First Report of Leaf Spot Caused by Cladosporium herbarum on Centaurea solstitialis in Greece

Abstract

Centaurea solstitialis L. (yellow starthistle), family Asteraceae, an invasive weed in California and the western United States, is targeted for biological control. In the summer of 2003, an epidemic of unknown etiology on dying C. solstitialis plants was observed near Kozani, Greece (40°22′07″N, 21°52′35″E, elevation, 634 m). Plants had necrotic light brown leaf spots on the lower leaves and the decurrent leaf bases along the stems. Often, necrotic lesions extended along the stems to the capitula. Virtually all plants in a solid stand of C. solstitialis (approximately 0.5 ha) showed disease symptoms. Diseased plants were collected, air dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. On the basis of culture growth (45-cm diameter after 2 weeks at 25°C on malt extract agar), fungal morphology (1), and comparison with 21 internal transcribed spacer sequences in GenBank, the putative causal organism was identified as Cladosporium herbarum (Pers.:Fr.) Link. (teleomorph = Davidiella tassiana (De Not.) Crous & U. Braun). Sixteen C. solstitialis plants in the rosette stage and 16 plants in the bolted stage were inoculated with an aqueous suspension of spores (106 conidia ml-1) and placed in an environmentally controlled chamber at 25°C with 8 h of dew and 12 h of light daily. Plants in the rosette stage were resistant, but the fungus was very aggressive on bolted plants. Within 4 to 6 days of inoculation, necrosis developed on leaves and stems and then spread up the stems to the capitula, often resulting in plant death. The fungus also infected developing flowers. Cladosporium herbarum was reisolated from each of the 16 bolted C. solstitialis plants in two separate tests at the FDWSRU and from all bolted inoculated plants at the European Biological Control Laboratory (EBCL) in Greece. In the greenhouse at the EBCL, the pathogen readily spread to (and was isolated from) another 10 noninoculated C. solstitialis plants in close vicinity to the inoculated C. solstitialis plants. Results of host range tests will establish if this isolate of Cladosporium herbarum has the potential as a biological control agent of C. solstitialis in the United States and does not pose a threat to other Centaurea spp. used in horticulture. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 863446). Live cultures are being maintained at the FDWSRU and EBCL, Greece. To our knowledge, this is the first report of a disease caused by Cladosporium herbarum on C. solstitialis. Reference: (1) M. H. M. Ho et al. Mycotaxon 72:115, 1999.

Morphological, molecular characterization, plant pathogenicity and biocontrol of Cladosporium complex groups associated with faba beans

“…Twenty-six strains of four species of Cladosporium , collected from diseased leaves and pods of Vicia faba , were tested for their pathogenicity effect on Vicia faba seedlings as method described with Berner et al 26 . Vicia faba seeds were grown in a glasshouse.…”

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“…The re-inoculation test of pathogenicity was done by the method according to Berner et al (2007), the pathogen was injected on PDA media and incubated at 28 ℃ for 11 days. The harvested conidia were suspended in sterilized water at 1 x 10P 6 P Conidia/ ml, the sweet melon fruits were sprayed by the conidial suspension then covered with bags and incubated at 28℃ for two weeks.…”

Leaf spot disease of Hyoscyamus muticus (Egyptian henbane) caused by Cladosporium herbarum

“…Perelló et al (2003) reported the infection of wheat leaves by m Disease symptoms on the leaves of H. muticus inoculated with a conidial suspension prepared from a single-spore isolate of C. herbarum from a diseased H. muticus plant C. herbarum in Argentina. The fungus also causes leaf spot disease of Centaurea solstitialis in Greece (Berner et al 2007) and Caltha leptosepala (marsh marigold) in North America (Johnson et al 2008). In Egypt, C. herbarum causes leaf spot disease in Cleome amblyocarpa, Haplophyllum tuberculatum, and Pluchea dioscorides, which grow naturally in the Mediterranean coastal area (El Naggar and Abdel-Hafez 2003).…”

“…Pathogenicity was tested by the inoculation method described by Berner et al (2007). The isolate was grown on PDA.…”