Communicated by Edîte Kaufmane To evaluate the occurrence of nine viruses infecting
Apple chlorotic leaf spot virus (ACLSV), Apple stem pitting virus (ASPV), Apple stem grooving virus (ASGV) and Apple mosaic virus are economically important viruses infecting fruit tree species worldwide. To evaluate the occurrence of these pome fruit viruses in Latvia, a large-scale survey was carried out in 2007. Collected samples were tested for infection by DAS ELISA and multiplex RT-PCR. The accuracy of the detection of the viruses in multiplex RT-PCR was confirmed by sequencing amplified PCR fragments. The results showed a wide occurrence of viruses in apple and pear commercial orchards established from nontested planting material. More than 89% of the tested apple trees and more than 60% of pear trees were infected with one or more pome fruit viruses. Analyses showed that the high occurrence of viruses in several apple cultivars is due to the propagation of infected clonal rootstocks and scions from infected mother trees. Sequence analyses targeting the 3¢-terminal region of the tested viruses showed various degrees of genetic diversity within respective virus isolates. This is the first report of the occurrence of ACLSV, ASGV and ASPV in apple and pear trees in Latvia and demonstrates their genetic diversity in different host genotypes.
Cecidophyopsis mites are important pests in all cultivation regions of Ribes causing bud galls and sterility. Despite their economic importance, the knowledge on Cecidophyopsis species infesting Ribes in various areas of the world is still deficient. The present study was carried out to identify Cecidophyopsis species occurring in Latvia on cultivated and wild Ribes, to assess their host range and gain insight into the genetic diversity of these insufficiently studied pests by use of multiplex PCR, rDNA sequences and morphological characters. Cecidophyopsis alpina, C. aurea, C. spicata and C. selachodon were detected to occur in all surveyed habitats. For the first time, C. alpina was identified on blackcurrants and redcurrants, and C. aurea on redcurrants, blackcurrants and alpine currants. The presence of C. ribis was not confirmed with molecular tools during this study. Phylogenetic analyses confirmed the presence of four Cecidophyopsis species identified by multiplex PCR. A close phylogenetic relatedness was found for C. aurea and C. alpina, and for C. ribis and C. spicata highlighting the necessity for additional studies. Our findings suggest a need to consider also other Cecidophyopsis species besides C. ribis in breeding programs for host resistance to mites.
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.
Apple scab caused by the heterothallic ascomycetous fungus Venturia inaequalis is one of the most severe diseases in apple-growing regions worldwide. Annual sexual reproduction of the pathogen ensures the formation of populations with high variability and better adaptability to resistant cultivars. The present study aimed to assess the virulence of the V. inaequalis population in the experimental orchard where introduction, evaluation and breeding of apple cultivars are carried out, and the apple germplasm collection of Latvia is located. Fifteen differential Malus genotypes, obtained within the international Vinquest initiative, were planted in 2016 in the germplasm collection sector of the orchard in five blocks, each containing one tree of each geno-type. In 2017–2021, apple scab symptoms on the leaves were scored according to the methodology used in the Vinquest network. The disease severity increased with each vegetation season, and more genotypes were affected, reaching the maximum in 2021 and clearly indicating the infection source build-up and pathogen’s adaptation on particular genotypes due to the absence of scab control. At least four races of V. inaequalis were found to be established in Latvia, and the resistance genes Rvi1, Rvi3, Rvi4, and Rvi8 have been overcome. On h(9) and h(13), the first symptoms appeared in 2021, indicating the first signs of Rvi9 and Rvi13 gene breakdown.
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