During a survey conducted in October 2005, cucurbit leaf samples showing virus-like symptoms were collected from the major cucurbit-growing areas in Tunisia. DAS-ELISA showed the presence of Moroccan watermelon mosaic virus (MWMV, Potyvirus), detected for the first time in Tunisia, in samples from the region of Cap Bon (Northern Tunisia). MWMV isolate TN05-76 (MWMV-Tn) was characterized biologically and its full-length genome sequence was established. MWMV-Tn was found to have biological properties similar to those reported for the MWMV type strain from Morocco. Phylogenetic analysis including the comparison of complete amino-acid sequences of 42 potyviruses confirmed that MWMV-Tn is related (65% amino-acid sequence identity) to Papaya ringspot virus (PRSV) isolates but is a member of a distinct virus species. Sequence analysis on parts of the CP gene of MWMV isolates from different geographical origins revealed some geographic structure of MWMV variability, with three different clusters: one cluster including isolates from the Mediterranean region, a second including isolates from western and central Africa, and a third one including isolates from the southern part of Africa. A significant correlation was observed between geographic and genetic distances between isolates. Isolates from countries in the Mediterranean region where MWMV has recently emerged (France, Spain, Portugal) have highly conserved sequences, suggesting that they may have a common and recent origin. MWMV from Sudan, a highly divergent variant, may be considered an evolutionary intermediate between MWMV and PRSV.

A study was conducted to better understand the population structure of Zucchini yellow mosaic virus (ZYMV), a severe virus affecting cucurbit crops worldwide, in Tunisia and to estimate whether the use of resistant cultivars may provide durable control. Analysis of the polymerase and coat protein (NIb-CP) partial sequences of 83 isolates collected in the three main cucurbit-growing areas in Tunisia showed that ZYMV grouped into two distinct clusters within ZYMV molecular group A. An important variability was observed in the MREK motif of the P3 protein, a motif associated with tolerance breaking in ZYMV-tolerant zucchini squash cultivars. Interestingly, significant differences were found in the distribution of the MREK variants in the two clusters defined by the partial NIb-CP sequences, MREK and MKEK sequences being more common in cluster 1 and cluster 2, respectively. When combining NIb-CP and P3 sequence information, ZYMV molecular variability was shown to be significantly higher in the Cap Bon region than in the Bizerte area. An important biological variability was observed in a subset of 23 isolates regarding symptomatology in susceptible or resistant cucurbits. Some isolates overcame ZYMV tolerance or resistance in zucchini squash and melon, but not in cucumber. Three serotypes were differentiated using a set of 13 monoclonal antibodies (MAbs). Seven parameters characterizing the 23 isolates, including molecular, serological and biological properties, were used for a multiple component analysis (MCA). This analysis revealed that symptom intensity of a given isolate was similar in different susceptible cucurbit hosts, suggesting similar degrees of aggressiveness in different hosts.

A major limiting factor in grape production throughout the world is grapevine trunk diseases (e.g. eutypa dieback, esca, black dead arm, phomopsis cane and leaf spot) (Pearson & Goheen, 1988). In 2005, a survey was carried out in north-eastern Spain to determine fungal pathogens associated with such diseases. Symptoms observed during this survey included general decline of vine, internal black wood streaking, central and sectorial necrosis and wood decay. A plant with necrosis around the pith of the trunk, visible in a transverse section was sampled and isolations made. Necrotic material was selected, surface sterilized in 70% ethanol for 1 min, air-dried under sterile conditions and plated onto streptomycinamended malt extract agar (MEA).Several Phaeoacremonium spp. were isolated. Of these, P. aleophilum was the most prevalent species. One isolate, however, was identified as P. viticola based on conidiophore-and conidia-morphology (short and unbranched, often consisting of a single cylindrical phialide of 2-5 μ m in length; hyaline, obovoid or reniform, 4 μ m long), and colony colour on MEA (greyish pink). Identity was confirmed by PCR using the species-specific primer pair T1-Pbr8 (Mostert et al ., 2006). Pathogenicity of P. viticola isolated from this study was tested by inoculation of 2-month-old pot grown seedlings of Vitis vinifera cv. Malvar. The soil of seven plants was inoculated by drenching with 40 mL spore suspension (10 7 spores mL -1 ).A further seven control plants were inoculated with 40 mL of sterile distilled water. The plants were maintained in a growth chamber at 24ºC and 40% relative humidity. Symptoms were checked periodically for two months. By the end of the experiment all seedlings inoculated with P. viticola showed symptoms which ranged from defoliation (four plants with only the apical leaf remaining), crown necrosis (one plant), epinasty (one plant), to death (one plant). Control plants inoculated with sterile water remained symptomless. Phaeoacremonium viticola was re-isolated from the infected plants. Similar symptoms caused by P. viticola have been previously described (Dupont et al ., 2000), but this is the first report of the disease in Spain. ) showing necrotic spots on leaves, occasionally followed by death of affected plants, were observed in commercial, plastic houses heated by geothermic water in Kebili (southern Tunisia). Crude sap from leaves with symptoms was used for mechanical inoculation onto a set of differential host plants. Necrotic local lesions on inoculated leaves or cotyledons and systemic necrotic spots were observed on melon plants. Necrotic local lesions and no systemic symptoms were produced on cucumber ( Cucumis sativus ). In contrast, no symptoms were observed on non-cucurbit plants. ReferencesThe observed symptoms and host range were similar to those described for Melon necrotic spot virus (MNSV). The presence of MNSV was established by DAS-ELISA using a specific antiserum prepared at INRA. MNSV was detected in seven samples with symptoms.

A potyvirus was isolated from a naturally infected squash plant in Algeria in 1986. Biological and serological data have revealed that the virus, initially described as H4, is related to other cucurbit-infecting potyviruses, particularly Moroccan watermelon mosaic virus (MWMV) and Papaya ringspot virus (PRSV). To establish unequivocally the taxonomic status of H4, its full-length genome sequence was established. H4 shared identities of 70% and 65% at the amino acid level with MWMV and PRSV, respectively, indicating that H4 is a distinct species of the PRSV cluster. The name Algerian watermelon mosaic virus (AWMV) is proposed for this new potyvirus species.