C. Cappelli

Sphingomonas melonis sp. nov., a novel pathogen that causes brown spots on yellow Spanish melon fruits

A polyphasic taxonomic study was performed on the phytopathogenic bacterial strains DAPP-PG 224(T) and DAPP-PG 228, which cause brown spot on yellow Spanish melon (Cucumis melo var. inodorus) fruits. Based on the presence of glucuronosyl ceramide (SGL-1) in cellular lipids, the results of fatty acid analysis and 16S rDNA sequence comparison, the strains had been identified as belonging to the genus Sphingomonas and as phylogenetically related to Sphingomonas mali, Sphingomonas pruni and Sphingomonas asaccharolytica. The levels of 16S rDNA sequence similarity of these three species to strain DAPP-PG 224(T) were respectively 98.0, 98.0 and 97.4%. DNA-DNA hybridization experiments between strains pathogenic on melon fruit and S. mali, S. pruni and S. asaccharolytica revealed < or = 16% relatedness. Based on these results, the two isolates studied are regarded as independent from the type strains of the three species mentioned above. Sphingomonas strains from melon fruits are recognized as forming a genetically and phenotypically discrete species and to be differentiated by phenotypic characteristics from all 29 named species of the genus. Thus, the name Sphingomonas melonis sp. nov. is proposed for the isolates from diseased melon fruits. The type strain is DAPP-PG 224(T) (= LMG 19484(T) = DSM 14444(T)). The G+C content of DNA of the type strain is 65.0 mol%.

Occurrence of Pseudoperonospora cubensis pathotype 5 on squash in Italy.

During the period of May to August 2002, typical symptoms of downy mildew were observed on squash (Cucurbita pepo L.) in both tunnel and open field cultivation in central Italy (Latium and Umbria). The disease spread rapidly and because the control measures used were not effective, growers suffered severe yield losses. Infected plants showed yellow spots on the upper leaf surface. Based on morphological features observed at ×10 to ×40 magnification, the pathogen was identified as Pseudoperonospora cubensis (Berk. & M.A. Curtis) Rostovzev. To verify the pathogenicity of the fungus, a sporangial suspension (1 × 104 sporangia per ml) was sprayed on leaves of squash plants with two expanded leaves, which were held in dark moist chambers at 20 ± 2°C for 48 h. Control plants were sprayed with sterile water. Inoculated and control plants were kept in a growth chamber at 24 ± 2°C with 14/10 h day/night cycles. Chlorotic spots and sporulation were observed on inoculated plants. The morphological features of the fungus obtained from the inoculated plants were identical to those from the original diseased plant. Previous observations of downy mildew in Italy suggested that squash was not susceptible (1). The physiological specialization among isolates of P. cubensis based on the compatibility of different cucurbit hosts (2) was not tested previously in Italy. To determine the pathotype of four fungal isolates obtained from squash cultivated in different localities, 10 plants per species of the cucurbit species (2) were inoculated with each isolate using the same procedure described for the pathogenicity test. Disease symptoms were detected on all inoculated hosts, including squash, suggesting that all the fungal isolates obtained from squash are pathotype 5. Only pathotype 5 is a common causal agent of downy mildew of squash and other cucurbit hosts. During the period of our observations, climatic conditions were unusually wet because frequent storms occurred during the summer providing favorable environmental conditions for the development of secondary spread. Today, it appears there are no commercially acceptable cultivars of squash resistant to downy mildew available to growers in Italy. References: (1) F. Ciccarese et al. Phytopathol. Mediterr. 29:14, 1990. (2) C. E. Thomas et al. Phytopathology 77:1621, 1987.

Vegetative Compatibility Grouping of Fusarium oxysporum f. sp. gladioli from Saffron

Fusarium corm rot of saffron (Crocus sativus L.), incited by Fusarium oxysporum f. sp. gladioli, causes severe yield losses in Italy. Major symptoms during flowering (October–November) include yellowing and wilting of shoots, basal stem rot and corm rot. Sixty-four isolates of F. oxysporum f. sp. gladioli, obtained from infected saffron crops located in Italy (Abruzzi, Tuscany and Umbria) and in Spain, were characterized by pathogenicity and vegetative compatibility. Chlorate-resistant, nitrate-nonutilizing (nit) mutants were used to determine vegetative compatibility among the isolates of the pathogen with the aim of examining the genetic relatedness among populations from different locations. All the isolates belonged to vegetative compatibility group 0340. Since saffron shares susceptibility to F. oxysporum f. sp. gladioli with other ornamental plants of the Iridaceae (Crocus, Gladiolus, Iris and Ixia), it is likely that a clone of the pathogen (VCG 0340) was introduced with other hosts and is responsible for the disease outbreak observed on saffron in Italy. Alternatively, or additionally, the clone of F. oxysporum f. sp. gladioli causing disease on saffron in other countries may have spread to the saffron fields in Italy through the import and dispersal of infested propagation material.

Occurrence of anthracnose caused by Colletotrichum malvarum on Althaea officinalis in Italy

The cultivation of medicinal plants is increasing in some areas of central Italy where the climate is suitable for organic farming and the production of high-quality plant products. During April and May 2003, plants of Althaea officinalis L. at the seedling stage (two-to-four true leaves) maintained in unheated greenhouses before their transplantation to open fields showed an unusual foliar disease. Necrotic leaf spots of variable shape and size were followed by a rapid wilting of leaves that frequently resulted in a blight of the young plants. Small leaf pieces showing symptoms were sampled, surface treated in 0.1% HgCl2 for 30 s, rinsed twice in sterile water, placed on potato dextrose agar (PDA) (pH 5.5) in petri dishes, and incubated for 7 days at 25 ± 2°C. Colletotrichum malvarum (Braun & Casp.) Southworth (1,2) was consistently recovered from affected tissues. The fungus produced dark colonies with whitish aerial mycelium and acervuli containing hyaline, cylindrical conidia (14 to 25 × 3 to 6 μm) on PDA. The pathogenicity of four fungal isolates was tested by inoculating two, true leaves of 10 plants (A. officinalis) with a conidial suspension (5 × 105 conidia ml-1) from a 10-day-old culture. Plants sprayed with water served as controls. All seedlings were placed in a greenhouse at 24± 2°C under natural light conditions and covered with plastic bags for the first 24 h. Each pathogenicity test was repeated one time. After 5 to 7 days, the inoculated seedlings showed small necrotic leaf spots identical to those observed under natural conditions. Affected leaf areas rapidly enlarged and within a few days, the young plants wilted. No symptoms appeared on the noninoculated controls. C. malvarum was consistently reisolated from the symptomatic test seedlings, whereas the fungus was never isolated from control plants. Standard seed health methods (agar plate and blotter) carried out on samples from the same seed lots used for the unheated greenhouse trials were negative for the presence of the pathogen. The occurrence of anthracnose may be attributed to windborne conidia of C. malvarum coming from infected wild malvaceae species and cultivated hosts grown in open fields in the neighborhood of seedling greenhouses. To our knowledge, this is the first report of C. malvarum on A. officinalis in Italy. References: (1) W. Brandenburger. Page 386 in: Parasitische pilze an gefäbpflanzen in Europa. Fisher Verlag, Stuttgart, Germany, 1985. (2) B. C. Sutton. The genus Glomerella and its anamoroph Colletotrichum. Pages 1-26 in: Colletotrichum, Biology, Pathology and Control. J. A. Bailey and M. J. Jeger eds. CAB International, Wallingford, U.K., 1992.

Rhizoctonia solani Kühn AG 2-1 on kohlrabi in Italy.

Rhizoctonia solani AG 2-1 was recorded in Central Italy on kohlrabi plants showing root and stem rot. After artificial inoculation the fungus caused damping-off of 7-day-old seedlings and root and stem rot of 4-month-old plants developed after 15 days of incubation. This seems to be the first record ofR. solani AG 2-1 on kohlrabi.