Genetic variability, chemotype distribution, and aggressiveness of Fusarium culmorum on durum wheat in Tunisia

Fusarium culmorum is the most commonly reported root rot pathogen in Tunisian durum wheat. Isolates of the pathogen from four durum wheat growing areas in the north of Tunisia were analyzed for their chemotypes. Two chemotypes were detected at unequal abundance (96% of 3-ADON and 4% of NIV). Distribution of a SNP mutation located at the position 34 bp after the first exon of the EF-1\u3b1 partial sequence was analysed, to verify whether the haplotype was specifically associated to Fusarium root rot. A and T haplotypes were homogeneously distributed in three different Tunisian regions (Mateur, Beja and Bousalem) but not for the region of Bizerte, from which greatest number of A haplotype strains were detected. The isolates were tested for their virulence under glasshouse conditions, and a mean of 91% of crown and root infection was observed. Chemotype influenced virulence, but there was no significant influence of the geographical origin or haplotype on virulence. The distribution of three inter simple sequence repeats (ISSR) was examined, to better understand the structure of F. culmorum populations in Tunisia. A total of 27 fragments were obtained with eight polymorphic bands. Cluster analysis showed a high level of similarity between isolates. Analysis of molecular variance confirmed that there was little genetic differentiation among F. culmorum strains from different locations

Identification of 16SrII-E Phytoplasmas in Calendula arvensis L., Solanum nigrum L. and Chenopodium spp.

Epidemiological surveys were performed in Northern Sardinia (Italy) in a 10-year-old vineyard affected by \u201cBois noir\u201d disease. Samples collected between May and October 2003 from chlorotic and stunted weeds belonging to 14 different taxonomic groups were indexed molecularly for detection of phytoplasmas. Nested polymerase chain reaction (PCR) assays using primers specific for the phytoplasma 16SrDNA gene showed three of six Calendula arvensis, one of two Solanum nigrum, and one of seven Chenopodium spp. assayed positive. Restriction fragment length polymorphism analyses and sequencing of amplified 16SrDNA fragments identified a putative phytoplasma in the ribosomal subgroup 16SrII-E. Further characterization of the rps3 gene, coding a ribosomal protein, confirmed the identification. However, the weeds and leafhopper species collected in the vineyard tested negative by PCR assays for the Stolbur phytoplasma, the causal agent of \u201cBois noir\u201d. This is the first report of a phytoplasma of the 16SrII-E subgroup infecting C. arvensis, S. nigrum, and Chenopodium spp

Myrtus communis: nuovo ospite di fitoplasmi in Sardegna.

Myrtus communis L., a bushy species of Mediterranean maquis, covers thousands of hectares in Sardinia (Italy). It is found from the coast to the interior of the island and in different soils and climatic zones. The berries and the leafy biomass are used in the food industry and, in the present case in the production of liquors. These liquors are Red Mirto, which is made from cold infusions of the berries in hydro-alcoholic solution, and White Mirto, which is made in the same way but using the young leaves. These products are very popular with around three million bottles a year being sold, and have a growing market. Given the species importance for the regional economy, many studies have been made in recent decades which have increased our knowledge of the process of domestication by defining the best cultivation techniques. Nowadays many cultivars which have been selected for their productive characteristics are available in the nurseries. In this context the sanitary status of the plants is of great importance. In 2003, during field studies comparing the performance of different cultivars, a severe series of symptoms was observed. The syndrome, although prevalent in certain cultivars, affected the majority of the plants, and was characterised by significant vegetative anomalies. These were a yellowing of the leaves showing also witches\u2019-broom aspects, and strong microphyllia. The basal vegetation was prostrate and abnormally striped. As the epidemic developed, the previously mentioned alterations quickly spread from some plants to other on the rows, and, over a period of two years, to the entire plot, although the seriousness of the infection varied from plant to plant. These symptoms could be related to phytoplasmas infection resembling those mentioned by Camele et al. (1996). Studies aimed to assess the phytoplasmas presence were carried out in the autumn of 2004 on six samples of vein tissue from affected plants collected from two different fields. The plant DNA was extracted and amplified in direct PCR with universal primers (P1/P7), in nested PCR with F1/B6, and in a second nested PCR with R16F2n/R2 (Gundersen et al., 1996). The amplified products digested with TruI allowed to identify 16SrIII-B phytoplasma (reference strain Clover yellow edge) on one sample and 16SrX phytoplasma group, on the others. To confirm these results the F1/B6 products were further amplified in nested PCR with R16(X)F1/R1. The RFLP analyses with RsaI and SspI, allowed to identify the phytoplasmas as belonging to the 16SrX-A subgroup (reference strain Apple proliferation). A further nested PCR with R16(I)F1/R1 on the F1/B6 template, after RFLP with TruI, showed that 16SrXII-A phytoplasmas were present, in mixed infection with 16SrX-A, in two samples. This is the first time, as far as we know, that phytoplasmas 16SrIII-B, 16SrX-A and 16SrXII-A are detected on Myrtus communis. Epidemiological and molecular studies are in progress towards designing the possibility to contain further disease spreading

Indagine epidemiologica in un vigneto affetto da \u201clegno nero\u201d nel nord-Sardegna.

An epidemiological study aimed to identify potential insect vectors was carried out on a Vermentino and Chardonnay vineyard in north Sardinia (Italy) which was affected by \u201cBois noir\u201d phytoplasma disease. The Auchenorrhyncha populations were monitored from April to November in 2003 and 2004, using sweep net. The following insects were captured: Delphacidae (Laodelphax striatellus), a Cercopidae, Cicadellidae Deltocephalinae (Agallia ribauti, Eupelix cuspidata, Euscelis lineolatus, Euscelidius variegatus, Exitianus taeniaticeps, Goniagnathus guttulinervis, Neoaliturus fenestratus, N. guttulatus, Phlepsius intricatus, Psammotettix alienus and Tamnotettix zelleri) and Typhlocybinae (Empoasca vitis and Zyginidia scutellaris). In 2003 the molecular analyses (PCR and RFLP), carried out on insects samples, were aimed to assess the presence of the 16SrXII phytoplasma group, while in 2004 the detection was also extended to other groups. In total, 121 DNA samples belonging to 9 species of leafhoppers were amplified and digested with the MseI restriction endonuclease. In 2003 the DNA was extracted and amplified in direct PCR with the universal primers R16F2/R2, then a nested PCR with the specific primers R16(I)F1/R1 (Lee et al., 1995) was carried out. The amplified products were digested with the MseI restriction endonuclease, electrophoresed in agarose gel at 2% and visualised in a GEL DOC. In 2004 the extracted DNA was amplified in direct PCR with P1/P7, followed by two nested-PCR. The primers used in the first round were F1/B6 and in the second R16F2/R2 (Duduk et al., 2004). The amplified products were digested with TruI, RsaI and SspI, and then after electrophoresis in polyacrylamide gel at 5%, were visualised in an UV transilluminator. Results showed that the following species were infected: G. guttulinervis, in September was infected by a 16SrXII-A phytoplasma, Stolbur group (Garau et al., 2004); E. lineolatus in the preimaginal state in May and in the adult form in June and L. striatellus in October were infected by a 16SrI-C phytoplasmas, Aster yellows group. P. alienus was infected in different samples by phytoplasmas 16SrI-C and 16SrI-B. A Cercopidae was positive to 16SrX-A phytoplasmas, Apple proliferation group, in July. P. alienus is here reported as a new natural host for two aster yellows phytoplasma subgroups, 16SrI-C and 16SrI-B. Preliminary detection on samples from Chardonnay plants showed presence of 16SrI-B phytoplasmas, which indicate that the grapevine is probably involved in the lifecycle of this prokaryote in this specific environment. No positive results were obtained from spontaneous flora for the pathogens under investigation

Elisa for the detection and identification of grapevine viruses

National audienc

Molecular identification of phytoplasmas infecting myrtle plantations in Sardinia (Italy).

Myrtus communis is a bushy species of the Mediterranean area that produce very popular liquor: Red mirto and White mirto. Preliminary studies in North Sardinia, resulted in the observation of a severe symptomatology associated with phytoplasma presence. These studies continued, and recently a total of 33 symptomatic plants belonging to different cultivars in two plantations were mapped and repeatedly tested using molecular methods. Phytoplasmas belonging to the 16SrI, 16SrII-F, 16SrIII, 16SrV-A, 16SrX-A, and 16SrXII-A subgroups were identified. Molecular assays on potential insect vectors showed that 16SrX-A+16SrI-B, 16SrXII-A and 16SrIII subgroups were present