pathogenic fungi in cacao agroforests and surrounding natural ecosystems can inform the development of sustainable management strategies for new cacao disease outbreaks. In this study, we investigated the occurrence of fungi related to the Ceratocystisdaceae and their nitidulid beetle vectors in cacao agroforests in Cameroon, under diverse agroecological conditions. The fungi and their vectors were collected 1 from artificially induced stem wounds on cacao and associated shade trees. Collections were also made from abandoned cacao pod husks and other tree wounds within and around plantations. Fungal isolates were identified using DNA sequence-based phylogenies and morphological comparisons, and two representatives of each species were evaluated for pathogenicity on cacao. Five species of Ceratocystidaceae were recovered, including Huntiella chlamydoformis sp. nov., H. pycnanthi sp. nov. and H. moniliformis, as well as Thielaviopsis cerberus and Th. ethacetica. The incidence of these fungi appeared to be influenced by the prevailing agroecological conditions. Nitidulid beetles in the genus Brachypeplus were found to be their most common insect associates on cacao. Both Th. ethacetica and H. pycnanthi produced extensive lesions after inoculation on branches of mature cacao trees, while Th. ethacetica also caused pod rot. Although their impact remains unknown, fungi in the Ceratocystidaceae and their nitidulid beetle vectors are common and likely contribute to the parasitic pressure in Cameroonian cacao agrosystems.
Southern Forests: a Journal of Forest Science, 2015
Zimbabwe embarked on planting Eucalyptus species in the early 1900's. Based on a robust breeding ... more Zimbabwe embarked on planting Eucalyptus species in the early 1900's. Based on a robust breeding programme, it has become a major source of seed for other countries in and outside Africa. Tree health surveys conducted on Eucalyptus in some east and southern Africa countries over the past two decades have revealed several important fungal diseases that were previously not known in the region, but little is known regarding these problems in Zimbabwe. The aim of this study was to identify important eucalypt diseases across Zimbabwe's agro-climatic regions. Morphological characteristics and DNA sequence data were used to identify pathogens collected to species level. Widespread stem canker diseases, caused by species belonging to the Botryosphaeriaceae and Teratosphaeriaceae, and leaf spot diseases caused by fungi in the Capnodiales, were identified. Armillaria root and stem rot was restricted to a single site in the Eastern Highlands. Fungi that could cause canker or blue stain of timber were isolated from recently harvested stumps and included species of Ceratocystis and Ophiostoma. This study is the first to identify Eucalyptus pathogens to species level in Zimbabwe and we report for the first time the presence of the stem canker pathogen T. 1 gauchensis in southern Africa. The results will provide a foundation for the formulation of future disease management strategies in the country.
During routine surveys for possible fungal pathogens in the rapidly expanding plantations of Euca... more During routine surveys for possible fungal pathogens in the rapidly expanding plantations of Eucalyptus and Cunninghamia lanceolata in China, numerous isolates of unknown species in the genus Ceratocystis (Microascales) were obtained from tree wounds. In this study we identified the Ceratocystis isolates from Eucalyptus and Cunninghamia in the GuangDong, GuangXi, FuJian and HaiNan Provinces of South China based on morphology and through comparisons of DNA sequence data for the ITS, partial β-tubulin and TEF-1α gene regions. Morphological and DNA sequence comparisons revealed two previously unknown species residing in the Indo-Pacific Clade. These are described here as Ceratocystis cercfabiensis sp. nov. and Ceratocystis collisensis sp. nov. Isolates of Ceratocystis cercfabiensis showed intragenomic variation in their ITS sequences and four strains were selected for cloning of the ITS gene region. Twelve ITS haplotypes were obtained from 17 clones selected for sequencing, differing i...
Identification of fungi and the International Code of Nomenclature underpinning this process, res... more Identification of fungi and the International Code of Nomenclature underpinning this process, rests strongly on the characterisation of morphological structures. Yet, the value of these characters to define species in many groups has become questionable or even superfluous. This has emerged as DNA-based techniques have increasingly revealed cryptic species and species complexes. This problem is vividly illustrated in the present study where 105 isolates of the Botryosphaeriales were recovered from both healthy and diseased woody tissues of native Acacia spp. in Namibia and South Africa. Thirteen phylogenetically distinct groups were identified based on Internal Transcribed Spacer (ITS) rDNA PCR-RFLP and translation elongation factor 1-α (TEF1-α) sequence data, two loci that are known to be reliable markers to distinguish species in the Botryosphaeriales. Four of these groups could be linked reliably to sequence data for formerly described species, including Botryosphaeria dothidea, ...
The Ceratocystis paradoxa complex accommodates a group of fungal pathogens that have become speci... more The Ceratocystis paradoxa complex accommodates a group of fungal pathogens that have become specialized to infect mostly monocotyledonous plants. Four species currently are recognized in this group, including C. paradoxa, which has a widespread distribution and broad host range. In this study, multigene phylogenetic analyses involving sequences of the ITS, β-tubulin and TEF-1α gene loci, in combination with phenotypic and mating studies, were used to characterize purported C. paradoxa isolates from Cameroon and to compare them with isolates from elsewhere, including protologs and type specimens of known species. We show that the C. paradoxa complex comprises substantially greater species diversity than previously recognized. One new species in this group is described from Cameroon as Ceratocystis cerberus, while C. paradoxa sensu stricto (s. str.) and four other species are redefined. Lectotypes are designated for C. ethacetica and Endoconidium fragrans (synonym of C. ethacetica), w...
ABSTRACT Kirramyces stem canker, caused by species of Raederiella (previously Coniothyrium) is on... more ABSTRACT Kirramyces stem canker, caused by species of Raederiella (previously Coniothyrium) is one of the most important eucalypt stem diseases in the southern hemisphere. During a disease survey conducted in Zimbabwe, symptoms of the disease, characterised by discrete dark brown sunken lesions, kino exudation and pockets in the wood, were observed in four sites on E. grandis, E. camaldulensis, E. grandis-X-camaldulensis hybrid clone and E. propingua. The ITS region, exons 3 through 6 of the β-tubulin gene and the intron of the translation elongation factor 1-α gene were sequenced to identify the causal pathogen. Representative isolates from Zimbabwe were compared with authenticated isolates of T. zuluensis and T. gauchensis. Sequence comparisons identified the pathogens as T. gauchensis. This study is the first to confirm the presence of Kirramyces stem canker on eucalypts in Zimbabwe. Furthermore, it is the first to report T. gauchensis in Southern Africa.
In a survey for Cryphonectria and Chrysoporthe species on Myrtales in South Africa, a fungus rese... more In a survey for Cryphonectria and Chrysoporthe species on Myrtales in South Africa, a fungus resembling the stem canker pathogen Chrysoporthe austroafricana was collected from native Syzygium cordatum near Tzaneen (Limpopo Province), Heteropyxis canescens near Lydenburg (Mpumalanga Province) and exotic Tibouchina granulosa in Durban (KwaZulu-Natal Province). The fungus was associated with dying branches and stems on S. cordatum, H. canescens and T. granulosa. However, morphological differences were detected between the unknown fungus from these three hosts and known species of Chrysoporthe. The aim of this study was to characterise the fungus using DNA sequence comparisons and morphological features. Pathogenicity tests were also conducted to assess its virulence on Eucalyptus (ZG 14 clones), H. natalensis and T. granulosa. Plants of H. canescens were not available for inoculation. Results showed distinct morphological differences between the unknown fungus and Chrysoporthe spp. Phylogenetic analysis showed that isolates reside in a clade separate from Chrysoporthe and other related genera. Celoporthe dispersa gen. et sp. nov. is, therefore, described to accommodate this fungus. Pathogenicity tests showed that C. dispersa is not pathogenic to H. natalensis, but that it is a potential pathogen of Eucalyptus and Tibouchina spp.
Species of Ceratocystis are well-known wound related pathogens of many tree species, including co... more Species of Ceratocystis are well-known wound related pathogens of many tree species, including commercially planted Acacia spp. Recently, several Ceratocystis isolates were collected from wilting A. mangium in plantations in Indonesia. The aim of this study was to identify these Ceratocystis isolates and to investigate their ability to cause disease on two plantation-grown Acacia spp. using greenhouse and field inoculation experiments. For identification, morphological characteristics and comparisons of DNA sequence data for the ITS, β-tubulin and TEF 1-α gene regions, was used. Ceratocystis isolates were identified as C. manginecans, a serious pathogen of mango trees in Oman and Pakistan and a previously undescribed species, described here as C. acaciivora sp. nov. Both fungi produced significant lesions in inoculation experiments on A. mangium and A. crassicarpa, however, C. acaciivora was most pathogenic suggesting that this fungus is the primary cause of the death of trees under natural conditions.
The Botryosphaeriaceae is a species-rich family that includes pathogens of a wide variety of tree... more The Botryosphaeriaceae is a species-rich family that includes pathogens of a wide variety of trees, including Eucalyptus species. Symptoms typical of infection by the Botryosphaeriaceae have recently been observed in Eucalyptus plantations in South China. The aim of this study was to identify the Botryosphaeriaceae associated with these symptoms. Isolates were collected from branch cankers and senescent twigs of different Eucalyptus spp. All isolates resembling Botryosphaeriaceae were separated into groups based on conidial morphology. Initial identifications were made using PCR-RFLP fingerprinting, by digesting the ITS region of the rDNA operon with the restriction enzymes CfoI and KspI. Furthermore, to distinguish isolates in the Neofusicoccum parvum/N. ribis complex, a locus (BotF15) previously shown to define these species, was amplified and restricted with CfoI. Selected isolates were then identified using comparisons of DNA sequence data for the ITS rDNA and translation elongation factor 1-alpha (TEF-1α) gene regions. Based on anamorph morphology and DNA sequence comparisons, five species were identified: Lasiodiplodia pseudotheobromae, L. theobromae, Neofusicoccum parvum, N. ribis sensu lato and one undescribed taxon, for which the name Fusicoccum fabicercianum sp. nov. is provided. Isolates of all species gave rise to lesions on the stems of an E. grandis clone in a glasshouse inoculation trial and on the stems of five Eucalyptus genotypes inoculated in the field, where L. pseudotheobromae and L. theobromae were most pathogenic. The five Eucalyptus genotypes differed in their susceptibility to the Botryosphaeriaceae species suggesting that breeding and selection offers opportunity for disease avoidance in the future.
Recent disease surveys in the Western Cape province of South Africa have revealed a previously un... more Recent disease surveys in the Western Cape province of South Africa have revealed a previously unknown and serious stem canker disease on native Rapanea melanophloeos (Myrsinaceae, Ericales) trees. Cankers commonly result in the death of branches or entire stems. Fruiting structures typical of fungi in the Cryphonectriaceae were observed on the surfaces of cankers. In this study, the fungus was identified and its pathogenicity to R. melanophloeos was tested. Multigene phylogenetic analyses based on DNA sequences of the partial LSU gene, ITS region of the nuclear ribosomal DNA gene and two regions of the b-tubulin (BT) gene, showed that the fungus represents a formerly undescribed genus and species in the Cryphonectriaceae. The fungus was also morphologically distinct from other genera in this family. Inoculation trials showed that the fungus described here as Immersiporthe knoxdaviesiana gen. et sp. nov. is an aggressive pathogen of R. melanophloeos trees.
The genus Ceratocystis includes many important tree pathogens and agents of sap stain. These fung... more The genus Ceratocystis includes many important tree pathogens and agents of sap stain. These fungi have a global distribution and commonly infect wounds on trees. During a survey of woundinfecting pathogens in the genus Ceratocystis on plantation-grown Acacia mangium trees in Indonesia, several isolates resembling Ceratocystis moniliformis sensu lato (s.l.) were obtained. The aim of this study was to identify these isolates and to test their pathogenicity on commercially grown Acacia spp. in the country. Use was made of morphology and comparisons of DNA sequence data for the ITS, β-tubulin, and transcription elongation factor 1-α gene regions to identify the isolates. Three previously undescribed species in the C. moniliformis s.l. species complex were identified and are described here as C. inquinans sp. nov., C. sumatrana sp. nov., and C. microbasis sp. nov. Pathogenicity trials on Acacia mangium and A. crassicarpa in the greenhouse and in the field indicated that all three species have the potential to infect A. mangium and A. crassicarpa, although they are not considered important pathogens.
The emergence of wattle wilt disease on non-native Acacia mearnsii trees in Africa, caused by the... more The emergence of wattle wilt disease on non-native Acacia mearnsii trees in Africa, caused by the indigenous fungus Ceratocystis albifundus, has highlighted a need to better understand the diversity, ecology and distribution of Ceratocystis species in natural African environments. In this study we applied phylogenetic inference to identify and characterize isolates of Ceratocystis collected in a natural savanna ecosystem in South Africa. Three new species were recognized and are described as C. cryptoformis sp. nov. in the C. moniliformis complex, as well as C. thulamelensis sp. nov. and C. zambeziensis sp. nov., both residing in the C. fimbriata complex. Incorporating the new species into global phylogenies of Ceratocystis provided insights into the patterns of evolution and biogeography of this group of fungi. Notably, the African continent was identified as an important centre of diversification of Ceratocystis spp., from which several lineages of these fungi were shown to have radiated. A vivid illustration of the consequences associated with the adoption of wild plant pathogens in cultivated plant systems is found in the Wattle Wilt Disease (WWD) system affecting forest plantations based on Australian Acacia species in Africa. The WWD is caused by the fungus Ceratocystis albifundus M. J. Wingf., De Beer & M. J. Morris (Wingfield et al. 1996). The disease was first discovered in South Africa on A. mearnsii De Wild. (Morris et al. 1993). It is now known to be distributed, at least, across southern and eastern Africa (Roux et al. 2001b, 2005; Heath et al. 2009) and may affect other non-native Acacia species (Morris et al. 1993). Interestingly, C. albifundus has been found colonizing wounds on several native African trees in natural ecosystems, in the absence of disease (Roux et al. 2007; Kamgam et al. 2008). This, in addition to supporting evidence from population genetic studies (Roux et al. 2001a; Barnes et al. 2005), has led to the view that the wattle wilt pathogen is native to Africa. The WWD is the most serious Ceratocystis disease affecting plantation forestry using A. mearnsii in Africa (Roux and Wingfield 2009), and as an emerging "new encounter disease" (Parker and Gilbert 2004), could result in terrible ecological consequences if it were to be introduced into the natural range of wattle trees in Australia (Roux and Wingfield 2013). Ceratocystis species are ascomycete fungi residing in the order Microascales (Schoch et al. 2009; Réblová et al. 2011). Their morphological characteristics typically combine bulbous ascomatal bases with extended necks in their sexual states and deep-seated, tubular phialides in their asexual states (Nag Raj and Kendrick 1975, Upadhyay 1981). DNA sequence data and molecular phylogenetics have profoundly impacted on the taxonomy of this group of fungi, starting with the recognition of C. albifundus as a novel species, distinct from C. fimbriata Ellis & Halst. (Wingfield et al. 1996). This group is now recognized, based on DNA sequence comparison, morphology and ecology, to include very distinct evolutionary lineages and species complexes for which discrete genera will be established (Wingfield et al. 2013). One of these will accommodate species in the C. fimbriata complex that includes C. albifundus and many other, mainly pathogenic species (Baker et al. 2003; Johnson et al. 2005; Van Wyk et al. 2013). However, taxonomic studies of Ceratocystis spp. are still compounded by the lack of distinctive morphological characters between closely related species and the limited resolution of molecular markers available (Van Wyk et al. 2010, 2011a, b, 2012; Kamgan Nkuekam et al. 2012a, b), limiting quick and accurate identification of these pathogens. One of the first studies to consider the identity of Ceratocystis spp. in natural woody ecosystems in South Africa resulted in the discovery of C. savannae Kamgan & Jol. Roux in the savanna dominated Kruger National Park (KNP) and C. tsitsikammensis Kamgan & Jol. Roux in the Garden Route National Park 2.3. Species delineation and primary identification Consensus sequences were assembled from forward and reverse sequencing reads using MEGA version 5 (Tamura et al. 2011). Multiple sequence alignments were constructed using MAFFT (http://www.align.bmr.kyushu-u.ac.jp/mafft/online/server/) version 6 (Katoh et al. 2005) and edited manually in MEGA. The ITS sequence dataset was used for species delineation in the C. fimbriata s.l. and T. thielavioides s.l. groups, while the β-tubulin dataset was used for the C. moniliformis s.l. group. For this purpose, we applied the General Mixed Yule Coalescent (GMYC) model statistical approach developed by Pons et al. (2006). The GMYC model uses branching patterns in an ultrametric phylogenetic tree to C. acaciivora CMW22562 EU588655 EU588635 EU588645 Acacia mangium Indonesia M. Tarigan Tarigan et al. (2010a) C. acaciivora CMW22563 EU588656 EU588636 EU588646 Acacia mangium Indonesia M. Tarigan Tarigan et al. (2010a) C. albifundus CMW5329 AF388947 DQ371649 EF070401 Acacia mearnsii Uganda J. Roux Roux et al.(2001b) C. albifundus CMW23825 CBS119681 EU245010 EU244982 EU244942 Acacia mearnsii South Africa R.N. Heath Heath et al. (2009) C. albifundus CMW37312 KC691452 KC691476 KC691500 Terminalia sericea South Africa M. Mbenoun & J. Roux Present study C. albifundus CMW37313 KC691453 KC691477 KC691501 Combretum zeyheri South Africa M. Mbenoun & J. Roux Present study C. atrox CMW19383 CBS 120517 EF070414 EF070430 EF070402
Species in the Botryosphaeriaceae represent some of the most important fungal pathogens of woody ... more Species in the Botryosphaeriaceae represent some of the most important fungal pathogens of woody plants. Although these fungi have been relatively well studied on economically important crops, hardly anything is known regarding their taxonomy or ecology on native or non-commercial tree species. The aim of this study was to compare the diversity and distribution of the Botryosphaeriaceae on Terminalia catappa, a tropical tree of Asian origin planted as an ornamental in Cameroon, Madagascar and South Africa. A total of 83 trees were sampled, yielding 79 Botryosphaeriaceae isolates. Isolates were initially grouped based on morphology of cultures and conidia. Representatives of the different morphological groups were then further characterised using sequence data for the ITS, tef 1-alpha, rpb2, BOTF15 and beta-tubulin gene regions. Five species of the Botryosphaeriaceae were identified, including Neofusicoccum parvum, N. batangarum sp. nov., Lasiodiplodia pseudotheobromae, L. theobromae and L. mahajangana sp. nov. Lasiodiplodia pseudotheobromae and L. theobromae, were the most commonly isolated species (62%), and were found at all the sites. Neofusicoccum parvum and N. batangarum were found in South Africa and Cameroon, respectively, whereas L. mahajangana was found only in Madagascar. Greenhouse inoculation trials performed on young T. catappa trees showed variation among isolates tested, with L. pseudotheobromae being the most pathogenic. The Botryosphaeriaceae infecting T. catappa appear to be dominated by generalist species that also occur on various other hosts in tropical and subtropical climates.
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