Tracking Phytophthora infestans with SSR markers within and between seasons – a field study in Sweden

The dynamics of a late blight epidemic and sexual reproduction in Phytophthora infestans were studied in an experimental field in mid‐Sweden. The field was inoculated with six isolates of P. infestans taken from another potato field where sexual reproduction of the pathogen was suspected. Three weeks after inoculation single‐lesion leaflets were sampled and the resulting isolates characterized using microsatellites (SSRs) and mating type as markers. Among the 151 isolates analysed, the inoculum genotypes constituted more than 80% of the genotypes found, with three other genotypes making up the remainder. The following year, P. infestans obtained from soil samples taken from this field were analysed, and six novel genotypes were identified. Genotypes from the previous summer’s population were not detected. Analysis of the genotypes recovered was consistent with them being recombinants, with the previous summer’s population acting as parents. These findings are consistent with the hypothesis that oospores produced during a summer epidemic in Sweden can overwinter and cause infection the next year.     

Antifungal activity toPhytophthora infestans of sesquiterpenoids from infected potato tubers

Summary The sesquiterpenes 2-(1',2'-dihydroxy-1'-methylethyl)-6,10-dimethyl-spiro-[4,5]dec-6-en-8-on (1) and its 2'-O-β-d-glucopyranoside (2) were isolated from the stress zones of potato tubers infected withPhoma foveata andFusarium spp., and rishitin and solavetivone from tuber slices inoculated withErwinia carotovora. The influence of these compounds, and of the naturally occurring plant sesquiterpenoids abscisic acid, cedrol and farnesol, on the mycelial growth ofPhytophthora infestans were tested on agar plates using a defined medium. All sesquiterpenoids suppressed the growth of the pathogen, except for1 and its glucoside2 which induced a slight, however significant, growth stimulation. Compounds1 and2 could not be isolated fromE. carotovora orP. infestans-inoculated tuber tissue.     

FARMFLOW—A dynamic model for phosphorus mass flow,simulating conventional and organic management of a Swedish dairy farm

A farm systems mass-balance calculation model, FARMFLOW, was applied to a case study comparing organic and conventional management of a Swedish experimental dairy farm, Öjebyn. Parameterisation of the model is implemented using detailed field data from the Öjebyn farm where the two management systems have been run parallel for more than 11 years. Simulations were made to compare the stocks, flows and resulting balances of phosphorus (P) in the two systems during six crop rotations (36 years). In addition, a maximum animal density scenario was tested, in order to analyse the effects of increased production intensity. Results show that FARMFLOW can be a useful tool for analysing the impact of management on internal farm P dynamics, as well as imports and exports. The organic management results in a higher proportion of internal P flows whereas the conventional system relies more on imports of P in feed and mineral fertilisers. In both management systems, the crop rotation cause large temporal and spatial variation in the application of manure P to the soil system. The resulting field specific soil P accumulation can indicate which fields to target with changed fertilisation management. In the maximum animal density scenario, both management systems led to an application rate of manure P in excess of crop demands.     

The expression of general resistance to late blight (Phytophthora infestans) in potato leaves

Summary Resistance toPhytophthora infestans was evaluated histologically using leaves of potato cultivars with different levels of general resistance. Host genotype did not influence the preinfectional processes of encysted zoospores, e.g. frequency of germination, length of germ tubes, or frequency of formation of appressoria. Most of the appressoria on the leaf surface were attached to epidermal cells, but they were also found on cells of the stomatal complexes, on hairs and glands, and on cells adjacent to vascular tissue. There were significant differences between cultivars in the extension of intercellular hyphal growth and branching 24 and 48 h after inoculation, the differences increasing with time. In contrast to cv. Bintje, the hyphae in the most resistant cultivar Matilda were mostly confined to the epidermal and palisade cells even 48 h after infection, the number of hyphae per section was much lower, and sporulation capacity was reduced.     

Storm-induced tree resistance and chemical differences in Norway spruce (Picea abies)

Introduction   

Windstorm is one of the most destructive environmental disturbance factors on forests, but its influence on conifer defense chemistry and susceptibility to insects and diseases is not well understood.     

Phenotypic variation within a clonal lineage of Phytophthora infestans infecting both tomato and potato in Nicaragua

Late blight caused by Phytophthora infestans (Mont.) de Bary is a constraint to both potato and tomato crops in Nicaragua. The hypothesis that the Nicaraguan population of P. infestans is genotypically and phenotypically diverse and potentially subdivided based on host association was tested. A collection of isolates was analyzed using genotypic markers (microsatellites and mitochondrial DNA haplotype) and phenotypic markers (mating type, virulence, and fungicide sensitivity). The genotypic analysis revealed no polymorphism in 121 of 132 isolates of P. infestans tested. Only the Ia haplotype and the A2 mating type were detected. Most of the tested isolates were resistant to metalaxyl. The virulence testing showed variation among isolates of P. infestans. No evidence was found of population differentiation among potato and tomato isolates of P. infestans based on the genotypic and phenotypic analysis. We conclude that the Nicaraguan population of P. infestans consists of a single clonal lineage (NI-1) which belongs to the A2 mating type and the Ia mitochondrial DNA haplotype. Moreover, based on the markers used, this population of P. infestans does not resemble the population in countries from which potato seed is imported to Nicaragua or the population in neighboring countries. The data presented here indicate that the NI-1 clonal lineage is the primary pathogen on both potato and tomato, and its success on both host species is unique in a South American context.     

Cytokine production and proliferation upon in vitro oligodeoxyribonucleotide stimulation of equine peripheral blood mononuclear cells

Synthetic oligodeoxyribonucleotides (ODN) may prove useful immune modulators in equine medicine. It is however important to assess the effects of each specific ODN in the species it is intended to be used in. The present study therefore aimed to evaluate some ODN for induction of cytokine production; i.e. type I interferons (IFN), IFN-γ, tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β), and proliferation of equine peripheral blood mononuclear cells (PBMC). A panel of four ODN containing unmethylated cytosine-guanosine sequences (CpG) was used: ODN 1 and ODN 8 representing A-class; ODN 2006 representing B-class and ODN 2395 representing C-class-ODN. In addition, two ODN where CpG-motifs were reversed to GpC were included; ODN 2137 otherwise identical to ODN 2006 and ODN 5328 otherwise identical to ODN 2395. Cytokine concentrations were measured in cell culture supernatants after 24h of induction and proliferation was determined after 72 h of induction. Each ODN was tested with PBMC from at least 5 individual horses with and without the addition of lipofectin to cell cultures. Type I IFN, IFN-γ and TNF-α production was readily induced by ODN 1, ODN 2006 and ODN 2395 both in the presence and absence of lipofectin and all three types of ODN induced similar levels of cytokines. Proliferation of PBMC was clearly induced by ODN 2006 and ODN 2395 while ODN 1 only induced low-level proliferation. The levels of proliferation induced were not influenced by the presence of lipofectin. TGF-β production was not induced by any of the tested ODN. ODN 8, ODN 2137 and ODN 5328 were largely inactive in all assays. Thus, responses seemed dependent on or increased by CpG-motifs but presence of CpG-motifs did not necessarily confer activity since ODN 8 was inactive despite its CpG-motifs. Taken together, with equine PBMC distinctions in induction of different leukocyte functions between A-, B-, and C-class ODN were less obvious than what has been observed for human cells. These observations further stress the presence of species differences in ODN-induced responses.     

Feeding habits of lycosid spiders in field habitats

Generalist arthropod predators are potential drivers of population dynamics in a wide variety of ecosystems but their feeding habits are often difficult to reveal as they are small, mobile, and live among dense vegetation or in soils. DNA-based gut-content analysis is a powerful tool that enables studies on arthropod predator–prey interactions. We studied lycosid spiders (Pardosa spp.) in agroecosystems to see if they consumed cereal aphids (Rhopalosiphum padi) and Collembolans at random, i.e., in proportion to their abundance in the field. We also tested if consumption of the target prey items was affected by the presence of alternative food. Spiders were captured in farmers’ fields and their gut-contents screened by PCR with R. padi and Collembola primers. On all sampling occasions, concurrent assessments of total prey availability were carried out. Spider predation rates on R. padi always exceeded 50 %. Spiders also tested positive for Collembola but to a lower and more varying degree. In general, Pardosa did not consume R. padi and Collembolans in relation to their abundance in the field. Aphid predation was much higher than expected whereas consumption of Collembolans was considerably lower. The presence of alternative prey influenced consumption of the aphid. It was concluded that prey consumption by Pardosa spiders generally cannot be assumed to simply mirror prey availability. The spatial distribution of the target prey needs to be considered as well as the abundance, composition, and nutritional content of potential alternative food items.     

Stakeholders' perceptions of consultations as tools for co-management — A case study of the forestry and reindeer herding sectors in northern Sweden

The forestry and reindeer herding sectors utilize the same land in northern Sweden, and adversely affect each other's productivity. The common pool resource character of this situation has made it difficult to find ways to resolve conflicts that could threaten the two sectors' continued co-existence. A consultation procedure that was introduced to reduce conflicts does not appear to be effective, since conflicts between the two actors still occur. One reason for this failure might be found in the power distribution between forestry and reindeer herding. Earlier research has shown that a co-management system in which the allocation of power between the stakeholders is uneven is difficult to maintain in the long term. However, it is unclear just how uneven the power distribution is between the two actors in this case, and the consequences the disparity might have for the viability and stability of the management system. Focusing on the power relations within the consultation procedures, this paper explores the potential of the present institutional system to take the different interests of the stakeholders into account and to use the consultation procedures as tools for co-managing the forest resources in northern Sweden.