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Stem Canker (stem + canker)

Distribution by Scientific Domains

Life Sciences	100%

Distribution within Life Sciences

Plant Science	76%
Plant Pathology	23%

Kinds of Stem Canker

phoma stem canker

Selected Abstracts

Anisogramma virgultorum on saplings of Betula pendula and Betula pubescens in a district of northern Sweden

FOREST PATHOLOGY, Issue 4-5 2002
J. WITZELL
Summary During the autumn of 1999, the occurrence of the ascomycete Anisogramma virgultorum on saplings of Betula pubescens and Betula pendula was studied in two stands of B. pubescens, two stands of B. pendula and two mixed (B. pubescens and Pinus sylvestris) stands (age approximately 10 years, mean height 2,4 m, d.b.h. 10,20 mm) in a district in the vicinity of Umeå, northern Sweden. Stem and branch cankers associated with A. virgultorum were found on 54.8% of the investigated saplings, without significant difference between B. pendula and B. pubescens. Cankers were observed on 16.0% of stems and on branches of 54.2% of the saplings. Stem cankers appeared on the current year's shoot, as well as at the base of the trees. The mean diameter of the damaged saplings was significantly greater than the mean diameter of undamaged saplings. All samples of cankers with stromata examined in the laboratory showed perithecia with asci. Résumé Anisogramma virgultorum sur jeunes plants de Betula pendula et Betula pubescens dans un district du nord de la Suède Pendant l'été 1999, le développement de l'ascomycète Anisogramma virgultorum a étéétudié sur de jeunes plants de Betula pendula et Betula pubescens dans deux peuplements de B. pubescens, deux peuplements de B. pendula et deux peuplements mélangés (B. pubescens et Pinus sylvestris) (âge: environ 10 ans, hauteur moyenne: 2 à 4 m, dbh: 10 à 20 mm), dans un district près d'Umeå au nord de la Suède. Des chancres de tige et de branches associés àA. virgultorum ont été trouvés sur 54,8% des plants, sans différences significative entre B. pendula et B. pubescens. Les chancres de tige étaient présents sur 16% des plants, et les chancres de branches sur 54,2%. Les chancres de tige étaient situés sur les pousses de l'année en cours aussi bien qu'à la base des arbres. La diamètre moyen des plants attaqués était significativement plus grand que celui des arbres sains. Tous les chancres avec stromas examinés au laboratoire présentaient des périthèces avec des asques. Zusammenfassung Anisogramma virgultorum an Sämlingen von Betula pendula und Betula pubescens in einem Distrikt in Nordschweden Im Herbst 1999 wurde das Vorkommen des Ascomyceten Anisogramma virgultorum an Betula pubescens und Betula pendula in jeweils zwei Reinbeständen dieser Baumarten sowie in zwei Mischbeständen (B. pubescens und Pinus sylvestris) in einem Distrikt in der Nähe von Umeå, Nordschweden, untersucht (Alter ca. 10 Jahre, mittlere Baumhöhe 2,4 m, DBH 10,20 mm). Bei 54,8 % der untersuchten Bäumchen wurden an Stamm und Zweigen Krebse gefunden, die für A.virgultorum typisch sind. Zwischen B. pendula und B. pubescens gab es keine signifikanten Unterschiede. Bei 16 % der Pflanzen wurden Krebse an den Stämmen, bei 54,2 % an den Zweigen beobachtet. Die Stammkrebse traten sowohl am diesjährigen Gipfeltrieb auf als auch an der Stammbasis. Der mittlere Durchmesser geschädigter Pflanzen war signifikant grösser als derjenige von ungeschädigten Pflanzen. Alle Proben von Krebsen mit Stromata, die im Labor untersucht wurden, enthielten Perithecien mit Asci. [source]

Methods for inoculum production and inoculation of Cistella japonica, the causal agent of resinous stem canker in Chamaecyparis obtusa

FOREST PATHOLOGY, Issue 1 2008
T. Yamanobe
Summary The ascomycete Cistella japonica was cultured on potato dextrose agar medium (PDA) for inoculation into Chamaecyparis obtusa, enabling the development of an inoculation method suitable for use in a breeding programme aimed at selecting for families of Ch. obtusa resistant to resinous stem canker. Using PDA to generate the inoculum resolved the problems encountered with the previously used mixed medium of rice bran and wheat bran, including unfavourable characteristics, uncertain growth of Ci. japonica mycelia, and a complex culturing operation. The inoculation test induced resin exudation similar to that observed in natural infections, and reproduced clonal differences with regard to damage severity. [source]

Seasonal resin canal formation and necroses expansion in resinous stem canker-affected Chamaecyparis obtusa

FOREST PATHOLOGY, Issue 4-5 2002
T. YAMADA
Summary The season of disease development on the basis of two major internal symptoms, resin canal formation and necrotic lesion expansion in phloem, were anatomically determined in Chamaecyparis obtusa (Hinoki cypress) affected by resinous stem canker. Newly formed resin canals were mostly observed at first from July to August in samples of the canker-affected C. obtusa phloem. This result indicates the occurrence of stimuli causing resin canal formation and the beginning of the formation from May to July of the same year. This and the beginning of resin exudation observed in May or June indicated that resin, exuded at least before August, originated from resin canals formed in the previous year(s). The expansion of phloem necrotic lesions began in June and continued until October, and was conspicuous in the August samples. Stimuli causing necrotic lesion development were also suggested to occur from May to August of the same year. It is hypothesized that excess resin production induces lesion development and that expansion of necrotic lesion induces both resin exudation from previously formed resin canals and new resin canal formation. The causal agent of the disease could be activated in the late spring or summer season. Résumé Formation saisonnière de canaux résinifères et extension des nécroses chez Chamaecyparis obtusa atteint par le chancre résineux du tronc Chez Chamaecyparis obtusa affecté par le chancre résineux du tronc, la saison de développement de la maladie a été déterminée anatomiquement en se basant sur deux symptômes internes majeurs: la formation de canaux résinifères et l'extension des nécroses au niveau du phloème. Des canaux résinifères récemment formés ont surtout été observés à partir de juillet et en août dans le phloème de C. obtusa atteint par la maladie. Ce résultat montre l'existence de stimuli de la formation de canaux résinifères, ceux-ci commençant à se former en mai jusqu'en juillet. Jointe au fait que l'exsudation de résine a lieu en mai ou juin, cette observation montre que la résine (au moins celle exsudée avant août) provient des canaux formés au cours de la ou des années précédentes. L'extension de la nécrose du phloème débutait en juin, était forte en août et se poursuivait jusqu'en octobre. Il est suggéré que les stimuli du développement de la nécrose ont lieu entre mai et août de la même année. Il est supposé, d'une part que la production excessive de résine induit le développement des lésions, et d'autre part que l'extension des nécroses induit l'exsudation de résine à partir des canaux antérieurement formés ainsi que la formation de nouveaux canaux. L'agent causal de la maladie pourrait être activéà la fin du printemps ou en été. Zusammenfassung Saisonale Harzkanalbildung und Entwicklung der Nekrosen bei Chamaecyparis obtusa mit ,HarzigemStammkrebs' Bei Chamaecyparis obtusa mit Befall durch den ,Harzigen Stammkrebs' wurde die Phänologie der Krankheitsentwicklung anhand der Harzkanalbildung und der Ausbreitung der Nekrosen im Phloem anatomisch erfasst. Im krebsbefallenen Phloem wurden neu gebildete Harzkanäle zuerst im Juli und August beobachtet. Dies weist darauf hin, dass die Stimulation für die Harzkanalbildung und die Entwicklung der Harzkanäle in der Zeit von Mai bis Juli des laufenden Jahres erfolgt. Diese Beobachtung und der Beginn des Harzflusses, welcher im Mai und Juni auftritt, deuten darauf hin, dass der Harzfluss vor dem August aus Harzkanälen stammt, die bereits im Vorjahr oder noch früher angelegt worden waren. Die Expansion der Phloem-Nekrosen begann im Juni und hielt bis Oktober an, im August war sie besonders stark ausgeprägt. Der Reiz für die Ausdehnung der Nekrosen dürfte somit von Mai bis August des laufenden Jahres vorhanden sein. Es wird die Hypothese aufgestellt, dass die stark gesteigerte Harzproduktion die Nekrosenentwicklung fördert und dass die Expansion der Nekrosen sowohl den Harzfluss aus den früher gebildeten Harzkanälen anregt als auch die Bildung neuer Harzkanäle induziert. Der ursächliche Faktor für diese Krankheit dürfte im späten Frühjahr oder im Sommer aktiv sein. [source]

The stem canker (blackleg) fungus, Leptosphaeria maculans, enters the genomic era

MOLECULAR PLANT PATHOLOGY, Issue 3 2005
T. ROUXEL
SUMMARY Leptosphaeria maculans is the most ubiquitous pathogen of Brassica crops, and mainly oilseed brassicas (oilseed rape, canola), causing the devastating ,stem canker' or ,blackleg'. This review summarizes our current knowledge on the pathogen, from taxonomic issues to specific life traits. It mainly illustrates the importance of formal genetics approaches on the pathogen side to dissect the interaction with the host plants. In addition, this review presents the main current research topics on L. maculans and focuses on the L. maculans genome initiative recently begun, including its main research issues. Taxonomy:,Leptosphaeria maculans (Desm.) Ces. & de Not. (anamorph Phoma lingam Tode ex Fr.). Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes (Loculoascomycetes), Order Pleosporales, Genus Leptosphaeria, Species maculans. Host range:, cultivated Brassicas such as Brassica napus (oilseed rape, canola), B. rapa, B. juncea, B. oleracea, etc., along with numerous wild crucifers species. Arabidopsis thaliana was recently reported to be a potential host for L. maculans. Primary disease symptoms are greyish-green collapse of cotyledon or leaf tissue, without a visible margin, bearing tiny black spots (pycnidia). The fungus then develops an endophytic symptomless growth for many months. Secondary symptoms, at the end of the growing season, are dry necroses of the crown tissues with occasional blackening (stem canker or blackleg) causing lodging of the plants. Pseudothecia differentiate on leftover residues. Seedling damping-off and premature ripening are also reported under certain environmental conditions. Useful websites:,Leptosphaeria maculans sequencing project at Genoscope: http://www.genoscope.cns.fr/externe/English/Projets/Projet_DM/organisme_DM.html; the SECURE site: http://www.secure.rothamsted.ac.uk/ the ,Blackleg' group at the University of Melbourne: http://www.botany.unimelb.edu.au/blackleg/overview.htm [source]

Dual control of avirulence in Leptosphaeria maculans towards a Brassica napus cultivar with ,sylvestris -derived' resistance suggests involvement of two resistance genes

PLANT PATHOLOGY, Issue 2 2009
A. P. Van de Wouw
Blackleg disease (phoma stem canker) of Brassica napus (canola, oilseed rape) is caused by the fungus Leptosphaeria maculans. In some regions of Australia, resistance in oilseed rape cultivars derived from B. rapa subs. sylvestris (e.g. cv. Surpass 400) became ineffective within three years of commercial release. The genetic control of avirulence in L. maculans towards cv. Surpass 400 is described. When Australian field isolates were screened on this cultivar, three phenotypic classes were observed; virulent, intermediate and avirulent. Analysis of crosses between fungal isolates varying in their ability to infect cv. Surpass 400 demonstrated the presence of two unlinked avirulence genes, AvrLm1 and AvrLmS. Complementation of isolates (genotype avrLm1) with a functional copy of AvrLm1, and genotyping of field isolates using a molecular marker for AvrLm1 showed that virulence towards Rlm1 is necessary, but not sufficient, for expression of a virulent phenotype on cv. Surpass 400. Taken together, these data strongly suggest that cv. Surpass 400, with ,sylvestris -derived' resistance, contains at least two resistance genes, one of which is Rlm1. [source]

Quantitative resistance to symptomless growth of Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape)

PLANT PATHOLOGY, Issue 2 2009
Y. J. Huang
Quantitative resistance to Leptosphaeria maculans in Brassica napus was investigated in field and controlled environments using cultivars Darmor (with quantitative resistance) and Eurol (without quantitative resistance). In field experiments, numbers of phoma leaf spot lesions in autumn/winter and severity of stem canker the following summer were assessed in three growing seasons. There were no differences between Darmor and Eurol in number of leaf lesions in autumn/winter. However, stem cankers were less severe on Darmor than Eurol at harvest the following summer. In controlled-environment experiments, development of leaf lesions at different temperatures (5,25°C) and wetness durations (12,72 h) was investigated using ascospore inoculum; symptomless growth of L. maculans along leaf petioles towards the stem was quantified using quantitative PCR and visualized using GFP-expressing L. maculans; growth of L. maculans within stem tissues was investigated using GFP-expressing L. maculans. There were more leaf lesions on Darmor than Eurol, although there was no difference between Darmor and Eurol in L. maculans incubation period. There were no differences between Darmor and Eurol in either distance grown by L. maculans along leaf petioles towards the stem or quantity of L. maculans DNA in leaf petioles, but L. maculans colonized stem tissues less extensively on Darmor than Eurol. It was concluded that quantitative resistance to L. maculans operates during colonization of B. napus stems by the pathogen. [source]

Resistance to Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape) induced by L. biglobosa and chemical defence activators in field and controlled environments

PLANT PATHOLOGY, Issue 3 2006
S. Y. Liu
Effects of pretreatment of Brassica napus leaves with ascospores of Leptosphaeria biglobosa or chemical defence activators [acibenzolar- S -methyl (ASM) or menadione sodium bisulphite (MSB)] on infection by ascospores of Leptosphaeria maculans (phoma stem canker) and development of disease were studied in controlled-environment (phoma leaf spot) and field (phoma leaf spot and stem canker) experiments. In controlled-environment experiments, pretreatment of oilseed rape leaves (cv. Madrigal) with L. biglobosa, ASM or MSB delayed the appearance of L. maculans phoma leaf spot lesions. These pretreatments also decreased the phoma leaf spot lesion area in both pretreated leaves (local effect) and untreated leaves (systemic effect). In winter oilseed rape field experiments in the 2002/03 and 2003/04 growing seasons, pretreatment with L. biglobosa or ASM in October/November decreased not only the number of phoma leaf spot lesions per leaf caused by L. maculans in autumn/winter, but also the severity of phoma stem canker in the subsequent spring/summer. Effects were greater in 2002/03 (when natural L. maculans ascospore release began in September 2002) than in 2003/04 (when ascospore release began in December following a period of dry weather in August/September 2003). These results suggest that pretreatment with biological or chemical defence activators can induce local and systemic resistance to L. maculans, with both short-term effects on the development of phoma leaf spotting and long-term effects on the development of stem canker 8 months later. [source]

Molecular analysis of the major Phytophthora species on cocoa

PLANT PATHOLOGY, Issue 2 2004
A. A. Appiah
The internally transcribed spacer (ITS) regions of the ribosomal RNA (rRNA) gene cluster of 161 isolates of Phytophthora species involved in pod rot, stem canker and leaf blight of cocoa were analysed to determine inter- and intraspecific variation in this disease complex. The species P. palmivora, P. megakarya, P. capsici, P. citrophthora and P. nicotianae could all be clearly distinguished by PCR amplification of the ITS region followed by restriction analysis with HaeIII, HinfI, PvuII and AluI. This method provided a relatively rapid identification procedure for these species, and was able to distinguish isolates that had previously been misidentified by morphological methods. Sequence analysis showed that the four main cocoa-associated species formed two distinct groups, one comprising P. capsici and P. citrophthora, and the other P. palmivora and P. megakarya. Detailed sequence analysis and comparison with published literature suggested that P. capsici isolates from cocoa may be closely related to P. tropicalis, a species recently described from Cyclamen and Dianthus. [source]

Menadione sodium bisulphite: a novel plant defence activator which enhances local and systemic resistance to infection by Leptosphaeria maculans in oilseed rape

PLANT PATHOLOGY, Issue 4 2003
A. A. Borges
Pretreatment of the first true leaves of oilseed rape plants (Brassica napus cv. Bristol) with menadione sodium bisulphite (MSB) locally and systemically induced resistance, as shown by reduced lesion size and number, to infection by the fungal pathogen Leptosphaeria maculans, the causal agent of stem canker. Using a known systemic activator of salicylic acid-dependent PR-1 induction, acibenzolar- S -methyl (BTH; S -methylbenzo[1,2,3]thiadiazole-7-carbothiate) as a comparison, real-time PCR expression analysis of genes encoding a pathogenesis-related protein 1 (PR-1) and an ascorbate peroxidase (APX) demonstrated a systemic enhancement of APX expression in MSB-pretreated plants, with no effect on PR-1 expression, suggesting augmented reactive oxygen species production in MSB-pretreated plants. The results demonstrate MSB to be an effective resistance activator in oilseed rape, and potentially useful for the control of stem canker. [source]

Epidemiology and management of Leptosphaeria maculans (phoma stem canker) on oilseed rape in Australia, Canada and Europe

PLANT PATHOLOGY, Issue 1 2001
J. S. West
Phoma stem canker (blackleg), caused by Leptosphaeria maculans, is an important disease on oilseed rape (canola, rapeseed, Brassica napus, Brassica juncea, Brassica rapa) causing seedling death, lodging or early senescence in Australia, Canada and Europe, but not in China. The two forms of L. maculans (A group and B group) that occur on oilseed rape are now considered to be separate species. The epidemiology and severity of phoma stem canker differs between continents due to differences in the pathogen population structure, oilseed rape species and cultivars grown, climate and agricultural practices. Epidemics are most severe in Australia, where only the A group occurs, and can be damaging in Canada and western Europe, where both A and B groups occur, although their proportions vary within regions and throughout the year. Epidemics are slight in China, where the A group has not been found. Dry climates (Australia, western Canada) lengthen the persistence of infected debris and may synchronize the release of airborne ascospores (after rain) with seedling emergence. L. maculans spreads from cotyledon and leaf infections down petioles to reach the stem, with infections on cotyledons and leaves early in the season producing the most damaging stem cankers at the stem base (crown). Development of both crown cankers and phoma stem lesions higher up stems is most rapid in regions with high temperatures from flowering to harvest, such as Australia and Canada. Breeding for resistance (genetic, disease escape or tolerance), stubble management, crop rotation and fungicide seed treatments are important strategies for control of phoma stem canker in all areas. Fungicide spray treatments are justified only in regions such as western Europe where high yields are obtained, and accurate forecasts of epidemic severity are needed to optimize their use. [source]

Effects of stem canker (Leptosphaeria maculans) and light leaf spot (Pyrenopeziza brassicae) on yield of winter oilseed rape (Brassica napus) in southern England

PLANT PATHOLOGY, Issue 4 2000
Y. Zhou
The relationships between yield loss and incidence or severity of stem canker and light leaf spot in winter oilseed rape were analysed by correlation and regression analyses, using data from experiments at Rothamsted, England in 1992/93, 1994/95 and 1995/96. Growth stages (GS) 6,3/6,4 and 4,0/4,5 were identified as the critical points for relating percentage yield loss to stem canker and light leaf spot (on stems), respectively. Critical point (CP) and area under disease progress curve (AUDPC) models relating percentage yield loss to combined incidence or severity of stem canker and light leaf spot (stems) in each experiment were constructed by linear regression. There were no differences in the CP models for incidence between 1992/93, 1994/95 and 1995/96 experiments, or in the AUDPC models for incidence between 1992/93 and 1994/95 experiments. Therefore, a general CP model relating percentage yield loss (,Y) to combined incidence of stem canker (Si) at GS 6,3/6,4 and light leaf spot (stems) (Li) at GS 4,0/4,5 was constructed using data from the three experiments: ,Y = 0·85 + 0·079Si + 0·065Li (R2 = 43·7%, P < 0·001, 92 df). A general AUDPC model relating ,Y to the AUDPC of combined incidence of stem canker (Sia) from GS 5·7 to GS 6·5 and light leaf spot (stems) (Lia) from GS 4·0 to GS 6·3 was constructed using data from the 1992/93 and 1994/95 experiments: ,Y = 0·07 + 0·00096Sia + 0·0026Lia (R2 = 43·6%, P < 0·001, 68 df). These two general yield-loss models were tested with data from Rothamsted in 1993/94 and Boxworth in 1992/93. The predictive accuracy of the CP model based on combined incidence of stem canker and light leaf spot (stems) was better than that of the AUDPC model. Yield losses predicted by summing the estimates from individual models for incidence of stem canker alone (GS 6,3/6,4) and light leaf spot alone (on leaves at GS 3,3) were greater than observed yield losses in experiments at Rothamsted in 1992/93, 1993/94, 1994/95 and 1995/96 and at Boxworth in 1992/93. [source]

Analysis of leaf appearance, leaf death and phoma leaf spot, caused by Leptosphaeria maculans, on oilseed rape (Brassica napus) cultivars

ANNALS OF APPLIED BIOLOGY, Issue 1 2010
S.J. Powers
Development of phoma leaf spot (caused by Leptosphaeria maculans) on winter oilseed rape (canola, Brassica napus) was assessed in two experiments at Rothamsted in successive years (2003,04 and 2004,05 growing seasons). Both experiments compared oilseed rape cultivars Eurol, Darmor, Canberra and Lipton, which differ in their resistance to L. maculans. Data were analysed to describe disease development in terms of increasing numbers of leaves affected over thermal time from sowing. The cultivars showed similar patterns of leaf spot development in the 2003,04 experiment when inoculum concentration was relatively low (up to 133 ascospores m,3 air), Darmor developing 5.3 diseased leaves per plant by 5 May 2004, Canberra 6.6, Eurol 6.8 and Lipton 7.5. Inoculum concentration was up to sevenfold greater in 2004,05, with Eurol and Darmor developing 2.4 diseased leaves per plant by 16 February 2005, whereas Lipton and Canberra developed 2.8 and 3.0 diseased leaves, respectively. Based on three defined periods of crop development, a piece-wise linear statistical model was applied to the progress of the leaf spot disease (cumulative diseased leaves) in relation to appearance (,birth') and death of leaves for individual plants of each cultivar. Estimates of the thermal time from sowing until appearance of the first leaf or death of the first leaf, the rate of increase in number of diseased leaves and the area under the disease progress line (AUDPL) for the first time period were made. In 2004,05, Canberra (1025 leaves ×°C days) and Lipton (879) had greater AUDPL values than Eurol (427) and Darmor (598). For Darmor and Lipton, the severity of leaf spotting could be related to the severity of stem canker at harvest. Eurol had less leaf spotting but severe stem canker, whereas Canberra had more leaf spotting but less severe canker. [source]

Effects of temperature and rainfall on date of release of ascospores of Leptosphaeria maculans (phoma stem canker) from winter oilseed rape (Brassica napus) debris in the UK

ANNALS OF APPLIED BIOLOGY, Issue 1 2007
Y.J. Huang
Abstract Data from a controlled environment experiment investigating effects of temperature on maturation of Leptosphaeria maculans pseudothecia were used to derive equations describing the times until 30% or 50% of pseudothecia were mature as a function of temperature. A wetness sensor was developed to estimate the oilseed rape debris wetness and operated with debris exposed in natural conditions in 2000 and 2001. The maturation of L. maculans pseudothecia on debris and concentrations of airborne L. maculans ascospores were observed from 1999 to 2004. There were considerable differences between years, with the first mature pseudothecia observed in September in most years. There were linear relationships between the first date when 10% of maximum ascospore release was observed and the dates when 30% or 50% of pseudothecia were mature. By summing the daily temperature-dependent rate of pseudothecial maturation for days after 1 August with rainfall >0.5 mm, the dates when 30% or 50% of pseudothecia were mature were predicted. There was good agreement between predicted and observed dates when 30% or 50% of pseudothecia were mature. These equations for predicting the timing of L. maculans ascospore release could be incorporated into schemes for forecasting, in autumn, the severity of phoma stem canker epidemics in the following spring/summer in the UK. [source]

The stem canker (blackleg) fungus, Leptosphaeria maculans, enters the genomic era

Occurrence of the wattle wilt pathogen, Ceratocystis albifundus on native South African trees

FOREST PATHOLOGY, Issue 5 2007
J. Roux
Summary Ceratocystis albifundus causes the disease known as wattle wilt of non-native Acacia mearnsii trees in South Africa, Uganda and Kenya. Infection results in rapid wilt and death of susceptible trees and stem cankers on more tolerant trees. It has been suggested that C. albifundus is indigenous to southern Africa, possibly having spread from native Protea spp. to non-native A. mearnsii and A. decurrens trees. Although C. albifundus has been collected from Protea spp., these reports are based on limited records for which only aged herbarium specimens exist. During surveys of wound-infecting fungi on native tree species in South Africa, a fungus resembling C. albifundus was collected from Protea gaguedi, Acacia caffra, Burkea africana, Combretum molle, C. zeyheri, Faurea saligna, Ochna pulchra, Ozoroa paniculosa and Terminalia sericea. The identity of the fungus was confirmed as C. albifundus, using comparisons of DNA sequence data for the ITS and 5.8S gene of the rRNA operon. In pathogenicity trials, lesions were produced on C. molle and A. caffra, with some trees beginning to die at the termination of the experiment. This study represents the first report of C. albifundus from native tree species in South Africa and provides unequivocal evidence that the fungus occurs naturally on native Protea spp. The wide host range of C. albifundus, as well as its abundance on these indigenous hosts lends further support to the view that it is a native African pathogen. [source]

Patterns of Multiple Virus Infections in the Conifer Pathogenic Fungi, Diplodia pinea and Diplodia scrobiculata

JOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2008
Juanita De Wet
Abstract Diplodia pinea and Diplodia scrobiculata are opportunistic pathogens associated with various disease symptoms on conifers that most importantly include die-back and stem cankers. Two viruses with dsRNA genomes, Sphaeropsis sapinea RNA virus 1 and 2 (SsRV1 and SsRV2) are found in D. pinea and an undescribed dsRNA element is known to occur in D. scrobiculata. We have partially characterized the putative RNA-dependent RNA polymerase (RdRp) of the undescribed dsRNA element and designed virus-specific primers from the RdRp regions of all three virus genomes. This made it possible to screen for the presence of the three viruses in a collection of D. pinea and D. scrobiculata isolates using real-time PCR. Triple infections with all three viruses occurred in D. pinea and D. scrobiculata. Co-infections with SsRV1 and SsRV2 were common but found only in D. pinea. Co-infection with SsRV1 and the undescribed dsRNA element was rare and observed only in D. pinea. Single infections with either SsRV1 or SsRV2 were equally common, while the undescribed dsRNA element never occurred alone. SsRV1 occurred alone in both D. pinea and D. scrobiculata while SsRV2 occurred alone only in D. pinea. There were only two instances where the undescribed dsRNA element was observed in D. pinea and it was otherwise found only in D. scrobiculata. This study highlights the complex interactions between the viruses found in the closely related plant pathogenic fungi, D. pinea and D. scrobiculata. It illustrates the importance of not only characterizing viruses infecting fungi but also of determining the interactions between mycoviruses and their fungal hosts. [source]

Quantitative resistance to symptomless growth of Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape)

Phomopsis alnea, the cause of dieback of black alder in Italy

PLANT PATHOLOGY, Issue 6 2002
S. Moricca
Black alder (Alnus glutinosa) occurs naturally on moist soils and along streams and rivers throughout most of its range. Groves of this species in north-central Italy were recently found to be attacked by the mitosporic coelomycete Phomopsis alnea, which causes perennial stem cankers and dieback. The fungi Melanconium apiocarpium and a Hymenopsis sp. were also frequently found on necrotic alder tissue, occasionally invading the living bark. All these fungi were tested for pathogenicity in two seasonal inoculation trials on seedlings of black alder, Italian alder (Alnus cordata) and green alder (Alnus viridis) that were either normally watered or water-stressed. Phomopsis alnea actively colonized the seedlings and reproduced the symptoms observed in the field. The other fungi behaved as weak parasites, only occasionally spreading to apparently healthy bark tissue. It appears that these fungi are saprobes, commonly colonizing bark and twigs already killed by P. alnea. Symptoms caused by P. alnea in the field were exacerbated on dry sites and by seasonal drought stress. On artificially inoculated and water-stressed seedlings, both the incidence and severity of P. alnea also increased, causing extensive mortality. The data provide evidence for the belief that P. alnea becomes a factor in the dieback of natural black alder woodlands when trees are first impaired by wounding agents and then subjected to unusual extended drought. [source]