Editorial: Protecting Our Crops - Approaches for Plant Parasitic Nematode Control

In agricultural history, the Green Revolution generated by the development of breeding technology, chemical fertilizers, and pesticides has enabled mass production of agricultural crops and solved many (but not all) hunger problems around the world (Pingali, 2012). Plants make up about 80% of the food we consume, while about 40% of food crops are lost by agricultural pests, including plant nematodes (FAO, 2019). The world population in 2021 is  7.8 billion and is estimated to reach 10 billion in 2050 (United Nations, 2019). The current proposition imposed on us is to develop methods to increase crop yield and quality while suppressing damage from pests and also reducing the impact on the natural environment. Plant-parasitic nematodes (PPNs) are one of the major constraints in agriculture. Damage caused by PPNs has been estimated from $US80 billion (Nicol et al., 2011) to$US157 billion per year (Abad et al., 2008). However, the full extent of nematode damage is likely underestimated as many growers, particularly in developing countries, are unaware of the presence of PPNs (Jones et al., 2013). This was assumed as nematodes are usually small-body-size, soil-borne pathogens, and the symptoms they cause are often non-specific (Jones et al., 2013). The damage caused by PPNs could be even worse in the future in the context of a growing world population under a Climate Change scenario and the removal or reduction in the use of some nematicides in many parts of the world. Set in the context of the 2020 International Year of Plant Health, this Research Topic “Protecting Our Crops - Approaches for Plant Parasitic Nematode Control” gives new insights into Integrative Approaches for Sustainable PPN Control. Many of the articles are excellent reviews of their specific topic, which could help in pointing out new research directions

Prevalence, incidence and molecular identification of root-knot nematodes of tomato in Pakistan

Tomato is a widely grown vegetable in Pakistan. However, its production is severely constrained by root knot nematodes (RKNs). Accurate identification of RKNs is essential for an appropriate control program. The current study evaluated the prevalence, incidence and diversity of RKNs of tomato crops grown in the Khyber Pakhtunkhwa Province and their identification using molecular tools. A field survey, including 30 commercial tomato fields, was conducted in ten major tomato growing areas of Swat and Malakand divisions during spring 2010. The overall prevalence and incidence in the study area was 83.3 and 52.0%, respectively. Three species of RKNs, Meloidogyne arenaria, M. incognita and M. javanica were found alone or in mixed populations. Disease incidence ranged from 10% in Malakandher to 100% and 90 to 100% in Jabban and Malakand, respectively. The greatest galling index (GI) (5.0) and egg mass index (EMI) (5.0) was recorded in samples from Jabban, whereas the lowest GI and EMI were recorded in samples from Malakandher and Peshawar. The population density of RKNs was highest in roots (633.0 eggs and second-stage juveniles) and soil (533.0 eggs and second-stage juveniles) samples of Jabban. DNA amplification with rDNA (D2A-D3B) and (194 to 195) primers amplified 750 and 720 bp products for M. arenaria, M. incognita and M. javanica, respectively. Amplification with sequence characterized amplified regions (SCAR) primers produced characteristic products of 420 bp for M. arenaria (Far/Rar), 1200 bp for M. incognita (Finc/Rinc), and 670 bp for M. javanica (Fjav/Rjav). DNA amplification of mtDNA with C2F3/1108 primers yielded a 1700 bp size product for all three species of RKNs in comparison with 520 and 750 bp for M. chitwoodi and enterolobii, respectively, which were utilized as control. Sequencing the 28S rDNA product generated with the D2A-D3B primers did not differentiate among the three Meloidogyne spp. from the study area.Key words: Meloidogyne, species identification, perineal pattern, sequence characterized amplified regions (SCAR) primers

Description and molecular phylogeny of one new and one known needle nematode of the genus Paralongidorus (Nematoda: Longidoridae) from grapevine in Portugal using integrative approach.

A new and a known longidorid nematode, Paralongidorus lusitanicus n. sp. and Paralongidorus plesioepimikis, are described and illustrated from populations extracted from soil associated with grapevine (Vitis vinifera L.) from Escaroupim and Pó (central-Western Portugal), respectively. The new needle nematode P. lusitanicus n. sp. is characterised by a very large body size (8072–12,022 μm), an expanded and rounded lip region, ca 30 μm wide, with a clear constriction followed by a depression posterior to the amphidial aperture, amphidial fovea very large (11.0–19.0 μm), stirrupshaped, with conspicuous slit-like aperture as shown in scanning electron microscopy studies, a very long and flexible odontostyle (180.0–223.0 μm), guiding ring located at 28.0–41.5 μm from anterior end, vulva anterior to the mid-body (34–41%), a dorsally convex-conoid tail with rounded terminus (29–42 μm long), bearing two or three pairs of caudal pores and males common (ratio 1:1.6 females) with spicules ca 80 μm long. Morphological and morphometric traits for P. plesioepimikis fit well with the original description, and is reported for the first time in Portugal. Integrative diagnosis of both species was completed with molecular data obtained using D2-D3 expansion segments of 28S rDNA, ITS1-rDNA and partial 18S–rDNA. The phylogenetic relationships of these species with other Paralongidorus spp. using these three molecular markers indicated that P. lusitanicus n. sp. clustered together with other Paralongidorus spp. forming a sister clade with P. plesioepimikis, both of them sharing a large body, long odontostyle, an anteriorly located vulva and an expanded and rounded lip region with a clear constriction followed by a depression posterior to the amphidial apertur

First report of root-knot nematode Meloidogyne hispanica infecting grapevines in southern Spain

Artículo open access.Some commercial vineyards producing the ‘Condado de Huelva’ wine denomination of origin in Almonte, Bonares, and Rociana (Huelva Province), southern Spain, showed general decline in sandy soils in 2009. Disease surveys revealed severe infections of grapevine rootstock Richter 110 feeder roots and heavy soil infestations by a root-knot nematode (Meloidogyne sp.).Peer Reviewe

Description of the first-stage juveniles of Xiphinema cretense and X. herakliense - Distribution of Xiphinema and Longidorus species in olive orchards and grapevines in Crete, Greece

The occurrence of nematodes of the family Longidoridae was investigated in soil samples collected from cultivated and wild olives and grapevines in Crete. The first-stage juveniles of Xiphinema cretense and X. herakliense are described for the first time. The species X. israeliae, X. cretense, X. herakliense and Longidorus pseudoelongatus, previously recorded exclusively from olives in Crete, are herein reported in the rhizosphere of grapevines. Also L. iranicus is reported for the first time in cultivated olive, while X. italiae and L. closelongatus are reported for the first time in wild olive in Crete. Data on the occurrence of phytoparasitic nematode species in cultivated olives, wild olives and grapevines are updated with those previously published.This research was supported by grant KBBE 219262 ArimNET-ERANET FP7 2012-2015 Project PESTOLIVE ‘Contribution of olive history for the management of soilborne parasites in the Mediterranean basin’ from Hellenic Agricultural Organization-DEMETER and Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), grant AGR-136 from ‘Consejería de Economía, Innvovación y Ciencia’ from Junta de Andalucía, and Union Europea, Fondo Europeo de Desarrollo regional, “Una manera de hacer Europa”. I.G. Birmpilis and E. Nasiou were employed by the ARIMNET-PESTOL-IVE project.Peer reviewe

A new endosymbiotic bacterium species associated with a nematode species of the genus Xiphinema (Nematoda, Longidoridae)

2021 virtual edition of the Conference Microscopy at the Frontiers of Science, september 29 and October 1st.Nematodes are the third largest group of metazoans; among them, the Family Longidoridae comprises two main genera of plant parasitic nematodes, Xiphinema and Longidorus, which contain several virus-vector species, e.g. the species X. index, the vector of grape fanleaf virus (GFLV), a serious pathogen of grapes. Bacterial endosymbionts of plant-parasitic nematodes represent a field of research that has become active in recent years. In this work we present a detailed characterization of the endosymbiont bacterium found in the nematode X. pachtaicum from the rhizosphere of sour orange trees (Citrus x aurantium L.) from Cordoba, Spain, and, based on morphological, phylogenetic and genomic characteristics propose a novel candidate genus and species for this uncultured bacterium (strain IAST). An intracellular bacterium, strain IAST, was observed to infect several species of the plant-parasitic nematode genus Xiphinema (X. astaregiense, X. incertum, X. madeirense, X. pachtaicum, X. parapachydermum and X. vallense). The bacterium could not be recovered on axenic medium. The localization of the bacterium (via light and fluorescence in situ hybridization microscopy) is in the X. pachtaicum females clustered around the developing oocytes, primarily found embedded inside the epithelial wall cells of the ovaries, from where they are dispersed in the intestine. Transmission electron microscopy (TEM) observations supported the presence of bacteria inside the nematode body, where they occupy ovaries and occur inside the intestinal epithelium. Ultrastructural analysis of the bacterium showed cells that appear as mostly irregular, slightly curved rods with rounded ends, 0.8–1.2 μm wide and 2.5–6.0 μm long, possessing a typical Gram-negative cell wall. The peptidoglycan layer is, however, evident only occasionally and not detectable by TEM in most cells. Another irregularly occurring shell surrounding the endosymbiont cells or the cell clusters was also revealed, probably originating from the host cell membrane. Flagella or spore-like cells do not occur and the nucleoid is diffusely distributed throughout the cell. This endosymbiont is transmitted vertically through nematode generations. These results support the proposal of IAST as a new species, although its obligate intracellular and obligate endosymbiont nature prevented isolation of a definitive type strain. Strain IAST is therefore proposed as representing ‘Candidatus Xiphinematincola pachtaicus’ gen. nov., sp. nov