Interspecific and intraspecific competition in the potato cyst nematodes Globodera pallida and G. rostochiensis

The effects of interspecific competition between the potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis, under variable population conditions were examined. PCN-susceptible potato cultivars were inoculated with single- and mixed-species populations of PCN. There was a significant difference in species multiplication between single- and mixed-species populations. Globodera rostochiensis multiplication in mixed-species populations was significantly lower than single-species populations. Density-dependent trials showed a significantly greater increase in multiplication of G. pallida at low inoculation densities relative to G. rostochiensis. These results indicate that G. pallida has a negative effect on G. rostochiensis populations and is the more successful species when competing. A staggered inoculation trial showed that the greater competitiveness of G. pallida was not wholly attributed to its later hatch. Globodera pallida outcompeted G. rostochiensis regardless of the timing of inoculation; however, G. pallida multiplication was lowest when plants were simultaneously inoculated with both species.

First Report of Sclerotinia Blight Caused by Sclerotinia sclerotiorum on Fan Columbine (Aquilegia flabellata) in Italy

Fan columbine is a perennial garden species belonging to the family Ranunculaceae. During the spring of 2011, extensive wilting was observed on 5-month-old potted plants of Aquilegia flabellata grown in an experimental glasshouse belonging to the Center AGROINNOVA at Grugliasco (northern Italy). First symptoms included stem necrosis and darkening and withering of leaves. Plant wilt occurred a few days after the appearance of the first symptoms. Infected plants were characterized by the presence of soft, watery tissues. In the presence of high relative humidity, lesions became covered with a whitish mycelium and irregular, dark gray sclerotia (1.5 to 4.0 × 1.0 to 2.8, average 2.8 × 2.1 mm) were produced on the mycelium. Diseased tissue was surface sterilized for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 mg/l of streptomycin sulfate. Sclerotinia sclerotiorum (Lib.) de Bary (2) was consistently recovered from infected stem pieces. Sclerotia produced on PDA measured 2.0 to 7.0 × 2.0 to 5.0 (average 4.2 × 2.9) mm. The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS1F/ITS4 and sequenced. BLAST analysis (1) of the 575-bp segment showed a 100% homology with the sequence of S. sclerotiorum (EF091809). The nucleotide sequence has been assigned the GenBank Accession No. JN013184. Pathogenicity of one isolate obtained from sclerotia of infected plants was confirmed by inoculating three 6-month-old plants transplanted in 16-cm-diameter pots in a glasshouse in a sphagnum peat/pomix/pine bark/clay (50:20:20:10) mix. Inoculum that consisted of 3 g/l of substrate of sterile wheat kernels infested with mycelium and sclerotia was placed in the soil and around the base of each plant. Three noninoculated plants served as controls. Plants were maintained in a growth chamber at 21 ± 1°C and relative humidity >90%. The inoculation trial was carried out twice. All inoculated plants developed leaf yellowing within 15 days of soil infestation. White, cottony mycelium and dark sclerotia developed on stems and at the base of all inoculated plants. Eventually, infected plants wilted. Control plants remained symptomless. S. sclerotiorum was reisolated from the stems of inoculated plants. To our knowledge, this is the first report of S. sclerotiorum on A. flabellata in Italy. The disease has been previously reported on A. vulgaris in the United States (3) and A. glandulosa in Russia (4). The economic importance of this disease in Italy is currently limited. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) N. F. Buchwald. Kgl. Veterisk Landb. Aarssk. 75, 1949. (3) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrived from http://nt.ars-grin.gov/fungaldatabases/ , July 7, 2011. (4) P. M. Zhiboedov et al. Mikol. Fitopatol, 36:48, 2002.

First Report of Sclerotinia sclerotiorum on Argyranthemum frutescens in Italy

Paris daisy (Argyranthemum frutescens (L.) Sch. Bip.) is an economically important crop on the Riviera Ligure (northern Italy), where approximately 10 million plants per year are produced for export. In the winter of 2007, extensive wilting was observed on 5-month-old potted plants of A. frutescens grown in a commercial greenhouse near Albenga. First symptoms included stem necrosis, darkening and withering of leaves, and wilting of young buds. As stem and foliar necrosis progressed, infected plants wilted and died. Wilt occurred a few days after the appearance of the first symptoms. Infected plants were characterized by the presence of soft, watery tissues. Lesions became covered with a whitish mycelium and dark sclerotia were produced on the mycelium. Diseased stem tissue was surface sterilized for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 mg/l streptomycin sulfate. Sclerotinia sclerotiorum (Lib.) de Bary (2) was consistently recovered from infected stem pieces. Sclerotia produced on PDA measured 1.4 to 5.2 × 2.3 to 6.7 (average 3.3 to 4.2) mm. The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and then sequenced. BLAST analysis (1) of the 531-bp segment showed a 100% homology with the sequence of S. sclerotiorum. The nucleotide sequence has been assigned GenBank Accession No. EU 556701. Pathogenicity of two isolates obtained from infected plants was confirmed by inoculating 10 90-day-old plants for each isolate. Plants were grown singly in 18-cm-diameter pots maintained in a greenhouse under shade and were regularly irrigated and fertilized. Mycelium plugs 1 cm2 were excised from a 10-day-old PDA culture of both isolates and placed on the soil surface around the base of each plant. Ten noninoculated plants served as controls. Plants were maintained in a greenhouse under shade at temperatures ranging between 6 and 22°C (average 18°C) and relative humidity at >90%. The inoculation trial was carried out twice. All inoculated plants developed leaf yellowing by 22 days after inoculation. White, cottony mycelium and black sclerotia developed on stems and at the base of all inoculated plants. Eventually, infected plants wilted. Control plants remained symptomless. S. sclerotiorum was reisolated from the stems of inoculated plants. To our knowledge, this is the first report of S. sclerotiorum causing white mold on A. frutescens in Italy as well as worldwide. The economic importance of this disease can be considered limited at the moment. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997 (2) N. F. Buchwald. Kongl. Veterisk Landb. Aarssk. 75, 1949.

First Report of Southern Blight on Firewheel Tree, Bay Laurel, Bird of Paradise, Mediterranean Fan Palm, and Liverwort Caused by Sclerotium rolfsii in Italy

During the summer of 2006, a widespread blight was observed on 6-month-old potted plants of firewheel tree (Stenocarpus sinuatus Endl.) and 3-month-old potted plants of bay laurel (Laurus nobilis L.) growing in a nursery in eastern Sicily, Italy. On both species, symptomatic plants initially had sunken, tan lesions at ground level where white mycelia and small (1 to 2 mm in diameter), brown, spherical sclerotia typical of Sclerotium rolfsii Sacc. were formed. As the disease progressed, the mycelia extended up the stem and entire plants collapsed. A sudden wilting affecting 4-month-old potted seedlings of bird of paradise (Strelitzia reginae Aiton) and 5-month-old potted seedlings of Mediterranean fan palm (Chamaerops humilis L.) was occasionally detected in other greenhouses of the same nursery. Liverwort (Marchantia polymorpha L.) was abundantly present on the surfaces of the containers where these plants were grown. Circular and crescent-shaped patches as much as 100 cm in diameter were observed on the massed liverwort plants. In these patches, the liverwort died and sclerotia typical of S. rolfsii were dispersed on white mycelial strands. Symptomatic tissues of the ornamental plants and liverwort were surface disinfested in 1% NaOCl for 1 min, rinsed in sterile water, and plated on potato dextrose agar. Tissues consistently yielded S. rolfsii (teleomorph Athelia rolfsii (Curzi) Tu & Kimbrough) and typical sclerotia with internally differentiated rind, cortex, and medulla were produced within 6 or 7 days (3). Pathogenicity tests were performed by placing 30 sclerotia obtained from 10-day-old cultures in the soil below the crown portion on each of 2-month-old healthy seedlings of Stenocarpus sinuatus, L. nobilis, Strelitzia reginae, and C. humilis (20 seedlings per host). In addition, liverwort growing in 10 pots (7 cm in diameter) was inoculated with 30 sclerotia per pot. For each species, the same number of plants or pots served as control. All ornamental plants and liverwort were maintained in a growth chamber at 25 ± 1°C and enclosed for 7 days in polyethylene bags and then moved to a greenhouse where temperatures ranged from 24 to 28°C. The inoculation trial was repeated once. Symptoms of southern blight developed after 5 to 20 days on all inoculated plants of Stenocarpus sinuatus and sporadically (two to five plants) after 20 days on L. nobilis, Strelitzia reginae, and C. humilis. After 5 days, liverwort in all inoculated pots was colonized and plants died within 12 days. Control plants of all species remained symptomless. S. rolfsii was reisolated from symptomatic plants. S. rolfsii was reported for the first time in Sicily in 2004 on ornamental plants (2). Strelitzia reginae was previously reported as a host of Corticium rolfsii (synonym S. rolfsii) in Portugal (1). To our knowledge, this is the first report of S. rolfsii on Stenocarpus sinuatus, L. nobilis, and C. humilis. In addition, this is the first report of the susceptibility of M. polimorpha to S. rolfsii. Liverwort could provide a food source for the fungus in container-grown nursery plants. References: (1) M. R. de Sousa Dias and M. T. Lusas. Bol. Soc. Brot. 53:469, 1980. (2) G. Polizzi et al. Plant Dis. 88:310, 2004. (3) Z. K. Punja and A. Damiani. Mycologia 88:694, 1996.

First Report of White Mold Caused by Sclerotinia sclerotiorum on Iberis sempervirens in Italy

Iberis sempervirens (candytuft) is an ornamental plant that thrives in cool conditions, and its growth as a potted plant has been increasing in Liguria (northern Italy). In the spring of 2004, extensive chlorosis was observed on 10-month-old potted plants of I. sempervirens grown in a plastichouse on a commercial farm near Albenga in northern Italy. Initial symptoms included stem necrosis at the soil level and darkening of leaves. As stem and foliar necrosis progressed, infected plants wilted and died. Wilt occurred within a few days on young plants, characterized by the presence of soft, watery tissues, particularly on affected leaves. Symptomatic plants were found on many farms, with an average disease incidence of 5 to 10%. Necrotic tissues became covered with a whitish mycelium that produced dark sclerotia. The diseased stem tissue was surface sterilized for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm of streptomycin sulfate. Sclerotinia sclerotiorum (Lib.) de Bary (1) was consistently recovered from infected stem pieces. Sclerotia observed on infected plants measured 1.4 to 3.2 × 2.1 to 4.1 mm (average 2.1 to 2.7 mm). Sclerotia produced on PDA measured 1.2 to 4.2 × 1.4 to 6.1 mm (average 2.5 to 3.1 mm). Pathogenicity of three isolates obtained from infected plants and used in a mixture was confirmed by inoculating 10 single-potted 120-day-old plants grown in 18-cm diameter pots maintained outside under shade. Inoculum that consisted of 1 cm2 of mycelium excised from a 10-day-old PDA culture plate of each isolate was placed on the soil surface around the base of each plant. Ten noninoculated plants served as control. The inoculation trial was repeated once. All plants were kept at temperatures ranging between 8 and 17°C (average 12.5°C) and watered as needed. All inoculated plants developed symptoms of leaf yellowing within 18 days, soon followed by the appearance of white mycelium and sclerotia, and then eventual wilt. Control plants remained symptomless. S. sclerotiorum was reisolated from the stems of inoculated plants. S. sclerotiorum has been previously reported only on I. umbellata (2). To our knowledge, this is the first report of white mold on I. sempervirens in Italy as well as worldwide. The economic importance of this disease can be considered low at the moment in the case of field-grown plants. References: (1) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift 75, 1949. (2) J. M. Waterston. Report of the Plant Pathologist, 1946. Dep. Agric. Bermuda, 1947.

First Report of Southern Blight Caused by Sclerotium rolfsii on Lily in China

Lily (Lilium spp.) is an economically important cut flower cultivated in China. The soilborne fungus, Sclerotium rolfsii, is a major pathogen on many plants. During July 2005, severe basal stem rot and bulb rot symptoms were observed on an oriental lily cultivar (Sorbonne) in some commercial fields in northern Kunming (China). Disease incidence ranged from 20 to 30% across fields. Leaves of infected plants were chlorotic initially. As the disease progressed, stems and bulbs rotted and plants wilted. In the presence of abundant moisture, a white mycelium occurred on infected tissues. White or light-to-dark brown sclerotia (1 to 3 mm in diameter) developed from mycelium. Fungal isolates from infected bulbs grown on potato dextrose agar (PDA) produced white mycelia and 1- to 2-mm diameter dark brown sclerotia. Sclerotia were nearly round with smooth surfaces and distributed over the entire colony. Isolates were identified as S. rolfsii on the basis of mycelial characteristics and color, size, and distribution of sclerotia. Pathogenicity was tested in the greenhouse on oriental lily cv. Sorbonne grown in pots (1 plant per pot, five replicates). Inoculum that consisted of 1 g per pot of wheat kernels infested with mycelium and sclerotia was placed at the base of each inoculated plant. Five noninoculated plants served as controls. The inoculation trial was repeated once. After inoculation, all plants were covered with a polyethylene bag for 72 h and kept at temperatures ranging between 25 and 27°C. Inoculated plants developed symptoms of leaf yellowing within 12 days, soon followed by the appearance of white mycelium and sclerotia, and then eventually wilted. Control plants remained symptomless. S. rolfsii was reisolated from inoculated plants. To our knowledge, this is the first report of southern blight caused by S. rolfsii on lily in China. Infection of lily bulbs by S. rolfsii may cause losses in production fields in China, and the presence of infected bulbs may also interfere with bulb shipment.

First Report of Southern blight Incited by Sclerotium rolfsii on Dichondra repens in Italy

Kidney weed (Dichondra repens) is increasingly used for low maintenance turf in Italy, particularly for gardens and parks in areas characterized by mild climate. During September 2003, on the D. repens turf of a private garden located near Imperia (northern Italy), yellow, circular areas as much as 60 cm in diameter appeared with the grass becoming chlorotic and thin. A ring of the patch at its periphery exhibited a reddish brown color and eventually died. An area of green grass remained in the center of the patch. Rings of dead grass enlarged rapidly during hot, humid weather. In the presence of abundant moisture, a white mycelium occurred on the dying grass at the periphery of the ring. White or light-to-dark brown sclerotia (1 to 3 mm in diameter) developed from mycelium on the dead grass. The diseased tissue was disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar amended with 100 mg/l of streptomycin sulphate. Sclerotium rolfsii was consistently isolated from infected plants. Pathogenicity of three isolates obtained from infected plants was confirmed by inoculating healthy D. repens turf (1 m2 plots and three replicates). Inoculum that consisted of wheat kernels infested with mycelium and sclerotia of each isolate was placed on the soil surface. Noninoculated plots served as controls. The inoculation trial was repeated once. Turf was covered with a plastic film for 7 days, kept at temperatures ranging between 22 and 25°C, and watered as needed. Inoculated plants developed symptoms of leaf yellowing within 11 days, soon followed by the appearance of white mycelium and sclerotia, and then eventually wilted. Control plants remained symptomless. Sclerotium rolfsii was re-isolated from inoculated plants. To our knowledge, this is the first report of S. rolfsii on D. repens in Italy. This disease has been reported on kidney weed in several countries such as the United States (3), Brazil (1), and India (2). References: (1) M. Menezes and J. A. A. Lima. Fitossanidade 1:18, 1974. (2) K. Ranganathan and N. Shanmugam. Indian Phytopathol, 27:113, 1974. (3) J. D. Smith et al. Fungal Diseases of Amenity Turf Grasses. E & F.N. Spon, London, 1989.

First Report of White Mold Caused by Sclerotinia sclerotiorum on Thymus × citriodorus in Italy

Thymus × citriodorus is well known for the citrus aroma released by its leaves and is grown as a potted plant in northern Italy. This species is widely used in gardens and landscapes and for culinary purposes. In the Liguria Region alone, 1.5 million plants are grown. In the winter of 2002, extensive chlorosis was observed on potted plants of Thymus × citriodorus cv. Silver Queen grown outdoors on commercial farms near Albenga. Initial symptoms included stem necrosis at the soil level and darkening of leaves. As stem necrosis progressed, infected plants wilted and died. Wilt, characterized by the presence of soft and watery tissues, occurred within a few days on young plants. Necrotic tissues became covered with whitish mycelium that produced dark sclerotia. Sclerotinia sclerotiorum (Lib.) de Bary (1) was consistently recovered from infected stem pieces of Thymus × citriodorus. The diseased stem tissue was disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm of streptomycin sulfate. Sclerotia produced on PDA were ellipsoid and measured 5.2 to 4.4 × 2.1 to 1.5 mm (average 3.5 × 3.0 mm). Pathogenicity of three isolates obtained from infected plants was confirmed by inoculating 30-day-old plants grown in 14-cm-diameter pots in a screenhouse. Inoculum that consisted of wheat kernels infested with mycelium and sclerotia of each isolate was placed on the soil surface around the base of each of 10 plants. Noninoculated plants served as controls. The inoculation trial was repeated once. All plants were kept at temperatures ranging between 5 and 26°C and watered as needed. Inoculated plants developed symptoms of leaf yellowing within 13 days, soon followed by the appearance of white mycelium, and eventually wilted. Control plants remained symptomless. White mycelium and sclerotia developed on infected tissues and S. sclerotiorum was reisolated from inoculated plants. To our knowledge, this is the first report of white mold of Thymus × citriodorus caused by S. sclerotiorum. The economic importance of this disease for the crop can be considered low. Reference: (1) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift, 1949.

First Report of White Mold Caused by Sclerotinia sclerotiorum on Hutchinsia alpina in Italy

Hutchinsia alpina (Chamois cress), a plant belonging to the Brassicaceae family, is cultivated as a potted ornamental plant in Italy. In the winter of 2002, leaves and stems of plants grown in pots (14-cm diameter) in commercial farms near Albenga (northern Italy) developed soft and watery tissues covered with whitish mycelium at the soil line. As necrosis progressed, infected plants wilted and died. Dark sclerotia developed on infected tissues. Because of high planting density, the infection spread very rapidly. Sclerotinia sclerotiorum was consistently recovered from infected stem pieces of H. alpina disinfested 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm of streptomycin sulfate. Sclerotia produced on PDA were ellipsoid and measured 1.3 to 9.3 × 1.3 to 4.5 mm (average 3.9 × 2.8 mm) (1). Pathogenicity of three isolates obtained from infected plants grown in a single greenhouse was confirmed by inoculating 90-day-old plants grown in pots (14 cm). Inoculum that consisted of wheat kernels infested with mycelium and sclerotia of each isolate were placed on the soil surface around the base of each of 10 plants. Plants treated with plain wheat kernels served as controls. The inoculation trial was repeated once. All plants were kept at temperatures ranging between 5 and 26°C and watered as needed. Inoculated plants developed symptoms of leaf yellowing, followed by the appearance of white mycelium within 15 days, and eventually wilted while control plants remained symptomless. White mycelium and sclerotia developed on infected tissues, and S. sclerotiorum was reisolated only from inoculated plants. To our knowledge, this is the first report of white mold on Hutchinsia alpina caused by S. sclerotiorum. Reference: (1) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift, 1949.

First Report of White Mold Caused by Sclerotinia sclerotiorum on Blue Marguerite (Felicia amelloides) in Italy

Felicia amelloides (Asteraceae family), also known as blue marguerite, is cultivated as a potted plant in Italy and increasingly used for ornamental purposes. In winter 2002, plants grown outdoors in 14-cm-diameter pots (2 liters) in commercial farms near Albenga (northern Italy) showed leaf yellowing. At the soil level, soft and watery tissues covered with whitish mycelium were evident. Later, dark brown sclerotia differentiated from the mycelium. As necrosis progressed, infected plants wilted and died. Sclerotinia sclerotiorum (1) was consistently recovered from infected stem pieces of F. amelloides that were disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm of streptomycin sulfate. Sclerotia produced on PDA were ellipsoid and measured 1.3 to 6.1 × 1.1 to 3.3 mm (average 2.9 × 2.3 mm) (2). Pathogenicity of three isolates (used as a mixture and obtained from infected plants from the same farm) was confirmed by inoculating 90-day-old plants grown in 14-cm-diameter pots. Inoculum that consisted of wheat kernels infested with mycelium and sclerotia of each isolate was placed on the soil surface around the base of each of 20 plants. Ten noninoculated plants served as controls. The inoculation trial was repeated. All plants were kept outdoors at temperatures ranging between 5 and 26°C and watered as needed. All inoculated plants developed symptoms of leaf yellowing, followed by the appearance of white mycelium within 15 days, and then eventually wilted. Control plants remained symptomless. White mycelium and sclerotia developed on infected tissues, and S. sclerotiorum was reisolated from inoculated plants. To our knowledge, this is the first report of white mold of F. amelloides caused by S. sclerotiorum in Italy as well as elsewhere in the world. References: (1) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift, 32:75, 1949. (2) C. M. Messiaen et al. Les Maladies des Plantes Maraichères. INRA, Paris, 1991.