Ann-Charlotte Wallenhammar

Detection of plasmodiophora brassicae by PCR in naturally infested soils

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.

Clubroot, a persistent threat to Swedish oilseed rape production

Abstract 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.

Quantification of Plasmodiophora brassicae using a DNA-based soil test facilitates sustainable oilseed rape production

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.

Special issue on clubroot and blackleg diseases of brassicas - Foreword

The two plant pathogens Leptosphaeria maculans (anamorph Phoma lingam), causal agent of blackleg disease, and Plasmodiophora brassicae Wor., causal agent of clubroot disease, are leading to significant yield and quality losses in both agricultural and horticultural brassica crops worldwide. The increasing economic and social importance of brassica crops, which are hosts to both pathogens, has enhanced and financed international research collaborations over the past two decades. Both are aggressive and race-forming pathogens that have thrived because of intensive cropping of oilseed rape (B. napus). Clubroot, in particular, has caused increasing devastation in high value horticultural crops such as cauliflower or broccoli. Extensive broad-acre field crops are frequently grown in short rotations, which include only a few non-host crops such as cereals or legumes. Farming systems increasingly include contract machinery cultivating many hectares of land in short periods with only very limited opportunities for cleaning. Both farming practices increase the incidences and spread of these diseases. High value horticultural brassicas have long been hosts to both pathogens. Brassica crops are more and more valued as contributing significantly to human health and wellbeing. Consequently, research interest in both pathogens has grown rapidly and our present knowledge has benefitted from several research initiatives. This Special Issue of the European Journal of Plant Pathology is the third such publication produced in the last 7 years regarding clubroot, and is supplemented by papers on blackleg. It highlights significant advances in the understanding of both host-pathogen interactions at the populations and molecular level. Genomic studies of the brassica hosts and on the two pathogens have revealed their biology and the manner in which they interact. The drive for environmentally sustainable control has created opportunities for breeding, biological control, and agronomical measures which employ intelligent systems of integrated control. Many of the Eur J Plant Pathol (2016) 145:515–516 DOI 10.1007/s10658-016-0963-1

Functional divergence effects of intercropped faba bean and maize in organic production for forage increase mineral contents and reduces leaf spots

Eva Stoltz1, Ann-Charlotte Wallenhammar1 and Elisabet Nadeau2, 3 1Research & Development, Rural Economy and Agricultural Society|HS Konsult AB, Box 271, 701 45 Örebro, Sweden 2Department of Animal Environment and Health, Swedish University of Agricultural Sciences, Box 234, 53223 Skara, Sweden 3Research & Development, Rural Economy and Agricultural Society Sjuhärad, Rådde Gård, Box 5007, 514 05 Länghem, Sweden

Micronutrients reduce root rot in red clover ( Trifolium pratense )

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.The field study found an inverse relationship between increasing micronutrient (Cu, Mn, Zn) concentrations in plant roots and decreasing internal DSI. Internal DSI decreased with low element translocation from root to shoot and with increased Mn in the root as a result of Mn and Zn application. In contrast, the application of B or Cu slightly increased internal DSI.Thus, an inverse correlation exists between some micronutrients and severity of root rot in red clover. The addition of Mn and Zn can reduce root rot and thereby increase the sustainability of red clover.