Plant Pathogenic Viruses & Plant-Parasitic Nematodes Lecture 6 PDF

LECTURE 6 PLANT PATHOGENIC VIRUSES PLANT-PARASITIC NEMATODES Dr. Mandy Maid  Plant pathogenic viruses Viruses are unique, submicroscopic obligate pathogens Composed of RNA or DNA genomes surrounded by a protein coat (capsid) They replicated through the assembly of existing...

LECTURE 6 PLANT PATHOGENIC VIRUSES PLANT-PARASITIC NEMATODES Dr. Mandy Maid  Plant pathogenic viruses Viruses are unique, submicroscopic obligate pathogens Composed of RNA or DNA genomes surrounded by a protein coat (capsid) They replicated through the assembly of existing components, with no membrane separation of cellular contents The naming of plant virus species according to the plant host and major symptom Vectored by insects, mites, nematodes, parasitic seed plants, fungi, seed, and pollen Can be detected and identified by biological, physical, Examples of p l a nt v i rus es as observed with the el e c t r on protein, and nucleic acid properties m i c r o s c o p e. R i gi d r o d s of t o b a c c o m o s a i c v i rus 20XX presentation title 2  HOW ARE VIRUSES NAMED? Name of the host infected, and the principal symptoms they cause Example: Tobacco mosaic virus (TMV) Species concept in plant virology (van Regenmortel et al. 2000): Following the first use of the species name, then refer to the abbreviation in (parentheses) Taxonomic level: Genus: a collection of viruses with similar properties Family: a collection of related virus genera Example: Cowpea mosaic virus (CPMV), genus: Comovirus, family: Comoviridae 20XX presentation title 3  HOW ARE VIRUSES NAMED? Strains  when the virus isolate proves to differ from the type isolate of the species in a definable character but does not differ enough to be a new species (Matthews, 1991)  represent mutations or adaptations in the type virus  Virus strain may have altered reactions or have important serological differences Isolates  Any propagated culture of a virus with a unique origin or history  Do not differ sufficiently from the type isolate of a virus to be a strain 20XX presentation title 4  WHAT IS A PLANT VIRUS? Diverse groups infecting hosts from unicellular plants to trees Have nucleic acid genomes (RNA or DNA), single- or double-stranded, linear or circular, single-piece or multiple pieces Have protein coats or capside, one or more types They are obligate parasites – depend on the host for all functions, e.g. accumulation of metabolites, energy generation, synthesis of nucleic acid and amino acids Viruses infect the cellular structure of the host and control a part of the subcellular systems of the plant 20XX presentation title 5  https://cdn1.byjus.com/wp-content/uploads/2022/06/tmv-diagram.png 20XX presentation title 6  WHAT IS A PLANT VIRUS? Viral replication assembles new particles from pools of required components Components are synthesized as separate proteins or nucleic acids using the host enzyme systems and the infecting viral genome Plant viruses cannot cause entry wounds on plants Depend on vectors to breach the epidermal layer of the plant and place them within a living host cell Vector: insects, mites, nematodes, fungi, seed, dodder, man, animals, other organism through mechanical transfer 20XX presentation title 7  SYMPTOMS FOUND IN PLANTS INFECTED WITH THE VIRUS? SYMPTOMS – host’s response to infection Viral diseases may be misidentified SYMPTOMS CAUSED BY LOCALIZED INFECTION Local lesions Local lesions occur when the virus infection fails to spread systematically due to the host response The virus overcome this initial reaction Chlorotic or necrotic Can be used to quantify infectivity in a virus solution 20XX presentation title 8  SYMPTOMS FOUND IN PLANTS INFECTED WITH THE VIRUS? SYMPTOMS BASED ON CHANGES IN CHLOROPHYLL OR OTHER PIGMENTS 1. Mosaics and mottles Patterns of lighter and darker pigmentation Lighter pigmentation such as pale green, yellow or white due to decreased chlorophyll Damage to chloroplasts Or increased pigmentation in dark green areas E.g. TMV 20XX presentation title 9 2. Stripes and streaks 3. Ringspots and line patterns In monocots, pigmentation restricted in Ringspots – concentric circles of chlorotic or spread by parallel venation of leaves necrotic tissue In short segments or extend the entire E.g. Tomato spotted wilt virus (TSWV) length of the leaf Line – extension of ringspots, occur near the Wheat Streak Mosaic Virus (WSMV) or edge of the leaf, following the outline of the Maize Dwarf Mosaic Virus (MDMV) leaf E.g. Rose mosaic virus (RMV) https://alchetron.com/cdn/maize-dwarf- mosaic-virus-afc969e2-f408-44b4-9249- 4031494d052-resize-750.jpeg https://ars.els-cdn.com/content/image/3-s2.0-B0122276205001087- gr2.jpg 20XX presentation title 10 4. Vein banding 5. Vein clearing Occurs wen areas of intense A loss of pigmentation (clearing or pigmentation form bordering the translucence of tissue) in the veins veins of the leaves Viewed by passing light through the Seen as dark green bands along leaf major leaf veins Caused by enlargement of the cells near the vein, sometimes preceed the formation of mosaic https://agritech.tnau.ac.in/crop_protection/Vein%20clearing_4.png https://upload.wikimedia.org/wikipedia/commons/thumb/4/40/SVBV_symptomatology.jpg/440 px-SVBV_symptomatology.jpg 11  SYMPTOMS THAT ARE CAUSED BY GROWTH ABNORMALITIES 1. Stunting and dwarfing 2. Tumors and galls Reduction in the size of the infected Hyperplasia – enlargement in cell size host plant Hypertrophy – increase in cell The most prominent symptoms number from a viral infection E.g. Wound tumor virus (WTV) Stunting – change in the size of plant parts, shortening of the internodes (bushy stunt) 20XX presentation title 12 3. Distortion 4. Enations Changes in the lamina of the host Small overgrowths occurring on the leaves result in areas that are leaf twisted, deformed, or distorted E.g. Pea enation mosaic virus (PEMV) Symptoms: blisters, bubbles, rumpling, rugosity, or twisting E.g. Bean pod mottle virus (BPMV) 20XX presentation title 13  SYMPTOMS AFFECTING REPRODUCTION 1. Sterility 2. Yield loss Host plants infected with plant viruses Maybe a reduction in the total reproduction may lose their ability to produce viable of the plant, seed, and fruit production seed Shriveled, reduced in size, distorted, or Linked with floral abnormalities, decreases inferior in quality in flowering, seed development, or seed WSMV, yield loss due to undersized, set shriveled grain Change in plant metabolism and Plum pox virus (PPV) reduce carbohydrate biochemical signalling levels in fruits 20XX presentation title 14  TRANSMISSION OF PLANT VIRUSES Mechanical transmission of plant viruses Mechanical transmission allows the transmission of plant viruses without a vector An abrasive – to penetrate epidermal layers, cell wall, and cell membrane Nonlethal wounding Effective for viruses that infect epidermis cells Transmitted through accidental contact between healthy and infected plants Can be used to evaluate new plant cultivars for viral disease resistance 20XX presentation title 15  PLANT-PARASITIC NEMATODES 20XX presentation title 16  Plant-parasitic nematodes Most important pest in plant-production systems Many species have very wide host ranges Are obligate parasites – feed on living plant cells They almost never kill their hosts because dependent Parasites have a hardened spear-like stylet for feeding on living plant cells Do not produce any obvious diagnostic symptoms in plants Plant damages are dependent on the number of nematodes or eggs present at planting Soil and root assays can provide information on nematode populations https://sodsolutions.com/wp-content/uploads/2022/02/Plant-Parasitic-Nematode- 1536x864.jpg  PLANT PARASITIC NEMATODES CHARACTERISTICS Usually found in the soil & plant roots, sometimes on above-ground parts Most are microscopic, with a length of 300-4000 μm, & a diameter of 15-35 μm (similar to large fungal hyphae) Can be observed under 40x-1000x magnification Nematode is the Greek word for thread-like, worm-like body shape, undergo four molts during the life cycle takes a few weeks to a year to complete a life cycle, depend on species Morphology is a tube within a tube; outer layer is tough, flexible cuticle Within the cuticle, the from contains the esophagus & the rear contains the intestines & reproductive organ, have excretory, nervous systems, several types of muscles NO circulatory or respiratory organ 20XX presentation title 18 20XX presentation title 19  Have hardened spear-like feeding structure called stylet, in the anterior portion of the head region Stylet is hollow and operates like a hypodermic needle, removing nutrients from plant cells, Stylet is used to penetrate & burrow through the plant tissues & locate preferred feeding sites Glands located in the posterior secrete compounds into the plant cells through the stylet – cause extreme structural & physiological modification Ectoparasites – feed on roots from the outside Endoparasites – feed from the inside of the roots Some sp. are migratory, move around throughout the life cycle Some are sedentary and settle in one location to establish a permanent feeding site 20XX presentation title 20  Root-knot nematode Meloidogyne species, 100 species Wide-spread, sedentary endoparasite Four important species: M. arenaria, M. hapla, M. incognita, M. javanica cause damage to agricultural crops Found worldwide but more common in warm climates and sandy soils Infected plants are stunted, chlorotic, moderate wilting on hot days Galls or knots form on the host roots – for easy diagnosis 20XX presentation title 21  https://www.researchgate.net/profile/Chandan- 20XX presentation title Shivamallu/publication/345045207/figure/fig1/AS:952583900364802@1604125108663/ 22 Morphology-of-male-and-female-root-knot-nematodes-Source-Handoo-et-al-2004.png  Practical 4 Assessment 1. Symptom and sign identification and description 2. Macroscopic fungal colony description 3. Microscopic fungal description 20XX presentation title 23 thank you Dr. Mandy Maid [email protected]