Editorial: impact of global climate change on the interaction between plants and plant-parasitic nematodes

Global climate change is an important environmental influence on plant ecosystems. Temperature, precipitation, duration and quality of sunlight, availability of nutrients, such as nitrogen, phosphorus and potassium, are determinants of plant growth that are likely to change due to global climate change effects. Climate change-induced high levels of atmospheric CO2 promote plant growth due to increased photosynthesis, at the cost of decreased evaporative cooling. In parallel, elevated CO2, temperature and altered precipitation levels strongly influence the biology of nematodes including plant and insect-parasitic nematodes. Although nematode development occur at a faster rate in warmer soil temperature, it is not yet clear about the precise implications of climate change effects on nematode biology as well as on plant-nematode interaction continuum

Transcriptome analysis reveals the high ribosomal inhibitory action of 1,4-naphthoquinone on Meloidogyne luci infective second-stage juveniles

The root-knot nematode (RKN) Meloidogyne luci presents a threat to the production of several important crops. This nematode species was added to the European Plant Protection Organization Alert list in 2017. The scarce availability of efficient nematicides to control RKN and the phasing out of nematicides from the market have intensified the search for alternatives, such as phytochemicals with bionematicidal properties. The nematicidal activity of 1,4-naphthoquinone (1,4-NTQ) against M. luci has been demonstrated; however, knowledge of the potential mode(s) of action of this compound is still scarce. In this study, the transcriptome profile of M. luci second-stage juveniles (J2), the infective stage, in response to 1,4-NTQ exposure was determined by RNA-seq to identify genes and pathways that might be involved in 1,4-NTQ’s mode(s) of action. Control treatments, consisting of nematodes exposed to Tween® 80 (1,4-NTQ solvent) and to water, were included in the analysis. A large set of differentially expressed genes (DEGs) was found among the three tested conditions, and a high number of downregulated genes were found between 1,4-NTQ treatment and water control, reflecting the inhibitory effect of this compound on M. luci, with a great impact on processes related to translation (ribosome pathway). Several other nematode gene networks and metabolic pathways affected by 1,4-NTQ were also identified, clarifying the possible mode of action of this promising bionematicide

Biometrical, biochemical and molecular diagnosis of Portuguese Meloidogyne hispanica isolates

Meloidogyne hispanica infects many economically important crops worldwide. The accurate identification of this pathogen is essential for the establishment of efficient and sustainable integrated pest management programs. Portuguese M. hispanica isolates were studied by biometrical, biochemical, and molecular characteristics. Biometrical characteristics of M. hispanica females, males, and second-stage juveniles were similar to the original description. Biochemical studies revealed a unique enzyme pattern (Hi4) for M. hispanica esterases that allowed for species differentiation. Molecular analysis of the mtDNA region from COII and 16S rRNA genes resulted in amplification products (1,800 bp) similar to M. hispanica, M. ethiopica, and M. javanica, and the described HinfI was unable to discriminate M. hispanica from the other two species. Analysis of the mtDNA sequences revealed altered nucleotides among the isolates that created new restriction sites for AluI and DraIII. The resulting restriction patterns successfully discriminated between the three species, providing a new tool for Meloidogyne identification. Finally, the phylogenetic relationship between M. hispanica and several Meloidogyne spp. sequences was analyzed using mtDNA, confirming the divergence between meiotic and mitotic species and revealing the proximity of M. hispanica to closely related species. Based on the studies conducted, the application of isozyme or polymerase chain reaction restriction fragment length polymorphism analysis would be a useful and efficient methodology for M. hispanica identification. </jats:p

In vitro nematicidal activity of naphthoquinones against the root-lesion nematode Pratylenchus thornei

The root-lesion nematode Pratylenchus thornei is a widely distributed and important parasite of cereals and legumes. As migratory endoparasites, P. thornei are difficult to manage  because they enter and leave host roots and may remain quiescent inside roots or in soil when conditions are unfavourable for plant growth. The number of available nematicides to manage these nematodes is restricted, so new, effective and eco-friendly sustainable management strategies are needed. The effects of naphthoquinones (juglone, 1,4-naphtoquinone and plumbagin) produced by some plants species, including walnut (Juglandaceae), were assessed against P. thornei. An additional treatment of a mixture of juglone and 1,4-naphtoquinone (2:1, w/w), was included because these compounds are frequently found at these propotion in walnut extracts. Juveniles and adult nematodes were exposed to different concentrations of each naphthoquinone and nematode mortality was assessed. Juglone and 1,4-naphthoquinone (at 500 ppm) were more effective than plumbagin, and gave 100% mortality after 24 h of exposure. A synergistic effect was not detected when juglone and 1,4-naphthoquinone (2:1, w/w) were combined. Estimated lethal concentrations causing 50% P. thornei mortality (LC50s) (72 h exposure) were: 134.7 ppm for juglone, 161.2 ppm for 1,4-naphthoquinone, 207.6 ppm for juglone + 1,4-naphthoquinone (2:1, w/w), and 178.8 ppm for plumbagin. This study has demonstrated the nematicidal potential of these naphthoquinones against P. thornei, and has shown that walnut residues may be valuable sources for extraction of these compounds

Laimaphelenchus suberensis sp. nov. associated with Quercus suber in Portugal

Laimaphelenchus suberensis sp. nov. obtained from declining Quercus suber trees of Herdade da Gouveia de Baixo, Alentejo, Portugal, is described and illustrated based on morphological, biometrical and molecular characters. The diagnosis of Laimaphelenchus species has been commonly based on the presence or absence of a vulval flap and on the shape structure of the tail tip. The species described here has been included in the Laimaphelenchus group without vulval flap, and can be distinguished from morphologically similar species by its tail tip shape structure that has a stalk-like terminus and three diffuse tubercles with 4–6 finger-like protrusions. For the molecular analyses, the mitochondrial DNA region from the cytochrome oxidase subunit I (mtCOI), the D2-D3 expansion segments of the large subunit (LSU) and small subunit (SSU) of rRNA gene were amplified and sequenced. Sequences of L. suberensis sp. nov. clustered separately from all Laimaphelenchus spp. with available sequences in Genbank, confirming its identification as a new species. This is the second report of the genus Laimaphelenchus in Portugal, associated with Q. suber: L. heidelbergi and L. suberensis sp. nov.This research was supported by CFE, CIEPQPF and FEDER funds through the ‘Programa Operacional Factores de Competitividade – COMPETE’ and by national funds through FCT–Fundação para a Ciência e a Tecnologia under the projects UID/BIA/04004/2013, PEst-C/EQB/UI0102/2013 and FCOMP-01-0124-008937 (Ref. PTDC/BIA–BEC/102834/2008) and by Instituto do Ambiente, Tecnologia e Vida (IATV). Carla Maleita (SFRH/BPD/85736/2012) and Sofia Costa (SFRH/BPD/ 102438/2014) were financed by MEC National funding and The European Social Fund through POCH (Programa Operacional Capital Humano).info:eu-repo/semantics/publishedVersio