Biological Sciences
Nematology
Nematology is the scientific study of nematodes, which are roundworms found in diverse environments. This field encompasses research on the biology, ecology, taxonomy, and control of nematodes, which can be both beneficial and harmful to plants, animals, and humans. Nematologists investigate the impact of nematodes on agriculture, ecosystems, and human health, and develop strategies for managing nematode populations.
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7 Key excerpts on "Nematology"
- Kaushal, K K(Authors)
- 2021(Publication Date)
- Biotech(Publisher)
Cannot be resold/distributed. Nematologia Mediterranea (Istituto di Nematologia Agraria of the C.N.R.) Japanese Journal of Nematology (JSN) Indian Journal of Nematology (NSI) African Plant Protection (NSSA) Nematropica (ONTA) Organization of Nematologists of Tropical America Newsletter (ONTA) Pakistan Journal of Nematology (PSN) Pakistan Society of Nematologists Newsletter (PSN) Russian Journal of Nematology (RSN) Nematology (Brill Academic Publishers) Nematology, Pakistan Journal of Nematology and Chinese Journal of Nematology coming into being in 1971, 1982 and 1996, respectively. Plant Nematology developed as the knowledge regarding all forms of nematodes as also in all aspects of the science increased. The workers started paying attention to interactive associations of nematodes with other biological agents like fungi, bacteria and viruses. The ‘Friendly Fungi” by Duddington, (1957) was responsible for further enhancing the interest in studying the antagonists and parasites of nematodes as biological means of controlling them. This was the time when Hewitt, Raski and Goheen (1958) discovered that the plant parasitic nematode, Xiphinema index was responsible for transmission of grapevine fan leaf virus, thus, increasing the role of nematodes in disease etiology. Thereafter a series of books were published by leading nematologists in many countries, notable among them were: J.R Christie’s (1959) -Plant Nematodes-Their Bionomics and Control; J.F.Southey’s (1959)-Plant Nematology; Joseph N. Sasser and W.R.Jenkins’s (1960)-Nematology-Fundamentals and Recent Advances with emphasis on Plant Parasitic and Soil Forms (This book was the result of series of lectures offered by leading scientist at the course organized at the North Carolina State University sponsored by Shell Chemical Company); William F.
eBook - ePub- William R. Nickle(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
Taxonomic limits are also imposed on the study of nematode ecology: May and Seger (1986) deplored the unsatisfactory state of systematics, especially with invertebrates, and they recognized the importance of knowing what is where as a basis for understanding and managing the ecosystem. Problems exist even with extant nematode identifications let alone the myriad of species yet to be described. The limitations on studies of nematode biology and ecology due to sampling and extraction procedures are well documented but not inimical to valuable research (Barker and Noe, 1988; Ferris and Noling, 1987; McSorley, 1987).All the limitations notwithstanding, research into nematode ecology has progressed increasingly rapidly in the past decade. Movement in mathematical and molecular ecology should enhance rather than replace studies in the classical and traditional areas. In this treatment, we do not wish merely to present a collation of facts but to give examples as a basis for understanding these organisms, an inadequate as our understanding may be. Nor are these examples presented to elucidate a “principle.” Although one cannot ignore the human factor in discussions of agriculture, nematodes are not inclined to behave according to human-contrived principles. We do search for common patterns, but the student, matriculating or lifelong, should not be conditioned to think or search in learning from principles to cases. Thus, our examples, but we hope that they are pertinent.Our knowledge and ability to manage nematode populations when desired is still much too meager. This chapter can only be a preliminary statement concerning a phase of Nematology in which most questions are yet to be answered. Even so, the literature is too vast to be exhaustively treated here, so the reader is referred to review articles and books wherever possible.II. General Biology
A. Life Cycles
Life cycles of most plant nematodes are not complex. There are six stages, including the undifferentiated egg, four juvenile stages (J1-J4), and the adult. In the Secernentea, the “tylenchid” plant parasites, the J1 forms in the egg where it molts into the J2, which is the stage that hatches. In the Adenophorea, the “dorylaimids,” the hatching stage is the Jl.
- Muthukumaran Gunasekaran, Darrell Jack Weber(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
5The Role of Molecular Biology in Developing Biological Controls for Plant Parasitic Nematodes
Graham R. Stirling, Lois Eden and Elizabeth AitkenTABLE OF CONTENTS
I. Introduction II. Resolution of Taxonomic Problems A. Improving Species Identification and Understanding Phylogeny B. Assessing Variability within Species III. Understanding Host Specificity IV. Monitoring Introduced Biological Control Agents A. Detection Using Reporter Genes B. Detection Using DNA Probes V. Determining Mechanisms of Action VI. Manipulation of Useful Genes VII. Concluding Remarks ReferencesI. Introduction
Plant parasitic nematodes are ubiquitous in their distribution but because of their small size and cryptic habitat, their economic importance is frequently underestimated. Nevertheless, nematode population densities reach damaging levels in manyagricultural cropping systems and the problems they initiate cause losses worth billions of dollars to the world’s food and fiber crops.1 Effective controls have not been developed for all crops, but losses from nematodes are sometimes reduced through strategies such as crop rotation and cultivar resistance. Chemical nematicides are also widely used, particularly in intensively managed horticultural and ornamental crops, but their future is uncertain because of health and environmental concerns2 and community demands for more environmentally friendly pest and disease control practices.Plant parasitic nematodes spend most, if not all, of their lives in soil, where they co-exist with a wide range of other soil organisms. Since some of these organisms parasitise or prey on nematodes, or have the capacity to influence nematode behaviour, they are therefore of interest to those involved in the development of biological control strategies for nematodes. A broad overview of the parasites and predators of nematodes is available in several texts,3 ,4 and5 but the most important antagonists are the nematophagous fungi, obligately parasitic bacteria in the genus Pasteuria , predatory mites, predacious nematodes, and a number of miscellaneous organisms (mainly bacteria) whose mechanisms of action are still to be determined. Many of these biological control agents, particularly the nematode-trapping and egg-parasitic fungi and the bacterium Pasteuria penetrans (Thorne) Sayre & Starr, have been tested for activity against nematodes in small-scale tests in the laboratory, glasshouse, and field,5
eBook - ePub- Donald L Lee(Author)
- 2002(Publication Date)
- CRC Press(Publisher)
In this discipline, biological control has usually required a detailed knowledge of the population dynamics of the pest and natural enemy. Although some mathematical models have been developed for the biological control of nematodes (see below), little is known of the quantitative relationships between nematodes and their natural enemies. In general, most knowledge of the biological control of nematodes concerns microbial agents and these are notoriously difficult to quantify in soil. Standard procedures, such as the use of the serial dilution plating of soil samples onto semi-selective media, may provide valuable information on relative changes in the abundance of culturable bacteria and fungi that are nematophagous or antagonistic to nematodes (Kerry et al., 1993). However, interpretation of the data requires care, as such changes in abundance may not be correlated with changes in activity of the stages that affect nematodes. In general, there is a dearth of quantitative methods for the estimation of microbial populations in soil and several methods are required to obtain data that may be reliably interpreted. Entomologists are also familiar with the concept of multitrophic interactions, which include hyperparasites that attack natural enemies and other organisms that may disseminate microbial agents. Insect herbivory induces the release of a range of signals from plants that may involve volatile and non-volatile compounds (Pickett et al., 1992). These compounds may provide natural enemies with extremely sensitive cues to locate their hosts (Powell et al., 1998). Such interactions are likely in the rhizosphere and within the root but their importance in the biological control of nematodes is unknown. The root-knot nematode, Meloidogyne javanica, altered the composition of tomato root exudates and resulted in Rhizoctonia solani changing from a rhizosphere saprophyte to a root pathogen (Van Gundy, Kirkpatrick and Golden, 1977)
- Prasad, D(Authors)
- 2021(Publication Date)
- Biotech(Publisher)
Chapter 32 Biology and Life-Cycle of Economically Important Plant Parasitic Nematodes Kabindra Singh Rathour * and D. Prasad Division of Nematology, I.A.R.I., New Delhi – 110 012 The word ‘Nematode’ is derived from the Greek words- ‘nema’ meaning thread, and ‘oides’ meaning resembling or form ( i.e. threadworms). They are also known as roundworms being tubular in shape and rounded in cross section. In USA they are often nick-named nemas and Britishers call them eelworms. Nematodes may be defined as triploblastic, bilaterally symmetrical, unsegmented, pseudocoelomate, vermiform metazoans with well developed reproductive, digestive, excretory, nervous and musculature systems and with lacking specialized organs for respiration and circulation. They have tubular gonads which open separately in females but join elementary canal in males to open through a cloacal aperture. Life-Cycle The life-cycle of plant parasitic nematodes start with eggs, the embryonic and post-embryonic stages. Generally, there are six stages in the life cycle– the egg, four larval or juvenile stages, and the adult male or female. The life cycle is simple and direct ( Figures 32.1A and 1B ). This ebook is exclusively for this university only. Cannot be resold/distributed. After a series of cell divisions (transverse and longitudinal), the 1 st stage larva (lacking of stylet) is formed. However, in the dorylaims ( Longidorus spp.; Trichodorus spp. and Xiphinema spp. etc.), a weak stylet is discernible. In majority of plant parasitic nematodes except the dorylaims, after embryogenesis the 1 st stage larva (J1) is formed and still enclosed within the egg-shell and it is the only second stage larva (J2) which normally emerges as the infective stage. In the dorylaim nematodes, the first stage larva itself emerges from egg followed by a quick moult in to second-stage larva.
eBook - PDF- Sarma, Brinchi Kuamr(Authors)
- 2018(Publication Date)
- Biotech(Publisher)
The nematodes are basically aquatic animals but they have adopted terrestrial habits (Tunlid and Ahren, 2011). Cobb (1914) remarked that .... if all matter in universe except nematodes were swept away, the world will still be recognizable dimly by its mountains, hills, valleys, lakes and oceans represented by a film of nematodes. At present, the number of known species is about 15,000 but the estimate of existing species is around 5,00,000 or more. It is only in the last few decades ecologist have undertaken detailed studies of belowground soil processes, and this has led to a better understanding of the nature of the soil environment and the complex biological communities that live in soil (Stirling, 2011, Tunlid and Ahren, 2011). Earlier it was assumed that bacteria and fungi are the most numerically abundant member of the soil biota, but culture-independent molecular tools are now indicating that they are far more numerous and diverse than previously thought (Tunlid and Ahren, 2011). Knowledge of the feeding habits of the microfauna ( e.g. protozoa), mesofauna ( e.g. rotifers, nematodes, tardigrades, collembolans, mites and enchytraeids) and macrofauna (e.g. earthworms, termites and millipedes) is also improving, and this is giving us a better insight into the numerous biotic interactions that occur within the soil environment, and how these interactions influence ecosystem processes (Stirling, 2011, Tunlid and Ahren, 2011). Within soil ecosystems, thousand of the nematodes of different kinds-the free living (microbivorous), the predators, and a few hundreds of them plant parasites were living inside the soil (Walia and Bajaj, 2003; Upadhyay and Dwivedi, 2008). For the vast majority of plant-parasitic nematodes, the soil system and its various components constitute their environments.
- Gero Benckiser, Sylvia Schnell, Gero Benckiser, Sylvia Schnell(Authors)
- 2006(Publication Date)
- CRC Press(Publisher)
12.2.3 N EMATODES IN B IOLOGICAL C ONTROL OF A GRICULTURAL P ESTS Use of entomopathogenic nematodes in biological control in agroecosystems provides direct evi-dence of a positive feedback of nematode activity. Entomopathogenic nematodes such as Stein-ernema and Heterorhabditis (Rhabditina) are applied to manage insect pests of cranberries, turf-grass, artichokes, mushrooms, ornamentals, and many other pests in horticultural, agricultural, and domestic situations (Gaugler 2002). This effect is not due to nematodes alone. The pathogenicity depends on a mutualistic nematode–bacterial complex (with strains of Xenorhabdus and Photo-rhabdus, respectively). Slugs in agroecosystems can also be managed using the nematode Phas-marhabditis hermaphrodita and associated bacteria (Wilson et al. 1995). 12.3 DIVERSE NEMATODES OF EACH FEEDING GROUP COEXIST In most soils there is a range of morphologically distinct nematode species in each feeding group. Understanding the relationship between such taxa is a problem throughout soil biology (e.g., Giller et al. 1997; Griffiths et al. 2001; Maraun et al. 2003; Wardle et al. 2003a, 2003b). Conventional wisdom is that those species differ in their use of resources in time or in space. This section serves to indicate ways in which nematodes with broadly similar feeding habits may coexist in a soil. Host specificity (e.g., Heterodera avenae on wheat cf. H. trifolii on white clover), site differ-entiation (e.g., Anguina tritici in wheat florets cf. Heterodera avenae in wheat roots), and temporal TABLE 12.3 Increase in Percentage of 14 C in Soil Microbial Biomass in the Presence of Nematodes, 15 Days After Pulse-Labeling Pots of White Clover ( Trifolium repens ) Nematode 14 C in soil microbial biomass (control) 1.17 Heterodera trifolii 1.57 Meloidogyne hapla 1.72 Meloidogyne trifoliophila 1.47 Xiphinema diversicaudatum 2.45 Pratylenchus sp. 2.50 LSD (0.05) 0.49 Derived from Yeates et al. (1999a)
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