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Very few symptoms in plants can be associated unequivocally with PPNs as they are usually difficult to detect, with the exception of galls in roots or stems and necrosis or deformations in some hosts caused by specific species.
The fourth-stage juveniles penetrate plant trough buds, petioles, lenticels, or stomata and subsequently move intercellularly through the middle lamella. Some of these have been recently separated as individual species (i.e., D. (F) Longitudinal section of parenchyma of a stem portion showing sub-epidermal cavities (ca) surrounded by necrotic cells.
Symptoms in the plant are leaf or bulb deformities, short internodes, and in some species true neoplastic tissues similar to galls are formed (Figures 1A–G). (G) Cross-section of flower parenchyma showing a nematode (n), and hypertrophied nuclei (hn) in the attacked cells (Vovlas et al., 2015b; with permission of Cambridge University Press). doi: 10.1111/j.1364-3703.2009.00539.x Pub Med Abstract | Cross Ref Full Text | Google Scholar Hogenhout, S.
Some of them can also shield themselves against plant defenses to sustain a relatively long lasting interaction while feeding.
This paper is centered on cell types or organs that are newly induced in plants during PPN parasitism, including recent approaches to their study based on molecular biology combined with cell biology-histopathology. Transcriptional analysis through RNA sequencing of giant cells induced by Meloidogyne graminicola in rice roots.
In some cases, the effect of nematode parasitism is not only associated with the feeding site, but it extends to adjacent tissues; for example, in the case of Meloidogyne spp. “Nematode parasitism of plants,” in Physiology and Biochemistry of Free-Living and Plant Parasitic Nematodes, eds R.
or Nacobbus aberrans, the first produce coenocytes and the second a syncytium, both with similar cell proliferation around the feeding sites that finally form a root gall. Most nematode damage occurs through direct alteration of plant cells, usually interfering with the normal cell cycle or by withdrawing nutrients from cell cytoplasm. However, some groups also act as virus vectors of nepo- and tobraviruses (Longidorids and Trichodorids, respectively; Decraemer and Robbins, 2007). (Hoplolaimidae), two new spiral nematodes parasitic on olive trees in Italy. Other glands (amphids, phasmids, adanal glands, and the excretory/secretory system) as well as hypodermis secretions are important in nematode cross-talk with plants (Rosso et al., 1999; Haegeman et al., 2012). PPNs can be classified as: (i) Ectoparasites: the nematode remains outside of the plant and uses its stylet to feed from the plant root cells; (ii) Semi-endoparasites: nematodes partially penetrate the plant and feed at some point during their life cycle; (iii) Migratory endoparasites: nematodes spend much of their time migrating through root tissues destructively feeding on plant cells; and (iv) Sedentary endoparasites: the nematode spends the majority of their life span sedentary inside the plant tissue establishing a highly specialized parasitism. Development of the false root-knot nematode, Nacobbus aberrans, on sugarbeet. Nematode mode of interaction with plants is an active field of research targeting the design of effective new control strategies. Morphogenesis caused by stem, leaf, seed and root gall nematodes. doi: 10.1094/MPMI-22-2-0115 Pub Med Abstract | Cross Ref Full Text | Google Scholar Hussey, R. This review intends to describe those plant-nematode interactions that cause specific alterations in plant cells related to their feeding habit. Ditylenchus gigas (A–D): (A) Necrotic area on stem (arrowed). Ditylenchus, Subanguina), but may develop a specialized modification of the root system (e.g., unspecialized root galls or a profusion of roots). This review introduces new data on cell types and plant organs stimulated by PPNs using sources varying from traditional histopathology to new holistic methodologies. Morphological and biological characters of diagnostics significance in Tylenchulus and Trophotylenchus species. doi: 10.1163/002825988X00378 Cross Ref Full Text | Google Scholar Ithal, N., Recknor, J., Nettleton, D., Maier, T., Baum, T. Some estimates suggest that PPNs cause a 77 billion dollar loss in agricultural production worldwide each year (Sasser and Freckman, 1987). Additional losses could be related to food quality and visual imperfections or market devaluation associated with infection symptoms (i.e., carrots or potatoes affected by Meloidogyne spp.), restrictions to market exportation due to the imposition of quarantine trade rules, or measures of control aimed at keeping nematodes below damage threshold in the field.