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.
Neringa Rasiukevičiūtė, Inga Moročko-Bičevska and Audrius Sasnauskas
Botrytis cinerea Pers.:Fr. is a widespread necrotrophic pathogen causing grey mould on many economically important horticultural crops. The variability in various B. cinerea populations is known to be very high. Despite the economic importance, the variability of B. cinerea has not been investigated previously on fruit crops in Lithuania. The aim of the study was to characterise the variability of B. cinerea strains isolated from strawberry and apple in different growth conditions on various agar media and to assess mycelial compatibility among the isolates. Larger colony diameter after four days of incubation was observed for isolates from strawberry on potato dextrose and beer universal agars in 24 h dark or light regime, followed by pectin agar in 24 h light. Similarly, the maximum radial growth of the isolates from apple was on potato dextrose agar (dark), followed by beer universal agar (dark and light), after four days of incubation at 20 °C. In the mycelial compatibility tests, barrage formation was evident in mycelial contacts between several isolates, indicating their vegetative incompatibility. The tests revealed that 76% were compatible and 24% were incompatible among investigated strains.
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.
Development of fruit growing and fruit science in Latvia has always been closely linked to the development of the whole country. After the founding of the independent Latvia state in 1918, fruit growing developed rapidly. Although in the Soviet times the situation was not favourable for quality fruit growing, research and breeding continued with good results. After Latvia regained independence, private land property rights were restored, and interest in intensive orchard establishment and growing technologies increased rapidly, which demanded change in the research focus. At present, the Latvia State Institute of Fruit-Growing is the leading institution in this field, working in cooperation with Pūre Horticultural Research Centre, Latvian Plant Protection Research Centre, Institute of Agrobiotechology, and Faculty of Food Technology, Latvia University of Agriculture, Laboratory of Plant Mineral Nutrition, Institute of Biology, University of Latvia. Research is carried out in the following directions: breeding and cultivar evaluation; genetics and molecular biology; plant pathology and entomology; orchard management; experimental processing and storage.