Reflections on Plant and Soil Nematode Ecology: Past,Present and Future

The purpose of this review is to highlight key developments in nematode ecology from its beginnings to where it stands today as a discipline within nematology. Emerging areas of research appear to be driven by crop production constraints, environmental health concerns, and advances in technology. In contrast to past ecological studies which mainly focused on management of plant-parasitic nematodes, current studies reflect differential sensitivity of nematode faunae. These differences, identified in both aquatic and terrestrial environments include response to stressors, environmental conditions, and management practices. Methodological advances will continue to influence the role nematodes have in addressing the nature of interactions between organisms, and of organisms with their environments. In particular, the C. elegans genetic model, nematode faunal analysis and nematode metagenetic analysis can be used by ecologists generally and not restricted to nematologists.     

The role of phytohormones ethylene and auxin in plant-nematode interactions

The phytohormones ethylene and auxin regulate many important processes in plants, including cell differentiation, cell expansion, and responses to abiotic stresses. These hormones also play important roles in many plant-pathogen interactions, including regulation of plant defense responses and symptom development. Sedentary plant-parasitic nematodes, which require the formation of a complex feeding site within the host root, are among the world’s most destructive plant pathogens. Nematode-induced feeding sites show dramatic changes in host cell morphology and gene expression. These changes are likely mediated, at least in part, by phytohormones. In the present review, current knowledge of the roles of ethylene and auxin will be explored in two main areas: the specific role of phytohormones in mediating feeding site development by plant-parasitic nematodes and the general role of phytohormones in affecting the ability of parasitic nematodes to cause disease. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 1, pp. 3–7. This article was presented in original.     

Trends in the journal of nematology, 1969-2009: authors, States, nematodes, and subject matter

Issues of the Journal of Nematology from 1969-2009 were examined to determine trends in authorship and subject matter. Data were collected on authors, affiliations, locations, funding, nematodes, and nematological subject matter, and then compared among the 4 decades involved. Some of the more prominent changes noted included: a decrease (P < 0.05) in the number of papers published in the Journal of Nematology in the 1990s and 2000s from a peak in the 1980s; an increase (P < 0.05) in number of authors per paper in each decade; an increased (P < 0.05) percentage of international authors in the 1990s and 2000s compared to 1970s; and changing roles of the United States Department of Agriculture (USDA) and different states over a period of 4 decades. Plant-parasitic nematodes were the main organisms studied in 73.4% of all papers published the Journal of Nematology from 1969-2009. The greatest changes in subject matter were increases in papers on biological control and resistance in the 1990s and 2000s compared to the 1970s and 1980s. Additional trends and subjects are discussed, and data are provided comparing differences among the 4 decades for various aspects of nematology.     

In vivo and In vitro Rearing of Entomopathogenic Nematodes (Steinernematidae and Heterorhabditidae)

Entomopathogenic nematodes (EPN) (Steinernematidae and Heterorhabditidae) have a mutualistic partnership with Gram-negative Gamma-Proteobacteria in the family Enterobacteriaceae. Xenorhabdus bacteria are associated with steinernematids nematodes while Photorhabdus are symbionts of heterorhabditids. Together nematodes and bacteria form a potent insecticidal complex that kills a wide range of insect species in an intimate and specific partnership. Herein, we demonstrate in vivo and in vitro techniques commonly used in the rearing of these nematodes under laboratory conditions. Furthermore, these techniques represent key steps for the successful establishment of EPN cultures and also form the basis for other bioassays that utilize these organisms for research. The production of aposymbiotic (symbiont–free) nematodes is often critical for an in-depth and multifaceted approach to the study of symbiosis. This protocol does not require the addition of antibiotics and can be accomplished in a short amount of time with standard laboratory equipment. Nematodes produced in this manner are relatively robust, although their survivorship in storage may vary depending on the species used. The techniques detailed in this presentation correspond to those described by various authors and refined by P. Stock’s Laboratory, University of Arizona (Tucson, AZ, USA). These techniques are distinct from the body of techniques that are used in the mass production of these organisms for pest management purposes.     

Developmental and behavioural effects of the endophytic Fusarium moniliforme Fe14 towards Meloidogyne graminicola in rice

The root‐knot nematode, Meloidogyne graminicola, is an important pest of rice in many rice production areas worldwide. The endophyte Fusarium moniliforme strain Fe14, isolated from a disinfected root of rice, has previously shown potential antagonistic activity against M. graminicola. This study shows the effects of Fe14 on M. graminicola behaviour, infection, development and reproduction. The endophyte Fe14 colonisation significantly reduced M. graminicola penetration into rice roots by 55% and increased the male to female ratio nine times. The endophyte also delayed juvenile development into female inside the rice root. These results suggest a suboptimal performance of the giant cell and a cumulative effect of the endophyte on the long‐term root‐knot nematode population development. In split‐root assays, the application of Fe14 at the inducer side significantly reduced nematode invasion at the responder side by 38% and 60% in two independent trials. This result suggests a systemic effect of the endophyte on rice plants. The root exudates from Fe14‐treated plants were either less attractive or had repellent effect on nematode movement. The results, when compared to what was described for other endophytic Fusarium against other nematode species, may indicate a basal response mechanism initiated in the plant by endophytic Fusarium spp. The present study may give leads for unravelling the molecular mechanisms responsible for the induced systemic defence responses in plants.     

Cloning of a Putative Pectate Lyase Gene Expressed in the Subventral Esophageal Glands of Heterodera glycines

We report the cloning of a Heterodera glycines cDNA that has 72% identity at the amino acid level to a pectate lyase from Globodera rostochiensis. In situ hybridizations showed that the corresponding gene (Hg-pel-1) is expressed in the subventral esophageal gland cells of second-stage juveniles. The deduced amino acid sequence of the H. glycines cDNA shows homology to class III pectate lyases of bacterial and fungal origin.     

Extraction Efficiency of Belonolaimus longicaudatus from Sandy Soil

Numbers of Belonolaimus longicaudatus extracted from sandy soils (91-92% sand) by sieving and centrifugation were only 40-55% of those extracted by sieving and incubation on a Baermann tray. Residues normally discarded at each step of the sieving plus Baermann tray extraction procedure were examined for nematodes to obtain estimates of extraction efficiencies. For third-stage and fourth-stage juveniles, males, and females, estimates of extraction efficiency ranged from 60 to 65% in one experiment and 73 to 82% in another. Estimated extraction efficiencies for second-stage juveniles were lower (33% in one experiment, 67% in another) due to losses during sieving. When sterilized soil was seeded with known numbers of B. longicaudatus, 60% of second-stage juveniles and 68-76% of other stages were recovered. Most stages of B. longicaudatus could be extracted from these soils by sieving plus Baermann incubation with an efficiency of 60-70%.     

The history of the Nematology Department at Rothamsted

This is a review of the activities of what rapidly became the leading plant nematology department in the world, based in what was at that time not only the most important but also the most distinguished agricultural research station in the world. We first briefly review the research done in the period under each head of department before recording in more detail some of the long‐term research programmes, including work on potato cyst nematode hatching factors, chemical control and biological control. These strong research activities flourished until the radical funding constraints that were introduced nationally following release of the Rothschild Report in 1973 forced the adoption of various management actions at research stations. The changed pattern of research funding systems, which evolved gradually from 1973 onwards, resulted in a different style of research collaboration and changes in research focus by institutes and their staff. It became fashionable for institutes to have mission statements and these were changed frequently by directors due to the need to respond to funding possibilities. Successive severe and progressive reductions in staffing and, inevitably, outputs culminated in the complete cessation of nematology research at Rothamsted in 2013, even though cutting edge work on biological control and molecular interactions between nematodes and their plant hosts was still being carried out.     

Building soil suppressiveness against plant-parasitic nematodes

Damage caused by plant-parasitic nematodes (PPNs) represents significant losses in agriculture worldwide. Sustainable and non-agrochemical practices have been sought out for the last few years aiming the reduction of PPN outbreaks, as such practices represent less interference in the soil health. In addition, certain soils naturally show high levels of suppressiveness against nematodes. Natural suppressive soils do not allow PPN increment by a balance in soil biotic and abiotic conditions. Such soils must be better understood by which components are responsible for their natural suppressiveness. Hence, keeping, stimulating or and even creating suppressive conditions in agricultural rhizosphere has been studied and applied to reduce PPN populations. There are many aspects that implicate in soil suppressiveness against PPN, such as microbiota activities, organic matter amount, chemical composition and physical constitution. However, any of those conditions is a single driver in suppressive soils against PPN. In this context, we intend to bring up an overview concerning the natural occurrence of suppressive soils against the most devastating PPNs worldwide and discuss the means used to induce suppressiveness in agricultural fields by sustainable management practices.