Domenico Bertetti

First report of leaf blight on coral bells (Heuchera sanguinea) caused by Rhizoctonia solani AG 1A in Italy.

Heuchera sanguinea (Saxifragaceae), coral bells or alum root, is an herbaceous perennial used in parks and gardens and sometimes grown in pots for its heart-shaped leaves and upright panicles of bright red, tiny flowers produced in late spring. At the end of fall 2006, a leaf blight was observed on 50% of a crop of potted 45-day-old plants grown in a sphagnum peat/clay/perlite (70:20:10) substrate at temperatures ranging between 20 and 25°C in a nursery. Semicircular, water-soaked lesions developed on leaves just above the soil line at the leaf-petiole junction and later along the leaf margins. For several days, lesions expanded along the midvein until the entire leaf was destroyed. Blighted leaves turned brown, withered, clung to the shoots, and matted on the surrounding foliage. Mycelia were often seen on and suspended between leaves. Blight progressed up the plant from the leaves to the shoot tip. Affected plants often died leaving wide empty areas. Diseased tissue was disinfected for 1 min in 1% NaOCl, rinsed with sterile water, and plated on potato dextrose agar (PDA) amended with 100 μg/liter of streptomycin sulfate. A fungus with the morphological characters of Rhizoctonia solani was consistently and readily recovered, then transferred and maintained in pure culture (3). The isolates of R. solani obtained from affected plants were successfully anastomosed with tester isolate AG 1 (ATCC 58946). The hyphal diameter at the point of anastomosis was reduced, the anastomosis point was obvious, and cell death of adjacent cells was observed. Results were consistent with other reports on anastomosis reactions (1). Pairings were also made with tester isolates of AG 2, 3, 4, 5, 6, 7, and 11 with no anastomoses observed between the recovered and tester isolates. Sclerotia were of uniform size with a diameter from 0.4 to 4 mm and sometimes joined laterally. The description of sclerotia was typical for subgroup 1A Type 2 (2). For pathogenicity tests, the inoculum of R. solani was prepared by growing three isolates of the pathogen on PDA for 7 days. Plants of 30-day-old H. sanguinea were grown in 10-liter containers (6 plants per container) on a steam disinfested peat/clay/perlite substrate (70:20:10)). Inoculum consisted of an aqueous suspension of PDA and mycelium disks (1 cm2 of mycelium per plant) and was placed at the base of the plant stems and on leaves. Plants inoculated with water and PDA fragments alone served as control treatments. Three replicates were used. Plants were maintained in a growth chamber at 24°C with 12 h of light/dark. The first symptoms, similar to those observed in the nursery, developed 12 days after the artificial inoculation. R. solani was consistently reisolated from infected leaves and stems. Control plants remained healthy. The pathogenicity test was carried out twice with similar results. This is, to our knowledge, the first report of leaf blight of H. sanguinea caused by R. solani in Italy and probably in the world. References: (1) D. E. Carling. Grouping in Rhizoctonia solani by hyphal anastomosis reactions. In: Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease control. Kluwer Academic Publishers, the Netherlands, 1996. (2) R. T. Sherwood. Phytopathology, 59:1924, 1969. (3) B. Sneh et al. Identification of Rhizoctonia species. The American Phytopathological Society, St Paul, MN, 1991.

Sensitivity to Anilinopyrimidines and Phenylpyrroles in "Botrytis cinerea" in North-Italian Vineyards.

Several commercial vineyards, located in Piedmont (Northern Italy), were monitored in order to evaluate the sensitivity of Botrytis cinerea Pers., the causal agent of grey mould, to five classes of botryticides: benzimidazoles, dicarboximides, phenylcarbamates, anilinopyrimidines and phenylpyrroles. Strains of B. cinerea resistant to anilinopyrimidines were easily detected, particularly in 1999, a year characterized by high disease pressure, even in vineyards not sprayed with that class of fungicides. Fludioxonil-resistance, on the contrary, was not detected. Resistance to benzimidazoles and dicarboximides was at previous observed levels. For the first time, resistance to phenylcarbamates was detected in the field. Strains of B. cinerea showing multiple resistance to benzimidazoles, dicarboximides and anilinopyrimidines and maintaining a good level of virulence, as shown by tests carried out on wounded apples, are present in Italian vineyards. Strategies in the use of the botryticides are discussed, in order to avoid a loss of disease control.

First Report of Fusarium oxysporum Causing Wilt on Jade Plant (Crassula ovata) in Italy

During summer 2010, symptoms of a wilt disease were observed in a commercial farm in northern Italy on Crassula ovata (jade plant). First symptoms consisted of chlorosis and premature drop of still turgid leaves. As the disease progressed, leaves turned yellow and wilted before dropping off and the stem wilted, bent, and eventually rotted starting from the base. In some cases, the stem broke or the basal portion of the leaf rotted. Brown discolorations were observed in the vascular system. Of 10,000 plants, 65% (cv. Mini) and 5% of 600 plants (cv. Magical Tree) were affected. Premature dropping of leaves was more frequent on cv. Magical Tree. Using the Komadas Fusarium-selective medium, a fungus was consistently and readily isolated from symptomatic vascular tissues of plants belonging to both cultivars. Isolates obtained from both cultivars were purified, subcultured on potato dextrose agar (PDA), and single-spore cultures were obtained. On PDA, both isolates produced pale violet, abundant, aerial mycelium, felted in old cultures, with purple pigments in the agar. The isolates were grown on Spezieller Nährstoffarmer agar for characterization of macroconidia and microconidia (1). Both isolates produced sparse, 3 to 5 septate, nearly straight macroconidia measuring 30 to 56 × 3 to 5 (average 40 × 4) μm with a short apical cell and a foot-shaped basal cell. Sporodochia were not observed. Unicellular, oval-elliptical microconidia measuring 5 to 13 × 3 to 4 (average 8 × 3) μm were produced on short monophialides. Chlamydospores were abundant, single and sometime in pairs, terminal and intercalary, rough walled, and measured 6 to 9 μm. Such characteristics are typical of Fusarium oxysporum (3). The ITS region (internal transcribed spacer) of rDNA was amplified with primers ITS1/ITS4 (4) and sequenced. BLASTn analysis of an isolate from C. ovata cv. Mini (515 bp, Accession No. HQ682196) and C. ovata cv. Magical Tree (509 bp, Accession No. HQ682197) showed an E-value of 0.0 with F. oxysporum. For these sequences, pairwise alignment of EMBOSS (E.B.I. - The European Bioinformatics Institute) revealed identity and similarity of 99.0%. To confirm pathogenicity, tests were conducted on 5-month-old plants of cvs. Mini and Magical Tree. Plants (three per treatment) were inoculated by dipping roots in a 1 × 106 CFU/ml conidial suspension of the two isolates of F. oxysporum prepared from 10-day-old cultures grown on casein liquid medium (2), shaken (90 rpm) for 10 days at 24°C ± 1 (12-h fluorescent light, 12-h dark). Inoculated plants were transplanted into pots filled with steamed mix (sphagnum peat/perlite/pine bark/clay; 50:20:20:10) and maintained in a plant growth chamber at 25 ± 1°C under a regimen of 12 h per day of fluorescent light. Inoculated plants belonging to both cultivars showed typical first symptoms of Fusarium wilt after 13 days. In the following days, leaves dropped, stems wilted, and plants died. Noninoculated plants remained healthy. F. oxysporum was reisolated from inoculated plants. The pathogenicity test was conducted twice. This is, to our knowledge, the first report of F. oxysporum on C. ovata in Italy or worldwide. References: (1) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Professional, Ames, IA, 2006. (2) A. Minuto et al. Phytoparasitica 36:294, 2008. (3) B. A. Summerell et al. Plant Dis. 87:117, 2003. (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.

OUTBREAK OF POWDERY MILDEW CAUSED BY ERYSIPHE sp. ON EVENING PRIMROSE IN ITALY

Oenothera biennis, family Onagraceae, is a biennial species used as border and potted plant. In summer 2011, severe out- breaks of a powdery mildew were observed in a private garden near Biella (northern Italy). Leaves were covered with a dense white mycelium, especially on the adaxial surface, which was also present on stems, pedicels of flowers and bracts. Conidia were hyaline, ellyptical, borne singly, and measured 25.0-38.4×17.8- 25.4 (average: 31.5×21.0) μm. Germ tubes were produced termi- nally. Fibrosin bodies were absent. Conidiophores were erect, with a cylindrical foot cell measuring 18.0-49.4×7.5-9.6 (average: 30.9×8.4) μm, followed by 1-2 shorter cells, measuring 15.5- 35.0×8.8-12.8 (average: 22.5×10.5) μm. Chasmothecia were not observed. The ITS region of rDNA was amplified using primers ITS1/ITS4 and sequenced (Altschul et al., 1997) (GenBank ac- cession No. JQ288740). The amplified 603 bp product showed 98% similarity with a comparable sequence of Erysiphe pisi. To determine pathogenicity, diseased leaves of O. biennis were pressed against leaves of four healthy plants of the same host. Four plants of Pisum sativum were also inoculated. Controls con- sisted of four non-inoculated plants for each tested species. Plants were maintained at temperatures from 23 to 33°C. Symp- toms were reproduced only on inoculated plants of O. biennis. The pathogen was retained as Erysiphe sp. since P. sativum re- mained healthy. E. howeana was reported on O. biennis in several European countries (Braun, 1995) as well as in New Zealand, while E. polygoni was reported in the USA (Farr et al., 1989).

POWDERY MILDEW OF MICHAELMAS DAISY IN ITALY

Michaelmas daisy (Aster novi-belgii), family Asteraceae, is a herbaceous plant used in low maintenance gardens and for cut flower production. During summer 2011, three-year-old plants grown in a garden near Biella (northern Italy) showed symptoms of an unknown powdery mildew. Both leaf surfaces were covered with white mycelium that was also observed on stems and flower calyxes. Conidiophores were erect, with a cylindrical foot cell measuring 45-85×10-12 μm (average: 64×11 μm) followed by 1-2 shorter cells, measuring 11-36×6-16 μm (average: 22×11 μm). Conidia were hyaline, elliptical, borne in short chains and meas- ured 31-43×16-23 μm (average: 37×19 μm). Fibrosin bodies and chasmothecia were not observed. The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS1/ ITS4 and sequenced (Altschul et al., 1997) (GenBank accession No. JQ015394). The 558-bp amplicon had 95% homology with the sequence of Golovinomyces cichoracearum (AB077627). Path- ogenicity was confirmed by gently pressing diseased leaves onto leaves of five healthy A. novi-belgii plants. Five non-inoculated plants served as control. Plants were maintained at temperatures from 15 to 25°C. Ten days post inoculation, symptoms of pow- dery mildew developed only on inoculated plants. G. ci- choracearum (syn. E. cichoracearum) has been reported on A. novi-belgii from several countries, among which the USA (Farr et al., 1989) and Denmark (Mork et al., 2011). To the best of our knowledge, this is the first report of G. cichoracearum affecting A. novi-belgii in Italy.

First Report of Powdery Mildew Caused by Podosphaera fusca on Coreopsis lanceolata in Italy

Coreopsis lanceolata L. (Asteraceae) is an ornamental species grown in parks and gardens and very much appreciated for its long-lasting flowering period. During the summer and fall of 2006, severe outbreaks of a previously unknown powdery mildew were observed on plants in several gardens near Biella (northern Italy). Both surfaces of leaves of the affected plants were covered with dense white mycelia and conidia. As the disease progressed, infected leaves turned yellow and died. Mycelia and conidia also were observed on stems and flower calyxes. Conidia were hyaline, ellipsoid, borne in short chains (5 to 6 conidia per chain) and measured 33 × 20 (27 to 35 × 17 to 22) μm. Conidiophores, 68 × 11 (62 to 76 × 10 to 12) μm, showed the foot cell measuring 50 × 11 (38 to 58 × 10 to 12) μm, followed by one shorter cell measuring 18 × 12 (13 to 19 × 12 to 13) μm. Fibrosin bodies were present. Chasmothecia were spherical and amber with a diameter of 99 (93 to 105) μm. Each chasmothecium contained one ascus with eight ascospores. On the basis of its morphology, the causal agent was determined to be a Podosphaera sp. (1). The ITS region (internal transcribed spacer) of rDNA was amplified using primers ITS4/ITS6 and sequenced. BLASTn analysis (1) of the 531 bp obtained showed an E-value of 0.0 with Podosphaera fusca (3). The nucleotide sequence has been assigned GenBank Accession No. EF 442023. Pathogenicity was confirmed through inoculations by gently pressing diseased leaves onto leaves of healthy C. lanceolata plants. Three plants were inoculated. Three noninoculated plants served as the control. Plants were maintained in a greenhouse at temperatures ranging from 20 to 28°C. Twelve days after inoculation, typical symptoms of powdery mildew developed on inoculated plants. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on C. lanceolata in Italy. Species of Coreopsis were previously described as host to Erysiphe cichoracearum, Sphaerotheca macularis and Leveillula taurica and S. fusca (2,4). Voucher specimens are available at the AGROINNOVA Collection, University of Torino. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) U. Braun. A Monograph of the Erysiphaceae (Powdery Mildews). Cramer, Berlin, GDR, 1987. (3) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000 (4) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society. St Paul, MN, 1989.

First Report of the Presence of Albugo tragopogonis on Cineraria maritima in Italy

Cineraria maritima L. (synonym Senecio cineraria DC.), commonly known as dusty-miller, is grown in Italy for landscape use in parks and gardens. In the spring of 2001, severe outbreaks of a previously unknown disease were observed in commercial farms located in northern Italy. Leaves of infected plants showed several sori on the abaxial surface, progressing to the adaxial surface, and often in the interveinal areas. On the adaxial surface of leaves, chlorotic areas developed and eventually turned brown. Severely infected leaves wilted, but remained attached to the stem. Signs of the fungus were present as whitish and catenulate sporangia emerging from the sori. Sporangia, organized in chains, had an average diameter of 20.5 × 26.5 μm. On the basis of the microscopic observations, the causal agent of the disease was identified as Albugo tragopogonis. Pathogenicity was confirmed by inoculating leaves of healthy C. maritima plants with a sporangial suspension (5 × 102 sporangia per ml) obtained from infected plants. Noninoculated plants served as a control. Plants were kept covered with plastic bags for 72 h and maintained at 15°C. After 10 days, typical symptoms of white rust developed on inoculated plants starting from the basal leaves. Within 30 days, affected leaves were completely wilted. Microscopic examination of sporangia within sori verified the pathogen to be A. tragopogonis. No symptoms developed on the control plants. A. tragopogonis has been reported as the causal agent of white rust on several species belonging to the genus Senecio in the United States (1). In New Zealand, the presence of A. tragopogonis was reported on the genus Cineraria in 1959 (2). To our knowledge, this is the first report of the presence of white rust on Cineraria maritima in Italy. References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (2) J. M. Dingley. N. Z. J. Agric. Res. 2:380, 1959.