M. Tessitori

Grape and environmental mycoflora monitoring in old, traditionally cultivated vineyards on Mount Etna, southern Italy

BACKGROUND Grape contamination by several fungal species occurs during a vineyards preharvest and harvest. Agronomic management and microclimatic conditions can affect fungi occurrence and epidemiology, thus explaining qualitative differences in mycoflora composition, including the presence of phytopathogenic or mycotoxigenic fungi. In this study a two-year grape, air and soil mycoflora monitoring programme was undertaken in vineyards on Mount Etna (eastern Sicily, Italy). The mycoflora composition was investigated at pea berry and veraison phenological phases from air and soil and at ripening from sample grapes. RESULTS Mycoflora in air and soil varied according to the phenological stage. In the air samples, penicillia were dominant over aspergilli at the pea berry phase, but their ratio was inverted at early veraison. Black aspergilli (BA) were isolated from the vine environment and grape samples, where BA were represented mainly by Aspergillus niger aggregate, which showed no or low ochratoxin A (OTA) production. Aspergillus carbonarius was either not identified or identified at low frequency, although most of the isolates produced OTA. CONCLUSION Monitoring focused on the environmental mycoflora composition and highlighted the good health profile of various Sicilian autochthonous grape cultivars. In addition, data suggest that the lower relative humidity occurring at the highest altitudes reduces BA incidence.

Bois noir phytoplasma variability in a Mediterranean vineyard system: new plant host and putative vectors

The presence of Bois noir phytoplasma (BNp, Stolbur, 16SrXII-A) in Sicily, one of the most important Italian grape-producing regions, has been known since 1996, but its epidemiology and distribution in the region have been studied only recently. Grapevines and weeds showing symptoms of phytoplasma infection were collected in an organic Chardonnay vineyard, chosen as model vineyard, and tested to verify BNp presence. Leaf- and plant-hoppers were also captured in the same field and included in the analysis. Plant and insect infections were assessed by nested PCR with universal and group-specific (16SrI and –V) phytoplasma primer pairs. BNp was detected in the weed species Erigeron bonariensis, which was then determined as a new natural host of this phytoplasma, and in several Auchenorrhyncha species besides Hyalesthes obsoletus, which can be regarded as new potential vectors. To further evaluate the genetic variability of BNp among host plants and potential vectors, PCR-RFLP of the Stolbur phytoplasma-specific vmp1 gene was carried out. The V1 profile was the most representative, other profiles (V4, V9, V10 and V11) were also detected.

Polygala myrtifolia as a New Natural Host of Cucumber mosaic virus

Cucumber mosaic virus (CMV), Tomato spotted wilt virus (TSWV), and Impatiens necrotic spot virus (INSV) are among the most important viral pathogens of ornamental plants (1). Polygala myrtifolia L. (myrtle-leaf milkwort), originating from South Africa, and a member of the Polygalaceae, was recently introduced in Italy as a cultivated ornamental shrub for its fast and attractive free-flowering growth and drought-resistant characteristics. It can become an invasive plant and is now considered a serious problem in coastal areas of Australia where it was introduced as a garden plant. In Italy, P. myrtifolia is propagated by cuttings in commercial nurseries during the summer. In the winter of 2002, plants of P. myrtifolia growing in pots in an ornamental nursery in Sicily showed virus-like mosaic and malformation of leaves that appeared lanceolate with a lack of flowering. Leaf tissue was analyzed by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with polyclonal antisera to CMV, TSWV (Lettuce type), and INSV. Positive ELISA results were obtained only with the CMV polyclonal antisera. Complete remission of symptoms was observed on new flushes after pruning and incubation of infected plants at warm temperatures (30 and 20°C, day and night, respectively). This evidence led to the hypothesis that the disease or virus was disseminated by transportation and propagation of plants without visible symptoms during the hot season. A survey was also performed in two historical gardens of Catania (Sicily) where a group of apparently healthy P. myrtifolia plants, from the previously mentioned ornamental nursery in Sicily, were introduced as a single specimen or to form a hedge. These plants showed the same leaf malformations and mosaic symptoms observed in the nursery. DAS-ELISA confirmed the presence of CMV but not TSWV and INSV. To our knowledge, this is the first report of CMV on P. myrtifolia and it adds a new host to over 1,000 species (85 plant families) infected by this virus. Reference: (1) M. L. Daughtrey et al. Plant Dis. 81:1220, 1997.

Apscaviroids Infecting Citrus Trees

Abstract Of the seven known citrus viroids, four are apscaviroids: citrus bent leaf viroid (CBLVd), citrus dwarfing viroid (CDVd), citrus viroid V (CVd-V), and citrus viroid VI (CVd-VI). Two (CDVd and CVd-V) are restricted to citrus, while CBLVd naturally infects hop and is also experimentally transmitted to avocado, and CVd-VI is present in natural infections of persimmon. The economic impact of these viroids on citrus is not only due to the direct damage caused by their specific diseases, but also to the synergistic effect of coinfection with other viroids. CDVd differs from the other citrus apscaviroids in that it causes reduction in size in susceptible hosts without any detrimental effects. It is used to obtain dwarfed trees for high-density plantings in several countries. CBLVd, CDVd, and CVd-V are reported in almost all citrus-growing countries, while CVd-VI has only been reported in Japan.

Citrus psorosis virus Bark Scaling on Tarocco Sweet Orange

Despite the wide distribution of vein flecking of citrus leaves in Italy, psorosis bark scaling has been reported only on Navelina sweet orange (Citrus sinensis L.), and Thompson and Washington navel oranges (1). Infection has not been found on any local sweet orange cultivars. Among these is Tarocco, a sweet orange cultivar that originated in Sicily, is very common because of the high fruit quality, has an attractive fruit appearance, and has blood-red pigmented flesh. In April 2001, classic psorosis bark scaling symptoms were observed on the main limbs of 10-year-old Tarocco trees grafted on sour orange rootstock, originally obtained by topworking Clementine (C. reticulata Blanco) trees with scions collected from 19-year-old Tarocco trees with no bark scaling at that time. The symptomatic trees first displayed one or two isolated circular patches of scales with gumming on the main or secondary limbs. As the disease progressed, the number of patches increased and coalesced to form bigger scales, resulting in bark flaking. Approximately 15% of trees in the field showed different stages of the disease. All of the affected trees showed vein flecking of young leaves. A leaf pattern was also present in a few plants without bark symptoms. Bark symptoms were correlated with the presence of Citrus psorosis virus (CPsV). Samples (110 representing 10% of the total number of trees in a field located in the area of Catania, Sicily) were collected during the spring flush using a W-pattern sampling method and tested by double-antibody sandwich enzyme-linked immunoassay (DAS-ELISA) (monoclonal antibody [MAb] PS29) (2). Of trees tested, 14% showed bark scaling, and 86% were symptomless. All symptomatic plants were tested and 70% of symptomless trees were positive based on DAS-ELISA. To confirm DAS-ELISA results, 10 field samples were also tested by bioassay on indicator plants (Navelina sweet orange ISA 315 and Pineapple sweet orange), triple-antibody sandwich enzyme-linked immunoassay (TAS-ELISA), and immunosorbent electron microscopy (ISEM) with a different antiserum (MAb 13C5). DAS-ELISA-positive samples produced vein flecking on indicator plants, were positive based on TAS-ELISA, and contained typical CPsV particles based on ISEM (R. G. Milne, IFA, CNR, Turin). To our knowledge, this is the first demonstration of psorosis bark scaling reaction of Tarocco sweet orange due to CPsV infection. References: (1) A. Catara et al. Proc. Int. Soc. Citri. 1:426, 1981. (2) M. Tessitori et al. Proc. 15th Conf. IOCV, IOCV, Riverside. In press.