Browsing by Author "Crous, P. W."
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- ItemThe essential symbiosis of mycology and plant pathology : present and future needs(Academy of Science of South Africa, 1995) Crous, P. W.Correct disease diagnosis is essential for plant pathologists striving to combat plant disease. To support them, mycologists are integrating traditional and molecular techniques. Attention must therefore be given to harnessing the power of molecular genetics to provide rapid methods of identification, and to study the adaptability of plant pathogens in terms of virulence and sensitivity to fungicides. To combat African plant diseases effectively, better co-operation bem'een mycologists and plant pathologists is essential.
- ItemFirst report of Phyllosticta citricarpa and description of two new species, P. paracapitalensis and P. paracitricarpa, from citrus in Europe(Elsevier, 2017) Guarnaccia, V.; Groenewald, J. Z.; Li, H.; Glienke, C.; Carstens, E.; Hattingh, V.; Fourie, P. H.; Crous, P. W.The genus Phyllosticta occurs worldwide, and contains numerous plant pathogenic, endophytic and saprobic species. Phyllosticta citricarpa is the causal agent of Citrus Black Spot disease (CBS), affecting fruits and leaves of several citrus hosts (Rutaceae), and can also be isolated from asymptomatic citrus tissues. Citrus Black Spot occurs in citrus-growing regions with warm summer rainfall climates, but is absent in countries of the European Union (EU). Phyllosticta capitalensis is morphologically similar to P. citricarpa, but is a non-pathogenic endophyte, commonly isolated from citrus leaves and fruits and a wide range of other hosts, and is known to occur in Europe. To determine which Phyllosticta spp. occur within citrus growing regions of EU countries, several surveys were conducted (2015–2017) in the major citrus production areas of Greece, Italy, Malta, Portugal and Spain to collect both living plant material and leaf litter in commercial nurseries, orchards, gardens, backyards and plant collections. A total of 64 Phyllosticta isolates were obtained from citrus in Europe, of which 52 were included in a multi-locus (ITS, actA, tef1, gapdh, LSU and rpb2 genes) DNA dataset. Two isolates from Florida (USA), three isolates from China, and several reference strains from Australia, South Africa and South America were included in the overall 99 isolate dataset. Based on the data obtained, two known species were identified, namely P. capitalensis (from asymptomatic living leaves of Citrus spp.) in Greece, Italy, Malta, Portugal and Spain, and P. citricarpa (from leaf litter of C. sinensis and C. limon) in Italy, Malta and Portugal. Moreover, two new species were described, namely P. paracapitalensis (from asymptomatic living leaves of Citrus spp.) in Italy and Spain, and P. paracitricarpa (from leaf litter of C. limon) in Greece. On a genotypic level, isolates of P. citricarpa populations from Italy and Malta (MAT1-2-1) represented a single clone, and those from Portugal (MAT1-1- 1) another. Isolates of P. citricarpa and P. paracitricarpa were able to induce atypical lesions (necrosis) in artificially inoculated mature sweet orange fruit, while P. capitalensis and P. paracapitalensis induced no lesions. The Phyllosticta species recovered were not found to be widespread, and were not associated with disease symptoms, indicating that the fungi persisted over time, but did not cause disease.
- ItemFungicide sensitivity of phaeomoniella chlamydospora, the causal organism of petri grapevine decline(South African Society for Enology and Viticulture, 2000) Groenewald, M.; Denman, S.; Crous, P. W.Twelve fungicides, benomyl, chlorothalonil, fenarimol, fosetyl-Al, iprodione, kresoxim-methyl, mancozeb, metalaxyl, prochloraz manganese chloride, quintozene, tebuconazole and thiram were screened in vitro for their ability to inhibit mycelial growth of Phaeomoniella chlamydospora, the causal organism of Petri grapevine decline. Isolates of Pa. chlamydospora were obtained from different geographical areas in the Western Cape province. The effective concentration at which 50% of mycelial growth was inhibited (EC50) was calculated for each fungicide. Benomyl, fenarimol, kresoxim-methyl, prochloraz manganese chloride and tebuconazole were the most effective in inhibiting mycelial growth of Pa. chlamydospora with ECso values ranging from 0.01 to 0.05 μg/mL. Data obtained in this study represent the base-line sensitivity of local isolates to these fungicides, which is important for monitoring the development of pathogen resistance to fungicides.
- ItemGenera of phytopathogenic fungi : GOPHY 2(Elsevier, 2019) Marin-Felix, Y.; Hern andez-Restrepo, M.; Wingfield, M. J.; Akulov, A.; Carnegie, A. J.; Cheewangkoon, R.; Gramaje, D.; Groenewald, J. Z.; Guarnaccia, V.; Halleen, F.; Lombard, L.; Luangsa-ard, J.; Marincowitz, S.; Moslemi, A.; Mostert, L.; Quaedvlieg, W.; Schumacher, R. K.; Spies, C. F. J.; Thangavel, R.; Taylor, P. W. J.; Wilson, A. M.; Wingfield, B. D.; Wood, A. R.; Crous, P. W.This paper represents the second contribution in the Genera of Phytopathogenic Fungi (GOPHY) series. The series provides morphological descriptions and information regarding the pathology, distribution, hosts and disease symptoms for the treated genera. In addition, primary and secondary DNA barcodes for the currently accepted species are included. This second paper in the GOPHY series treats 20 genera of phytopathogenic fungi and their relatives including: Allantophomopsiella, Apoharknessia, Cylindrocladiella, Diaporthe, Dichotomophthora, Gaeumannomyces, Harknessia, Huntiella, Macgarvieomyces, Metulocladosporiella, Microdochium, Oculimacula, Paraphoma, Phaeoacremonium, Phyllosticta, Proxypiricularia, Pyricularia, Stenocarpella, Utrechtiana and Wojnowiciella. This study includes the new genus Pyriculariomyces, 20 new species, five new combinations, and six typifications for older names.
- ItemGenetic diversity among isolates of Phaeomoniella chlamydospora on grapevines(2006) Mostert, L.; Abeln, E. C. A.; Halleen, F.; Crous, P. W.Phaeomoniella chlamydospora is one of the main causal agents of Petri disease and esca of grapevines. Although it is known to have a coelomycete synanamorph, no teleomorph has thus far been reported for P. chlamydospora, and its disease cycle remains largely unknown. The present study compared the genetic diversity of P. chlamydospora isolates from different grapevine-growing countries using amplified fragment length polymorphisms. Sixty-three isolates from South Africa and 25 from grapevine regions in Australia, France, Iran, Italy, New Zealand, Slovenia and the USA were studied. Two primer combinations were used producing 138 scorable markers, of which 33% were polymorphic. An unweighted paired group method of arithmetic averages analysis showed a high similarity (≥94.5%) among the different isolates. The overall low level of genetic variation confirmed asexual reproduction to be dominant in the field. Different genotypes were found among isolates of P. chlamydospora within the same grapevine, suggesting multiple infections from different inoculum sources. Isolates from different production areas and countries had a high percentage of similarity and clustered together, indicating the absence of genotype-geographic structure. The presence of the same genotype in different vineyards and production areas suggests that long-range dispersal through aerial inoculum or infected plant material play an important role in genotype distribution. © Australasian Plant Pathology Society 2006.
- ItemIn vitro screening of fungicides against phomopsis viticola and diaporthe perjuncta(South African Society for Enology and Viticulture, 2000) Mostert, L.; Denman, S.; Crous, P. W.Phomopsis viticola is the cause of Phomopsis cane and leaf spot disease of grapevines, while Diaporthe perjuncta is associated with bud mortality. The efficacy of nine fungicides (azoxystrobin, flusilazole, folpet, fosetyl-Al + mancozeb, kresoxim-methyl, mancozeb, penconazole, spiroxamine and trifloxystrobin) against isolates of P. viticola and D. perjuncta was determined in vitro using the mycelial growth test. Additionally, azoxystrobin, folpet, kresoxim-methyl, mancozeb, propineb and trifloxystrobin were tested for their ability to inhibit spore germination in vitro. Ten isolates of P. viticola and three of D. perjuncta were used in the mycelium inhibition tests, and five isolates of P. viticola in the spore germination tests. The effective concentration at which mycelial growth was inhibited by 50% and at which 50% of the spores (EC50 value) were inhibited from germinating was calculated for each isolate/fungicide combination. In the mycelium growth test flusilazole, penconazole and trifloxystrobin gave better inhibition at lower concentrations than folpet and fosetyl-Al + mancozeb. No significant differences in the mean ECso values were detected among azoxystrobin, flusilazole, kresoxim-methyl, penconazole, spiroxamine and trifloxystrobin. There were also no significant differences among the mean EC50 values of azoxystrobin, kresoximmethyl and mancozeb. Flusilazole and penconazole inhibited mycelial growth at the lowest mean EC50 values obtained. Kresoxim-methyl and trifloxystrobin inhibited spore germination at lower concentrations than folpet or mancozeb. Folpet required the highest concentration to inhibit 50% germination and was significantly different from mancozeb and propineb. There were also no significant differences among the mean EC50 values of mancozeb, propineb and azoxystrobin. The mean EC50 values of the strobilurin fungicides were not significantly different from one another. These results indicate that the strobilurin fungicides inhibited mycelial growth and spore germination of P. viticola. Trials need to be conducted to verify these findings under field conditions.
- ItemPhylogeny and taxonomy of the scab and spot anthracnose fungus Elsinoe (Myriangiales, Dothideomycetes)(Elsevier, 2017) Fan, X. L.; Barreto, R. W.; Groenewald, J. Z.; Bezerra, J. D. P.; Pereira, O. L.; Cheewangkoon, R.; Mostert, L.; Tian, C. M.; Crous, P. W.Species of Elsinoe are phytopathogens causing scab and spot anthracnose on many plants, including some economically important crops such as avocado, citrus, grapevines, and ornamentals such as poinsettias, field crops and woody hosts. Disease symptoms are often easily recognisable, and referred to as signaturebearing diseases, for the cork-like appearance of older infected tissues with scab-like appearance. In some Elsinoe-host associations the resulting symptoms are better described as spot anthracnose. Additionally the infected plants may also show mild to severe distortions of infected organs. Isolation of Elsinoe in pure culture can be very challenging and examination of specimens collected in the field is often frustrating because of the lack of fertile structures. Current criteria for species recognition and host specificity in Elsinoe are unclear due to overlapping morphological characteristics, and the lack of molecular and pathogenicity data. In the present study we revised the taxonomy of Elsinoe based on DNA sequence and morphological data derived from 119 isolates, representing 67 host genera from 17 countries, including 64 ex-type cultures. Combined analyses of ITS, LSU, rpb2 and TEF1-α DNA sequence data were used to reconstruct the backbone phylogeny of the genus Elsinoe. Based on the single nomenclature for fungi, 26 new combinations are proposed in Elsinoe for species that were originally described in Sphaceloma. A total of 13 species are epitypified with notes on their taxonomy and phylogeny. A further eight new species are introduced, leading to a total of 75 Elsinoe species supported by molecular data in the present study. For the most part species of Elsinoe appear to be host specific, although the majority of the species treated are known only from a few isolates, and further collections and pathogenicity studies will be required to reconfirm this conclusion.