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Presence of Colletotrichum acutatum causing leaf spot on Azalea japonica in Italy
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Molecular Evolution.
2004 (English)In: Plant Disease, ISSN 0191-2917, Vol. 88, no 5, 572- p.Article in journal (Refereed) Published
Abstract [en]

Rhododendron cultivation has a long history in northern Italy where a wide selection of varieties and hybrids are grown. In the fall of 2002, a previously unknown disease was observed on Azalea japonica cv. Palestrina in several commercial farms in the Province of Verbania. Leaves showed irregular necrotic areas that were 1 mm in diameter. Lesions were dark brown to black and were surrounded by a chlorotic halo. Eventually, lesions coalesced, forming large irregular spots. Heavily infected leaves fell prematurely, resulting in severe defoliation. On the infected leaves, acervuli were present from which cylindrical tapered conidia measuring 4.8 to 7.2 × 11.0 to 22.8 μm at one end were released. Fifty conidia per isolate were measured. Fungus identified as Colletotrichum acutatum was consistently recovered from infected leaves, disinfested in 1% NaOCl for 1 min, and plated on potato dextrose agar amended with 100 mg/l of streptomycin sulfate. Pathogenicity of three fungal isolates was confirmed by inoculating healthy A. japonica (cvs. Palestrina and Snow) plants grown in plastic pots (18-cm diameter, 3 liters). Plants (five per treatment) were sprayed with a conidial suspension (1 × 106 conidia per ml) of the three isolates of C. acutatum. Noninoculated plants served as a control. Inoculated and control plants were covered with plastic bags to maintain high relative humidity conditions. All plants were maintained in growth chambers at 20 ± 1°C (12 h per day of fluorescent light). Six days after the artificial inoculation, plants developed typical symptoms on the leaves. C. acutatum was consistently reisolated from infected plants. The pathogenicity test was carried out twice. Sequencing of the internal transcribed spacer region of the rDNA and a portion of the β-tubulin gene were performed, and the obtained sequences were compared with those available in GenBank. Identification of the fungus as C. acutatum, therefore was confirmed. To our knowledge, this is the first report of the presence of C. acutatum on A. japonica in Italy. Although observed presently only in a few nurseries, the disease has the potential to spread, becoming more relevant in an area where rhododendron cultivation is economically important. Anthracnose on rhododendron has already been described in several countries (1,2).

Place, publisher, year, edition, pages
2004. Vol. 88, no 5, 572- p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-91185DOI: 10.1094/PDIS.2004.88.5.572AOAI: oai:DiVA.org:uu-91185DiVA: diva2:163834
Available from: 2003-12-19 Created: 2003-12-19 Last updated: 2013-07-01Bibliographically approved
In thesis
1. Approaches to Species Delineation in Anamorphic (mitosporic) Fungi: A Study on Two Extreme Cases
Open this publication in new window or tab >>Approaches to Species Delineation in Anamorphic (mitosporic) Fungi: A Study on Two Extreme Cases
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Since the beginning of mycology, studies of species concept in fungi have been mainly based on morphology, partially due to the history of mycology as part of botany. Current advances in biochemical and molecular research have provided mycologists with powerful tools that can be used for delineation of fungal taxa. Recently, an integrated approach to fungal taxonomy involving both morphological and molecular traits has found a wide application for identification of species, especially in anamorphic (mitosporic) fungi.

In this thesis, I have tried to use this approach for identification of species units in two rather unrelated groups of organisms. One of the case studies concerned Colletotrichum acutatum – a worldwide economically important plant pathogenic anamorphic fungus, which is exhibiting a high level of variation in both morphological and molecular features. This fungus has been intensively studied during the past decades, and several attempts have been made to find reliable markers to separate it from other closely related species of Colletotrichum. The second case studied in this thesis was Mycelia Sterilia – an artificial group of fungi, which are deficient in production of spores of any kind, therefore lacking the main morphological feature used for assigning them to any certain fungal taxon below class level. Due to this peculiarity, Mycelia Sterilia have usually been neglected, and currently there is no working species concept applicable to these fungi.

In this work, I have tried to clarify the relationships among C. acutatum and several other anamorphic (C. gloeosporioides and C. fructigenum) and teleomorphic (Glomerella acutata, G. cingulata and G. miyabeana) taxa that are closely related to each other. For this purpose, examination of morphological traits was employed in combination with comparison of DNA sequencing data from three loci and subsequent phylogenetic analysis. As a result, re-description of C. acutatum and separation of (at least) two new species was proposed.

For studies of Mycelia Sterilia, a large collection of sterile strains was screened in search for biologically interesting organisms. One novel pathogen has been found, and two plant growth promoting strains with antifungal properties were selected. Attempt for tentative identification of those fungi was made based on their morphological, physiological and molecular features. Sequencing of several genes and spacers of the ribosomal DNA array revealed that the plant pathogenic strain is closely related to the teleomorphic basidiomycete genus Campanella, and plant growth-promoting isolates were identified as belonging to the anamorphic ascomycete genus Phoma. However, assigning the sterile strains to any existing species was not possible.

The main conclusion of the thesis is that species in anamorphic fungi should be defined based on a combination of morphological and molecular methods, both equally important, involving as many aspects of fungal biology as is possible at our current state of knowledge.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 72 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 917
Biology, fungal taxonomy, Colletotrichum acutatum, Mycelia Sterilia, Phoma, Campanella, phylogeny, species concept in fungi, Biologi
National Category
Biological Sciences
urn:nbn:se:uu:diva-3902 (URN)91-554-5832-7 (ISBN)
Public defence
2004-01-28, Lindahlsalen, EBC, Norbyvägen 18 A, Uppsala, 10:00
Available from: 2003-12-19 Created: 2003-12-19 Last updated: 2011-03-04Bibliographically approved

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