Pathogenicity Tests (pathogenicity + test)

Distribution by Scientific Domains


Selected Abstracts


Comparisons of Isolates of Fusarium avenaceum from White Lupin and Other Crops by Pathogenicity Tests, DNA Analyses and Vegetative Compatibility Tests

JOURNAL OF PHYTOPATHOLOGY, Issue 4 2000
K. Satyaprasad
Isolates of Fusarium avenaceum, mostly from crops of white lupin or wheat, were tested for pathogenicity on white lupin and wheat plants and compared by DNA tests and, in a limited study, vegetative compatibility. Most of the 80 isolates were pathogenic on both plant species after inoculation on shoot bases. Disease severity was greater at higher incubation temperatures that ranged from 15/10°C to 25/20°C (day/night temperatures). Isolates from lupin crops tended to be more pathogenic, on average, on lupins than on cereals. Polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer region of the rDNA distinguished two groups of isolates that occurred in different proportions among isolates from lupins and cereal crops. Random amplified polymorphic DNA (RAPD)-PCR analyses indicated considerable genetic variation among isolates, but there was some similarity among groups of isolates from populations in the same field. Genetic diversity was confirmed by a high degree of vegetative incompatibility among 20 isolates using nitrate nonutilizing mutants. There were no relationships among pathogenicity, RFLP group, RAPD group and vegetative compatibility group. Zusammenfassung Fusarium-avenaceum -Isolate, die überwiegend von Weißier Lupine oder Weizen stammten, wurden hinsichtlich ihrer Pathogenität für Weißie Lupine und Weizenpflanzen getestet und durch DNA-Tests verglichen. In einer kleineren Studie wurde zudem ihre vegetative Kompatibilität geprüft. Die meisten der 80 Isolate waren nach Inokulation der Stengel-bzw. Halmbasis für beide Pflanzenarten pathogen. Bei hohen Inkubationstemperaturen im Bereich von 15/10°C bis 25/20°C (Tag/Nacht-Temperaturen) war der Befall stärker. Von Lupinen stammende Isolate waren im Durchschnitt stärker pathogen für Lupinen als für Getreide. Eine PCR-RFLP-Analyse der Internal-transcribed-spacer-Region der rDNA teilte die Isolate in zwei Gruppen, die bei den Isolaten von Lupinen und Getreide in verschiedenen Anteilen vertreten waren. RAPD-PCR-Analysen zeigten eine beträchtliche genetische Variation bei den Isolaten, aber auch gewisse Ähnlichkeiten bei den Isolatgruppen, die von Populationen im selben Feld stammten. Die genetische Diversität wurde auch durch ein hohes Ausmaßi an vegetativer Inkompatibilität bei 20 Isolaten deutlich; hier wurden Nitrat nicht verwertende Mutanten verwendet. Zwischen Pathogenität, RFLP-Gruppe, RAPD-Gruppe und vegetativer Kompatibilitätsgruppe bestanden keine Beziehungen. [source]


First Report of Rhizoctonia solani AG-7 on Cotton in Egypt

JOURNAL OF PHYTOPATHOLOGY, Issue 4 2010
Kamel A. Abd-Elsalam
Abstract Eighty-two isolates of Rhizoctonia solani were recorded from roots of naturally-infected seedlings of the Egyptian cotton (Gossypium barbadense L.). Anastomosis groups (AGs) of the isolates were determined by using 13 different AGs testers. Three (3.7%) of the isolates were identified as R. solani AG7, while the remaining isolates were belonging to the AG 2-1, AG4 and AG5. The identification of the three isolates was based on the frequency of the C2 reaction with the AG7 tester isolate. No fusion was observed between AG7 and isolates representing the other 13 AGs. Colonies of AG7 isolates grown on potato dextrose agar (PDA), malt yeast agar (MYA) and melt peptone agar (MPA) were brown to dark brown with aerial mycelium and sclerotia. The isolates had pitted sclerotial clusters and brownish exudates after 21 days of culturing on PDA, but without clear zonation. Pathogenicity test under greenhouse conditions revealed that AG7 caused the common symptoms of damping,off, which included seed rot, lesions on the hypocotyls and root rot. [source]


Identity and Pathogenicity of Fungi Associated with Root and Crown Rot of Soft Red Winter Wheat Grown on the Upper Coastal Plain Land Resource Area of Mississippi

JOURNAL OF PHYTOPATHOLOGY, Issue 2 2000
M. S. Gonzalez
Seedling stand, disease severity and fungal incidence were determined from untreated ,Wakefield' soft red winter wheat planted on a Leeper silty clay loam in field tests conducted at the Mississippi Agricultural and Forestry Experiment Station, Plant Science Research Center, Mississippi State University, Starkville, Mississippi during the 1996,97 and 1997,98 growing seasons. Seedling stand was reduced by 40% each year in plots established with untreated seed. Cochliobolus sativus was the most frequently isolated fungus. Fusarium acuminatum, Fusarium equiseti and Fusarium solani were the most prevalent Fusarium spp. Seven other Fusarium spp. and 23 species of other fungal genera were isolated. Pathogenicity tests with three isolates each of C. sativus, Cochliobolus spicifer, F. acuminatum, F. solani, F. equiseti, Fusarium compactum, Embellisia chlamydospora and Microdochium bolleyi were performed in test tube culture and two isolates each of C. sativus, C. spicifer, F. acuminatum, E. chlamydospora and M. bolleyi under greenhouse conditions. In test tubes and in the greenhouse, seedlings infected with isolates of C. sativus developed seedling blight, discoloration and necrosis, primarily in seminal roots and crowns. In the greenhouse, C. sativus induced lesions on the lower leaf sheath and reduced seedling height, seedling emergence, dry and fresh weight of roots and shoots. Isolates of F. acuminatum, F. solani, F. equiseti, F. compactum, E. chlamydospora and M. bolleyi induced slight to moderate orange to light-brown discoloration of crown and seminal roots in test tubes. Cochliobolus spicifer isolates had the most pre-emergence activity, inducing black root discoloration and root pruning of wheat seedlings and reducing seedling emergence, root fresh weight and shoot dry weight. In the greenhouse, F. acuminatum reduced seedling height, seedling emergence and root and shoot dry weights. Microdochium bolleyi and E. chlamydospora reduced fresh and dry weight of roots, plant emergence and shoot dry weight. Fusarium acuminatum and C. spicifer reduced the growth rate of wheat seedlings. All fungi evaluated showed increased disease severity compared to the untreated control. The high frequency of isolation of C. sativus from crown and root tissues can be partially explained by the dry, warm conditions during the early stages of wheat seedling development in the Upper Coastal Plain Land Resource Area of Mississippi. Zusammenfassung Die Auflaufrate von Sämlingen, die Stärke des Krank-heitsbefalls sowie die Häufigkeit von Pilzarten wurden bei nicht behandelten roten Weichwinterweizen der Sorte Wakefield ermittelt, welche in einem Leeper schlammigen Tonboden an der Mississippi Agricultural & Forestry Experiment Station, Plant Science Research Center, Mississippi State University, Starkville, Mississippi in der 1996,97 und 1997,98 Saison gesät worden waren. In beiden Jahren wurde die Auflaufrate von nicht behandeltem Saatgut um 40% reduziert. Cochliobolus sativus wurde am häufigsten isoliert. Fusarium acuminatum, Fusarium equiseti und Fusarium solani waren die überwiegenden Fusarium spp. Außierdem wurden sieben weitere Fusarium spp. sowie 23 weitere Pilzarten isoliert. Pathogenitätstests mit je 3 Isolaten von C. sativus, Cochliobolus spicifer, F. acuminatum, F. solani, F. equiseti, Fusarium compactum, Embellisia chlamydospora und Microdochiumbolleyi wurden in Reagenzröhrchen durchgeführt, sowie mit je 2 Isolaten von C. sativus, C. spicifer, F. acuminatum, E. chlamydospora und M. bolleyi unter Gewächshausbedingungen. Sowohl in den Reagenzröhrchen als auch im Gewächshaus entwickelten Sämlinge, die mit C. sativus inokuliert worden waren, eine Fäule, Verfärbung sowie Nekrosis, hauptsächlich in den sekundären Wurzeln und in den Halmbasen. Unter Gewächshausbedingungen verursachte C. sativus außierdem Läsionen der unteren Blattscheide sowie eine Reduzierung des Sämlingswachstums, des Sämlingsauflaufs, des Trocken-und Frischgewichts der Wurzeln und Sprossen. Im Reagenzröhrchentest induzierten Isolate von F. acuminatum, F. solani, F. equiseti, F. compactum, E. chlamydospora und M. bolleyieine schwache bis mäßiige orange bis hell braune Verfärbung des Halmbasis und der Sekundärwurzeln. Isolate von C. spicifer besaßien die höchste Vorauflaufaktivität und induzierten eine Verschwärzung und Verkürzung der Wurzeln sowie eine Reduzierung des Sämlingsauflaufs, des Wurzelfrischgewichts sowie des Sproitrockengewichts. Unter Gewächshausbedingungen reduzierte F. acuminatum die Sämlingshöhe, die Auflaufrate sowie das Trockengewicht der Wurzeln und Sproien. Microdochium bolleyi und E. chlamydospora reduzierten das Frisch-und Trockengewicht der Wurzeln, die Auflaufrate sowie das Sproßitrockengewicht. Die Wachstumsrate der Sämlinge wurde durch F. acuminatum und C. spicifer reduziert. Alle untersuchten Pilzarten erhöhten die Befallsstärke verglichen mit der unbehandelten Kontrolle. Die hohe Isolierungsrate von C. sativus aus dem Halmbasis-und Wurzelgewebe kann zum Teil dadurch erklärt werden, dass während der Frühentwicklungsphase der Sämlinge trockene und warme Wachstumsbedingungen in diesem Gebiet herrschten. [source]


Brenneria quercina and Serratia spp. isolated from Spanish oak trees: molecular characterization and development of PCR primers

PLANT PATHOLOGY, Issue 2 2008
C. Poza-Carrión
Brenneria quercina has been reported as one of the causal agents of oak decline in Spain. To investigate the bacterial variability of this pathogen from different Spanish oak forests, a collection of 38 bacterial isolates from seven geographic locations and from different oak species was analysed by sequencing 16S rDNA and rep-PCR fingerprinting. All Spanish isolates of B. quercina were grouped by rep-PCR into a homogenous cluster that differed significantly from B. quercina reference strains from California. 16S rDNA analysis revealed that 34 out of 38 isolates were Brenneria. However, four isolates belonged to the genus Serratia, suggesting that this bacterium could cause cankers in oak trees. The information obtained by rep-PCR fingerprint analysis was used to develop PCR primers for the sensitive and specific detection of B. quercina from infected plant tissues. Pathogenicity tests performed with Brenneria and Serratia isolates showed that both were able to grow and cause cankers in oak trees. [source]


A New Report of Fruit Rot of Lemon Caused by Ceratocystis radicicola from Iran

JOURNAL OF PHYTOPATHOLOGY, Issue 1 2005
M. R. Mirzaee
Abstract In the year 2000, a fungus was isolated from rotting lemon (Citrus limon) fruit in the Kahnouj region, south-eastern Iran and subsequently identified as Ceratocystis radicicola (anamorph: Chalara sp.). A pathogenicity test was carried out to fulfil Koch's postulates. The pathogen could only enter the ripen lemon fruit and cause the rot disease through the wounds and cracks. The fungus was also pathogenic on fruit of other citrus species as well as date palm (Phoenix dactylifera). Symptom development was slow on fruits on the tree but accelerated after fruit harvest. [source]


Fusarium culmorum Infection of Barley Seedlings: Correlation between Aggressiveness and Deoxynivalenol Content

JOURNAL OF PHYTOPATHOLOGY, Issue 6 2002
HELLE HESTBJERG
Fusarium culmorum is a serious plant pathogen, especially on cereals. The production of deoxynivalenol (DON) by F. culmorum is believed to play a role in pathogenesis. This relationship has been almost exclusively studied in connection with head blight. The present paper reports the first finding of DON in cereal seedlings infected with F. culmorum. A pathogenicity test was performed, including 70 isolates of this pathogen from different sites within northern and central Europe. All isolates caused disease on barley seedlings. For 15 isolates with varying aggressiveness, the DON content in the 19-day-old-barley seedlings was determined. There was a significant correlation between DON concentration and disease index. The aggressiveness of two outlying isolates with very low DON production is discussed. The results indicate that for F. culmorum isolates of the DON chemotype, production of this toxin influences the aggressiveness of the isolates towards barley seedlings. [source]


Listeria monocytogenes in spontaneous abortions in humans and its detection by multiplex PCR

JOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2007
S. Kaur
Abstract Aim: To assess the extent of Listeria monocytogenes in causation of human spontaneous abortions by isolation methods and PCR analysis for the presence of virulence-associated genes. Methods and Results: A total of 305 samples comprising blood, urine, placental bits, faecal and vaginal swabs were collected from 61 patients with spontaneous abortions. Listeria spp. were isolated from 10 samples collected from nine (14·8%) patients. Confirmation of these isolates was based on biochemical tests, haemolysis on blood agar, CAMP test, phosphatidylinositol-specific phospholipase C (PI-PLC) assay followed by in vivo pathogenicity tests and multiplex PCR to detect virulence-associated genes (prfA, plcA, hlyA, actA and iap). Three isolates were confirmed as L. monocytogenes. Of these, two isolates turned out to be pathogenic and found to posses all five genes. However, the remaining two haemolytic L. monocytogenes isolates lacking the plcA gene and activity in the PI-PLC assay were found to be nonpathogenic by in vivo tests. Conclusions: The occurrence of pathogenic L. monocytogenes in cases of spontaneous abortions was 3·3%. It seems that the plcA gene and its expression have an important role as essential virulence determinants in pathogenic Listeria spp. Significance and Impact of the Study: The recovery of pathogenic L. monocytogenes isolates from cases of spontaneous abortion indicates the significance of listeric infection in pregnant women. [source]


Use of RAPD and ISSR Markers in Detection of Genetic Variation and Population Structure among Fusarium oxysporum f. sp. ciceris Isolates on Chickpea in Turkey

JOURNAL OF PHYTOPATHOLOGY, Issue 3 2008
H. Bayraktar
Abstract Genetic variation among the isolates of Fusarium oxysporum f. sp. ciceris, the causal agent of chickpea wilt worldwide, was analysed using pathogenicity tests and molecular markers , random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) polymorphism. Hundred and eight isolates were obtained from diseased chickpea plants in 13 different provinces of Turkey, out of which 74 isolates were assessed using 30 arbitrary decamer primers and 20 ISSR primers. Unweighted pair-grouped method by arithmetic average cluster analysis of RAPD, ISSR and RAPD + ISSR datasets provided a substantially similar discrimination among Turkish isolates and divided into three major groups. Group 1, 2 and 3 consisted of 41, 18 and 15 isolates, respectively. These methods revealed a considerable genetic variation among Turkish isolates, but no correlation with regard to the clustering of isolates from different geographic regions. Analysis of molecular variance confirmed that most genetic variability resulted from the differences among isolates within regions. Our results also indicated that the low-genetic differentiation (FST) and high gene flow (Nm) among populations had a significant effect on the emergence and evolutionary development of F. oxysporum f. sp. ciceris. This is the first report on genetic diversity and population structure of F. oxysporum isolates on chickpea in Turkey. [source]


Characterization and Pathogenicity of Rhizoctonia spp. from Onion in Amasya, Turkey

JOURNAL OF PHYTOPATHOLOGY, Issue 2 2006
I. Erper
Abstract Forty-two isolates of Rhizoctonia spp. were obtained from onion in Amasya, Turkey. Of these, 29% were Rhizoctonia solani (AG-4), 69% were Waitea circinata var. zeae (Rhizoctonia zeae) and 2% were binucleate Rhizoctonia (AG-B). Most of the isolates were recovered from rhizosphere soil. In pathogenicity tests on onion, R. solani AG-4 caused the greatest disease severity, those of W. circinata var. zeae were moderately virulent but binucleate Rhizoctonia isolates were of low virulence. This is the first report of binucleate Rhizoctonia AG-B and W. circinata var. zeae occurring on onion in Turkey. [source]


Cultural Characterization and Conidial Dimorphism in Colletotrichum sublineolum

JOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2003
E. A. Souza-Paccola
Abstract Anthracnose, caused by Colletotrichum sublineolum, is one of the most important diseases of sorghum in Brazil. This fungus showed conidial dimorphism when cultivated on solid or in liquid media. In solid media only falcate conidia were produced, whereas in liquid media the conidia were of variable size, but mostly oval. Wild strains, differentiated by their , and , esterase electrophoretic profiles, were assessed. The effect of different culture media on the production of both conidial types was evaluated. Unlike that of oval conidia, the production of falcate conidia was light-dependent. Some strains failed to produce falcate conidia in solid media, but all produced oval conidia in all the liquid media. The falcate conidia were uninucleate, but oval conidia contained one to three nuclei, although most were uninucleate. Both types of conidia induced symptoms in inoculable sorghum plants under controlled conditions. Both oval and falcate conidia produced mutants after exposure to UV light, and hyphal anastomoses occurred in crosses between mutant conidia carriers of complementary markers. The production of these oval conidia in C. sublineolum is an alternative to pathogenicity tests and genetic studies, especially for strains that sporulate poorly in solid culture media. [source]


Rapid identification of pseudomonas avellanae field isolates, causing hazelnut decline in central italy, by repetitive PCR genomic fingerprinting

JOURNAL OF PHYTOPATHOLOGY, Issue 3 2000
M. Scortichini
Pseudomonas avellanae is the main cause of hazelnut (Corylus avellana L.) decline, the so called ,moria', in central Italy where it has already killed more than 30 000 trees. Its current identification is very long requiring biochemical, physiological and nutritional tests as well as pathogenicity tests and takes not less than 6 months for its completion. In the present study the reliability of the repetitive polymerase chain reaction (rep-PCR) technique for a rapid and accurate identification of such a pathogen was compared with the traditional identification method. In order to assess the variability of the pathogen, REP, BOX and ERIC primer sets were used in preliminary work to generate genomic fingerprints of 60 P. avellanae reference strains previously isolated from different areas of hazelnut cultivation. ERIC primers yielded the most discriminative clustering of strains that were grouped according to their geographic origin. Sixty field isolates collected from hazelnut orchards of central Italy, planted with different cultivars, during the years 1996,98 were submitted to either the traditional identification methods or to rep-PCR by using ERIC primers. The latter technique accurately identified all the isolates that were also identified by the traditional methods. Whole-cell protein analysis by means of sodium dodecyl sulphate-polyacrylamide gel electrophoresis confirmed this achievement. Rep-PCR can be successfully adopted for the rapid and accurate identification of P. avellanae in central Italy and it constitutes a very useful tool for the sanitation of the area. Zusammenfassung Eine schnelle Bestimmung von Pseudomonas avellanae -Feldisolaten, dem Erreger einer HaselnuIapoplexie in Zentralitalien, durch rep-PCR genomisches Fingerprinting [source]


Molecular, ecological and evolutionary approaches to understanding Alternaria diseases of citrus

MOLECULAR PLANT PATHOLOGY, Issue 6 2003
Kazuya Akimitsu
SUMMARY Alternaria fungi cause four different diseases of citrus: Alternaria brown spot of tangerines, Alternaria leaf spot of rough lemon, Alternaria black rot of several citrus fruits and Mancha foliar of Mexican lime. The first three diseases are caused by the small-spored species, Alternaria alternata and the causal agents can only be differentiated using pathogenicity tests, toxin assays or genetic markers. Mancha foliar is caused by the morphologically distinct, large-spored species A. limicola. Substantial progress has been made in understanding the biology, ecology, population biology, systematics, molecular biology and biochemistry of the interactions between these pathogens and citrus. Epidemiological studies have focused on brown spot of tangerines and their hybrids and have contributed to the development of a model of disease development which has improved control and reduced fungicide use. Studies of the population genetics, host specificity and ecology of A. alternata from different ecological niches on citrus have revealed host specific forms of the pathogen which cause disease on different citrus species, the existence of three phylogenetic lineages of the fungus which cause brown spot world-wide, and closely related non-pathogenic isolates which colonize healthy citrus tissue. The role of host-specific toxins in Alternaria diseases of citrus has been extensively studied for over 20 years, and these pathosystems have become model systems for host-pathogen interactions. Recent molecular research has started to unravel the genetic basis of toxin production and the host susceptibility to toxin, and the role of extracellular, degradative enzymes in disease. [source]


Pathogenicity of Phytophthora austrocedrae on Austrocedrus chilensis and its relation with mal del ciprés in Patagonia

PLANT PATHOLOGY, Issue 4 2010
A. G. Greslebin
Field observations, isolations and pathogenicity tests were performed on Austrocedrus chilensis (Cupressaceae) trees to determine the pathogenicity of Phytophthora austrocedrae and its role in the aetiology of the cypress disease mal del ciprés (MDC) in Argentina. It was found that P. austrocedrae is a primary pathogen of A. chilensis. It was isolated from large necrotic lesions in the inner bark, and superficially in the sapwood, at the root collar and stem, in most of the MDC-affected stands surveyed along the range of A. chilensis in Argentina. The main symptom in naturally infected trees was a necrotic lesion extending from killed roots up to 1 m up the tree bole. Seedlings, saplings and adult trees were all susceptible to inoculation with P. austrocedrae. Under favourable experimental conditions (flooding), inoculated seedlings suffered massive mortality in less than a month. The importance of diseases caused by Phytophthora spp. in South American forests is discussed. [source]


Causes of incipient rot and rot in regrowth Eucalyptus diversicolor (karri) trees

PLANT PATHOLOGY, Issue 6 2008
E. M. Davison
Eucalyptus diversicolor (karri) is the second most important commercial timber tree in Western Australia. Sawlogs from regrowth trees often have a discoloration in the heartwood that is more abundant than in sawlogs from mature trees. Other symptoms in regrowth logs include white rot, white pocket rot and brown rot. Fungal isolations and pathogenicity tests were conducted to determine whether this discoloration was incipient rot, and if so, what caused it and which rot(s) would eventually develop. A combined sample of 329 discs from recently felled trees and freshly cut scantling had discoloration in 48%, white rot in 14%, white pocket rot in 12% and brown rot in 4% of pieces of wood. Hymenochaete semistupposa was isolated from 22% of discoloured wood and 39% of white pocket rot samples. Stereum hirsutum was isolated from 4% of discoloured wood and 13% of white rot samples. Koch's postulates in regrowth karri trees showed that H. semistupposa caused extensive discoloration, with white pocket rot developing in the heartwood within 4 years, while S. hirsutum caused extensive discoloration, with white rot developing in both the heartwood and sapwood within 2 years. It was concluded that the discoloration was incipient rot, which would eventually develop into either white rot or white pocket rot. [source]


Distinguishing characteristics and vegetative compatibility of Colletotrichum kahawe in comparison with other related species from coffee

PLANT PATHOLOGY, Issue 2 2002
V. M. P. Varzea
On the basis of pathogenicity tests on green berries or hypocotyls of coffee and by morphological and biochemical characteristics in culture, 31 isolates of Colletotrichum were classified into C. kahawe (24 isolates), C. gloeosporioides (six isolates) or C. acutatum (one isolate). Within these groups of isolates, vegetative compatibility groups (VCGs) were determined by complementation tests with mutants in the nitrate assimilation pathway. There were distinct incompatibility barriers between the three species. Among the C. gloeosporioides group, the three isolates tested were self-compatible but incompatible with each other. Within C. kahawe, 18 isolates were self-compatible and only one main VCG was detected. However, partial compatibility in C. kahawe was also indicated by variation in the intensity of heterokaryon formation between different pairs of isolates and between different types of mutant. The existence of only one VCG in C. kahawe is consistent with the low level of variation found in previous work on DNA polymorphism. [source]