Hop Gardens Research Articles

Determination of C-factor for conventional cultivation and soil conservation technique used in hop gardens

Abstract The research presented in the article was focused on determining the C-factor for hops for conventional cultivation (CT) and soil conservation technique, which is based on the presence of cover crops (CC) in the inter-rows. The values of the soil loss ratio, which are the basis for the calculation of the C-factor, are also presented. The research activities were carried out between 2016 and 2023 and a field rainfall simulator was used for the measurements. Rainfall simulations were conducted at three developmental stages of CC. The results show a high C-factor value for CT (0.73), which indicates insufficient erosion control efficiency. In contrast, a C-factor of 0.16 was determined for the cover crop technique. This means that cover crops in the inter-rows of hop gardens can effectively reduce the risk of water erosion. The values reported in the article can be used as input parameters in various erosion models and equations to refine the subsequent calculation.

Optimization and Validation of Singleplex and Multiplex RT-qPCR for Detection of Citrus bark cracking viroid (CBCVd), Hop latent viroid (HLVd), and Hop stunt viroid (HSVd) in Hops (Humulus lupulus).

Direct crop losses due to plant diseases and the measures used to control them have significant agricultural and economic impacts. The shift from diverse small-scale to large-scale genetically uniform monoculture production, along with agricultural intensification and climate change, has led to several known epidemics in man-made agroecosystems that have been rendered more vulnerable to pathogens. One such example is hop growing, which is threatened by highly aggressive hop viroids. Since 2007, almost one-third (about 500 ha) of Slovenian hop gardens have been affected by severe hop stunt disease caused by Citrus bark cracking viroid (CBCVd), which continues to spread despite strict prevention measures. We have developed and validated a multiplex RT-qPCR (mRT-qPCR) for the sensitive detection of CBCVd, Hop latent viroid (HLVd), and Hop stunt viroid (HSVd). Singleplex RT-qPCR assays were designed individually and subsequently combined in a one-step mRT-qPCR assay. Hop-specific mRNA170 and mRNA1192 internal controls were also developed to detect possible PCR inhibition. Analytical specificity was tested on 35 samples from different hosts, geographic regions, and combinations of viroids. Method validation showed that mRT-qPCR had lower sensitivity than singleplex RT-qPCR, while specificity, selectivity, repeatability, and reproducibility remained unchanged. The newly developed assays were found to be robust, reliable, and suitable for large-scale screening of hop viroids.

First report of Sclerotinia sclerotiorum causing Sclerotinia wilt of hop (Humulus lupulus) in Poland.

The common hop (Humulus lupulus L., Cannabaceae) is a perennial plant cultivated in the temperate climate zone and used in the brewing and pharmaceutical industry. In June 2021, symptoms of wilting and subsequent drying of shoots were observed on hop plants (cv. Lubelski) in Lubelskie Province, in Poland (50°55'30.5"N, 22°10'35.4"E). Wilted shoots showed no symptoms of chlorosis. Usually both healthy and wilted shoots were present on the same plant. Approx. 20% of the plants in the 2 hectare hop garden showed these symptoms. An inspection of the underground parts of the infected shoots revealed a brown necrosis of the tissues partly covered by white mycelium with black sclerotia. These symptoms were characteristic for Sclerotinia sclerotiorum (Lib.) de Bary (Bolton et al. 2006), but this pathogen has never been detected in hop gardens in Poland before. In order to confirm the preliminary diagnosis, shoots from five different plants with symptoms of necrosis were collected, disinfected with 1% sodium hypochlorite for 1 min, rinsed with sterile water and dried. Twelve fragments from partially necrotized tissue were placed on potato dextrose agar (PDA) amended with chlortetracycline hydrochloride. After three days of incubation at room temperature and daylight, 75% of the explants had white or light grey mycelia present. Pure cultures were obtained by transplanting mycelium to fresh PDA. Within 4 days, the mycelium has reached the diameter of Petri dishes (90 mm). On PDA at room temperature and daylight, black spherical or cylindrical sclerotia formed after 6-14 days. Sclerotial size was 1.0 to 10.0 x 1.0 to 5.0 mm (average 2.8 x 2.0 mm; n = 57 from 3 plates). Five isolates were subjected to DNA extraction. Then ITS region was amplified and sequenced using primers ITS1/ITS4 (White et al. 1990). The sequences obtained from the five fungal isolates were identical with each other and BLAST analysis revealed also 100% identity with the GenBank records of S. sclerotiorum (e.g. KT224645, Baturo-Ciesniewska et al. 2017). One representative sequence of isolate Ss5HL was deposited to GenBank (OQ998981). Pathogenicity of the isolate Ss5HL was confirmed in inoculation tests on approx. 30 cm high, young shoots of hop plants (cv. Lubelski) grown from rootstock for 4 weeks in the greenhouse. Five plants were inoculated by placing mycelial discs from a 7-day-old culture on shoots and covering them with wet sterilized cotton pads and aluminum foil. Two control plants were treated in the same way but instead of mycelial discs pure agar discs were placed on the shoots. Then plants were kept in a climate chamber (80% relative humidity, 15-h light at 22°C, 9-h dark at 18°C). All fungal inoculated shoots wilted within 3-4 days, then necrosis developed and spread from the place of inoculation up the shoot. No tissue necrosis was observed below the place of inoculation. The control plants remained asymptomatic. The inoculation test was carried out twice with the same result. Fungal cultures reisolated from the inoculated shoots were morphologically identical with the culture used as inoculum. Isolate Ss5HL was deposited in the collection of the Westerdijk Fungal Biodiversity Institute (CBS 150077).To our knowledge, this is the first case of Sclerotinia wilt of hops in Poland and also in Europe, with the exception of one, nearly 100 years old report from the United Kingdom (Salmon and Ware 1936). S. sclerotiorum rarely occurs on hop but it can cause severe yield reduction if pathogen accumulates in the soil.

Alpha acids content in Czech hops from harvest 2022 - forecasts, reality and trends

From the brewing and commercial point of view, the content of alpha acids is the most important quality parameter of hops, which is subject to significant annual fluctuations. The established system for evaluating the content of alpha acids in Czech hops consists of pre-harvest and harvest predictions and a detailed analysis of reality based on the analysis of all purchasing lots of raw hops. It is differentiated according to varieties and hop growing areas. This article presents the results of the 2022 harvest, discusses the influence of weather conditions, the age of hop gardens and virus-free seedlings on the harvest results, and the relationship of predictions to reality. The average content of alpha acids in the majority Saaz variety in the Saaz, Auscha and Tirschitz hop growing regions was 2.88, 2.80 and 2.63% by weight in the original respectively. In all areas, the alpha acid content has been significantly affected by the age of the hop growths. Hybrid varieties coped with adverse weather conditions much better than most aromatic hops. The total production of alpha acids in Czech hops from the harvest of 2022 was 182.9 tons, one of the lowest in the last 15 years. It is due to the concurrence of two factors: the low yield per hectare and the content of alpha acids in Saaz hops. The cause was, similarly to Germany, an extreme deficit of precipitation and high temperatures during the vegetation season.

Alpha acids content in Czech hops from the harvest of 2021 – forecast, reality, trends

From the brewing and commercial point of view, the content of alpha acids is one of the most important quality parameter of hops, which is subject to significant annual fluctuations. The established system for evaluating the content of alpha acids in Czech hops consists of pre-harvest and harvest predictions and a detailed analysis of reality based on the analysis of all purchasing lots of raw hops. It is differentiated according to varieties and hop growing areas. This article presents the results of the 2021 harvest, discusses the influence of weather conditions, the age of hop gardens and virus-free seedlings on the harvest results, and the relationship of predictions to reality. The average content of alpha acids in the majority Saaz variety in the Žatec, Úštěk and Tršice areas was 4.45, 4.20 and 3.36% by weight in the original respectively. In all areas, the alpha acids content has been significantly affected by the age of the hop growths. The total production of alpha acids in hops harvested in the Czech Republic in 2021 was 414.5 tons. The harvest is the highest in the last 25 years; the result is due to the combination of two factors, both high yield per hectare and high alpha acids content.

Projection of 21st century irrigation water requirements for sensitive agricultural crop commodities across the Czech Republic

This study quantified the crop water consumption, crop-specific irrigation requirements, and availability of water resources to catchments under climate change in the Czech Republic (CZ). Within the SoilClim model and BILAN-WATERES hydrological water balance modeling process, we tried to answer the question of whether there are at least theoretical water resources in the individual catchments of the CZ that could cover possible higher demands for irrigation. An ensemble of five global climate models under the moderate representative concentration pathway (RCP4.5) from the EURO-CORDEX initiative was chosen to project the future water use indicators. The irrigation water requirement indicators for the growing season (GS) of vineyards, hop gardens, orchards, vegetables, and fodder crops were calculated in 1143 catchments for two periods, 2031–2050 (Sc1) and 2061–2080 (Sc2), compared to the observed period 1961–2020 (Obs). To project irrigation scenarios in agricultural water management, the following water use indicators were quantified: relative soil moisture at 0–40 cm (AWR1) and 0–100 cm (AWR), crop water balance (Rain-ETa), irrigation water requirement (Irrig), and the ratio of actual and reference evapotranspiration (ETratio). To assess areas with a critically low water supply and quantify the frequency of water deficit during the GS of each crop, we calculated the number of days with extreme values of water use indicators. Quantification of the extreme irrigation characteristics reflected the highest depletion of soil moisture and the highest water demands, i.e., when the assessed indicators reached the 25th percentiles. For highly marketable vegetables, the largest deficit in Rain-ETa during the GS for Sc1 was projected. If current vegetable growing areas and cropping systems remain unchanged, Irrig will increase by 10.2% by the end of the 21st century under RCP4.5. Although current potato planting areas have soils with a high available water capacity, they will become controlled by the water deficit over the next few decades. The accumulated vineyard water required suggests that 15% and 25% of irrigation water will be lost by evaporation from the soil surface during the 2030s and 2080s, respectively. However, changes in future hopyard irrigation extent and amounts may have important implications in largely cropped irrigation hotspots. In the main traditional hop region for the 2030s, we project a 25% depletion of soil moisture and an increase of ETratio< 0.4 by up to 5.3%. The projection of a high frequency of days with an ETratio< 0.4 and AWR1 < 30% for fodder crops was related to the most risk-prone areas with an extreme lack of moisture in the regions with the most developed animal production. Thus, there will be insufficient fodder supply to the livestock sector due to any water stress during the production season under climate change conditions.

Management of infiltration processes in hop gardens

Management of infiltration processes in hop gardens

Impact of cover crops in inter-rows of hop gardens on reducing soil loss due to water erosion

Soil degradation caused by water erosion in sloping hop gardens is definitely a serious issue because the space in inter-rows is without plant residues for most of the year in traditional cultivation. Cover crops in inter-rows of hop gardens and their efficiency in soil conservation are assessed in this article. There is only little research available in this area, and our data bring unique information on water erosion in hop gardens. Technologies with different types of cover crops were always compared with the conventional cultivation. The research was conducted within the years 2016–2020. A field rainfall simulator was used to determine the soil conservation effectiveness of selected technologies. The simulated rainfall was performed in two stages of cover crops growth with the main aim to measure the overall soil loss. The outcomes from the measurements confirmed that cover crops in inter-rows of hop gardens protect the soil surface from falling raindrops and significantly (P-value &amp;lt; 0.05) reduce soil loss. It can be concluded that this technology had a soil conservation effect already one month after sowing, and it is a basis for sustainable agricultural management on sloping hop gardens.

Правове регулювання галузі розсадництва України

The authors have analyzed the role of the nursery practice in the agricultural economics of Ukraine. The specificity of the technologies, organizational structures has been described as well as the material means of the production of the planting stock of the fruit and small fruit crops and grape. The comprehensive enumeration of the legislative acts and normative and lawful documents has been presented with which the state regulates the economic and organizational and lawful relations in the above mentioned industries. The latest three years data have been presented concerning the state financial support of the economic agents that establish young orchards, vineyards and hop gardens. The purpose and state have been noted of building the scientific-manufacturer biotechnological hothouse complex for the production of the high quality basic material on the basis of the principal scientific institution of the horticultural branch - Institute of Horticulture of NAAS of Ukraine. The calculations have been presented contained in the Programmer of the Development of the Horticulture of Ukraine up to 2025 as regards the necessity of planting new orchards end small fruit plantations in order to meet the needs of the population and processing enterprises and increase the vitamin product’s export. The analysis was corried out of the indices of the energy expenditures on the establishment of a hectare of a grape plantation. The methods of the perennial crops growing reproduction have been depicted. The necessity of the transfer of the nursery, farms on the virus-free standard planting stock adapted to the soil and climatic conditions of the concrete region has been substantiated of as well as of the establishment of new parental plantation of fruit and small fruit crops and grape, creation of parental-seed and parental-cutting gardens, of parental gardens of the grapevine rootstocks and graft sticks and nurseries for manufacturing of the necessary amount of the planting stock of the modern crop and varietal composition in Ukraine. The analysis has been conducted of the changes in the legislature of Ukraine which could be useful for seed growing. The problems of the nursery sector have been determined that require solving yet at the legislative level. The concrete propositions must be presented in the form of the recurrent changes in the law of Ukraine ‘On Seeds and Planting Stock’.

Distribution of root system of hop plants in hop gardens with regular rows cultivation

Spatial distribution of the root system of hop (Humulus lupulus L.) in the soil profile is a less explored issue. However, it is known that it can play an important role in the development of new tillage technologies, fertilisation and irrigation, including the use of precision farming principles. In the period from 2015 to 2018, the distribution of the hop root system was evaluated on twelve hop plants of five Czech hop cultivars. The age of the plants ranged from 3 to 15 years. The evaluation took place in the Saaz region at regularly cultivated hop gardens. As part of the evaluation, the root systems of hop plants were removed from the soil profile and subsequently spatially reconstructed. With the help of infrared image analysis, the root intensity in the soil profile and the morphology of the root systems were determined. The root depth of the plants ranged from 1 m to 2.25 m. The lateral width of the hop root system ranged from 0.6 m to 1.5 m. As a result of the rows cultivation, the lateral development of the roots in the upper soil layers was limited. The results were confirmed using the infrared image analysis method to specify the distribution of the root system and the root density of hop plants in the soil profile.

Real-time RT-PCR detection of Citrus bark cracking viroid (CBCVd) in hops including an mRNA-based internal positive control

Citrus bark cracking viroid (CBCVd), formerly known as pathogen in the genus Citrus and first detected in Slovenian hops in 2014, threatens hop production as it leads to important economic losses. Reduction in yield and quality and even death of the infected plants within a few years are typical observations due to CBCVd infections of hops. The viroid is easily transmitted and spreads rapidly. As it cannot be controlled by plant protection measures, avoiding its introduction into hop gardens and eradicating first centres of infection are of utmost importance. An indispensable prerequisite is a reliable detection method suitable for large-scale routine testing. In this study, the development of primers and probe for real-time RT-PCR for sensitive CBCVd detection is described. To exclude “false negative” results, a nad5 mRNA-based internal positive control was included. To our knowledge, this is the first time such a duplex real-time RT-PCR detection method for CBCVd at least in hops is described. In addition, first method validation data are presented.

Reduction in soil organic matter loss caused by water erosion in inter-rows of hop gardens

Currently, when cultivating Humulus lupulus, there is no systematic farming reducing soil erosion in the Czech Republic. As a result, annual irreversible soil and organic matter losses due to intensive rains occur on soils of hop gardens threatened by erosion. One of the possibilities how to reduce water erosion in hop gardens and thereby to decrease the amount of washed away organic matter is using the conservation effect of suitably selected catch crops in inter-rows. Two catch crops were selected to test: Phacelia tanacetifolia and a grass-legume mixture. Organic matter in soil is a key factor to maintain the stable soil environment and our results show that the amount of washed away organic matter was reduced by more than half compared to conventional farming (60% – naturally moist soil, 54.5% – soil already saturated). The research was conducted between the years 2016 and 2017 close to the village of Solopysky. Soil loss was investigated using a rainfall simulator from which the organic matter washing away was consequently determined. The rainfall simulator is a device enabling to measure not only the soil loss due to water erosion but also the volume of surface runoff, infiltration etc. From the outcomes of measurements carried out with rainfall simulator it is apparent that these technologies have a significant soil conservation potential in hop gardens.

Impact of the neozoic ladybird Harmonia axyridis on the coccinellid community in Bohemia

Since 2007, when Asian harlequin ladybird Harmonia axyridis (Pallas) has become a part of coccinellid entomofauna in Bohemian hop gardens, the spectrum of aphidophagous coccinelids has changed considerably. Whereas, in the period before its invasion native species Coccinella septempunctata L., Adalia bipunctata L. and Propylea quatuordecimpunctata L. used to be the dominant predators of damson hop aphid (Phorodon humuli Schrank), Harmonia axyridis has been the most frequent ladybird species in Zatec (Saaz) hop growing region nowadays. Population densities of adults of aphidophagous ladybirds in the middle of the eighties (1985), shortly before the invasion of the above-mentioned Asian species (2004) and in the recent years (2011 and 2015) are compared. Whereas four years ago harlequin ladybird represented just 10% of the total Coccinellidae, in 2015 it forms nearly half of coccinellid adults observed in hop gardens in NW Bohemia. It is followed by tiny species P. quatuordecimpunctata and A. bipunctata, which consist together more than one third, whereas in the middle of the eighties they generally formed two thirds of the coccinellid populations. On the other hand adults of C. septempunctata have become less abundant. It may be caused by aggressiveness of H. axyridis, whose larvae were observed to feed on eggs and young larvae of C. septempunctata. To prevent attacks from larvae of H. axyridis, females of C. septempunctata appear on hop plants and begin to lay eggs earlier as illustrated by the presence of the third and the fourth instars larvae in the time when larvae of H. axyridis reach much smaller size and are not competitive enough. Decline in population densities of native species of ladybirds on response to arrival of the Asian invasive species, their responses and potential efficiency of aphidophagous coccinelids, including H. axyridis, on damson hop aphid will need to be observed in the future so as us to know more about this issue.

Genome-Wide Transcriptomic Analysis Reveals Insights into the Response to Citrus bark cracking viroid (CBCVd) in Hop (Humulus lupulus L.).

Viroids are smallest known pathogen that consist of non-capsidated, single-stranded non-coding RNA replicons and they exploits host factors for their replication and propagation. The severe stunting disease caused by Citrus bark cracking viroid (CBCVd) is a serious threat, which spreads rapidly within hop gardens. In this study, we employed comprehensive transcriptome analyses to dissect host-viroid interactions and identify gene expression changes that are associated with disease development in hop. Our analysis revealed that CBCVd-infection resulted in the massive modulation of activity of over 2000 genes. Expression of genes associated with plant immune responses (protein kinase and mitogen-activated protein kinase), hypersensitive responses, phytohormone signaling pathways, photosynthesis, pigment metabolism, protein metabolism, sugar metabolism, and modification, and others were altered, which could be attributed to systemic symptom development upon CBCVd-infection in hop. In addition, genes encoding RNA-dependent RNA polymerase, pathogenesis-related protein, chitinase, as well as those related to basal defense responses were up-regulated. The expression levels of several genes identified from RNA sequencing analysis were confirmed by qRT-PCR. Our systematic comprehensive CBCVd-responsive transcriptome analysis provides a better understanding and insights into complex viroid-hop plant interaction. This information will assist further in the development of future measures for the prevention of CBCVd spread in hop fields.

Deep‐sequencing revealed Citrus bark cracking viroid (CBCVd) as a highly aggressive pathogen on hop

Newly emerging or re‐emerging diseases are a constant and significant threat to agricultural production, so prompt and accurate identification of the causative agents is required for rapid and appropriate disease management. Classical methods of pathogen detection can be successfully supplemented by next‐generation sequencing (NGS), whereby sequence analysis can help in the discovery of new or emerging diseases. In 2007, hop growers in Slovenia reported the appearance of severely stunted hop plants, a phenomenon that spread rapidly within hop gardens and among farms. Classical diagnostic methods were unable to detect a new pathogen; therefore, single step high‐throughput parallel sequencing of total RNA and small RNAs from plants with and without symptoms was employed to identify a novel pathogen. The sequences were assembled de novo and also mapped to reference genomes, resulting in identification of a novel sequence of Citrus bark cracking viroid (CBCVd) in the stunted hop plants. Furthermore, the presence of this novel pathogen on hop was confirmed by RT‐PCR analysis of 59 plants with symptoms from 15 hop gardens, representing the main outbreak locations identified by systematic disease monitoring, and small RNA Illumina sequencing of the bulked RNA sample. The high infectivity of the newly identified CBCVd was also confirmed by biolistic inoculation of two hop cultivars, which developed aggressive symptoms in controlled conditions. This study shows the feasibility of deep sequencing for the identification of causative agents of new diseases in hop and other plants.

THE INFLUENCE OF THE AGE OF A HOP PLANT ON THE QUALITY OF HOP AROMAS IN BEER

Hops (Humulus lupulus L.) are one of the most important ingredients in beer in terms of taste and quality - providing bitterness, aroma and fullness. However, it is difficult to produce beer products with a consistent level of quality as hop quality may vary due to the climate, cultivation method, soil conditions, root condition, etc. The purpose of this study was to elucidate the influence of hop hop plant age on beer quality, especially on the aroma of beer. We examined differences in hop aroma by means of sensory evaluation and chemical analysis. In addition, in order to assess how the vegetative growth and reproductive growth of hops were dependent on hop plant age, the length of the vine and leaf size, stem diameter and flowering were monitored throughout the growing season. The hop samples used were selected from 8 hop gardens in the Saaz region during the 2010 and 2011 growing seasons. A comparison of vegetative growth, leaf size and stem diameter showed that hop plants that were younger (in terms of hop plant age) were larger and flowered later. In addition, the α-acid content was higher in the younger hops. As a result, significant differences in hop aroma characteristics were observed in beer made from the different hop samples. Based on these results, it was concluded that the more luxuriant vegetative growth and late flowering associated with the younger roots changed secondary metabolism, which also affected the generation of terpenes, thereby altering hop aroma quality in the beer produced. This information can help the brewers improve quality and design hop and beer products with a better aroma.

Dose expression for plant protection products

Specific scopeThis standard defines how the dose of plant protection products is expressed and describes the parameters, specific to the site and type of application, which should be recorded so that the dose can be determined in a standard way whatever the crop or product, or the equipment used for treatment. Included in the standard is a description of dose expression methods in three‐dimensional crops (aerial parts of plants in commercial orchards (e.g. pome fruit, stone fruit), hop gardens and vineyards, small fruit and cane fruit crops (e.g. blueberries, gooseberries, raspberries), taller, isolated fruit trees and other high‐growing crops such as fruiting vegetables both in the open field and under protected cultivation) and methods for converting between different dose expression terms.Specific approval and amendmentFirst approved in 2005–09.Revision approved in 2012–09.

First Report of Hop stunt viroid Infecting Hop in Slovenia.

Hop (Humulus lupulus), of the Cannabaceae family, is a dioecious perennial climbing plant that is native to Asia, North America, and Europe and is commercially grown in many countries for its use in brewing and the pharmaceutical industry. Slovenia has a more than 100-year-old hop-growing tradition and it is an important national agricultural business, with 90% of production exported to foreign markets. Since 2007, symptoms similar to Hop stunt viroid (HSVd) infection have been observed in several hop gardens with cvs. Celeia, Bobek, and Aurora in the Savinja Valley and Koroška Region. Symptoms include stunting, leaf curl, small cone formation, and dry root rot. In the first year of finding the disease, the incidence varied from 1 to 30% and increased rapidly (by as much as 10%) each subsequent year, predominantly along plant rows. For molecular identification of the pathogen, RNA was extracted from leaves and cones of symptomatic and asymptomatic plants from two different hop gardens with cv. Celeia using Tri Reagent (T9424; Sigma-Aldrich, St Louis, MO). Reverse transcription-PCR was carried out using two pairs of specific HSVd primers, HSVdI/HSVdII and HSVdeI/HSVdeII (3,4). Both primer pairs gave a single PCR product from tissue from symptomatic plants, with expected lengths of ~300 bp, but no amplicons were produced using samples from asymptomatic plants. PCR products from HSVdI/HSVdII were subjected to direct sequencing and HSVdeI/HSVdeII products were cloned in PCR Script SK (+) (Stratagene, La Jolla, CA) vector and sequenced. Five sequences (EMBL Accession Nos. HE575344, HE575345, HE575346, HE575347, and HE575348) were obtained, which revealed 96 to 99% sequence identity with various HSVd variants (grapevine, citrus, and cucumber) reported in GenBank of the National Centre for Biotechnology Information (NCBI). HSVd belonging to the Hostuviroid genus, Pospiviroidae family, has been previously reported in hop in Japan, South Korea, North America, and China (1,2). To our knowledge, this is the first report of the detection of HSVd on hop in Europe. Strict phytosanitary measures have been taken to prevent further spread and to eradicate HSVd infections.

Composition and vertical distribution of free living and plant parasitic nematodes in hop gardens in the Czech Republic

Abstract Composition and vertical distribution of soil nematode communities within soil profile were investigated in eight hop gardens in Czech Republic. In total, the presence of 78 nematode genera was confirmed. Genus Drilocephalobus (Coomans &amp; Coomans, 1990) is new for fauna of the Czech Republic. The highest abundance of soil nematodes was found at a depth of 0–10 cm and declined with increasing depth of soil profile. The most dominant genus was Bitylenchus, followed by genera Acrobeloides, Ditylenchus, Chiloplacus and Cervidelus. Ten genera of plant parasitic nematodes were recorded: Bitylenchus (with prevalence of B. dubius), Helicotylenchus, Heterodera (with absolute prevalence of H. humuli), Geocenamus, Longidorella, Longidorus (only L. elongatus), Merlinius (with prevalence of M. brevidens), Paratylenchus and Pratylenchus. Low population densities of predators and omnivores, low values of the community indices (MI, ΣMI, SI, and CI), and high values of NCR, EI, and PPI/MI ratio indicated disturbed nematode communities in hop gardens and bacteria-dominated decomposition pathways in the soil food web.

Population genetic structure of the noxious weed Amaranthus retroflexus in Central Europe

Genetic variation was assessed in a range of populations of Amaranthus retroflexus using isoenzyme analysis. Population genetic diversity was measured by evaluating patterns of variation at six putatively neutral isoenzyme loci (comprising 24 putative alleles) within and among 20 populations of A. retroflexus collected in different habitats: ruderal habitats, cereal fields and hop gardens. Amaranthus retroflexus is a noxious weed of North American origin that infests various crops. Overall, A. retroflexus displayed moderate levels of genetic diversity in comparison with other herbaceous plants. The percentage of polymorphic loci was 50.0%, with mean values of 2.01, 0.142 and 0.227 for the average number of alleles per polymorphic locus ( A), observed heterozygosity ( H o) and expected heterozygosity ( H e), respectively. A discrepancy between observed and expected heterozygosity and significant differences from H-W expectation indicate that there is an excess of homozygotes in many populations. As a result, there is strong evidence of inbreeding within populations ( F IS = 0.382) and significant population differentiation ( F ST = 0.270). Even though the species is partly autogamous, inbreeding does not lead to strong inbreeding depression resulting from self-pollination, as inbreeding has no effect on the success of the species in today's countryside. Moreover, allele frequencies detected in agricultural habitats (i.e., cereal fields and hop gardens) differed from those detected in populations collected from ruderal habitats, which is probably caused by systematic application of herbicides in agricultural ecosystems.