Plant Virology 2024 - Translocation & Distribution of Viruses in Plants (PDF)

INTRODUCTION TO PLANT VIROLOGY l AG-MCCP4112 1st Semester, 2024-2025 l BSA 4 - Crop Protection VI. Translocation & distribution of viruses ILO: Explain the mechanism of virus infection, replication and translocation in plants. MARIA LIMA D. PASCUAL Professor, Dept. of Animal & Crop Science Co...

INTRODUCTION TO PLANT VIROLOGY l AG-MCCP4112 1st Semester, 2024-2025 l BSA 4 - Crop Protection VI. Translocation & distribution of viruses ILO: Explain the mechanism of virus infection, replication and translocation in plants. MARIA LIMA D. PASCUAL Professor, Dept. of Animal & Crop Science College of Agriculture, Business and Food Science CTU-Barili Campus VI. Translocation & distribution of viruses Virus movement - after the virus replicates it has to be able to move to new cells and Virus movement new tissues/organs in order to systemically infect Types of virus - viruses move around in plants by manipulating the plant’s own movement systems Cell-to-cell movement Plasmodesmata Infection of single Cell-to-cell Long distance Steps cells movement movement Basic strategies Non tubule guided movement Tubule guided movement Systemic movement Replication ✓ Replication ✓ Replication ✓ Movement to ✓ Movement to adjacent cells adjacent cells ✓ Movement to cells throughout the plant VI. Translocation & distribution of viruses Virus movement Virus movement To carry out cell-to-cell Types of virus & long-distance movement movements, viruses Cell-to-cell movement take advantage of Plasmodesmata plant existing routes, Steps including Basic strategies Non tubule plasmodesmata and guided movement phloem and follow the Tubule guided source-to-sink movement transportation of Systemic movement carbohydrates Local and long distance signaling systems integrate whole-plant functions. VI. Translocation & distribution of viruses Types of virus movement 1. Cell to cell (short distance) movement Virus movement - through plasmodesmata (slow), local Types of virus movement movement - the virus moves from one cell into neighboring Cell-to-cell movement cells Plasmodesmata - move as whole particles or as protein/nucleic Steps acid complex (no coat protein required) Basic strategies Non tubule 2. Systemic (long distance) movement guided movement - through the phloem (fast) Tubule guided - the virus moves from an infection site to distant movement parts of the plant by hitching a ride on the plant’s Systemic movement own supply lines (the veins) - move as particles or proteins/nucleic acid complex (coat protein required) VI. Translocation & distribution of viruses Cell-to-cell movement - to move from one cell to the next, Virus movement viruses exploit the channels that Types of virus plant cells use to communicate with movement each other; these channels are Cell-to-cell movement called plasmodesmata Plasmodesmata Steps Basic strategies Non tubule guided Plasmodesmata movement - are small tubes that connect the Tubule guided companion cell to the sieve tube & movement allow the transfer of molecules Systemic movement - are lined with proteins & can be tightly controlled by the plant VI. Translocation & distribution of viruses Structure of plasmodesmata & comparison to viral particles Virus movement Types of virus movement Cell-to-cell movement Plasmodesmata Steps Basic strategies Non tubule guided movement Tubule guided movement Systemic movement - relative to the diameter of plasmodesmata, virus particles are huge VI. Translocation & distribution of viruses Steps in cell-to-cell movement Virus movement 1. Viruses need to leave sites of replication Types of virus 2. Viruses need to locate the plasmodesmata movement 3. Viruses need to pass through the Cell-to-cell movement plasmodesmata Plasmodesmata Steps Basic strategies - Viral encoded “movement proteins (MPs)” Non tubule guided facilitate these steps and are used to movement overcome the plant’s control of the Tubule guided plasmodesmata. Most MPs are movement multifunctional. Systemic movement VI. Translocation & distribution of viruses Genes encoded by TMV Virus movement Types of virus movement Cell-to-cell movement Plasmodesmata Steps Basic strategies Non tubule guided movement Tubule guided movement Systemic movement VI. Translocation & distribution of viruses Movement proteins (MPs) - are non-structural protein which enable Virus movement virion movement from one infected cell Types of virus to neighboring cells by modifying movement plasmodesmata, thereby allowing local & Cell-to-cell movement systemic spread of viruses in plants Plasmodesmata Steps Basic strategies Functions Non tubule guided movement 1. MPs are required for movement Tubule guided 2. MPs bind to virus genomes movement 3. MPs interact with plant cytoskeleton Systemic movement 4. MPs localize to plasmodesmata 5. MPs gate plasmodesmata VI. Translocation & distribution of viruses Replication & early steps in movement Virus movement Types of virus movement Cell-to-cell movement Plasmodesmata Steps Basic strategies Non tubule guided movement Tubule guided movement Systemic movement VI. Translocation & distribution of viruses Basic strategies of virus movement Virus movement Types of virus movement Cell-to-cell movement Non tubule guided movement Tubule guided movement Plasmodesmata Steps Plasmodesmata are gated Plasmodesmata used for viral Basic strategies open at the infection & close transport are permanently Non tubule guided after. Thus, maintaining the modified by MPs forming a movement integrity of normal tubule through which virion Tubule guided intracellular communication moves movement Systemic movement VI. Translocation & distribution of viruses Non tubule guided movement The mechanism by Virus movement which movement Types of virus proteins work is by movement associating with and Cell-to-cell movement coating the genome of the virus, causing the Plasmodesmata ribonucleoprotein Steps complexes (RNP) to be Basic strategies transported through Non tubule guided the plasmodesmata into the neighboring movement cells Tubule guided - TMV forms a complex between its MPs and the viral RNA movement to move between cells Systemic movement - MP (TMV) targeting plasmodesmata, modifying the plasmodesma SEL (size exclusion limit), binding single- stranded nucleic acids, interacting with the cytoskeleton, & trafficking nucleic acid between cells VI. Translocation & distribution of viruses Non tubule guided movement Virus movement Types of virus movement Cell-to-cell movement Plasmodesmata Steps Basic strategies Non tubule guided movement Tubule guided movement Systemic movement PVX uses viral proteins to alter plasmodesmata and allow whole virus particles to move from cell to cell VI. Translocation & distribution of viruses Tubule guided movement The movement Virus movement proteins of many plant Types of virus viruses form a movement transport tubule within the pore of the Cell-to-cell movement plasmodesmata that Plasmodesmata allows the transport of Steps mature virus particles Basic strategies Examples of viruses Non tubule guided that use this movement mechanism are CPMV Tubule guided and TSWV movement CPMV uses protein tubule to line plasmodesmata Systemic movement and allow whole virus particles to move between cells VI. Translocation & distribution of viruses Tubule guided movement Virus movement TSWV, CPMV and CaMV Types of virus - these viruses require movement coat protein in addition Cell-to-cell movement to MP for cell to cell Plasmodesmata movement Steps - the viral genome, Basic strategies encapsidated in virus Non tubule guided particles, moves movement through MP-containing Tubule guided tubules that appear to movement Plant Cell 11, 535-548. emerge from highly Systemic movement modified plasmodesmata VI. Translocation & distribution of viruses Systemic movement (long distance) Virus movement - viruses move from Types of virus movement cell to cell through Cell-to-cell movement a leaf until they Plasmodesmata find a vein Steps Veins are used by the Basic strategies plant to supply growing Non tubule guided tissues. Food flows movement through the veins in the Tubule guided phloem. movement Systemic movement The flow of food through these pipe-like cells is always from mature leaves to younger leaves VI. Translocation & distribution of viruses Systemic movement (long distance) Virus movement - viruses enter veins and Types of virus movement move with the flow of Cell-to-cell movement food to healthy new Plasmodesmata leaves Steps Basic strategies - once in systemic leaves, Non tubule guided viruses can unload from movement the veins and spread into Tubule guided all cell types in the leaf movement - much faster than cell-to- Systemic movement cell movement VI. Translocation & distribution of viruses Systemic movement (long distance) Virus movement - viruses move from Types of virus movement cell to cell through Cell-to-cell movement a leaf until they Plasmodesmata find a vein Steps Veins are used by the Basic strategies plant to supply growing Non tubule guided tissues. Food flows movement through the veins in the Tubule guided phloem. movement Systemic movement The flow of food through these pipe-like cells is always from mature leaves to younger leaves VI. Translocation & distribution of viruses Systemic movement Virus movement - Long distance movement Types of virus movement involves passage of Cell-to-cell movement viruses through various Plasmodesmata cellular barriers including Steps the bundle sheath, Basic strategies vascular parenchyma, & Non tubule guided companion cells for virus movement loading into sieve Tubule guided elements movement Systemic movement - Viruses are then passively transported through the sieve elements to distant tissues VI. Translocation & distribution of viruses Virus movement Virus movement ▪ After inoculation, mostly into epidermal or Types of virus movement mesophyll cells, virions Cell-to-cell movement are disassembled for replication and Plasmodesmata translation of the viral Steps genome (1). Basic strategies ▪ Viral proteins, sometimes Non tubule guided associated to cellular factors, interact with the movement viral genome to form the transport complexes Tubule guided (virions or RNP movement complexes) allowing virus movement from cell-to- Systemic movement cell via plasmodesmata (1). Figure 1: A general view of virus cell-to-cell and long-distance movement in plant tissues. VI. Translocation & distribution of viruses Virus movement Viral replication and cell-to- Virus movement cell movement continue in and between nucleate Types of virus movement phloem cells, i.e., bundle Cell-to-cell movement sheath, vascular parenchyma and companion cells (2). Plasmodesmata Then, the transport Steps complexes (in the form of Basic strategies virions or RNPs) are loaded into sieve elements for long- Non tubule guided distance movement (2), movement before being finally released into systemic tissues to start Tubule guided a new infection site (3). movement The whole process requires Systemic movement an effective crossing of successive boundaries between different cell types and leads to systemic infection of the plant. Figure 1: A general view of virus cell-to-cell and long-distance movement in plant tissues. Thank you. INTRODUCTION TO PLANT VIROLOGY & BACTERIOLOGY l AG-MCCP4112 1st Semester, 2024-2025 l BSA 4 - Crop Protection VII. Virus-host interactions ILO: Discuss the mechanisms by which plant viruses induce diseases and the corresponding host response/symptoms MARIA LIMA D. PASCUAL Professor, Dept. of Agriculture and Food Science (DAFS) College of Agriculture, Business and Food Science CTU-Barili Campus VII. Virus-host interactions Virus-plant interactions Introduction - how virus can infect and cause Types of response by disease in its host plant and how plants to host plant restrict viral infections inoculation with a virus - studied through the application of Virus-host cell methods based on recombinant interactions DNA technology for studying the General steps in the role of viral gene products in induction of disease disease induction and host response Gene silencing VII. Virus-host interactions Types of response by Introduction plants to inoculation with a virus Types of response by Immune (non-host) plants to - virus does not replicate in protoplasts, inoculation with a nor in cells of the intact plant, even in virus initially inoculated cells Virus-host cell - inoculum virus may be uncoated, but no interactions progeny viral genomes are produced General steps in the induction of disease Infectible (host) and host response - virus can infect and replicate in Gene silencing protoplasts - can be resistant (extreme hypersensitivity, hypersensitivity); or susceptible VII. Virus-host interactions Infectible (host) Introduction Types of response by Resistant (extremely hypersensitivity) plants to - virus multiplication is limited to initially infected cells because inoculation with a of an ineffectual virus-coded movement protein, giving rise to virus subliminal infection Virus-host cell - plants are field resistant interactions General steps in the Resistant (hypersensitivity) induction of disease - infection limited by a host response to a zone of cell around and host response the initially infected cell, usually with the formation of visible Gene silencing necrotic local lesions - plants are field resistant VII. Virus-host interactions Infectible (host) Introduction Types of response by Susceptible (systemic movement & replication) plants to - can be sensitive or tolerant inoculation with a virus Sensitive Virus-host cell - plants react with more or less severe disease interactions General steps in the Tolerant induction of disease - there is little or no apparent effect on the plant, and host response giving rise to latent infection Gene silencing VII. Virus-host interactions Virus-host cell interactions Introduction - involved responses such as specific host resistance (R) genes Types of response by and/or generalized host defense systems plants to inoculation with a R genes virus - the classical ‘gene-for- Virus-host cell gene’ concept that interactions proposes that, for General steps in the resistance to occur, induction of disease complementary pairs of and host response dominant genes, one in Gene silencing the host and the other in the pathogen are required VII. Virus-host interactions R genes Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the The gene-for-gene hypothesis of Flor (1971). The reaction of the induction of disease host to the pathogen is indicated as: +, susceptible; -, resistant and host response Gene silencing - there are various hurdles that a virus has to overcome in establishing a full systemic disease VII. Virus-host interactions General steps in the induction of disease Introduction 1. Ability of virus to replicate in initial cell Types of response by 2. Ability of virus to move out of first cell plants to 3. Ability of virus to spread through various barriers inoculation with a 4. Development of symptom (ex. mosaic disease) virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing VII. Virus-host interactions Ability of virus to replicate in initial cell Introduction - there is no host specificity in uncoating of virus particle Types of response by - virus uncoat in non-host as in host species plants to - but non-host plant may not support the replication of the inoculation with a viruses as certain resistance genes operate at the single-cell virus level Virus-host cell Ex. TMV and the Tm-1 gene in tomato interactions - the multiplication of TMV is inhibited by the presence General steps in the of the Tm-1 gene in the protoplast induction of disease and host PVX and the Rx genes in potato response - extreme resistance to PVX in potato is provided by the Gene silencing Rx1 and Rx2 genes; Rx resistance operates in protoplasts by suppressing the accumulation of PVX VII. Virus-host interactions Examples (cont’d) Introduction Types of response by PSbMV and the sbm-1, sbm-3 & sbm-4 plants to - peas containing sbm-1, sbm-3 and sbm-4 are unable to inoculation with a support the replication of PSbMV pathotypes 1,3 &4 virus respectively Virus-host cell interactions General steps in the induction of disease and host response Gene silencing VII. Virus-host interactions Ability of virus to move out of first cell Introduction - the main limitation to a virus Types of response by moving from the cell that is plants to initially infected to adjacent inoculation with a cells is its ability to gate the virus plasmodesmata Virus-host cell interactions - other factor that influence the General steps in the ability of viruses to move: induction of Hypersensitive response disease and host (HR) response Gene silencing VII. Virus-host interactions Hypersensitive response Introduction - is induced if the virus can move from the initially infected cells Types of response by - a number of virus-host combinations produce necrotic local plants to lesions inoculation with a - Example: virus - Some varieties of tobacco respond to Virus-host cell infection with all known tobamoviruses by producing necrotic lesions and no interactions systemic spread, instead of the usual General steps in the chlorotic local lesions followed by mosaic induction of disease. This reaction is controlled by N gene found naturally in tobacco plants disease and host - TMV infection of N-gene containing response tobacco results in cell death at the site of Gene silencing infection and virus particles are found in but restricted to the region immediately surrounding the necrotic lesion VII. Virus-host interactions Hypersensitive response Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of - HR cell death and null responses of tobacco leaves following disease and host host and nonhost inoculations. response - HR cell death caused by TMV inoculation; HR cell death Gene silencing symptoms occurred 48h following infection; 10-week old tobacco plants were inoculated with sap prepared from TMV- infected tissues VII. Virus-host interactions Hypersensitive response Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host Tobacco mosaic virus (TMV). (A) Systemic response infections of Nicotiana tobacum plants showing TMV-associated mosaic. (B) Necrotic local Gene silencing lesions on N. tobacum leaf, demonstrating Holme’s N-gene resistance following inoculation with TMV. VII. Virus-host interactions Host protein changes in the Introduction hypersensitive response Types of response by plants to - includes the accumulation of cytotoxic inoculation with a virus phytoalexins, decomposition of callose and Virus-host cell lignin in the cell walls and the rapid cell death interactions of plant cells forming necrotic lesion General steps in the induction of disease and host response Gene silencing VII. Virus-host interactions Systemic necrosis Introduction Types of response by Specific necrotic response plants to - can range from necrosis in inoculation with a a few areas of upper virus leaves or sporadic necrotic Virus-host cell spots mixed with mosaic interactions symptoms to widespread General steps in the necrosis leading to death induction of of the plant disease and host - are dependent on host response genotype, virus strain & Gene silencing environmental conditions VII. Virus-host interactions Ability of virus to spread through various barriers Introduction Types of response by - the ability of a virus to pass plants to various tissue boundaries in inoculation with a reaching the sieve elements of an virus inoculated leaf, to spread through Virus-host cell the vascular system and to exit in interactions photosynthetic product sink General steps in the leaves induction of disease and host - Arabidopsis RTM1 gene is response necessary for restriction of long- Gene silencing distance movement of TEV without causing an HR or SAR VII. Virus-host interactions Systemic host response Introduction - the most common systemic symptom induced Types of response by by viruses is mosaic symptom; mosaic symptom plants to comprises areas of the leaf showing various inoculation with a degrees of chlorosis together with areas that virus remain green and are termed “dark green Virus-host cell islands” interactions General steps in the Chlorosis - in most mosaic symptom, there are regions induction of with different levels of chlorosis; the disease and host chlorotic response is the effect of the virus response either directly or indirectly on the Gene silencing chloroplasts in that region of the leaf causing loss of chlorophyll by perturbation of chloroplast structure and function VII. Virus-host interactions Systemic host response Introduction Vein clearing Types of response by - an early systemic symptom of mosaic-causing plants to viruses which occurs temporarily when the inoculation with a first flush of virus reaches the young leaves virus Virus-host cell Vein banding interactions - some mosaic-inducing viruses cause General steps in the characteristic chlorotic vein banding induction of Dark green islands disease and host - found in the mosaic pattern are cytologically and response biochemically normal, these portion contain low Gene silencing or zero amounts of infectious virus; these cells are in a resistant state or the virus had not entered before host defense mechanisms became activated VII. Virus-host interactions Inherent host response Introduction Gene silencing Types of response by plants to - involves the expression of viral sequences that would inoculation with a interfere with the normal functioning of the target virus virus (i.e. block crucial steps in viral replication and/or Virus-host cell propagation) interactions General steps in the - a process of interruption or suppression of gene during induction of disease transcriptional and post-transcriptional level and host response - the term gene silencing is generally used to describe the “switching Gene silencing off” of a gene by a mechanism other than genetic modification; that is, a gene which would be expressed (turned on) under normal circumstances is switched off by machinery in the cell VII. Virus-host interactions Post-transcriptional gene silencing Introduction - is the result of mRNA of a particular gene being destroyed or blocked Types of response by - the destruction of the mRNA prevents translation to form an active plants to gene product (in most cases, a protein) inoculation with a - A mechanism that plants have developed for protection from virus virus infection (i.e., the plant PTGS system degrades viral RNA) Virus-host cell interactions - A common mechanism of post-transcriptional gene silencing is RNAi General steps in the induction of disease and host response Gene silencing VII. Virus-host interactions What are small RNAs Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing VII. Virus-host interactions The core of RNA silencing – Dicers & Argonautes Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Recovery VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Recovery VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Recovery VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Recovery VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Recovery VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Recovery VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Recovery VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Recovery VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing VII. Virus-host interactions Introduction Types of response by plants to inoculation with a virus Virus-host cell interactions General steps in the induction of disease and host response Gene silencing Thank you. INTRODUCTION TO PLANT VIROLOGY l AG-MCCP4112 1st Semester, 2024-2025 l BSA 4 - Crop Protection VIII. Symptoms of plant virus ILO: Discuss the mechanisms by which plant viruses induce diseases and the corresponding host response/symptoms MARIA LIMA D. PASCUAL Professor, Dept. of Animal & Crop Science College of Agriculture, Business and Food Science CTU-Barili Campus VIII. Symptoms of plant viruses Symptoms Introduction - indispensable for the study of Terms virus diseases Classification of symptoms - are the observable signs of virus Internal symptoms infection in plants and provide External symptoms the first clue in the field Stunting & dwarfing Color deviation in - symptoms indicate the plant leaves reaction to virus infection Color deviation on stem, flower, fruits - viruses can produce different Malformations kinds of symptoms on different plants VIII. Symptoms of plant viruses Why study symptoms? Introduction Terms - correct symptom terms are Classification of important for communication symptoms Internal symptoms - symptoms determine the External symptoms name of a plant virus Stunting & dwarfing Color deviation in - symptoms determine the leaves name of virus diseases Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Important terms Introduction Local symptom/ primary symptom Terms - symptom at the point of entry of virus; Classification of develop at the site of virus entry in mechanically inoculated leaves; called as symptoms local lesions Internal symptoms External symptoms Systemic or secondary symptom Stunting & dwarfing - symptom at the non-inoculated plant parts; Color deviation in occurs when the virus is not confined to leaves the site of inoculation but it spreads to Color deviation on other cells within leaf mesophyll, usually stem, flower, fruits through plasmodesmata connections, and Malformations reaches vascular system, phloem in most of the cases - severe symptoms may develop when a virus has infected a plant systemically VIII. Symptoms of plant viruses Important terms Introduction Terms Incubation period Classification of - the time between entry of virus and symptoms the first appearance of symptoms in Internal symptoms plants External symptoms Stunting & dwarfing Color deviation in Latent infection leaves - no symptom in spite of multiplication Color deviation on and spread of the virus in plant stem, flower, fruits (latent, inapparent, symptomless) Malformations VIII. Symptoms of plant viruses Important terms Introduction Latent virus Terms - don’t induce reaction in their main host; a virus latent in one Classification of species or cultivar, may cause severe symptoms in others symptoms Internal symptoms Latency period External symptoms - time period acquisition of virus by vector and the time when the Stunting & dwarfing vector becomes viruliferous Color deviation in leaves Cryptic virus Color deviation on - don’t cause any visible abnormality stem, flower, fruits Malformations Masking - when symptoms are temporarily absent due to environmental factors VIII. Symptoms of plant viruses Classification of symptoms Introduction Terms 1. Internal symptoms Classification of - expressed as cytological and histological changes symptoms - inclusion bodies Internal symptoms - physiological changes External symptoms Stunting & dwarfing 2. External symptoms Color deviation in - are morphological deviations/changes that are leaves generally more obvious and striking Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Cytological and histological effects Introduction Terms - Hypotrophy (decrease in size of cell), hypoplasia (decrease in Classification of the number of cells) symptoms - Hypertrophy (increase in size of the cell), hyperplasia Internal symptoms (increase in the number of cells) External symptoms - Degeneration and necrosis (death of cells) Stunting & dwarfing - Inclusion bodies Color deviation in - highly characteristics of the virus irrespective of host leaves - have diagnostic value Color deviation on - amorphous (earlier called X-bodies) stem, flower, fruits - granular or crystalline Malformations VIII. Symptoms of plant viruses Inclusion bodies Introduction - are intracellular structures formed due to virus Terms infection Classification of - are found in cell cytoplasm, most commonly found in symptoms epidermis and leaf hairs Internal symptoms External symptoms - some can be seen in compound light microscope Stunting & dwarfing Color deviation in - may contain virus particles, virus related material or leaves degenerate conditions Color deviation on stem, flower, fruits - may be amorphous, crystalline or pinwheel Malformations VIII. Symptoms of plant viruses Inclusion bodies Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations Pinwheel inclusion bodies VIII. Symptoms of plant viruses Physiological and biochemical changes Introduction Terms - decreased photosynthesis and increased respiration in virus- Classification of infected plant (ex. mosaic, chlorosis) symptoms Internal symptoms - delayed translocation of starch from infected tissue results in External symptoms starch lesions Stunting & dwarfing Color deviation in - accumulation of starch and sugars in leaves lead to leaf leaves brittleness (phloem-limited luteo- and poleroviruses) Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Types of external symptoms Introduction 1. Stunting & dwarfing Terms Classification of 2. Color deviation in leaves symptoms - mosaic, mottle, variegation, vein flecking, vein Internal symptoms banding, vein yellowing, yellow mosaic External symptoms 3. Color deviation on stem, in flower, fruits Stunting & dwarfing - dark green patches, necrotic streak, color breaking Color deviation in (flower), dark green patches on cucumber (fruit); ring leaves spot on papaya fruits (fruit) Color deviation on stem, flower, fruits 4. Malformations Malformations - leaf rolling, leaf curling & leaf distortion; leaf narrowing; rugosity; rosetting; stem pitting & stem grooving; epinasty; hyponasty; enation; blisters; cupping; twisting VIII. Symptoms of plant viruses Stunting & dwarfing Introduction Terms Stunting Classification of - if the growth and symptoms development of Internal symptoms plant is arrested External symptoms Stunting & dwarfing Dwarfing Color deviation in - when the plants leaves remain below the Color deviation on ordinary size of its stem, flower, fruits kind Malformations VIII. Symptoms of plant viruses Mosaic Introduction - appearance of various shades of green & yellow color Terms which are irregularly angular but sharply delimited; Classification of diffusely bordered variegation is mottling symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations Tobacco mosaic virus symptom (w/ light & Mosaic symptom in Capsicum leaves dark green areas) infected with Cucumber mosaic virus (w/ yellow & green color patches) VIII. Symptoms of plant viruses Mosaic (in corn) Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations Corn plants showing striping along the veins caused by maize mosaic virus (MMV) VIII. Symptoms of plant viruses Yellow mosaic Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations Some leaves are completely yellow in color which can’t undergo photosynthesis anymore. VIII. Symptoms of plant viruses Mungbean yellow mosaic Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Bean golden mosaic disease Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Yellow vein mosaic in okra Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations - the veins become yellow in color & the leaf lamina remains in green color; with visible fine networks of veins and veinlets VIII. Symptoms of plant viruses Vein clearing Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Vein banding Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations - Development of greener bands along the veins VIII. Symptoms of plant viruses Vein necrosis Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations - Veins become necrotic (cells are dead) and no longer functional VIII. Symptoms of plant viruses Vein flecking Introduction Terms Classification of - symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations In some areas along veins shows flecks VIII. Symptoms of plant viruses Papaya ring spot Introduction Terms - ring spot can Classification of be chlorotic or symptoms necrotic Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Color breaking Introduction Terms Classification of - symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Tulip flower infected with virus Malformations VIII. Symptoms of plant viruses Leaf roll Introduction Terms Classification of - leaf rolling is used to symptoms describe folding of Internal symptoms leaves along their mid External symptoms axis resulting in a more or less tube-like Stunting & dwarfing structure Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Bunchy top Introduction Terms Classification of - the petioles symptoms arise from one point at the tip Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Enation Introduction Terms - abnormal Classification of outgrowth of symptoms vascular Internal symptoms tissue in External symptoms leaves or on Stunting & dwarfing the stem Color deviation in - Ex. Pea leaves enation Color deviation on mosaic stem, flower, fruits disease Malformations VIII. Symptoms of plant viruses Rugose Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Leaf distortion Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Leaf curling Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Tobacco leaf curl Introduction Terms Classification of symptoms Internal symptoms External symptoms Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Stem pitting Introduction Terms - Pits and Classification of grooves below symptoms the bark (ex. Internal symptoms Citrus tristeza External symptoms disease) Stunting & dwarfing Color deviation in leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Shoe-string of papaya Introduction Terms - or fern-leaf Classification of symptom; leaf symptoms lamina has not Internal symptoms grown, External symptoms underdevelop Stunting & dwarfing ed forming a shoe-string or Color deviation in fern leaf leaves Color deviation on stem, flower, fruits Malformations VIII. Symptoms of plant viruses Local lesion Introduction Terms Classification of - Small necrotic symptoms areas which are Internal symptoms restricted or External symptoms limited to these areas which reflect Stunting & dwarfing the entry site of Color deviation in the virus which leaves remain there due Color deviation on to host reaction stem, flower, fruits Malformations TMV local lesion VIII. Symptoms of plant viruses Virus disease symptoms in plants Introduction Terms - depends on host, virus and environment Classification of symptoms - often confused with symptoms of mineral nutritional Internal symptoms deficiency/toxicity, herbicide injury, and other abiotic External symptoms stress Stunting & dwarfing Color deviation in - not dependable for correct diagnosis leaves Color deviation on stem, flower, fruits Malformations Thank you. INTRODUCTION TO PLANT VIROLOGY l AG-MCCP4112 1st Semester, 2021-2022 l BSA - Crop Protection IX. Transmission of plant viruses ILO: MARIA LIMA D. PASCUAL Professor, Dept. of Animal & Crop Science College of Agriculture, Business and Food Science CTU-Barili Campus IX. Transmission of plant viruses Plant virus transmission Introduction - is a fundamental property of viruses Types of plant virus - Plant viruses being obligate parasites must be transmission spread from one susceptible host to another and Mode of transmission need to be introduced in living cell for their survival Vegetative and continuity propagation - generally, viruses must enter plant through wounds; Mechanical they do not enter through natural openings (no transmission receptors) Transmission by seed, pollen & dodder - insect vectors are most important means of natural Insect transmission spread Mite, nematode & fungi transmission - seed transmission is relatively common, but specific for virus and plant IX. Transmission of plant viruses The knowledge of virus transmission is important to: Introduction - recognize a virus as cause of the disease if Types of plant virus transmitted from infected to healthy plant transmission Mode of transmission - how virus spread in field – help in its control Vegetative propagation - establish biological relationship of interaction Mechanical between virus and its vector transmission Transmission by seed, - mechanical transmission is very important for lab pollen & dodder study of viruses Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses There are two types of plant virus transmission Introduction Horizontal transmission Types of plant virus - is by vectors, human pruning transmission shears and tools, and other Mode of transmission direct external contamination Vegetative - plant is infected by an propagation external source of the virus Mechanical transmission Vertical transmission Transmission by seed, - occurs when a plant gets it pollen & dodder from its parent plant either Insect transmission asexual propagation or in Mite, nematode & sexual reproduction via fungi transmission infected seeds IX. Transmission of plant viruses Mode of transmission Introduction Types of plant virus 1. Transmission of viruses by vegetative transmission propagation Mode of transmission Vegetative 2. Mechanical transmission through sap propagation Mechanical 3. Transmission of viruses by seed, pollen, dodder transmission Transmission by seed, 4. Transmission by vectors (insects, mites, pollen & dodder nematodes & fungi) Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Transmission by vegetative propagation Introduction - plants are propagated Types of plant virus vegetative by budding or transmission grafting or by cutting or by Mode of transmission the use of tubers, corms, Vegetative bulbs or rhizome propagation - any virus present in the Mechanical mother plant from which transmission these organs are taken will Transmission by seed, almost always be pollen & dodder transmitted to the progeny Insect transmission - transmission of viruses may Source: Agrios, 2005 Mite, nematode & also occur through natura fungi transmission root grafts of adjacent plant IX. Transmission of plant viruses Mechanical transmission through sap Introduction - occurs when plant come in contact Types of plant virus with other plant & leaves rub transmission together or by the action of humans Mode of transmission Vegetative - involves the introduction of infective propagation virus or biologically active virus into a Mechanical suitable site in the living cells transmission through wounds or abrasions in the Transmission by seed, plant surface pollen & dodder - this method is generally used for Insect transmission experimental purposes under lab Mite, nematode & conditions (also known as sap fungi transmission inoculation) IX. Transmission of plant viruses Mechanical transmission through sap Introduction Types of plant virus transmission - in the lab, this is usually Mode of transmission accomplished Vegetative by grinding propagation the leaf of a Mechanical diseased transmission plant and rubbing the Transmission by seed, infectious sap pollen & dodder on to the leaf Insect transmission of a healthy Mite, nematode & plant fungi transmission IX. Transmission of plant viruses Mechanical transmission through sap Introduction Types of plant virus - some viruses are transmitted only by mechanical means, transmission others can not be transmitted mechanically Mode of transmission Vegetative Prerequisite propagation - occurrence & multiplication in epidermal & parenchymatous Mechanical cells transmission Transmission by seed, Examples pollen & dodder Potato virus X Insect transmission Tobacco mosaic virus Mite, nematode & Cucumber mosaic virus fungi transmission IX. Transmission of plant viruses Transmission by seed Introduction - more than 100 viruses are transmitted Examples Types of plant virus by seed Barley stripe mosaic virus transmission - frequency of transmission varies with the Common bean mosaic virus Cowpea mosaic virus Mode of transmission host-virus combination & with the stage Cucumber mosaic virus Vegetative of growth of the mother plant Tobacco mosaic virus - tobacco ring spot virus in soybean may propagation be transmitted by almost 100% of the Mechanical seed of infected plant transmission Transmission by seed, pollen & dodder Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Transmission by pollen Introduction - virus transmitted by pollen may infect Examples Types of plant virus not only the seed but also seedling that transmission will grow from it Alfalfa mosaic virus Mode of transmission - cross pollination by pollen from virus Bean common mosaic virus Southern bean mosaic virus Vegetative infected plant may infect the seed and Prunus necrotic ring spot virus propagation the seedling that will grow from it - in some cases, can spread through the Mechanical fertilized flower down into the mother transmission plant Transmission by seed, pollen & dodder Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Transmission by dodder Introduction - transmitted from one plant to another Types of plant virus through the bridge formed between two transmission plants by twining the stem of parasitic plants, dodder (Cuscuta sp.) Mode of transmission - dodder is a phanerogamic plant parasite Vegetative - dodder can establish vascular connection propagation between virus donor and acceptor plants Mechanical transmission Examples Transmission by seed, Sugar beet curly top virus pollen & dodder Cucumber mosaic virus Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Insect transmission Introduction Types of plant virus - the most common & transmission economically most important Mode of transmission means of transmission of Vegetative viruses in the field propagation Mechanical transmission Transmission by seed, pollen & dodder Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Insect transmission Introduction - insect vectors of Types of plant virus plant viruses transmission include: Mode of transmission aphids, Vegetative leafhoppers, whiteflies, thrips, propagation mealybugs, Mechanical beetles transmission Transmission by seed, pollen & dodder Insect transmission Mite, nematode & fungi transmission Insect vectors of plant viruses. IX. Transmission of plant viruses Terms used in insect transmission Introduction Acquisition access period Types of plant virus - time for which an initially virus free vector is allowed to access a virus transmission source Mode of transmission Vegetative Acquisition feed period - time period necessary for successful acquisition of the virus by its vector propagation which then become viruliferous Mechanical transmission Inoculation access period Transmission by seed, - time for which a virus carrying vector is allowed to access a virus free pollen & dodder plant & could feed on it Insect transmission Inoculation feeding period Mite, nematode & - Time period for which a virus carrying vector appears to be feeding on a fungi transmission virus free plant to transmit it IX. Transmission of plant viruses Terms used in insect transmission Introduction Transmission/inoculation/inoculation access threshold Types of plant virus - The minimum initial time period that a vector need to acquire a virus & transmission inoculate it to the virus free plant Mode of transmission Vegetative Infective capacity or retention period of vector - time period for which a vector carries/retain/transmit the virus to host propagation plant & remain viruliferous Mechanical transmission Inoculation period or latent period Transmission by seed, - the time period from the start of acquisition feeding period until the pollen & dodder vector can infect the healthy plant with the virus Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Virus-vector relationships Introduction Based on virus retention time by the vector Types of plant virus transmission 1. Non-persistent Mode of transmission 2. Semi-persistent Vegetative 3. Persistent propagation Mechanical Based on site of retention of the virus in vector transmission Transmission by seed, 1. Stylet borne pollen & dodder 2. Circulative Insect transmission 3. Propagative Mite, nematode & 4. Transovarial fungi transmission IX. Transmission of plant viruses Non-persistent/stylet-borne viruses Introduction - such viruses are acquired by the Types of plant virus vector during probing & feeding transmission on host parenchyma including Mode of transmission epidermal cells Vegetative - probing takes as little as 5 propagation seconds Mechanical - vector becomes infective transmission immediately after feeding and Transmission by seed, can transmit the virus quickly pollen & dodder - are acquired in the stylets of Insect transmission insects (sucking) and persist in Mite, nematode & the vector for only a few to fungi transmission several hours IX. Transmission of plant viruses Semi-persistent Introduction - virus persist in its vector for Types of plant virus 10-100 hrs. transmission - acquired from phloem Mode of transmission region with long feeding Vegetative - no latent period propagation - do not circulate & multiply Mechanical in its vector transmission Transmission by seed, pollen & dodder Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Persistent viruses Introduction - the virus is acquired and Types of plant virus transmitted by the vector transmission after relatively long feeding Mode of transmission times and remains Vegetative transmissible for a propagation prolonged period while in Mechanical association with its vector transmission - virus acquired and Transmission by seed, transmitted during feeding pollen & dodder probes to phloem Insect transmission - can be circulative or Mite, nematode & propagative transmission fungi transmission IX. Transmission of plant viruses Circulative transmission Introduction - virus transmission Types of plant virus characterized by a long transmission period of acquisition of the Mode of transmission virus by a vector, a latent Vegetative period of several hours propagation before the vector for a long Mechanical period, usually several days transmission Transmission by seed, - the virus circulates in the pollen & dodder body of the vector Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Propagative transmission Introduction - some of circulative Types of plant virus viruses may multiply transmission in their respective Mode of transmission vectors Vegetative propagation - some transovarial Mechanical which produce transmission infected eggs and Transmission by seed, nmyphs pollen & dodder Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Schematic showing Introduction how the retention and Types of plant virus movement of plant viruses leads to transmission classification of Mode of transmission transmission mode, Whitfield et al. 2015 Vegetative , (Figure 1). In propagation this representation, the classification is Mechanical made in terms of: A transmission stylet retention (elsewhere described Transmission by seed, as non-persistent), B pollen & dodder foregut retention (semi-persistent), and Insect transmission C circulative Mite, nematode & movement (including both persistent- fungi transmission circulative and persistent- propagative. IX. Transmission of plant viruses Examples Introduction Leaf hopper transmitted virus Aphid transmitted viruses Types of plant virus Rice tungro (Nephotettix virescens) Bean common mosaic (Aphis Beet curly top (Circulifer tenellus) transmission craccivora) Mode of transmission Cucumber mosaic (Aphis gossypii) Planthopper transmitted virus Vegetative Papaya ring spot (A. gossypii) Rice grassy stunt – BPH (Nilaparvata propagation Potato virus Y (Myzus persicae) lugens) Mechanical Citrus tristeza (Toxoptera citricidus) Banana bunchy top (Pentalonia Mealybug transmitted virus transmission nigrovervosa) Cacao swollen shoot (Planococcoides Transmission by seed, njalensis) pollen & dodder Whitefly transmitted viruses Insect transmission Bean golden mosaic (Bemisia tabaci) Thrips transmitted virus Mite, nematode & Tobacco leaf curl Tomato spotted wilt Tomato yellow leaf curl Beetle transmitted virus fungi transmission Southern bean mosaic (Ceratoma African cassava mosaic Cotton leaf curl trifurcata) IX. Transmission of plant viruses Mite transmission Introduction Types of plant virus - mites of the family Eriophyidae transmit at transmission least 6 viruses including Wheat streak mosaic Mode of transmission virus Vegetative propagation Examples Mechanical transmission Wheat streak mosaic virus Transmission by seed, Peach mosaic virus pollen & dodder ryegrass mosaic virus Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Nematode transmission Introduction - plant viruses are transmitted by 3 Examples Types of plant virus genera of soil inhabiting transmission Tobacco rattle virus ectoparasitic nematodes: Mode of transmission (Tobraviruses) Longidorus, Paralongidorus & Vegetative Nepoviruses (nematode- Xiphinema propagation transmitted polyhedral Mechanical viruses) transmission Transmission by seed, pollen & dodder Insect transmission Mite, nematode & fungi transmission IX. Transmission of plant viruses Nematode transmission Introduction - Trichodorids may retain the virus for up to a year; acquisition Types of plant virus time may be less than an hour to several days, depending on transmission the feeding characteristics of the nematode Mode of transmission Vegetative propagation Retention sites Mechanical transmission Longidorus – odotostyle area Transmission by seed, Xiphinema – odontophore and pollen & dodder esophagus region Insect transmission Trichodorus – onchiostyle & esophagus Mite, nematode & fungi transmission IX. Transmission of plant viruses Fungus transmission Introduction - root-infecting fungal-like organisms, Examples Types of plant virus transmission the Plasmodiophoromycetes (Polymyxa Grape fanleaf Mode of transmission sp., Spongospora sp.) & Tobacco ring spot Vegetative Chitridiomycetes (Olpidium sp.) propagation transmit at least 30 plant viruses Mechanical transmission Transmission by seed, pollen & dodder Insect transmission Mite, nematode & fungi transmission Thank you.