Volume 76 (2022): Issue 4 (August 2022)

Sea buckthorn (Hippophae rhamnoides L.) is a native species in various regions of Asia and Europe. It is cultivated as a multipurpose horticultural species in northern temperate regions of Europe, Asia, and North America with large economic potential used for food, pharmacology, cosmetics, and environmental conservation. Diseases in natural populations and managed landscapes have increased, endangering sea buckthorn growth and cultivation worldwide. This review article focuses on sea buckthorn canker, wilt and decline diseases caused by pathogenic fungi, their distribution, hosts of involved pathogenic fungi and symptoms. Published information on sea buckthorn fungal diseases is available only about a few diseases, such as wilt (Verticillium dahliae), the dried-shrink disease caused by various fungi and abiotic factors, and stem canker (Hymenopleella hippophaeicola, Cytospora spp., Stigmina sp.). Some fungi reported on sea buckthorn are poorly studied, or the sea buckthorn is a newly discovered host, as in the case of Eutypa spp. The most often reported symptoms of these diseases are cankers and cracks on trunks and main branches, dead buds and leaves, necrosis of various tissues on branches, and root necrosis, resulting in the death of the shrubs. In general, the fungal diseases on sea buckthorn are not sufficiently addressed, and more research is needed.

Some 35 cultivars of Fragaria are preserved in the Swedish National Gene Bank for vegetatively propagated crops, which opened in 2016. The genebank includes a field collection in Alnarp, southern Sweden, and a back-up collection of virus-free plants at the Swedish Elite Plant Station. Here we document how the cultivars, the so-called mandate cultivars, were selected. Swedish origin was the primary criteria used in the selection process. In this category cultivars from historic Swedish breeding programmes are of particular interest. During 80 years, starting in the 1920s and ending in the late 1990s, 16 strawberries including three Fragaria × vescana hybrids were developed by Swedish breeders. Unfortunately, for three of these the accessions in the genebank are uncertain and four have not yet been recovered. The 16 cultivars bred in Sweden are presented with their year of introduction, parentage and short descriptions. Additionally, we also briefly describe local cultivars of strawberries and wild strawberries. Another category of mandate cultivars are foreign cultivars with a growing tradition in Sweden dating back to before 1966. Their age, country of origin, and importance for Swedish cultivation are discussed.

The goji berry (Lycium spp.) belongs to the Solanaceae family. The genus Lycium comprises 87 recognised species and is distributed in arid and semi-arid regions in temperate to subtropical zones in the world. In botanical terms, there are three types of Lycium species known as wolf-berry and commercially grown in the whole world: Lycium barbarum L. (2n = 24), Lycium chinense Miller (n = 12), and Lycium ruthenicum Murray (n = 12). Wolfberry is a herb growing naturally in both the mild and tropical areas of East, Southeast Asia, and Southern Africa. Also known as wolfberry (Lycium spp.), the motherland of wolfberry is China and it can even be grown in the Himalayas, the highest points of Tibet and Mongolia. Recently, in Turkey goji berry became a popular fruit due to its health benefit compounds, especially phenolic compounds (phenolic acids and flavonoids), carotenoids, tocopherol, ascorbic acid and antioxidant properties. The purpose of this study was to conduct a historical assessment of the botanic properties and cultivation of wolfberry plant and to provide information on the types and cultivars grown commonly in Turkey, distribution areas of production, consumption and use as a technologic product, marketing status, benefits for human health, multiplication and production techniques.

Wild fruits are essential genetic resources for fruit breeding and have either been domesticated or used to introgress disease resistance and tolerance to abiotic and biotic stress. Numerous studies have previously described the health benefits of wild berry fruits and reported their antioxidant, anti-inflammatory, antimicrobial, and anticancer activity. Turkey has a rich plant biodiversity thanks to its geographic location and encirclement by three seas, leading to a wide variety of climates. The great ecological diversity of the wild berry species in Turkey is a significant bio-gene pool that is vital to human life and can serve as a source of agricultural development in the future. This review aims to introduce some of the wild edible berry species naturally occurring in Turkey such as Morus spp., Hippophae rhamnoides L., Viburnum opulus L., Rubus idaeus L., Rubus fruticosus L., Sambucus nigra L., Vaccinium spp., Arbutus unedo L., Ribes spp., and Fragaria vesca L., and describe their distribution, uses, and fruit characteristics. Conservation of these wild fruit genetic resources is necessary for use in breeding for novel traits.

The commercial apple growing industry in Latvia has a lack of climate adapted modern cultivars. The Latvian apple breeding programme is targeted at cultivars adapted to the cool climate of Baltic countries and Scandinavia, with fruit quality and storage suitable for commercial production. Since 1989, scab resistance (Rvi6, Rvi5) donors are included in crosses. Several cultivars already show commercial promise — ‘Dace’, ‘Gita’, ’Monta’ (Rvi6) and the polygenic resistant ‘Laila’ and ‘Pure Ametist’. However, in 2020, the Rvi6 resistance was overcome in Latvia. Donors of polygenic scab tolerance may prove a better alternative. The most successful donors have been ‘Iedzēnu’, ‘Eksotika’, ‘Alesya’, and ‘Bohemia’. Marker assisted gene pyramiding was started, including markers linked to the resistance genes Rvi5 and Rvi6. Scab resistant cultivars ‘Edite’, ‘Felicita’, ‘Ligita’, and ‘Paulis’ show low susceptibility to Neonectria ditissima canker. To achieve high fruit quality and good storage, worldwide commercial cultivars are crossed with local adapted cultivars. Such crosses that have been registered include ‘Inta’, ‘Lora’, and ‘Saulesmeita’. Recent crosses for quality include ‘Honeycrisp’, where H-1-07-36 and H-1-07-42 show most promise. Improved biochemical content and flesh structure is one of the main targets. An additional line of breeding is aimed at ornamental and cider apples. The scab resistant Nr.19-97-154 (Cidross) was selected for cider. The red leaf columnar apple ‘Karlens’ and the compact red-leaf crab ‘Auce’ have been registered.

The paper considers the possibilities of expanding the assortment of plum cultivars in world production by hybridising large-fruited myrobalan plum (Prunus cerasifera Ehrh.) cultivars with those of Japanese plum (Prunus salicina Lindl.) and other diploid stone fruit species. Because of many years of breeding work in Russia, cultivars of a new hybridogenous species Prunus × rossica Erem. (Russian plum) have been created, which can ensure a stable supply of fresh fruit from late June to September and complement the assortment of common plum cultivars. A description is given for the best adaptive, high-yielding cultivars with good taste and high canning qualities — ‘Kubanskaya Kometa’, ‘Globus’, ‘Gek’, ‘Iyulskaya Roza’, ‘Dynnaya’, ‘Kolonnovidnaya’, and ‘Podarok Sad-Gigantu’. The efficiency of their cultivation using intensive technologies and own-rooted plants, as well as clonal rootstocks bred at the Krymsk Station, has been shown. It is recommended to carry out intensive cultivation of Russian plum using medium vigorous rootstocks like Kuban 86, Evrika 99, Zarevo, Fortuna and dwarf rootstocks VVA 1, Best, Upryamets and VSV 1.

Pears (Pyrus communis L.) are not native plant species in Latvia but have a long history of introduction and growing, using various sources of plant material over time. Therefore, the existing collection of genetic resources combines accessions of different origin. To plan the further development of this crop and to ensure its successful preservation, this study aimed to characterise the Latvian Pyrus germplasm collection using SSR molecular markers and to estimate the level of genetic diversity within the pear germplasm collection. Six SSR markers were used to genotype 206 pear accessions of different origin, such as cultivars and hybrids bred in Latvia, landraces collected during expeditions throughout the country, and introduced foreign cultivars. The marker set identified 197 accessions with unique genotypes, and enabled a comparison of different origin groups, and an assessment of genetic diversity. Allele numbers ranged from 15 to 28 for the markers used, whereas observed heterozygosity ranged from 0.519 to 0.956. Grouping of accessions according to geographical origin was not observed. However, the genetic background of Latvian samples was entirely in alignment with international germplasm.

The evaluation of cultivars of red and white currant (Ribes rubrum L.) was carried out in 2019–2020 at the Polli Horticultural Research Centre of the Estonian University of Life Sciences, South-Estonia. The aim of this study was to estimate traits of red and white currant cultivars of both Estonian and introduced origin. An evaluation plot was established in the autumn of 2016. During two consecutive years (2019–2020), 11 promising cultivars were evaluated for the beginning of flowering and fruit ripening, winter hardiness, resistance to diseases (expressed in scores 1–9), yield per bush, fruit weight, drop of flowers and premature berries, as well as the content of the soluble solids (°Brix), titratable acids, ascorbic acid, total phenols and total anthocyanins. The highest yield was determined in cultivars ‘Bayana’ and ‘Viksnes’, while cvs. ‘Rovada’, ‘Jonkheer van Tets’, ‘Kurvitsa 4’ and ‘Valko’ had larger berries. The highest soluble solid content was found in the berries of red currant ’Krameri punane’ (13.8 °Brix) and white currant ’Bayana’ (12.4 °Brix).

Oregano (Origanum vulgare L.) is one of the priority medicinal and aromatic plants in Europe because of its broad potential for use and distribution assessments of the species. The involvement of oregano genetic resources in cultivation can solve the problems of depletion of natural habitats and allows receiving high yield in marginal meteorological conditions. Also, ex situ conservation is the most applicable method for conserving local species of medicinal and aromatic plants in Nordic Europe. There is limited information about the characterisation and evaluation of oregano genetic resources in Latvia and Europe. In this study, long-term observations on 44 oregano accessions maintained at the ex situ collection of medicinal and aromatic plants of the Latvia University of Life Sciences and Technologies, were characterised by the Draft Descriptor List under the agro-climatic conditions of Latvia. Integrated assessment of oregano genetic resources was made to recommend the most valuable accessions for growing.

Strawberry growing in high tunnels is widely used in many countries and the area under cover is increasing. Usually, early ripening cultivars are planted in high tunnels to obtain even earlier yield in the season. In this investigation, several new strawberry cultivars and one hybrid (of Dutch breeding) with medium and late ripening time were evaluated for growing in high tunnels in soil. The trial was established in 4 August 2016 in a FVG type tunnel (60 × 4 × 3.35 m). Frigo plants of the following categories of cultivars and hybrids were used in the investigation: ‘Sonata’ (A) and ‘Sonsation’ (A+) of medium ripening time; ‘Faith’ (A+) and hybrid 09-90s-05 (A) of late ripening time; ‘Malwina’ (A+) and ‘Magnus’ (A) of very late ripening time. The plants were grown on raised beds covered with black plastic mulch in double rows with drip irrigation. Soil type was heavy loam. Plant survival after winter, productivity potential, yield, fruit size, the ratio of high quality to damaged fruits in the crop, fruit sensory characteristics, shelf life and biochemical content after freezing were evaluated. According to three-year evaluation results, ‘Sonsation’ had better fruit quality and resistance to crown diseases than ‘Sonata’ and can be considered appropriate for yield forcing in high tunnels. Hybrid 09-90s-05 and ‘Faith’ are not appropriate for growing in high tunnels in heavy soils. Hybrid 09-90s-05 had good yield, but medium fruit quality and low taste score, and it was susceptible to grey mould. ‘Faith’ had low productivity potential and fruits of medium taste. The very late ripening cultivars ‘Malwina’ and ‘Magnus’ had low productivity in all evaluation years, probably because of too heavy soil.

The aim of the study was to characterise the variability of flower bud frost tolerance, self-pollination and fruit quality in Latvian local sour cherries; and to select the most promising aces-sions. Data on fruit set after self-pollination, frost tolerance of flower buds, fruit and stone weight, stem retention force and soluble solid content were collected for 29 accessions of local cherries in 2016–2019. Sour cherry cv. ‘Latvijas Zemais’ clones no. 64, D7, and 4 were the most promising for fruit processing; clones no. 62, 65, Matkules, and Lietuvas were promising as pollinators due to tolerance to spring frosts and high level of fruit set after self-pollination, and cv. ‘Latvijas Zemais’ clones Eglīša, Piïkas 3, Matkules, and Dumbrava had relatively high fruit weight and soluble solid content for fresh consumption. ‘Latvijas Zemais’ clone no. 62 was superior with stable fruit set after self-pollination (21.54%), cold resistant flower buds (89.5%) and high proportion of fruit flesh (93.8 %), clone no. 52 had high soluble solid content (18.88 Brix) and clone Eglīša had large fruit (5.56 g). The highest contribution to variability was provided by fruit weight, stone weight, and soluble solid content, which explained 79.90% of total variability.

The aim of the trial was to determine the optimal propagation methods for three Japanese quince cultivars. Rooting trials with cultivars ‘Darius’, ‘Rasa’, and ‘Rondo’ were conducted in 2017–2019 in a greenhouse, to investigate the rooting and shoot quality of softwood cuttings, using different treatments. At the beginning of fruit production, growth and amount of the first yield was evaluated depending on propagation method. Softwood cuttings of Japanese quince rooted well (average 82–93%) in a greenhouse with heated substrate and partly automated temperature and moisture control, in spite of different weather conditions during three vegetation periods. The best results for rooting were found for cultivar ‘Rondo’. On average, better results of rooting for all cultivars were obtained when cuttings were soaked in indolylbutiric acid solution and trichodermin was added to the substrate. Significant differences in length and diameter of the bush shoots found between years for both propagation methods and also between years for one type of propagation. On average, microproagated plants had the highest shoot length. After evaluating the first yield, no significant differences were found between cultivars during the first two trial years, but micro-propagated plants had significantly higher yield per bush.

Modern reviews of challenges related to deep learning application in agriculture mention restricted access to open datasets with high-resolution natural images taken in field conditions. Therefore, artificial intelligence solutions trained on these datasets containing low-resolution images and disease symptoms in the advanced stage are not suitable for early detection of plant diseases. The study aims to train a convolutional neural network for apple scab detection in an early stage of disease development. In this study a dataset was collected and used to develop a convolutional neural network based on the sliding-window method. The convolutional neural network was trained using the transfer-learning approach and MobileNetV2 architecture tuned on for embedded devices. The quality analysis in laboratory conditions showed the following accuracy results: F₁ score 0.96 and Cohen’s kappa 0.94; and the occlusion maps — correct classification features.

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.

The negative influence of pathogens on plant development is well known. However, the negative impact depends on various factors: cultivar and rootstock resistance, nutrition, the environment, the virulence, and concentration of pathogens in the plant tissue. The evaluation of apple chlorotic leaf spot virus (ACLSV) influence on apple tree growth and production was performed at Institute of Horticulture (LatHort) from 2012 to 2020. Virus-free and ACLSV-infected trees from the traditional cultivar ‘Antonovka’ and new scab resistant cultivar ‘Gita’ were evaluated on dwarfing rootstock B.396. The presence of four common apple viruses (apple mosaic virus (ApMV), ACLSV, apple stem grooving virus (ASGV), apple stem pitting virus (ASPV)) was assayed in the planting year and repeated at the end of the study period. The vigour of planting material, growth, yield, and yield efficiency were compared between virus negative and ACLSV-infected trees. During eight growing seasons (2013–2020), no statistically significant negative impact of ACLSV infection on tree growth or yield was observed for the cultivars. A larger canopy volume was observed for ACLSV-infected trees (p = 0.01), but the cumulative yield per canopy volume was equivalent between virus-negative trees and ACLSV-infected trees (p = 0.07).

Cold resistance of fruit tree buds is very important. Climate change brings unstable winters, and the temperature often fluctuates and creates many problems in fruit growing. Research on bud cold damage was conducted during three years (2019–2021) at the Institute of Horticulture. Three Latvian plum cultivars, ‘Ance’, ‘Adelyn’, and ‘Sonora’, were studied, while cultivar ‘Jubileum’ was used as a control. This study aimed to determine the cold resistance of flower buds and vegetative buds of plum cultivars after the deep dormancy period. Evaluation of buds was done on one-year-old shoots and spurs. Evaluation of cold damage on flower buds and vegetative buds was done after the deep dormancy period: in February 2019 and at the end of January 2020 and 2021, after keeping the buds for a limited time in temperatures thresholds of –20 °C, –25 °C, –30 °C, –35 °C in alternating climate chambers. The results showed significant differences among cultivars, years, and between branch types. Vegetative buds for all cultivars were without significant cold damage. Up to –30 °C wood browning was observed near the base of buds. A significant amount of flower bud damage (up to 100%) was observed in 2020, in a temperature threshold until –30 °C for both types of branches. The most durable cultivars were ‘Ance’ and ‘Adelyn’ (up to –25 °C, bud survival was near 100%) all three years. ‘Jubileum’ had the most vulnerable flower buds. The lowest low-temperature damage for all cultivars was in 2021. For one-year-old shoots, bud damage only occurred at –35 °C for all cultivars all years.

The goal of our work was to assess the ability of hybrid apple seedlings and their parent forms to maintain frost resistance during the thaw period, by using artificial freezing methods. Apple resistance was studied in the laboratory by modelling the damage factors of the frost resistance component III with the use of a climatic chamber. All of the studied hybrid apple seedlings from all used crossing combinations showed a sufficient level of frost resistance under modelling of a three-day artificial thaw (+2 °C) with subsequent temperature lowering to –25 °C. The damage of bark, cambium and wood in all of the studied hybrid seedlings was reversible and did not exceed a 2.0 point rating on a 5-point scale. The temperature rise up to +2 °C during three days in February did not cause the activation of growth processes in buds and bark and did not dramatically affect hybrid apple seedlings. According to the results of the artificial freezing, hybrid apple seedlings of the 6026 family (‘Imrus’ × ‘Krasa Sverdlovska’) and hybrids of the 6030 family (‘Svezhest’ × ‘Pepin Orlovsky’) showed the largest potential frost resistance after a thaw in winter.

European wild garlic (Allium ursinum L.) syn. wood garlic, ramsons or bear’s garlic is a perennial plant that is common in Europe and Asia, but rare in the Mediterranean region. Bear’s garlic is included in the Latvian Red Data Book. The plant species has high commercial value and a high amount of biologically active compounds. Because of the conservation status of wild populations, raw material should be obtained by cultivation. For the experiment, leaves of six accessions of bear’s garlic from the ex situ collection of medicinal and aromatic plants at the Latvia University of Life Sciences and Technologies, were used. The aim of this study was to identify the individual phenolic compounds in bear‘s garlic leaves. The composition of the phenolic profile was determined using a high-performance liquid chromatograph (HPLC) Shimadzu Nexera LC-40 with diode-array detector (DAD). Overall, 18 phenolic compounds (gallic acid, 3.5-diOHbenzoic acid, catechin, chlorogenic acid, 4-hydroxybenzoic acid, epicatechin, homovanillic acid, caffeic acid, vanillic acid, syringic acid, vanillin, p-coumaric acid, rutin, sinapic acid, ferulic acid, 2-OHcinnamic acid, quercetin, luteolin, and kaempferol) were detected in the samples. The gallic acid was the predominant phenolic compound, with a range in concentration from 75.8 mg·100 g⁻¹ to 322.5 mg·100 g⁻¹ in bear’s garlic.

Content of leaf pigments such as chlorophyll a and b, chlorophyll a+b and carotenoids can provide valuable insight into the physiological performance of plants. These compounds have selective proprieties for light absorption and reflectance in the visible spectra that can be used to evaluate alternative methods to biochemical to estimate their content. Numerous studies in the literature have established correlations between these compounds, spectral reflectance and vegetation indices. Nevertheless, the appropriate use of these indices depends on plant species and cultivars. Thus, the objective of this study was to assess the most common vegetation indices for the estimation of chlorophyll a and b, chlorophyll a+b and carotenoids of three olive tree cultivars (Olea europaea L, cv. Cobrançosa, cv. Verdeal Transmontana and cv. Madural) under six irrigation treatments, using spectroscopy. The results showed that the correlation between leaf pigments and vegetation indices depends not only on the type of pigment but also on the cultivar. Among the studied cultivars, cv. Cobrançosa showed the best correlation between the “M Locherer chlorophyll” index (MLO) and chlorophyll a content (r2 = 0.66) and for the carotenoid reflectance index (CRI) 2 and carotenoids content (r2 = 0.87). Although the results are preliminary, it seems that vegetation indices could be a useful tool for leaf pigment evaluation, and to give information about plant interactions with biotic and abiotic environmental stress conditions.

The olive tree (Olea europaea L.), widely cultivated in the Mediterranean countries for olive oil and table olive production, has an important economic role. In the age of climate change, it is crucial to know the importance of environmental impacts associated to the production system. Thus, the aim of this study was to characterise the environmental impacts of a semi-intensive olive orchard drip irrigated with ground water, located in the Northeast Region of Portugal. Life cycle analysis was conducted according to ISO 14040. We used openLCA software, the Agribalyse V. 3 database, and a cradle-to-gate analysis in the impact assessment (Recipe Midpoint (H) V1.13). In the climate change category, the results indicated that for production of 1 kg olives, a total of 0.249 kg CO₂-Eq. were emitted to the atmosphere. Regarding the direct impact of production system, a total of 0.177 kg CO₂-Eq. (71.5%) were emitted, followed by indirect impacts associated with raw material of the irrigation system (0.032 kg CO₂-Eq. total, 12.7%), and electricity needed to pump ground water (0.012 kg CO₂-Eq., 4.8%). In relation to inputs for production, the raw material for urea production contributed 0.013 kg CO₂-Eq. (5.0%) of total emissions. To the best of our knowledge, this study was the first carried out in this region, and contributes to a better understanding of environmental impacts that will allow their minimisation and ensure olive orchard sustainability.

Although golden currant has been grown in Latvia for several decades, mainly as ornamental plant, there is little experience on the most suitable cultivation systems for berry production. Two cultivars of golden currant — ‘Laila’ and ‘Uzbekistanskaya Krupnoplodnaya’, were planted in 2017 in two cultivation systems — vertical trellis and shrub form and assessed in the first two seasons with harvest. In addition, plots with and without organic mulch were established in the shrub system. The aim of the study was to investigate the growth, development and yield of golden currant depending on the cultivation system. All plants bloomed abundantly and practically at the same time in both years, while no significant differences were found between cultivation systems and cultivars. The annual growth of shoots in 2020 was significantly affected by the cultivation system — on average 0.66 m in the trellis system, 0.41 m in the shrub system in mulched plots, and 0.43 m in unmulched plots. Cultivar ‘Laila’ tended to produce longer shoots (average 0.51 m) than the ‘Uzbekistanskaya Krupnoplodnaya’ (average 0.47 m). The yield was low because of poor fruit set and did not significantly differ between cultivar and cultivation systems, though cultivar ‘Laila’ and shrub systems still had higher yields.

The effects of hydrogel granules mixed with peat substrate on germination, morphological and physiological parameters of plugged seedlings were tested in tomato seedlings, at two different irrigation regimes. Due to hydrogel presence, the germination speed was increased, whereas mean germination time was significantly reduced. Slight improvement was recorded regarding final germination, but no effect was found regarding the synchronisation index and seedling vigour index. Due to addition of hydrogel granules a significant increase occurred in dry matter of shoots and plants. No effect was found regarding dry matter of roots, but the presence of hydrogel granules significantly reduced the length of tap root. Interestingly, stomata conductance and chlorophyll index were higher than in control plants. No statistically significant interaction was found between hydrogel variants and irrigation frequency, i.e., the effect of different levels of hydrogel variants did not depend on irrigation frequency. Therefore, we recommend mixing hydrogel capsules into the substrate of plug seedlings to improve the morphological and physiological parameters of seedlings and reduce water and fertiliser leaching into the environment.

Most apple cultivars tend to bear biennially, i.e. produce many fruits in one and few fruits in the next year, or do not have a nature of self-thinning. The effectiveness of chemical thinning depends on conditions, particularly temperature, at the time of application. In some other fruit-growing regions, the mechanical thinning of flowers is adapted to some cultivars by changing the speed of moving and rotation of the mechanisms to conduct partial thinning — removing of flowers. The investigation aimed to evaluate the effectiveness of total flower removal mechanically on one side of the tree row, and on the other side the next year, during the full production period (8^th to 12^th year after planting) to obtain regular yields. Seven cultivars on dwarfing rootstocks M.9 and B.396 were compared. Apple trees on the dwarfing rootstock B.396 were less affected by biennial yielding. Cultivars had a strong relation to yield — ‘Gita’ (Vf), ‘Konfetnoye’ and ‘Kovalenkovskoye’ had less fluctuation yearly, while ‘White Transparent’, ‘Rubin’ (Kazah.), ‘Antei’, and ‘Ligol’ performed opposite. There was a positive influence observed on reduction of periodicity by mechanical flower thinning, however, there is a discussion on cumulative yield reduction.

Data from monitoring of weed populations are relevant for successful integrated weed management. The purpose of this experiment was to compare the diversity of weed species in red raspberry plantation rows. The red raspberry plantation was established in August 2019. The plantation is located in the south part of Latvia, Zemgale region (N56°33’29.5302”, E23°46’26.04”). The red raspberry cultivars ‘Daiga’, ‘Shahrazada’, ‘Norna’, and ‘Polana’ were grown in the plantation. The bushes were spaced at 0.6 m in rows and 3 m between rows in a plot with size 0.51 ha. Weed infestation in the red raspberry plantation was determined by using the counting method. The counting of weeds and identification of weed species were done three times during the vegetation at the 16^th,22^nd, and 30^th week of 2021. In total, 34 weed species, including 18 annual and 16 perennial weeds were present in the red raspberry plantation. Poa annua (5–60 plants per m-2) and Elytrigia repens (6–393 plants m⁻²) were found as dominant weeds. During experiment there were differences in weed populations and density between red raspberry cultivars. The cultivar ‘Norna’ was dominated by perennial weeds, while ‘Polana’ by annual weeds.

Gooseberries are very popular in home gardens and have a long growing history in Latvia, although nowadays they are not among the most widely grown commercial berry crops. Growing was initiated by some enthusiastic breeders during the previous century, who developed many cultivars. Unfortunately, some part of this breeding material has already disappeared. Several expeditions were organised to collect still available genotypes. Plants of the obtained material were propagated and planted at the collections of Institute of Horticulture. During 2019–2021, to select the most valuable material for preservation in the National Genetic Resources Collection, an evaluation of the collected material as well as of cultivars of Latvian origin, was carried out. In total 23 genotypes were evaluated. Plant morphological, phenological, yield and fruit quality traits as well as resistance to pests and diseases and biochemical value were investigated. Evaluated genotypes showed great variability within the evaluated traits. GEN 693, GEN Drudze, GEN 88A, GEN 774 and Nr. 269 were selected as the most valuable and diverse genotypes from the collected and preserved breeding material. The Latvia origin cultivars: ‘Avenīte’, ‘Kuršu Dzintars’, ‘Maija’, ‘Mazērkšíotā’, and ‘Rita’, were selected for preservation in the recovered core collection.