Prunus necrotic ring spot ilarvirus (PNRSV) and Apple chlorotic leaf spot trichovirus (ACLSV) are common in plum orchards. The aim of the study was to obtain virus-free planting material of Prunus domestica L. by chemotherapy in vitro. Ribavirin at concentrations of 10 to 50 mg·l−1 was added to Murashige–Skoog (MS) nutrition medium for virus eradication from microshoots. After a two-week period of chemotherapy, meristems were subcultured monthly on MS medium and proliferation index of shoots was estimated. Microshoots were retested by reverse transcription polymerase chain reaction for presence of virus. At lowest concentrations of 10 mg·l−1 ribavirin was entirely ineffective for ACLSV and 10 to 30 mg·l−1 was ineffective for PNRSV elimination. Ribavirin concentrations of 40 and 50 mg·l−1 destroyed both pathogens. However, at higher concentrations of 40 and 50 mg·l−1 ribavirin exhibited some signs of phytotoxicity on microshoots in the first sub-cultivation period. In order to test the genetic stability of the microplants after chemotherapy the amplified fragment length polymorphism (AFLP) method was applied. Plant genome stability in ‘Magna Glauca’ at concentrations of 40 mg·l−1 was damaged, as the presence of polymorphic AFLP markers were observed.
To evaluate the occurrence of nine viruses infecting Prunus a large-scale survey and sampling in Latvian plum orchards was carried out. Occurrence of Apple mosaic virus (ApMV), Prune dwarf virus (PDV), Prunus necrotic ringspot virus (PNRSV), Apple chlorotic leaf spot virus (ACLSV), and Plum pox virus (PPV) was investigated by RT-PCR and DAS ELISA detection methods. The detection rates of both methods were compared. Screening of occurrence of Strawberry latent ringspot virus (SLRSV), Arabis mosaic virus (ArMV), Tomato ringspot virus (ToRSV) and Petunia asteroid mosaic virus (PeAMV) was performed by DAS-ELISA. In total, 38% of the tested trees by RT-PCR were infected at least with one of the analysed viruses. Among those 30.7% were infected with PNRSV and 16.4% with PDV, while ApMV, ACLSV and PPV were detected in few samples. The most widespread mixed infection was the combination of PDV+PNRSV. Observed symptoms characteristic for PPV were confirmed with RT-PCR and D strain was detected. Comparative analyses showed that detection rates by RT-PCR and DAS ELISA in plums depended on the particular virus tested. The results obtained in this study revealed that commonly grown plum cultivars in Latvia are infected with economically important stone fruit viruses and highlight the need to implement a programme to produce and propagate virus-free planting material.
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