Methods And Techniques In Plant Nematology Pdf


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Nematode Interactions

Plant-parasitic nematodes are costly burdens of crop production. Ubiquitous in nature, phytoparasitic nematodes are associated with nearly every important agricultural crop and represent a significant constraint on global food security. Root-knot nematodes Meloidogyne spp.

Limitations on the use of chemical pesticides have brought increasing interest in studies on alternative methods of nematode control. Among these strategies of nonchemical nematode management is the identification and implementation of host resistance.

In addition, nematode genes involved in parasitism represent key targets for the development of control through gene silencing methods such as RNA interference. Recently, transcriptome profiling analyses has been used to distinguish nematode resistant and susceptible genotypes and identify the specific molecular components and pathways triggered during the plant immune response to nematode invasion. This summary highlights the importance of plant-parasitic nematodes in agriculture and the molecular events involved in plant-nematode interactions.

Nematology - Concepts, Diagnosis and Control. Over millions of years, the association of plants and nematodes has resulted in the evolution of the plant-parasitic nematode. Widely distributed pathogens of vascular plants, enormous losses in yields have been attributed to the presence of nematodes.

Phyto-parasitic nematodes have evolved strategies to suppress host immune responses for the development of feeding sites. In turn, plants have developed specific molecules to recognize pathogens signaling the activation of immune responses.

Declining use of chemical pesticides has brought great attention to research in alternative methods of nematode control. An effective strategy for nematode management involves the utilization and implementation of nematode-resistant cultivars into crop breeding programs.

Currently, genetic sequencing analyses are widely utilized in the identification of molecular components of nematode parasitism and is also used to distinguish nematode-resistant and susceptible plant genotypes. These detailed analyses have significantly contributed to our overall understanding of the dynamic and complex nature of plant-nematode interactions. Nematodes are a fascinating, biologically diverse group of organisms. Their ability to adapt to a wide variety of habitats including; marine, soil and aquatic, provides an evolutionary advantage for species longevity.

Phylum Nematoda is largely distinguished by three major monophyletic groups including: Enoplia marine , Dorylaimia parasitic trichinellids and mermithids and Chromadoria nematodes of various environments.

Nematodes belong to the group Ecdysozoa, which comprises animals that can shed their cuticle. Over 30, species of round worms are found in Nematoda [ 1 ] typically ranging in size from 0.

Nematode body structure is relatively simple and characterized as limbless, cylindrical, and elongated. These muscles are activated by the dorsal and ventral nerves and their contractions allow for locomotion in sinusoidal waves.

In plant-parasitic nematodes, a primary infection structure called a stylet is located at the anterior end of the nematode which is followed by an esophageal region that connects the stylet to the intestines. A typical tylenchoid esophagus consists of an anterior procorpus, a median bulb and the posterior basal bulb. The median bulb functions in the transfer of enzymes involved in primary infection and facilitates the movement of plant nutrients into the intestine.

Inside of the exterior body wall lies the pseudocoelom, a unlined, pressurized, fluid-filled cavity formed directly from the blastula surrounding the gut cavity. The pseudocoelom is filled with fluid which provides turgor pressure for the entire body containing the internal organs and aides in the transfer of nutrients, oxygen and metabolic products. The excretory system is composed of four distinctive cells, an excretory pore cell, a duct cell, one canal cell, and a fused pair of gland cells.

Nematodes are enclosed within an exoskeleton called a cuticle which is secreted by inner hypodermal cells, and is primarily composed of collagens, insoluble proteins cuticlins , glycoproteins and lipids. The cuticle plays an important role in movement, environmental protection and growth and development [ 2 ].

The typical male reproductive structures include a testis, a seminal vesicle and a vas deferens leading to a cloaca, while the female reproductive system is tubular containing one or two ovaries, seminal receptacles, an uterus, ovijector and a vulva. Why do some nematodes become plant parasites? The dynamic association of nematode and plant host has resulted in plant parasitism which has evolved three times culminating in substantial benefits for nematode survival and development [ 3 , 4 ].

Evidence suggests the initial presence of plant-parasitic nematodes to have occurred around BC [ 6 ] while the first described plant parasitic nematodes were reported by Needham who observed symptoms of galling in wheat [ 7 ]. An agriculturally important species of plant-parasitic nematodes called root-knot nematodes, were initially identified by Berkeley who observed the presence of galls on cucumber roots [ 8 ].

The plant-nematode association has resulted in the development of specific feeding structures and secretory products that are involved in host infection and nutrient absorption. Plant-parasitic nematodes utilize a hollow, needle-like, protrusible stylet to probe plant tissue and release an assortment of proteinaceous secretions from the subventral and dorsal glands which comprises the integrity of the host cell and allow for nematode entry.

These glandular secretions induce cellular remodifications that are essential for development of a metabolically active feeding cell [ 10 ]. Among the secretory molecules are a group of carbohydrate-active enzymes. Genomic analyses of root-knot nematodes have revealed the presence of a suite of enzymes called CAZymes cellulases, xylanases and other glycosyl hydrolase family members GHFs [ 11 ].

Beta-1,4-endoglucanase genes have been isolated from plant-parasitic cyst nematodes with catalytic domains belonging to family 5 of the glycosyl hydrolases [ 12 , 13 ]. Glycosyl hydrolase families G5 and G45 have been identified in plant-parasitic nematodes. Plant-parasitic nematode GH5 cellulases show closes homologies with bacterial G5s, which suggests an initial horizontal gene transfer of bacterial G5 cellulases into nematode genomes during the evolution of the plant-parasitic order Rhabditida suborder Tylenchina [ 14 , 15 ].

G45 cellulases have been found in plant-parasitic nematode Bursaphelenchus xylophilus of the Aphelenchida order [ 16 ]. Phylogenetic analyses have shown similarities in gene structure between G45 sequences found in these nematodes and ascomycetous fungi which supports the hypothesis of a horizontal gene transfer event from fungi to nematodes [ 17 ].

Plant-parasitic nematodes differ in lifestyles. Some nematodes will invade the plant cells while others simply obtain nutrition externally.

Ectoparasitic nematodes remain outside the host cells and feed on plant roots while endoparasitic nematodes establish residence within plant tissue. An example of ectoparasitic nematode is Xiphinema California dagger nematode which transmits the Grapevine fanleaf virus.

The resulting viral infection causes tremendous economic losses in grapes worldwide [ 18 ]. Endoparasitic nematodes are further divided into migratory and sedentary groups. Migratory endoparasitic nematodes move within the root and remove cytoplasm killing the host cell while sedentary nematodes become immobile after the development of a feeding site within the host tissue [ 19 ].

Migratory endoparasitic nematodes of economic significance include Pratylenchus spp. Plant-parasitic nematodes are a costly burden in agricultural crop production. Over species of plant-parasitic nematodes have been identified [ 20 ]. Nematodes in the order Tylenchida are pathogens of plants, invertebrates, and fungi and are considered the most important agricultural pests [ 22 ].

Of all the important plant-parasitic nematodes, the most successful species are the sedentary groups which establish a permanent feeding site within the plant host and obtain nutrients while completing their lifecycles. Sedentary nematodes have a natural advantage over their migratory relatives due to a fascinating and complex method of host cell transformation resulting in the development a sustainable feeding structure. Interestingly, with over described plant-parasitic nematodes, only a small amount produce significant economic losses in crops.

In a survey conducted on a variety of crops in the U. S, the major genera of phytoparasitic nematodes reported to cause crop losses were Heterodera , Hoplolaimus , Meloidogyne , Pratylenchus , Rotylenchulus , and Xiphinema [ 23 ]. Wheat Triticum aestivum is the most important cereal crop in the world.

Wheat yields are significantly decreased by the presence of cereal cyst nematodes Heterodera spp. An estimated 3. In some wheat fields, the losses caused by H.

In addition to cereal cyst nematodes, further losses of wheat are caused by root-lesion nematodes Pratylenchus neglectus and Pratylenchus thornei , and the seed gall or ear-cockle nematode, Anguina tritici. An inverse relationship between H. Anguina tritici is often a vector for Rathayibacter tritici , a Gram-positive soil bacterium which associates with Clavibacter tritici causing seed gall [ 29 ]. Rice Oryza sativa L. Over species of nematodes affect rice production.

Meloidogyne spp. One of the most important species of Meloidogyne , is M. Symptoms of infection manifests as hook shaped galls, stunting, decreased tiller numbers and poor growth and reproduction [ 33 ]. The rice root-nematode Hirschmanniella oryzae , i. Widely distributed, H. S states, Louisiana and Texas. Maize Zea mays is grown largely throughout the world with three largest production in North America Asia and Europe [ 21 ].

Over 50 species that are known to parasitize corn in the globally however, the most devastating genera include the root knot nematodes, Meloidogyne spp.

In the U. In most cases, symptoms of infection caused by these nematodes include poor development and leaf chlorosis with minor galling [ 36 ]. The potato Solanum tuberosum is a member of the Solanaceae family, and is considered the third most important crop in the world with total world potato production estimated at over million tonnes in [ 38 ]. Cyst nematodes are prolific pathogens of potato causing dramatic losses in yields. Globodera rostochiensis and Globodera pallida originate from S.

America and are known pests of other members of the Solanaceae family including tomatoes and woody nightshade [ 39 ]. These nematodes are classified as quarantine pests in a number of countries including the U. Other major plant-parasitic nematodes of potato include root-knot nematodes Meloidogyne spp. Among the four species of root-knot nematodes that affect potato production in the U.

In addition to potato, sweetpotato Ipomoea batatas L. Lam is a major host for D. The sweetpotato [ Ipomoea. Its cultivation dates to the prehistoric era, and it has been grown continuously as a staple food source.

Currently, the sixth most important food crop, sweetpotato production has improved the economic status for communities throughout the world particularly in developing nations where it ranks as the fifth most important crop [ 44 ]. Approximately Root-knot nematodes RKNs are significant pests of sweetpotato causing symptoms of infection which include: stunted plant growth, yellowing of leaves, abnormal flower production, and gall production on roots leading to decreased nutrient and water absorption and necrosis and cracking on fleshy storage roots.

Due to the economic importance of the storage root, root cracking is a primary concern for producers. Successful sweetpotato root-knot nematode resistant breeding programs involve the determination of resistance genes. Nematode resistance is governed by genotype [ 45 ] and is primarily quantitative [ 46 ]; therefore, the identification of genetic markers associated with root-knot nematode resistance requires broad scale molecular studies.

Plant Nematology 2nd Edition (PDF)

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Extraction methods for plant material (Fig. 7) are usually based on nematode mobility. These methods vary depending on whether or not the samples have been.


The Impact of Plant-Parasitic Nematodes on Agriculture and Methods of Control

Plant-parasitic nematodes are costly burdens of crop production. Ubiquitous in nature, phytoparasitic nematodes are associated with nearly every important agricultural crop and represent a significant constraint on global food security. Root-knot nematodes Meloidogyne spp.

Published on: Monday, December 23, Views:. Author: Roland N. We were delighted with the positive response to the 1st edition of Plant Nematology. Initially aimed at the MSc course in nematology at Ghent University, Belgium, the book has proved popular with students and staff worldwide.

Various methods have been used for the preparation of nematodes for light microscopical examination. Nematologists have not always agreed about the best methods to be used, but few studies evaluate the various methods of preparing slides to find the best procedure. The purpose of this chapter is two-fold: to review the methods used for the preparation of nematodes for identification, and to report results of our own observations on the use of different methods. Unable to display preview.

Plant Nematology N.G. Ravichandra

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Morphological Characters and Methods for Preparing Nematodes

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All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN The export rights of this book are vested solely with the publisher. Published by Asoke K.

И взмолилась о том, чтобы они сумели вовремя найти Северную Дакоту. - Поторопись, - крикнул ей вдогонку Стратмор, - и ты еще успеешь к ночи попасть в Смоки-Маунтинс. От неожиданности Сьюзан застыла на месте. Она была уверена, что никогда не говорила с шефом о поездке. Она повернулась. Неужели АНБ прослушивает мои телефонные разговоры.

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Джабба нередко прибегал к ВР, что в компьютерных кругах означало виртуальная реальность, но в АНБ это сокращение имело несколько иной смысл - визуальная репрезентация. В мире технических служащих и политиков, имеющих чрезвычайно разные уровни понимания, визуальная репрезентация нередко была единственным способом что-либо доказать: взмывающая вверх кривая производит куда более сильное впечатление, чем целые тома рассуждений. Джабба понимал, что ВР текущего кризиса со всей наглядностью объяснит то, что он хотел сказать. - ВР! - крикнула Соши, усаживаясь за компьютер в задней части комнаты. На стене ожила связанная с компьютером диаграмма. Сьюзан рассеянно подняла на нее глаза, безучастная к царившему вокруг нее безумию. Все в комнате дружно повернули головы.

Он схватился руками за боковые стороны проема и, одним движением вбросив свое тело внутрь, тяжело рухнул на лестницу.

Чутье мне подсказывает.  - Второе, что никогда не ставилось под сомнение, - это чутье Мидж.  - Идем, - сказала она, вставая.  - Выясним, права ли .

 Десять секунд. Глаза Сьюзан неотрывно смотрели на Танкадо. Отчаяние.

Звонивший некоторое время молчал. - О… понимаю. Прошу прощения. Кто-то записал его, и я подумал, что это гостиница.

Plant Nematology Lecture

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