Fluctuations in Prunus necrotic ringspot virus (PNRSV) concentration were researched in single plants of six peach (Prunus persicae) cultivars—Kurakata, Red Haven, Nectar Red, Start Delicious, Meadowlark, and Loadel—by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) of dormant buds (May, June), flowers (September), new sprouts (November), and mature leaves (January) (Southern Hemisphere). The optimum extract dilution (sample weight per buffer volume) to detect the virus was also quantified. The average absorbance patterns of the six cultivars show a steady increase in virus concentration, ranging from A 405nm 0.61 in May to A 405nm 0.86 in July for dormant buds, to A 405nm 1.22 in September in flowers, to 1.53 in November in new sprouts, where the highest concentration was found. Virus concentrations in mature leaves drop to values similar to those of noninfected plants in January ( A405nm 0.12). The yearly average (six noninfected peach trees) ranged from A405nm 0.04 to A405nm 0.08. This drop coincides with an increase in summer temperature and attenuates foliation symptoms caused by PNRSV. Analysis of dormants buds, flowers, or new sprouts with 5-cm-long leaves was reliable to differentiate infected from noninfected plants. Cluster analysis of absorbance profiles for single plants of cvs. Loadel and Meadowlark, however, showed a comparatively low profile, with a drop at flowering time (A405nm 0.20 in September) close to the average of healthy controls. The difference between infected and healthy plants did not become apparent in all cultivars from the analysis of plants at a given phenological stage, for example by the analysis of flower only, the material most preferred to diagnose the virus. Therefore, plants should be analyzed during flowering and sprouting or flowering and dormancy (dormant buds).

Sharka disease, caused by Plum pox virus (PPV), is probably the most important disease of stone fruits crops worldwide because of tremendous yield losses from infected trees (1). During November 2004, symptoms resembling sharka disease were observed in a plum and apricot orchard consisting of 5,000 trees in Pocito, San Juan Province, Argentina. Apricot leaves showed chlorotic spots while plum leaves showed chlorotic rings, spots, and irregular edges. Plum fruits were deformed and much smaller than those from symptomless trees. Samples collected from 70 symptomatic trees were tested using double-antibody sandwich enzyme-linked immunosorbent assays with a polyclonal antiserum anti-PPV from BIOREBA (Reinach BL1, Switzerland), and immunosorbent electron microscopy with a polyclonal antiserum from our laboratory made against a recombinant PPV capsid protein (CP). The samples were also tested using double-antibody sandwich indirect enzyme-linked immunosorbent assay using the REAL kit (Durviz, Valencia, Spain) with two different monoclonal antibodies including Mab 5b that recognizes all strains of PPV and Mab 4DG5 that is specific for PPV strain D. Samples were positive with both antibodies in 80% of the cases. Leaf extracts from symptomatic plum samples were also analyzed by immuno-capture reverse-transcription polymerase chain reaction. A 1,209-bp fragment was amplified with specific primers that anneal at the 5′ end of the coat protein coding region and the viral 3′ end poly A tail. The amplified fragment was cloned and the nucleotide sequence was determined for two of the resulting clones (Gen-Bank Accession Nos. DQ299537 and DQ299538). The sequences were 98% identical with the PPV-strain D from the United States (GenBank Accession No. AF360579) and Germany (GenBank Accession No. X81081). The restriction sites for AluI and RsaI, previously described (2) as typical for the PPV-D strain, were present in the expected positions. To our knowledge, this is the first report of PPV-D in Argentina. Reference: (1) M. Németh. Virus, Mycoplasma, and Rickettsia Disease of Fruit Trees. Martinus Nijhoff Publishers, Dordrecht, the Netherlands, 1986. (2) T. Wetzel et al. J. Virol. Methods 33:355, 1991.

Surveys done in the mid 1990s in Albania demonstrated that PPV was endemic in south-eastern areas. More than 60% of plum trees were infected, with rates close to 100% in several orchards. Other PPV foci were found in northern and central parts of the country. For apricot and peach orchards, only a few trees were found infected. A second survey was recently carried out to type PPV isolates from different host species (plum, peach and apricot) and different stone fruit cultivation areas. A total of 48 PPV isolates were identified in 12 orchards and typed by DASI-ELISA using monoclonal antibodies (MAbs): 5B-IVIA (universal), 4DG5 (PPV-D specific), AL (PPV-M specific), AC (PPV-C specific) and EA24 (PPV-El Amar specific). The majority of Albanian isolates (23) were PPV-M isolates (48%), 12 isolates were PPV-D (25%), whereas 13 of them were natural mixtures of both strains (M + D). No isolate was identified as PPV-C or PPV-EA. A recent study was carried out using RT-PCR followed by RFLP, targeting the CP and P3-6K1 genomic regions, to check for the presence of PPV-Rec. Three out of 10 isolates that were previously typed as PPV-M by MAbs were identified as PPV-Rec. PPV-M was confirmed as the dominant strain in Albania while PPV-D and PPV-Rec were less prevalent. During these studies, trees with single and mixed infections were found in the same orchards, a situation that appears more frequently in varietal collections. Natural mixed infections of M and D strains were found in 6 out of 12 orchards by DASI-ELISA which was higher than previously thought. However, previously collected data which has been found to contain M strain should be retested for the presence of recombinant isolates. The above strain analyses mainly concerned plum isolates, and therefore the situation on peach and apricot needs further investigation. This summary, in briefly describing the situation of PPV and its strains in Albania, reflects what has been prevailing for a long time in the country since all visited orchards were old. In recent years, numerous small peach and apricot orchards have been established in the coastal area of the country with propagation material frequently coming from abroad. More investigations in these new fruit tree growing areas are also needed. ? 2006 36 ? Plum pox virus in AlbaniaArgentinian stone fruit production includes peaches ( Prunus persica ), Japanese plums ( P. salicina ), European plums ( P. domestica ), sweet cherries ( P. avium ) and apricots ( P. armeniaca ), and covers about 56 000 ha. PPV was first detected in Argentina in 2004 on apricots and Japanese plum cv. Red Beaut, from a fruit tree orchard in Pocito, San Juan. Fruit were deformed and leaves presented chlorotic rings and spots. Samples (leaves and fruits) from symptomatic trees were first analyzed by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) using a kit from Bioreba at EEA-INTA Junín-Mendoza, where 8 out of 13 samples were positive for PPV. Confirmation and further analyses were performed at IFFIVE-INTA with the follo...

No abstract