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Clubroot, caused by

Blackleg is a devastating disease of winter oil seed rape (WOSR) caused by the two species Leptosphaeria maculans and L. biglobosa “brassicae”. In this study, Loop-Mediated Isothermal Amplification (LAMP) assays were developed using two primer sets, SirP and PKS5, to identify and monitor L. maculans “brassicae”, and one primer set PKS21 to monitor L. biglobosa “brassicae”. The three primer sets were tested in real-time LAMP with DNA templates from 38 Leptosphaeria spp. reference isolates. The SirP and PKS5 primer sets exclusively amplified DNA from L. maculans isolates whereas, the PKS21 primers amplified DNA solely from L. biglobosa. Further specificity tests with DNA templates from other ascomycetes showed that both PKS primers were highly specific to Leptosphaeria. The SirP primer set produced in a few cases non-specific amplifications, but they were easily differentiated from the positive reactions by the differences in melting curve temperatures. The detection limits of LAMP assays with PKS21, PKS5 and SirP primers were at 100 fg, 30 pg and 180 fg DNA, respectively. DNA from leaf segments with typical L. maculans lesions was successfully amplified using primer set SirP, as was visually indicated by the colour change of phenol red from pink to yellow. This feature makes the method suitable for simple screening of L. maculans in WOSR leaves and in spores collected by spore traps.

Clubroot, caused by Plasmodiophora brassicae, is a crucial oilseed rape disease worldwide. Information on the virulence of P. brassicae populations is essential to apply disease control with proper clubroot-resistant cultivars. In 2016–2020, 84 isolates of P. brassicae were collected in the Czech Republic (CZ), Germany (DE), Poland (PL), and Sweden (SW). Pathotypes were designated using 17 Brassica hosts, including the European Clubroot Differentials (ECD), Somé set, and clubroot-resistant oilseed rape cv. Mendel. According to the ECD set, virulence analyses differentiated the isolates into 42 pathotypes. The most common pathotypes were 16/31/31 (in DE, PL, and SW) and 16/06/12 (in CZ, DE, and PL). Six pathotypes were found according to the Somé set, including 1–4 pathotypes per country. P1 was most prevalent in DE, PL, and SW, while P3 was abundant in CZ, DE, and PL. The current study provides clear evidence for a shift towards increased virulence in P. brassicae populations compared to previous studies. Several isolates overcame the resistance of cv. Mendel and of Brassica rapa genotypes ECD 01 to ECD 04. Considering all investigated samples, significant negative correlations were found between clubroot incidence and the frequency of oilseed rape in crop rotation, as for clubroot incidence and soil pH.

A decision support system, SBN-Watch, was developed to demonstrate the influence of crop rotation and the choice of sugar beets (Beta vulgaris) varieties on the sugar beet cyst nematode Heterodera schachtii Schmidt (SBN) population and sugar beets yield. The database in SBN-Watch consists of a varietal unit with five sugar beet varieties representing the three categories "Standard," "Tolerant" and "semi-tolerant." Data of minimal yield (m), tolerance limit (T), and population dynamic parameters were obtained from published commercial field trials conducted in Sweden and Denmark in 2011. Additionally, a sanitation intercrop unit with different resistant classes of white mustard (Sinapsis arvensis) and oil seed radish (Raphanus sativus) was included. The relationship between initial population (Pi) and sugar yield as well as SBN final population in soil (Pf) was calculated by two Seinhorst equations. Few data inputs are required to be entered by the user in SBN-Watch, mainly the initial population (Pi), expected sugar price and exchange rate of € to SEK. The calculated reproduction factor (Rf) values using SBN-Watch corresponded well with varietal characteristics, where the standard variety Mixer had the highest (Rf) values. The influence of the initial SBN population on the calculated sugar yield (tonnes ha-1) was generally small at Pi < 2. A decision support system, SBN-Watch, was developed to demonstrate the influence of crop rotation and the choice of sugar beets (Beta vulgaris) varieties on the sugar beet cyst nematode Heterodera schachtii Schmidt (SBN) population and sugar beets yield. The database in SBN-Watch consists of a varietal unit with five sugar beet varieties representing the three categories “Standard,” “Tolerant” and “semi-tolerant.” Data of minimal yield (m), tolerance limit (T), and population dynamic parameters were obtained from published commercial field trials conducted in Sweden and Denmark in 2011. Additionally, a sanitation intercrop unit with different resistant classes of white mustard (Sinapsis arvensis) and oil seed radish (Raphanus sativus) was included. The relationship between initial population (Pi) and sugar yield as well as SBN final population in soil (Pf) was calculated by two Seinhorst equations. Few data inputs are required to be entered by the user in SBN-Watch, mainly the initial population (Pi), expected sugar price and exchange rate of € to SEK. The calculated reproduction factor (Rf) values using SBN-Watch corresponded well with varietal characteristics, where the standard variety Mixer had the highest (Rf) values. The influence of the initial SBN population on the calculated sugar yield (tonnes ha−1) was generally small at Pi < 2.

Use of resistant cultivars is considered the most effective tool in managing clubroot. Three clubroot-resistant commercial winter oilseed rape (OSR) cultivars and a susceptible ‘Cultivar mix’ were evaluated for disease severity index (DSI) and yield performance in field soils, selected for varying abundance of natural inoculum of Plasmodiophora brassicae. Seven field trials were carried out during 2017–2019 in winter OSR crops, and comparative bioassays were performed in a growth chamber. Substantial variation in clubroot infection between years was observed in the field trials. For Cultivar mix, a negative correlation (y = −252.3ln(x) + 58,897.6) was found between inoculum density and seed yield in five trials, whereas no correlation was found for the resistant cultivars. In bioassays, Cultivar mix exhibited a significantly high correlation between DSIb and number of gene copies g−1 soil (R2 = 0.72). For resistant cvs., Mentor and Alister, correlation was R2 = 0.45 and 0.58, respectively, indicating that resistance was under pressure. In field trials, DSIf of the resistant cultivars was lower (&lt, 27). The recommendation is thus to use clubroot-resistant cultivars of OSR as part of Integrated Pest Management in situations where abundance of P. brassicae DNA exceeds 1300 gene copies g−1 soil.

Background Oat (Avena sativa L.) is an important cereal crop for livestock feed and human consumption. The largest oat-producing countries are located in the Northern Hemisphere with Sweden as the tenth largest producer. Oat production is challenged by different diseases that can lead to significant yield reductions and impaired grain quality. The use of efficient and sustainable plant protection management is of great economic and ecological importance. The systematic map in this study aims to provide a knowledge base inventory and to identify areas that need to be researched in the future in terms of plant disease management for more sustainable oat production. Methods Literature searches were conducted in both academic bibliographic databases and relevant online sources of grey literature. A time-span restriction of 40 years (1978–2018) was applied to the searches. English was used in all searches, and Swedish, Norwegian and Danish languages were used in the grey literature searches. The screening process, which followed a protocol with eligibility criteria, was conducted at three levels: title, abstract and full text. Metadata incorporating bibliographic information, study location, climatic zone, disease name, the common and scientific names of the disease-causing organism, pathogen type, intervention and management methods, diseased plant part, plant stage, and outcome were extracted from the studies and included in the systematic map. The systematic map findings are visualized in figures and tables and described. All included studies can be found in a searchable database. Review findings A total of 58 eligible articles, most (n = 51) from scientific journals published in English, were included in the systematic map. A majority of the studies were conducted in the Northern Hemisphere in temperate climatic zones, where most of the world’s oats are produced. The earliest article was published in 1980, followed by an oscillating temporal distribution of articles over the following years. By country, Canada had the highest number of articles, and by region, Europe had the highest number. Fungi were the most studied pathogen type, and a total of 16 different diseases were reported. Fusarium head blight (Fusarium spp.) and crown rust (Puccinia coronata) were the most studied diseases. In total, 17 different intervention management approaches for controlling the diseases were analyzed in the articles, with cultivar resistance and pesticide application as the most studied methods. Conclusion The map highlights the low quantity of available relevant field research on oat disease management. To our knowledge, this is the first systematic map of crop protection. This map provides a database of scientific literature that can be used to develop sustainable disease management strategies. The method used in this study has great potential and can also be used to benefit other crops. Research is often based on the availability of funding, and this map could be a useful tool for researchers and funding organizations to identify relevant research topics that need to be further studied. In addition, this systematic map offers a useful tool for field-based advisors in providing scientifically relevant crop protection strategies for farmers.

Seed treatment with mineral nutrients in spring oilseed rape (SOR) under cold climatic conditions has the potential to improve the outcome of production. The objectives of this study were to investigate the effects of mineral nutrients applied as seed treatment on germination and growth of roots and biomass in SOR. In addition, seed yield and oil content were also measured. Seed vigour tests and in-field experiments were performed in Central Sweden in 2016 and 2017. Seven products with different composition of mineral nutrients were applied to the seed in a combination with binder, filler and fungicide (BFF), or applied directly onto the seed. The results showed that a treatment with mineral nutrients increased the plant size at stage BBCH 60 (early flowering stage) when the products were applied in combination with BFF in the field experiments. However, the increased plant size did not influence seed yield. Furthermore, when seeds were treated only with a nutrient product the addition of BFF decreased plant size by 10% on average and seed and crude fat yields by 4% on average. The use of BFF may thereby be questioned and is subject to further investigation.

A decision support system, SBN-Watch, was developed to demonstrate the influence of crop rotation and the choice of sugar beets (Beta vulgaris) varieties on the sugar beet cyst nematode Heterodera schachtii Schmidt (SBN) population and sugar beets yield. The database in SBN-Watch consists of a varietal unit with five sugar beet varieties representing the three categories “Standard,” “Tolerant” and “semi-tolerant.” Data of minimal yield (m), tolerance limit (T), and population dynamic parameters were obtained from published commercial field trials conducted in Sweden and Denmark in 2011. Additionally, a sanitation intercrop unit with different resistant classes of white mustard (Sinapsis arvensis) and oil seed radish (Raphanus sativus) was included. The relationship between initial population (Pi) and sugar yield as well as SBN final population in soil (Pf) was calculated by two Seinhorst equations. Few data inputs are required to be entered by the user in SBN-Watch, mainly the initial population (Pi), expected sugar price and exchange rate of € to SEK. The calculated reproduction factor (Rf) values using SBN-Watch corresponded well with varietal characteristics, where the standard variety Mixer had the highest (Rf) values. The influence of the initial SBN population on the calculated sugar yield (tonnes ha(−1)) was generally small at Pi < 2.

Multispecies cropping systems contribute to sustainable agriculture with multiple ecosystem services. Effects of intercropping of organically managed maize and faba beans to silage on acquisition of mineral nutrients in shoots of both crops and on leaf spot progression in faba beans were investigated. Three field experiments were performed with maize and faba bean intercropped or grown separately. Intercropping increased shoot concentrations of K, Ca, Mg, Na, S and B in faba bean, and shoot concentrations of Cu, Zn and Mo in maize. Thus, the ecological complementary effects enhance feed quality. Disease severity index (DSI) of leaf spots in faba beans was reduced by intercropping by 42–57%, partly due to an increased Cu acquisition at sites where the Cu availability was low. There was a significant negative linear relationship between Cu concentration in shoots and DSI of leaf spots. Total uptake of mineral nutrients per land area was greater in the intercropping system with a total LER > 1 for all mineral nutrients, except for P, Ca and Mn at one of the sites. Increased nutrient use efficiency, due to facilitative uptake from the soil, and the production of crops with higher contents of minerals compared with monocropping, are benefits of intercropped maize and faba beans.

Increased knowledge on how to use organic amendments will increase crop productivity in organic farming. The effect of autumn and spring application of organic fertilisers on the yield of organic winter oilseed rape (WOR) with various preceding crops was studied at eight organic farm sites in southern Sweden in 2008/2009 and 2009/2010, in a two-factor experiment. Autumn N fertilisation ( F 1) comprised Biofer, applied at 0 and 50 kg N ha −1 , and spring N fertilisation ( F 2) comprised increasing rates of Vinasse (0, 50, 100, 150, 200 kg N ha −1 ). How soil mineral N, N uptake in late autumn and early spring, plant-available soil N during spring and summer (SoilN plant ) and yield level was associated with economically optimum N fertilisation rate (OptN) in spring was investigated. Autumn N application (Biofer) only increased yield by 140–410 kg ha −1 at three sites, when there was a risk of low plant-available soil N during spring and summer, due to dry weather conditions or N immobilisation in soil caused by residues of previous grass ley crops. Nitrogen fertilisation during autumn cannot be recommended due to the high levels of soil mineral N in late autumn and risk for N leaching. Spring N fertilisation (Vinasse) can be recommended when the preceding crop is a grass ley, as yield increases were the highest, 820–1400 kg ha −1 . Spring N fertilisation had no impact on yield and cannot be recommended when the preceding crop is pasture or clover, providing that N uptake during autumn is great and/or if N availability in soil during spring and summer is not likely to be limited by e.g. dry weather conditions and weeds. Regression analysis confirmed that plant-available soil N was associated with OptN rate in spring and showed that factors such as soil mineral N, N uptake in late autumn, SoilN plant and yield level must be considered when estimating spring N fertilisation.

Manganese (Mn) deficiency is commonly connected with soil properties, and application of Mn is frequently performed to winter barley ( Hordeum vulgare L.) in fields with a history of deficiency. Since the availability of Mn also is affected by seasonal variations, there is a risk of excessive application in some seasons while the application is not sufficient in other seasons in such fields. The objective of this study was to investigate the effect of foliar application of Mn in autumn and early spring on barley winter hardiness, in combination with or without N application in autumn. We also evaluated a commercially available Mn-scanner as a tool to identify the need for Mn application. Two field experiments per growing season were performed in south Sweden in 2010–2011 and 2011–2012 in fields where Mn deficiency often occurs. Foliar applications of various Mn products were made once (in October) or twice (in October and in March the following year). A single dose of 0 or 30 kg ha −1 N was applied, as N NO 3 , in October. Barley leaves were collected and Mn status determined with the NN-Easy55 Mn-scanner. Yield was determined in the field experiments in 2011–2012. Our results showed that the requirement of Mn application varied between sites and seasons and was affected by N supply. Mn application increased the winter survival by 33% and the grain yield by 36% in the barley plants with the lowest Mn status in autumn. The risk of Mn deficiency increased when N (NO 3 N) was applied in autumn. In one of the harvested field experiments, yield was suppressed by N application in autumn and was recovered by Mn application. Repeated Mn applications might be required to increase winter survival and grain yield, especially when N has been applied in the autumn. To reach an optimal Mn application, tools such as the NN-Easy55 Mn-scanner can be used to monitor the Mn status of the plants. Thereby unnecessary application of Mn is prevented and sufficient amounts are applied during deficiency.

The efficiency of four different organic fertilisers applied to winter oilseed rape, before (early) or at the beginning of regrowth in spring (normal application time), was studied in two row spacing systems of 12 and 48 cm with inter row hoeing to provide strategies to optimise spring nitrogen (N) fertilisation to organic winter oilseed rape. Six annual field experiments were performed during 2005–2008 in south central Sweden. The following amendments, i.e., Vinass from yeast production, Biofer meat and bone meal, dairy slurry and chicken manure, were applied at a rate corresponding to 100 kg N ha−1. Crop N uptake, seed yield and oil content indicated greater and earlier N availability of Vinass after application compared with the other amendments. Yield increased by 1,300 kg ha−1 at early spring application (27 March) of Vinass and by 700 kg ha−1 when applied at normal application time (18–26 April). The yield increase was 400 kg ha−1 regardless of application time of Biofer, chicken manure and dairy slurry. The substantially greater yield increase in the Vinass application in relation to the other fertilisers demonstrated the yield potential when N is available earlier. The smaller effect on the yield by the other organic amendments indicated that the N release was not synchronised with the crop demand, and available too late during crop development to affect yield or less N was available due to N losses. Consequently, only Vinass can be recommended for spring application. The two row spacing systems tested can both be recommended, since yield levels were similar.

Cultivation of forage maize is increasing in Sweden. Sole maize is low in protein and supplementation of protein feed is needed. This study investigated whether forage maize and legumes can be intercropped in a system suitable for farmers (simultaneous sowing and harvest) under Swedish climate conditions, and whether intercropping maize and faba bean improves the forage quality compared with sole maize. Two field experiments were performed in which maize intercropped with faba bean (Vicia faba L.) in alternate rows with 0 or 60 kg N/ha was compared with sole maize crop with 120 kg N/ha. Maize dry matter (DM) yield decreased by intercropping (from mean 14,171 kg DM/ha for sole maize to 8,888–10,791 kg DM/ha for intercropped maize). Mean yield of faba bean ranged from 2,907 to 2,966 kg DM/ha. Compared with sole maize, intercropped treatments slightly increased forage protein content (mean increase 10–15 g/kg DM). Furthermore, intercropping increased forage in vitro organic matter digestibility by 4 % units (from 80.8 to 84.7 %), while the starch concentration slightly decreased from 316 to 236–254 g/kg DM. Intercropping increased neutral detergent fibre concentration from 435 to 478–497 g/kg DM and the sugar concentration from 57.3 to 61.5–72.3 g/kg DM. The results showed that intercropping silage maize and faba beans is possible under Swedish climate conditions.

Outbreaks of clubroot disease caused by the soil-borne obligate parasite Plasmodiophora brassicae are common in oilseed rape (OSR) in Sweden. A DNA-based soil testing service that identifies fields where P. brassicae poses a significant risk of clubroot infection is now commercially available. It was applied here in field surveys to monitor the prevalence of P. brassicae DNA in field soils intended for winter OSR production and winter OSR field experiments. In 2013 in Scania, prior to planting, P. brassicae DNA was detected in 60% of 45 fields on 10 of 18 farms. In 2014, P. brassicae DNA was detected in 44% of 59 fields in 14 of 36 farms, in the main winter OSR producing region in southern Sweden. P. brassicae was present indicative of a risk for >10% yield loss with susceptible cultivars (>1300 DNA copies g soil−1) in 47% and 44% of fields in 2013 and 2014 respectively. Furthermore, P. brassicae DNA was indicative of sites at risk of complete crop failure if susceptible cultivars were grown (>50 000 copies g−1 soil) in 14% and 8% of fields in 2013 and 2014, respectively. A survey of all fields at Lanna research station in western Sweden showed that P. brassicae was spread throughout the farm, as only three of the fields (20%) showed infection levels below the detection limit for P.brassicae DNA, while the level was >50,000 DNA copies g−1 soil in 20% of the fields. Soil-borne spread is of critical importance and soil scraped off footwear showed levels of up to 682 million spores g−1 soil. Soil testing is an important tool for determining the presence of P. brassicae and providing an indication of potential yield loss, e.g., in advisory work on planning for a sustainable OSR crop rotation. This soil test is gaining acceptance as a tool that increases the likelihood of success in precision agriculture and in applied research conducted in commercial oilseed fields and at research stations. The present application highlights the importance of prevention of disease spread by cleaning of farm equipment, footwear, etc.

First Online: 23 May 2016; Special issue on clubroot and blackleg diseases of brassicas - Foreword

Inter-row hoeing at wide row distance can form part of a weed management strategy in which mechanical and cultural tools are combined. Crop plant distribution is a key parameter for maintaining high grain yield levels and weed suppressive ability in such a system. The influence of seed distance in relation to row distance was studied in 10 field trials on spring wheat, spring oats and winter wheat. Post-emergence weed harrowing was applied at 12–12.5 cm row distance and inter-row hoeing at 24–25, 36–37.5 and 48–50 cm distance. Three seed distances within rows were applied: (1) Normal for the region, (2) reduced to 2/3 the normal, and (3) reduced to half the normal. To obtain normal seed distance at 12–12.5 cm row distance, 400, 525 and 600 germinable seeds m−2 were sown in winter wheat, spring oats and spring wheat, respectively. The highest grain yields were found after weed harrowing at row distance 12–12.5 cm; 5550 kg ha−1 of winter wheat, 3765 kg ha−1 of spring oats and 3105 kg ha−1 of spring wheat. Inter-row hoeing at the row distance 24–25 cm, while keeping seed distance constant, lowered grain yields of all crops by 12–16%, but had no significant influence on weed biomass. Increasing the row distance from 24–25 to 36–37.5 cm reduced grain yield by 450–460 kg ha−1 in winter wheat and oats, while a further increase to 48–50 cm reduced yield by an additional 450–520 kg ha−1 in all crops when averaged over seed distances. At row distance 24 cm and wider, grain yield of winter wheat and oats increased more when the seed distance was reduced from normal to 2/3 of normal than when reduced from 2/3 to half the normal distance. In inter-row hoed winter wheat and spring oats, weed biomass increased with increasing row and seed distance. Within the range of seed distances used in this study, a reduction to half of normal was considered as the most profitable when these crops are sown at row distances 24 cm or wider. There was no indication that seed distance in spring wheat should be changed when using wide row distances. Increased row and seed distances improved the content of gluten and reduced the content of starch in wheat grain, while protein content was increased in the grain of all crops. The response to treatments in terms of grain content of ergosterol was inconsistent between winter and spring wheat.

Red clover (Trifolium pratense) is an important component of mixed grass-legume leys; however, fungal root rot decreases red clover viability over time. Application of micronutrients may be one option to reduce the severity of the pathogens causing root rot. This study investigated the relationship between micronutrient (B, Cu, Mn, Zn) concentrations in red clover roots and the development of root rot, and examined whether the addition of micronutrients reduced root rot development. A field study was performed in 2009 to determine root rot incidence in red clover plants collected from four different field leys and a pot experiment was conducted in 2010 to determine the effect of micronutrient application (B, Cu, Mn, Zn) on root rot development in red clover. Disease severity index (DSI) and nutrient concentrations were determined in the plants.

Brassica oilseed crops have been grown by Swedish farmers since the early 1940s. Years of high market prices for vegetable oils resulted in intensive cultivation of Brassica oilseeds in various regions, which led to problems with soilborne pathogens including Plasmodiophora brassicae. This pathogen most likely was present in Swedish soils prior to the Brassica oilseed boom after World War II. Currently, reports of clubroot disease outbreaks in Sweden are frequent, with a trend of increasing incidence. Since 2012, DNA-based soil analyses for the presence of P. brassicae have been offered to farmers in order to improve their crop rotation planning. Other means of limiting the damage caused by P. brassicae also are presently under study, such as the effects of boron or different sources of nitrogen. The distribution and identification of different pathotypes/races of P. brassicae in Sweden could so far not be verified. To aid in race diagnostics, resistance breeding efforts, and in understanding the biology of this Plasmodiophorid, the sequencing of the P. brassicae genome has been initiated in Sweden.

A nested polymerase chain reaction (PCR) method was developed for detection of DNA from Plasmodiophora brassicae in naturally infested field soil samples. The target sequences 389 bp and 507 bp were amplified from Swedish populations of P. brassicae. The protocols described enabled detection of DNA in various soil classes with an inoculum level of P. brassicae corresponding to a disease severity index (DSI) higher than 21 in a greenhouse bioassay. Three sequenced Swedish P. brassicae isolates had identical sequence in the 18S/ITS 1 region, but differed by a few nucleotides from an isolate sequenced in the UK. The results indicate that the primers used are general for P. brassicae, and consequently the nested PCR assay has a potential to be developed as a routine diagnostic test.