Essential oils as phytochemical nematodicides with activity against plant parasitic nematodes

Synthetic pesticides used against plant parasitic nematodes (PPNs) have been discontinued due to serious environmental and public health concerns. Essential oils (EOs) are promising alternatives given they are easily accessible, show high biological activities, have low environmental impacts, and are subjected to less strict regulatory approval mechanismsWe reviewed the chemical composition of EOs with direct biological activity against the root-knot nematodes (RKNs), plant cyst nematodes (PCNs), and the pinewood nematode (PWN). The compositions (≥10%) of the top 10 most active EOs were compared

Biological interactions between nematophagous fungi, Esteya spp., and the pinewood nematode, Bursaphelenchus xylophilus

The pinewood nematode (PWN), Bursaphelenchus xylophilus, is a quarantine organism in several countries and the causal agent of pine wilt disease (PWD), a serious threat to pine forests worldwide. PWD results from complex interactions between the nematode, its insect vector, Monochamus spp., and host plants (conifers), being the nematode the common element in this interaction. The PWN is considered the sixth most economically important plant-parasitic nematode. In Europe, this pest was first reported in Portugal in 1999, in maritime pine, Pinus pinaster. Due to its economic importance and worldwide distribution, an enormous amount of effort is devoted to research on B. xylophilus and PWD. Scenarios strongly suggest that climate change is likely going to cause a spread of PWD and outbreaks in areas free of the disease. The urgent need for sustainable management strategies has led to an increasing interest in antagonists capable of suppressing the PWN. Nematophagous fungi belonging to the Esteya genus are reported as natural enemies of the PWN and promising biocontrol agents. There are currently two described species: E. vermicola and E. floridanum, the first of which is capable of mimicking volatile organic compounds produced naturally by Pinus spp. in order to attract PWN. However, few studies have been carried out on the development of Esteya spp. inside pine trees, and none using maritime pine, the main and most affected species in Portuguese forests and its largest carbon reservoir. It is therefore crucial to understand the plant-nematode-fungus interactions between P. pinaster, B. xylophilus and Esteya spp. In this sense, biological interactions between these two antagonists, the PWN and P. pinaster were investigated, namely fungus-fungus, fungus-nematode and fungus-tree, as well as feeding trials and chemotaxis assays, to determine the attractive power of both fungal species. These results will enlighten us on the most promising species for biocontrol and help us devise new ways to manage PWD

Profiling mycobiota communities associated with the Pine Wilt Disease

Pine wilt Disease (PWD) is one of the most damaging diseases for conifer forests worldwide. This complex disease involves the interaction between three primary biological elements - the pinewood nematode (PWN) Bursaphelenchus xylophilus, the insect-vector Monochamus sp., and the host tree Pinus spp. – and other secondary elements such as endophytic bacteria and fungi. The development of B. xylophilus is strongly associated with fungi that colonize the declining trees, with special impact in their reproduction and number of individuals carried by the vector. In light of previous knowledge, we are focused in obtaining a detailed characterization of the structure and dynamics of the nematode-fungi interactions. Using the ITS2 amplicon-based metagenomic approach, we compared the fungal communities from PWN infected and non-infected P. pinaster trees collected in two distint study sites, Tróia (location where PWN was first detected in 1999) and Seia (northwestern of Portugal)

Plant Metabolomics for the control of the root-lesion nematode Pratylenchus penetrans

Pratylenchus penetrans, one of the most detrimental root-lesion nematode species, greatly reduces the production in numerous important agronomic crops (e.g., corn, potato), ornamental plants (e.g., lily, roses) and fruit trees (e.g., almond, cherry orchards). In the EU, P. penetrans has been reported as the most damaging species associated with potato (Solanum tuberosum L.). In Portugal, this species was also detected in potato production fields across the country and often related with their low yield. Plant metabolomics is an emerging approach to the study crop resistance against plant-parasitic nematodes, which can be applied to expedite traditional crop breeding programs and the development of novel pesticides

Extracellular Fibrils of Pathogenic Yeast Cryptococcus gattii Are Important for Ecological Niche, Murine Virulence and Human Neutrophil Interactions

Cryptococcus gattii, an emerging fungal pathogen of humans and animals, is found on a variety of trees in tropical and temperate regions. The ecological niche and virulence of this yeast remain poorly defined. We used Arabidopsis thaliana plants and plant-derived substrates to model C. gattii in its natural habitat. Yeast cells readily colonized scratch-wounded plant leaves and formed distinctive extracellular fibrils (40–100 nm diameter ×500–3000 nm length). Extracellular fibrils were observed on live plants and plant-derived substrates by scanning electron microscopy (SEM) and by high voltage- EM (HVEM). Only encapsulated yeast cells formed extracellular fibrils as a capsule-deficient C. gattii mutant completely lacked fibrils. Cells deficient in environmental sensing only formed disorganized extracellular fibrils as apparent from experiments with a C. gattii STE12α mutant. C. gattii cells with extracellular fibrils were more virulent in murine model of pulmonary and systemic cryptococcosis than cells lacking fibrils. C. gattii cells with extracellular fibrils were also significantly more resistant to killing by human polymorphonuclear neutrophils (PMN) in vitro even though these PMN produced elaborate neutrophil extracellular traps (NETs). These observations suggest that extracellular fibril formation could be a structural adaptation of C. gattii for cell-to-cell, cell-to-substrate and/or cell-to- phagocyte communications. Such ecological adaptation of C. gattii could play roles in enhanced virulence in mammalian hosts at least initially via inhibition of host PMN– mediated killing

Determination of pathogenicity of Bursaphelenchus species on different pine species under natural conditions in Duzce

Akbulut, Suleyman/0000-0002-1497-3562WOS: 000458305800010The pinewood nematode, Bursaphelenchus xylophilus is a pathogen of conifer forest trees. This pest is characterized by the sudden death of infected pine trees. In this study, pathogenicity tests of six native Bursaphelenchus species (B. mucronatus, B. sexdentati, B. anamurius, B. vallesianus, B. andrassyi and B. hellenicus) on three pine species (Pinus pinaster, P. nigra and P. sylvestris) using two inoculum doses under natural conditions were conducted. For each treatment, 8 trees of each species were inoculated. For each tree species 8 trees were used as control groups. Inoculated trees were monitored for a year after inoculation. Monthly oleoresin flow measurements were carried out and external symptoms (foliage coloration) observed. Nematode inoculated trees did not die at the end of the study. The amount of oleoresin flow differed significantly among tree species. Inoculated Bursaphelenchus species did not cause any significant difference in the oleoresin flow between inoculated and uninoculated trees. We concluded that Bursaphelenchus species used in this study were not pathogenic to pine trees growing under natural forest stand conditions.Duzce UniversityDuzce University [2015.02.02.338]This study is supported by Duzce University, Research Fund Project Number 2015.02.02.338. The authors greatly acknowledged the assistance and permission of General Directorate of Forestry, Bolu Regional Directorate of Forestry. The authors thank to Abdulmutalip Ozturk and Eyup Ozturk for their help during field studies. The authors also kindly thank Dr. W. T. Stamps (University of Missouri-Columbia, USA) for his review of the manuscript