Neda Zuļģe, Anna Kāle, Alina Gospodaryk, Kristīne Vēvere and Inga Moročko-Bičevska
Apples and pears are among the most important commercial fruit species grown in Latvia. Because of suitability to local climatic conditions, mainly domestic cultivars and cultivars originating in neighbouring countries are grown. The planting material of pome fruits produced and used for establishment of new orchards in Latvia corresponds to the Conformitas Agraria Communitatis standard due to the unavailability of nuclear stock. To establish virus-tested, experimental nuclear stock for apple and pear, one to two years old candidate plants were exposed to thermotherapy at +38 °C for 40 to 70 days. The mother trees and candidate plants before treatment were tested for the presence of the four most widespread pome fruit viruses by RT-PCR. The shoot tips of the heat-treated plants were grafted onto seedling rootstocks and were re-tested for the four viruses by RT-PCR during the next three to five vegetation seasons. Several plants of apple cultivars ‘Dace’, ‘Zarja Alatau’, ‘Rubin’, and ‘Ausma’ remained infected either with Apple chlorotic leaf spot virus, Apple stem growing virus or Apple stem pitting virus after the thermotherapy. Tests on woody indicators were carried out to determine possible presence of graft-transmittable organisms according to EPPO guidelines for the establishment of nuclear stock material for pome fruits.
Alina Gospodaryk, Inga Moročko-Bičevska, Neda Pūpola and Anna Kāle
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.