Introduction to Plant Pathology PDF

CROP PROT 11-MBNAVAL Etymology Greek word: “PATHOS”-Suffering and “LOGOS”- to study CROP PROT 11-MBNAVAL  What is plant pathology? Plant Pathology also known as Phytopathology is the scientific study of diseases in plants caused by pathogens (infectious...

CROP PROT 11-MBNAVAL Etymology Greek word: “PATHOS”-Suffering and “LOGOS”- to study CROP PROT 11-MBNAVAL  What is plant pathology? Plant Pathology also known as Phytopathology is the scientific study of diseases in plants caused by pathogens (infectious organism) and environmental conditions (physiological factors). Plant pathology as a science Plant pathogen interaction characteristics causes Greenish, yellowing, Bacteria, fungi, curling, black spot nematodes, virus Host, environment , viroids and the pathogen CROP PROT 11-MBNAVAL  Plant Pathology as an Art  Diagnosis or recognizing particular disease  Disease assessment & forecasting  Recommendation of appropriate control measures  Field application of suitable control measure Pathogens that cause infectious diseases include fungi, oomytes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. CROP PROT 11-MBNAVAL  ULTIMATE OBJECTIVE OF PLANT PATHOLOGY To prevent or minimize plant diseases not only to increase food production but also to maintain the quality and quantity of the harvested fresh commodity until it reaches the consumer. CROP PROT 11-MBNAVAL CONCEPT OF PLANT DISEASES Definitions of Disease by the Following Author: Whetzel (1929) He defined disease as physiological malfunctioning if it is caused by living or animate agents and physiogenic disease if it is caused by non-living or inanimate agents. Stalkman & Harrar (1957) Disease is any deviation from normal growth or structure of plants. Horsfall and Diamond (1959) Disease is malfunctioning process caused by continuous irritation. Merril (1980) Disease is a dynamic interaction between an organism and its environment which results in abnormal physiological and often morphological or neurological changes in the organism. CROP PROT 11-MBNAVAL CONCEPT OF PLANT DISEASES Agrios (1978) Disease is any disturbance brought about by a pathogen or an environmental factor which interferes with manufacture, translocation, or utilization of food, mineral nutrients and water in such a way that the affected plant changes in appearance and yields less than a normal healthy plant of the same variety. Agrios (1998) Disease is any malfunctioning of host cells and tissues that results from continous irritation by a pathogen or an environmental factor and leads to the development of symptoms. National Academy of Science (1968) Disease is harmful alteration of the normal physiological and biochemical development of a plant. CROP PROT 11-MBNAVAL What are Physiological functions of a Plant ?  Photosynthesis  Respiration  Plant nutrition  Plant hormone functions  Photoperiodism & photomorphogenesis  Environmental stress physiology  Seed germination  Dormancy  Stomata function  Transpiration………etc PLANT PATHOGENS CAUSING A DISTURBANCE IN THESE PHYSIOLOGICAL FUNCTIONS. CROP PROT 11-MBNAVAL What is a pathogen / Pathogenic agent / Causal Organisms ? A living or non-living agent (infectious agent) that can cause a disease to the host plant is called a PATHOGEN / CAUSAL ORGANISM. CROP PROT 11-MBNAVAL ECONOMIC IMPORTANCE OF PLANT DISEASES Cadang-cadang disease of coconut (1918) Bicol term cadang-cadang which means dead or dying (Bicol Region) -Caused by viroid -The detection of two small disease- associated RNAs in 1975 provided the initial clue to the etiology of cadang- cadang. CROP PROT 11-MBNAVAL Downy mildew of corn- or nemesis of corn Peronosclerospora spp. is the causal agent of this disease. It is a fungi CROP PROT 11-MBNAVAL Tungro disease of rice (RTV-bacilliform virus) Tungro disease can cause great loss in rice production of the farmers. A total of 70 ha rice field was damaged by the virus in 1963. CROP PROT 11-MBNAVAL Coffee Rust It happened in Batangas province. This is coffee rust or roya, caused by the Hemileia vastatrix fungus Coffee's plague starts with yellow spots and what look like burn marks. They form on the leaves of the coffee plant, causing the foliage to wither until the tree resembles a skeleton Citrus decline It is concluded that the virus- induced disease which has been responsible for the great loss of citrus trees in the Philippines since the 1950's is identical to the so-called citrus dieback in India and that very probably it is the same as greening disease first described from South Africa. CROP PROT 11-MBNAVAL Stored corn and Peanut mold Aflatoxin is a naturally occurring toxin produced by the fungus Aspergillus flavus. The fungus can be recognized by a gray-green or yellow- green mold growing on corn kernels in the field or in storage CROP PROT 11-MBNAVAL COMMON TERMINOLOGIES IN PLANT PATHOLOGY Pathogen- an organism causing disease to its host, with the severity of the disease symptoms referred to as virulence. Pathogens are taxonomically widely diverse and comprise viruses and bacteria as well as unicellular and multicellular eukaryotes. is any agent (biotic or abiotic), that causes a disease. the term is generally used to refer to a living organism, such as a fungus or a bacterium, nematode, virus and viroid that causes disease. CROP PROT 11-MBNAVAL Parasite An organism which depends wholly or partly on another living organism for its food. Most parasites are pathogens. Two types of parasite Obligate parasite- is an organism that is restricted to subsist on living organisms and attacks only living tissues. Facultative parasite- an organism which has the ability to be a parasite although it is ordinarily a saprophyte. Saprophyte- is an organism that lives on dead organic or inorganic matter. Facultative saprophyte- has the ability to become a saprophyte but is ordinarily a parasite. CROP PROT 11-MBNAVAL  COMMON TERMINOLOGIES IN PLANT PATHOLOGY Host in plant pathology, refers to the plant that is being attacked by a parasite. A food relationship between the host and the parasite (pathogen) is implied. an organism (eg.: a plant) that is harboring a parasite or pathogen from which it obtains its nutrients. host range refers to the various kinds of host plants that a given pathogen may parasitize. A host is considered resistant when it has the ability to exclude, hinder or overcome the effects of a given pathogen or other damaging factor. Suscept, on the other hand is a plant that is susceptible to a disease whether or not the pathogen is parasitic. CROP PROT 11-MBNAVAL  COMMON TERMINOLOGIES IN PLANT PATHOLOGY Pathogenicity is the capacity of a pathogen to cause disease whereas pathogenesis refers to disease development in the plant. Virulence refers to the quantitative amount of disease that isolate of a given pathogen can cause in a group of plants in terms of size of lesions or number of lesions, for example. Aggressiveness measures the rate at which virulence is expressed by a given pathogenic isolate. Disease resistance is the inherent ability of an organism to overcome in any degree the effects of a pathogen (Merrill 1980) while susceptibility is the opposite of resistance. Resistance and susceptibility are relative terms and can be depicted on the same scale; the more resistant the plant is, the less susceptible it is and the more susceptible the plant, the less resistant it is. Tolerance is exhibited by a plant which is severely affected by a pathogen without experiencing a severe reduction in yield. CROP PROT 11-MBNAVAL THE DISEASE TRIANGLE Disease development requires the presence of (1) a susceptible plant, (2) the pathogen and (3) favorable environment. -When these three elements coincide, plant disease will occur. -Eliminating just one of them will keep the plants healthy CROP PROT 11-MBNAVAL SYMPTOMS AND SIGNS OF PLANT DISEASE  Classification of Plant Diseases A. On the basis of extent to which plant diseases associated with plant 1. LOCALIZED 2. SYSTEMIC B. On the basis of mode of infection 1. SOIL BORNE 2. AIR BORNE 3. SEED BORNE C. On the basis of symptoms of disease 1. RUSTS 2. SMUTS 3. ROTS 4. BLIGHT 5. LEAF SPOT 6. CANKER 7. WILT 8. DOWNY MILDEWS 9. POWDERY MILDEW 10. ANTHRACNOSE  Primary Symptoms and Secondary Symptoms Primary symptoms are the direct result of pathogen activity on invaded tissues (e.g., swollen clubs in club-root affected cabbage are formed by feeding of the root knot nematode). On the other hand, Secondary symptoms result from the physiological effects of disease on distant tissues and un-invaded organs (e.g., wilting and drooping of bean leaves in hot weather due to Fusarium root rot). Root is infected, but symptoms appears on leaves through drooping and wilting. Club-root of cabbage Fusarium root rot Local symptoms are physiological or structural changes within a limited area of host plant tissue around the infection site, such as leaf spots, galls, and cankers. leaf spots leaf galls CROP PROT 11-MBNAVAL Systemic symptoms are those involving the reaction of the entire / greater part of the plant, such as wilting, yellowing, and dwarfing. wilting yellowing dwarfing CROP PROT 11-MBNAVAL  Classification of plant Diseases Based on Infection Process  INFECTIOUS : All the diseases caused by VIRUSES and VIROIDS can be transmitted from infected host plants to the healthy plants and are called infectious.  NON-INFECTIOUS : Non-infectious diseases can not be transmitted to a healthy plant. Potato Spindle Tuber Disease transmitted by Viroids Early blight of potato is a non – infectious disease CROP PROT 11-MBNAVAL Classification of plant Diseases on the basis of occurrence and distribution Wart disease of potato 1. ENDEMIC : when a diseases more or less constantly prevalent from year to year in a moderate to severe form in a particular country. E.g., Wart disease of potato is endemic to Darjeeling. 2. EPIDEMIC / EPIPHYTOTIC: A disease occurring periodically but in a severe form involving major area of the crop. it may be constantly present in locality but assume severe form occasionally e.g. Rust of wheat, Late blight of Rust of wheat tomato, Powdery Mildews of Grapes CROP PROT 11-MBNAVAL  leaf blight of Maize 3. SPORADIC: Diseases which occur at very irregular interval and location in a moderate to severe form e.g., leaf blights, wilt. 4. PANDEMIC: Diseases occurring throughout the continent or sub- continent resulting in mass mortality e.g., Late blight of potato. Late blight of potato CROP PROT 11-MBNAVAL Microscopic Symptoms and Macroscopic Symptoms The disease symptoms may be microscopic or macroscopic. In Microscopic Symptoms, the expressions of disease are in the cell structure or cell arrangements, which can be seen under a microscope. In Macroscopic Symptoms the expressions of disease on the surface of plant parts that can be seen with the unaided eye in the form of symptoms on the plant. Macroscopic (morphological) symptoms can be classified as: A. Necrosis B. Hypoplastic C. Hyperplastic CROP PROT 11-MBNAVAL  DISEASE SYMPTOMS MICROSCOPIC SYMPTOMS MACROSCOPIC SYMPTOMS NECROSIS HYPOPLASTIC HYPERPLASTIC SPOT BLIGHT BLAST ROT DIE - BACK STRIPE HYDROSIS CANKER DWARFING LEAF CURL ROSETTIING SCAB CHLOROSIS GALL MOSAIC ROOT KNOT ALbication CROP PROT 11-MBNAVAL  Necrosis symptoms It is localized or the general DEATH / DEGENERATION of plant tissue (protoplast) due to invasion of disease causing agent. It includes leaf spots, blight, rots, cankers, hydosis etc. CROP PROT 11-MBNAVAL Some examples of the necrotic symptom Spot is a definite, localized, round to regular lesion, often with a border of a different colour, characterized by its location (leaf spot, fruit spot) and colour (brown spot, black spot). Septoria leaf spot of tomato Tikka leaf spot of Groundnut Angular leaf spot of beans If numerous spots enlarge and merge, a large irregular blotch or blight may develop, such as grey leaf spot of tomato; black spot of rose; angular leaf spot of beans, Tikka leaf spot with yellow halo, fruit spot etc. CROP PROT 11-MBNAVAL Some examples of the necrotic symptom Blight is the sudden or total discoloration and killing of large area of a leaf, shoots or stems or the entire plant. Usually young tissues are attacked. The disease name is often coupled with the name of the host and the part attacked, for example — blossom blight, twig blight, tip blight etc. it occurs mostly due to bacterial invasion. Bacterial blight of beans Bacterial blight of rice CROP PROT 11-MBNAVAL Some examples of the necrotic symptom Blast is sudden death of young buds, flowers, or young fruit and failure to produce fruit or seeds. such as Rice blast, Wheat Blast etc. Different symptoms of Rice blast disease Different symptoms of wheat blast disease CROP PROT 11-MBNAVAL Some examples of the necrotic symptom Damping off Damping off : symptoms are decay of seed in soil, rapid death of germinating seedlings before emergence, or emerged seedlings suddenly shows wilting symptoms, toppling over, and dying from rot at collar region. This is common disease found in seedbeds Damping off in seedbed. CROP PROT 11-MBNAVAL Some examples of the necrotic symptom DIE-BACk DIE-BACK is a plant disease, showing progressive browning and death of shoots, branches, and roots starting at the tips then moving downward e.g. Die back of chilli/ citrus / Mango. Die back of Citrus plant Die back of Mango plant CROP PROT 11-MBNAVAL Some examples of the necrotic symptom ROTS Root and Stem Rot ROTS refer to the decomposition and putrefaction of cells, tissues and organs. The rot may be dry, watery or mushy such as bacterial soft rot. Root rot of Beans Red Rot of sugarcane CROP PROT 11-MBNAVAL Some examples of the necrotic symptom ROTS Dry rot Dry rot of potato Dry rot of Ginger Dry root rot of Lentil CROP PROT 11-MBNAVAL Some examples of the necrotic symptom ROTS SOFT ROT Soft rot on Capsicum Soft rot symptoms on carrot SOFT ROT diseases are caused by pathogens that secrete enzymes capable of decomposing cell wall structure. Soft rots commonly occur on fleshy vegetables such as potato, carrot, capsicum, squash, and tomato. CROP PROT 11-MBNAVAL Some examples of the necrotic symptom ROTS BLACK ROT BLACK ROT OF CRUCIFERS caused by the bacteria Xanthomonas campestris p.v. campestris is also a plant disease where the vascular system is infected and leads to necrosis of the leaves. Symptoms of black rot on V-shaped lesions on mature cabbage transplants cabbage CROP PROT 11-MBNAVAL Some examples of the necrotic symptom ROTS BLACK ROT BLACK ROT OF GRAPE is a fungal disease, resulting hardened, black mummified fruit at the time of harvest. CROP PROT 11-MBNAVAL Some examples of the necrotic symptom ROTS Bulb rot of Onion & Garlic BULB ROT of Onion is a fungal disease, causing by the fungi Botrytis spp. White fluffy fungal growth appears on the base of the bulb and later it spread through out the bulb, with small, round, black structures. CROP PROT 11-MBNAVAL Some examples of the necrotic symptom ROTS GRAY MOULD ROT GRAY MOULD ROT is caused by fungi in the genus Botrytis. The disease is characterized by soft, tan to brown spots or blotches that become covered with a dusty white mould. CROP PROT 11-MBNAVAL Some examples of the necrotic symptom ROTS HEART ROT Heart rot of Carrot Heart rot of Pineapple HEART ROT is a fungal disease. Fungus produce a discoloured, lightweight, soft, spongy, stringy, crumbly, or powdery heart decay. Sugarbeet, Carrot, Pineapple are prone to this type of rot. Heart rot of Sugarbeet CROP PROT 11-MBNAVAL Some examples of the necrotic symptom STREAK LEAF STREAK: Narrow, elongated, somewhat superficial necrotic lesions with irregular margins develops on stems or leaf veins. The Causal Organism is Virus. Example : Leaf streak virus of Maize Leaf streak of Maize CROP PROT 11-MBNAVAL Some examples of the necrotic symptom Stripe LEAF STRIPE: narrow, elongated, parallel, necrotic lesions develops especially in leaf. These diseases are specific of cereals and grasses. Both fungus and bacteria causes this stripe symptoms. Helminthosporium stripe of barley Red stripe of Sugarcane CROP PROT 11-MBNAVAL Some examples of the necrotic symptom Hydrosis WATER-SOAKING / HYDROSIS is a translucent condition of tissues caused by water, moving from host cells due to rupturing of cell membranes into intercellular spaces. Examples are late blight lesions on potato and tomato leaves , bacterial soft rot of fleshy vegetables late blight lesions on potato CROP PROT 11-MBNAVAL  Some examples of the necrotic symptom Wilting Wilting : Wilting is loss of turgor pressure in a plant leading to temporary or permanent drooping of leaves, shoots, or entire plants from lack of water, due to infection by different plant pathogens. It is a secondary symptoms. Wilting results due to infestation of fungus as well as Bacteria in the plant. Bacterial wilt of tomato CROP PROT 11-MBNAVAL Some examples of the Necrotic symptom Canker CANKER is a definite, dead, often sunken or swollen and cracked area on a stem, limb, trunk, tuber, fruit or root surrounded by living tissues. The C.O. is often Bacteria or fungi. Citrus Canker on Fruits Tomato Canker on Stems CROP PROT 11-MBNAVAL  HYPOPLASTIC SYMPTOMS Hypoplasia is the failure of plants or organs to develop fully i.e to obtain normal size. Abnormal size and pale colouration is the most common hypoplastic symptom. CROP PROT 11-MBNAVAL Some examples of the Hypoplastic symptom DWARFING DWARFING is the under-development of the plant or some of its organs eg Maize Streak Virus, mosaic, curly top of beans etc. Dwarfing of Maize plant due to Maize streak virus Dwarfing of Papaya plant due to Papaya Mosaic virus CROP PROT 11-MBNAVAL Some examples of the Hypoplastic symptom ROSETTING ROSETTING is the shortening of internodes of shoots and branches, producing a bunchy growth habit example are the ground nut rosette. Ground Nut Rosette VIRUS CROP PROT 11-MBNAVAL Some examples of the Hypoplastic symptom ALBICATION ALBICATION is the complete repression of leaf colour caused by viruses, bacteria, fungi, and iron deficiency leading to whitening of leaf tissue. Broad Bean Stain Virus (BBSV) symptoms on pea plants include whitening of interveinal tissues. CROP PROT 11-MBNAVAL Some examples of the Hypoplastic symptom CHLOROSIS CHLOROSIS is the yellowing or whitening of normal green tissue due to partial or complete failure of chlorophyll to develop. This symptom can developed due to different diseases causing organisms. Chlorosis of Green leaves CROP PROT 11-MBNAVAL Some examples of the Hypoplastic symptom Mosaic MOSAIC is the abnormal coloration yellowing, reddening, bronzing, or purpling in localized areas of leaves where chlorophyll has been destroyed. This symptoms shows a clearing along the leaf veins (vein clearing). Yellow Mosaic virus on Moongbean Turnip Mosaic virus on cabbage leaves Yellow Mosaic virus on Okra leaf CROP PROT 11-MBNAVAL  HYPERPLASTIC SYMPTOMS Hyperplasia is the over-development (in size and colour) of the plant parts due to invasion of plant pathogen. CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom LEAF CURLS LEAF CURLS - overgrowth of tissue on one side of a leaf or petal resulting to leaves rolling. This symptoms appears mostly due to virus attack on plants. Leaf Curl of Chilli Leaf Curl of Tomato CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom LEAF CURLS (contd….) Leaf curl symptoms Leaf Curl of Papaya Leaf Curl of Tobaco Leaf Curl of Potato CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom SCABS Scabs develops crust like, more or less circular, slightly raised or sunken lesions on the surface of leaves, stems, fruit, or tubers. e.g. common scab of potato, apple scab and wheat scab. Apple Scab Potato Scab CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom GALLS GALLS are abnormal growths of plant cells that occur on leaves, twigs, roots, or flowers of many plants. Most galls are caused by irritation and/or stimulation of plant cells due to feeding or egg-laying by insects such as aphids, midges, wasps, or mites. Sometimes invasion of Fungi and / or Bacteria can results into gall formation. Galls on Rhododendron shoot caused by Fungi. Galls on Olive shoot caused by Bacteria. CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom WITCH’S BROOM A WITCH'S BROOM or witches' broom is a deformity in a woody plants, typically a tree, where a dense mass of shoots grows from a single point, with the resulting structure resembling a broom or a bird's nest. It is sometimes caused by pathogens, like Fungi, Insects, Mites, Nematodes , Phytoplasma and viruses. WITCH'S BROOM on Woody Plants CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom INTUMESCENCE INTUMESCENCE is a condition in which numerous small calluses grow on the surface of the leaves. They may occur on either the upper or lower surface, and may be scattered over inter-veinal tissue or clustered along the main veins. Intumescence does not appear to harm the plant. Small calluses grow on the surface of the leaves by Intumescence CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom TUMOURS TUMOURS are symptoms, caused by pathogens that stimulate uncontrolled multiplication of plant cells, resulting in the formation of abnormally large structures. e.g. Crown Gall on rose , caused by Bacteria Agrobacterium tumefaciens. Crown Gall on rose CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom CLUB ROOT CLUB ROOT symptom is where the roots appear swollen & club-shaped. Clubroot is a disease of the mustard family (Brassicaceae/ Cruciferae) caused by the fungus-like soil pathogen Plasmodiophora brassicaceae. Club root of Cruciferous crops CROP PROT 11-MBNAVAL Some examples of the Hyperplastic symptom ROOT KNOTS ROOT KNOTS are the formation of galls on the roots which is as a result of nematode infection. CROP PROT 11-MBNAVAL  Specific symptoms and their respective description are given below. Abscission Premature falling of leaves, fruits or flowers due to the early laying down of the abscission layer CROP PROT 11-MBNAVAL  Blast A term applied to the sudden death of young buds, inflorescence or young fruits CROP PROT 11-MBNAVAL Bleeding occurs due to the pressure of sap within the tissues that conduct water and sugars around the plant. CROP PROT 11-MBNAVAL Blight any of various plant diseases whose symptoms include sudden and severe yellowing, browning, spotting, withering, or dying of leaves, flowers, fruit, stems, or the entire plant CROP PROT 11-MBNAVAL Blotch tiny purplish to reddish spots that occur on leaf blades and leaf sheaths. Seedlings are very susceptible, but older plants rapidly become resistant. Affected seedlings wither, die, and turn brown. The roots and crowns of infected plants may develop small lesions and rot. CROP PROT 11-MBNAVAL Callus An overgrowth of tissue formed in response to injury in an effort of the plant to heal the wound A callus arises from cells of the cambium. When a callus forms, some of its cells may organize into growing points, some of which in turn give rise to roots while others produce stems and leaves. CROP PROT 11-MBNAVAL Canker a symptom of an injury often associated with an open wound that has become infected by a fungal or bacterial pathogen. Canker diseases frequently kill branches or structurally weaken a plant until the infected area breaks free, often in a wind or ice storm. An often sunken necrotic area with cracked border that may appear in leaves, fruits, stems and branches CROP PROT 11-MBNAVAL Chlorosis a yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots, high alkalinity, and nutrient deficiencies in the plant CROP PROT 11-MBNAVAL Curling caused by many problems, including insect damage, disease, abiotic disorders, or even herbicides. There are several insect pests that cause leaves to curl when they suck plant juices of new or young leaves that are still growing. These include aphids, thrips, and whiteflies. Abnormal bending or curling of leaves caused by over-growth on one side of the leaf or localized growth in certain portions CROP PROT 11-MBNAVAL Damping off a disease of seedlings caused by several different fungi and fungus- like organisms. This disease causes emerging seedlings to collapse, often submerged in a mass of white fungal growth. It is particularly a problem when sowing seed indoors or under glass. Rotting of seedlings prior to emergence or rotting of seedling stems at an area just above the soil line CROP PROT 11-MBNAVAL Die back common symptom or name of disease, especially of woody plants, characterized by progressive death of twigs, branches, shoots, or roots, starting at the tips. A drying backward of leaves twigs or branches from the tip CROP PROT 11-MBNAVAL Etiolation The process of growing flowering plants in partial or complete absence of light is referred to as etiolation. Etiolation causes weak, long stems and leaves that are smaller with pale yellow colour. An etiolated leaf has weak cells, long foliage and internodes. CROP PROT 11-MBNAVAL Fasciculation or fasciation a genetic mutation of a plant's growing tip, and it can visibly affect the stem, flowers, or fruits. It often leads to multiple extra flowers being produced on the affected stems, typically with many secondary blooms surrounding the normal, expected one. Clustering of roots, flowers, fruits, or twigs around a common focus CROP PROT 11-MBNAVAL Flecks Spotted leaves occur when fungal spores in the air find a warm, wet, plant surface to cling to. As soon as that microscopic spore gets comfortable in its new home, sporulation (the fungal method of reproduction) occurs and the tiny, brown fungal leaf spot begins to grow Extremely tiny spots on leaves, fruits, stems, etc CROP PROT 11-MBNAVAL Gumming or gummosis Gummosis is the formation of patches of a gummy substance on the surface of certain plants, particularly fruit trees. This occurs when sap oozes from wounds or cankers as a reaction to outside stimuli such as adverse weather conditions, infections, insect problems, or mechanical damage. CROP PROT 11-MBNAVAL Leak a characteristic symptom of the disease and is named due to the sign of cottony growth on plant parts. The disease severely affected stem and can be confused with white mold caused by Sclerotinia sclerotiorum. The host's juices exude or leak out from soft-rotted portions CROP PROT 11-MBNAVAL Mosaic The disease is characterized by leaves that are mottled with yellow, white, and light or dark green spots and streaks (in other words, a “mosaic” of these colors). CROP PROT 11-MBNAVAL Mottling mottling usually consists of yellowish spots on plants, and is usually a sign of disease or malnutrition. Mottling effect can be described as patches or irregular areas of lightness variations. A pattern or blotches of different colors and shades that cover the surface of a plant, usually caused by virus. CROP PROT 11-MBNAVAL Mummification a dried, shriveled fruit, plant part or organ that is partially or completely replaced with fungal structures, usually as the result of fungal infection and colonization of the fruit. CROP PROT 11-MBNAVAL Phyllody a condition where parts of a flower, or the entire flower, is replaced with leafy structures. Metamorphosis of sepals, petals, stamens or carpels into leaf-like structures CROP PROT 11-MBNAVAL Pitting Reduced growth and vigor of trees on any rootstock with a ropy appearance of the stems where the phloem tissue with the virus grows irregularly, producing pits in the wood CROP PROT 11-MBNAVAL Rosetting Shortening of the internodes of shoots and stems forming a crowding of the foliage in a rosette abnormal leaf formation in a plant due to disease CROP PROT 11-MBNAVAL  Root rot Roots turn from firm and white to black/brown and soft a disease that attacks the roots of trees growing in wet or damp soil. CROP PROT 11-MBNAVAL Russeting the presence of brown scars of the surface of the fruit. There are many different causes for russeting on fruit, which include frost damage, fungal infections like powdery mildew, yeast and bacteria growth, herbicide drift and phytotoxicity. A superficial brownish roughening of the skin of fruits, tubers or other fleshy organs usually due to the suberization of epidermal or subepidermal tissues following injury to epidermis CROP PROT 11-MBNAVAL Sarcody an abnormal outgrowth or deformation such as swelling above constricted or girdled areas of a branch or stem. Abnormal swelling of the bark above wounds due to the accumulation of elaborated food materials CROP PROT 11-MBNAVAL  Savoying The cupping or pocketing of parts of the leaf; also curling or puckering; due to underdevelopment of veins or leaf margins curled and wrinkled specifically : abnormally wrinkled as a result of disease (as a virus infection) —used of leaves or plants. Cupped, distorted and upright leaves showing the confluent scabby lesions along veins and petioles (J. O'Sullivan). CROP PROT 11-MBNAVAL Scab Slightly raised, rough, ulcer-like lesions due to the overgrowth of epidermal and cortical tissues accompanied with rupturing and suberization of cell walls any of several bacterial or fungal plant diseases characterized by crustaceous lesions on fruits, tubers, leaves, or stems. CROP PROT 11-MBNAVAL Shot-hole A perforated appearance of a leaf as the dead areas of local lesions drop out. Shot hole first appears in the spring as purplish or reddish spots about 1/10 inch in diameter on new buds, leaves, and shoots. CROP PROT 11-MBNAVAL Spot A localized necrotic area also referred to as a lesion. Individual spots may be circular, angular or irregularly shaped. Several spots may run together or coalesce forming large necrotic areas. CROP PROT 11-MBNAVAL Streak or stripe Symptoms begin as narrow leaf lesions with wavy edges that occur between the veins of corn leaves and can range between one-to-several inches long CROP PROT 11-MBNAVAL Vein clearing Vein clearing is the loss of normal green coloration of plant veins; usually they turn yellow first. Yellowing of the entire network of veins in the leaf blade CROP PROT 11-MBNAVAL Virescence or greening Virescence is the abnormal development of green pigmentation in plant parts that are not normally green, like shoots or flowers (in which case it is known as floral virescence). Development of chlorophyll in tissue or organs in which it is normally absent CROP PROT 11-MBNAVAL Wilting Slightly yellowing and wilting of the lower leaves CROP PROT 11-MBNAVAL SIGNS OF PLANT DISEASES CROP PROT 11-MBNAVAL  SIGNS OF PLANT DISEASES refer to the structures of the pathogen that are associated with the infected plant part. Some of these structures may not always be present in diseased plants because their formation depends on environmental conditions. Examples of signs are fungal mycelia, spores and fruiting bodies, bacterial ooze, sclerotial bodies, nematodes at various growth stages and plant parts of phanerogams (parasitic flowering plants). CROP PROT 11-MBNAVAL  General Categories of signs 1. Vegetative structures-fuction primarily in the absorption and storage of nutrients a. Felt A densely woven mat of mycelium b. Haustorium An absorbing organ of a fungus which penetrates a host cell without penetrating the plasma membrane c. Mycelium A mass of fungal threads or hyphae d. Pathogen cells Masses of bacterial cells generally e. Plasmodium Naked mass of protoplasm f. Rhizomorph Cordlike strand of fungal hyphae g. Sclerotium A hard, compact, resting body of a fungal hypahe CROP PROT 11-MBNAVAL Mycelium or Mould Growth Mycelium or Mould Growth: under some conditions, mycelia or fungal growth in infested plant parts is readily visible to the naked eye. CROP PROT 11-MBNAVAL  Different SIGNS of Plant Disease Sclerotia  A Sclerotium is a compact, often hard mass of dormant fungus mycelium.  Sclerotia are mostly dark in colour and are found mixed with the healthy grains as in the case of ergot of wheat and rye. Dark colored Sclerotium in the infected plant parts CROP PROT 11-MBNAVAL  General Categories of signs 2.Reproductive structures-those pathogen structures that function in reproduction of the organisams a. Acervulus i. Mushroom (toadstool) q. Spore b. Apothecium j. Perithecium r.sporodochium c. Ascus k. Pseudothecium s. Stroma d. Basidium l. mold t. Worms e. Cleistothecium m. Pycnidium f. Conidiophore n. Seed bearing plants g. Conk o. sorus h. Mildew p. Sporangium CROP PROT 11-MBNAVAL  Different SIGNS of plant disease Mildews Mildews consist of white, grey, brownish or purplish pathogen growth on the host surface. Powdery Mildews Downy Mildews CROP PROT 11-MBNAVAL  General Categories of signs 3. Disease products-gases and exudation products resulting from diesease a. Odor- characteristic smell associated with some host pathogen interactions. b. Ooze- viscid mass made up of plant juices and often pathogen cells. Signs of fungal disease- mycelia, spores, fruiting bodies etc. Signs of bacterial disease- Bacterial cells bacterial ooze Signs of nematode disease- eggs, juveniles, adults nematodes. Signs of virus disease- virus particles, inclusion bodies Signs of viroids disease- RNA fragments Signs of disease caused by parasitic flowering plants- seeds and the plant itself. CROP PROT 11-MBNAVAL EXUDATION Causal organism comes out from the infected plant part through exudation.  Mass of bacterial cells ooze out on the surface of the affected organs where they may be seen as a drop or smear in several bacterial diseases such as bacterial blight of paddy, gummosis of stone fruits and fire blight of apple and pear.  They form crusts after drying. Ooze from bacterial blight of paddy Gum coming out from Gummosis of Stone fruit. CROP PROT 11-MBNAVAL  Different SIGNS of plant disease Rust RUST appears as relatively small pustules of the spores, usually breaking through the host epidermis. The pustules may be dusty or compact, and red, brown, yellow or black in colour. Pea Rust Wheat Rust CROP PROT 11-MBNAVAL  Different SIGNS of plant disease White Blister White blister like pustules appear on the lower leaves and other parts of cruciferous plants which break open the epidermis and expose white powdery masses of spores. This disease is also called as White rust. White blister on Mustard leaves CROP PROT 11-MBNAVAL  Different SIGNS of plant disease BLOTCH consists of superficial growth of BLOTCH Fungus / Bacterium, giving the affected plant parts i.e., fruits and leaves a “Smoky (blotched) appearance”, e.g. Sooty Blotch of Apple. Sooty Blotch of Apple Bacterial fruit blotch of Cucurbits CROP PROT 11-MBNAVAL  Different SIGNS of plant disease  Smut means a sooty or charcoal like powder. SMUT  The affected parts of the plants show black or purplish black dusty areas.  Symptoms usually appear on floral organs. Eg. Wheat Smut, Corn Smut Wheat Smut Corn Smut False Smut of Paddy CROP PROT 11-MBNAVAL KOCH’S RULE of proof of PATHOGENECITY CROP PROT 11-MBNAVAL