Basics of Plant Pathology Pam Roberts Katherine Hendricks Southwest Florida Research and Education Center
Historical Significance of Plant Diseases Sri Lanka France Late Blight on potato caused the Irish Potato Famine in 1845-46 Coffee Rust on coffee in Ceylon reduced production from 100 million lbs in 1870 to 5 million lbs in 1989 Powdery and Downy Mildew of Grapes along with an insect, Phylloxera, reduced the grape industry by 80% in France
Tulipmania (1600s) Color break in petals Caused by a virus, TBV A single bulb sold for 3,000 guilders (US $1652) compared to Four fat oxen 480 guilders (US $264) Eight fat pigs 240 guilders (US $132) 1000 lb cheese 120 guilders (US $66) A skilled craftsman at the timer earned about 300 guilders per year Dollar values based on exchange rates of May 2011
Plant Pathology is the study of: Disease-causing agents and environmental conditions on disease development mechanisms by which plant disease occur interactions between the diseasecausing agents and the diseased plant methods of preventing or controlling disease and reducing damage
What is a plant disease? Any disturbance that interferes with its normal structure, function, or economic value What is a plant pathogen? An entity capable of inciting disease
Types of Pathogens Fungi Bacteria Viruses and Viroids Phytoplasmas Nematodes Parasitic Plants
Types of Pathogens Fungi - hyphae, lack chlorophyll, used to be considered a plant Bread molds, mushrooms are example more than 8,000 species are plant pathogenic
Types of Pathogens Bacteria - single celled, lack nuclei, possess cell walls Phytoplasma - bacteria-like but lack cell wall
Types of Pathogens Virus - nucleic acid and protein coat Viroid - nucleic acid Nematode - microscopic worm-like animals Parasitic Plant - lack chlorophyll, fuse vascular systems to obtain nutrients from host
Agrios 1997
Common Diseases Fungus Bacteria Virus/Viruslike Alternaria Canker Mottle Anthracnose Spot Mosaic Phytophthora Wilt Tristeza Leaf Spot Blights Scab
Pepper Mild Mottle Virus
APS Press Dasheen Mosaic Virus on Diffenbachia causing Ring Spots
APS Press APS Press Bacterial Spot on Tomato caused by Xanthomonas campestris pv. vesicatoria
APS Press Erwinia Stem Rot on Cordyline
Fusarium and Pythium Root Rot on Hedera APS Press
APS Press Late Blight on Tomato caused by Phytophthora infestans
Take-all Patch on Turf caused by Gaeumannomyces APS Press irregular, yellow (chlorotic) or light green patches
APS Press APS Press
Fungal Leaf Spot APS Press Copper Toxicity APS Press
Anthracnose on Piggy Back Plant and Venus Fly Trap APS Press APS Press
Fungus Bacteria Virus Infection Direct penetration Natural Openings Wounds Natural Openings Wounds Wounds made by mechanical or vector Infected pollen Spread Air, wind, Insects, Mechanical, Infected plants Wind/Rain Water Infected plants Insects Infected plant tissue
Fungus Bacteria Virus Survival On or in soil Host tissue Seed On or in insects On or in soil (with host tissue) Host tissue In host tissue In vector Control Cultural Biological Physical Chemical Cultural Biological Physical Chemical Certification Vector Control No commercial viricides
What is wrong with this plant?
What is wrong with this plant? Is there an actual problem with the plant? What are the normal growth characteristics for this season, age of plant, and variety? Compare to healthy plant sample, consult references.
What is wrong with this plant? What is the pattern of the symptoms? Uniform damage vs non-uniform Uniform indicates single event = abiotic Non-uniform and progressive = biotic Several symptoms and patterns (combination of uniform vs non-uniform patterns) indicates a complex of factors that could be abiotic and biotic.
Patterns and Time Development Individual plant Progression of symptoms present = biotic Pattern of symptoms uniform = abiotic or random = biotic
Patterns and Time Development Crop Spatial distribution around foci or unevenly distributed in field (=biotic) Severity of symptoms not uniform (=biotic) All plants exhibiting same level and placement of symptoms (= abiotic)
What is the Abiotic Agent? Physical damage (broken stems, girdled trunks from weed wackers, etc) Environmental extremes of drought, excessive rain, temperature, light, soil ph, air pollution Chemicals applied to plant or in vicinity of plant Nutritional disorder
What is the Biotic Agent? Signs and symptoms of pathogens Signs and symptoms of insects References and specialists that may be contacted What type of sample should be taken?
What if it is a complex of factors? Use a combined approach of biotic and abiotic questions.
Symptoms vs Signs Symptoms are expressed by host Signs of the causal agent on or within host mold, mildew, masses of spores, large or small reproductive structures (mushrooms, pycnidia, etc) for fungi ooze for bacteria hand lens or dissecting scope laboratory diagnostic procedures
Disease Diagnosis - Fungal APS Press - Bacterial APS Press APS Press - Viral
Fungal Disease Diagnosis Plant Symptom Expression Spots on leaf, stem, petioles, fruit, flower Blight (rapid necrosis on all or part of plant) Wilt Canker (oval-elongate necrotic lesion usually on stem) Dieback (inward-moving necrosis of various branches a plant s canopy, usually applied to woody trees and shrubs) Root Rot (disintegration of tissue) Damping off (sudden death and collapse of seedlings) Soft rots and Dry rots (wet vs. dry post-harvest decay) Galls (swelling or outgrowth of a plant)
Techniques Fungal Disease Diagnosis Macroscopic and Microscopic Observation Moist Chamber to induce sporulation Isolation General Media (carbon, nitrogen, vitamins, minerals) Selective (antibiotics, fungicides, limited carbon source) Baiting Nucleic Acid Detection (PCR) RFLP Serological
Bacterial Disease Diagnosis Plant Symptom Expression Spots on leaf, stem, petioles, fruit, flower Blight (rapid necrosis on all or part of plant) Wilt Canker Soft rots (post-harvest decay) Galls (swelling or outgrowth of a plant)
Bacterial Disease Diagnosis Microscopic Observation of Bacterial Ooze from a lesion Isolation General Media (carbon, nitrogen, vitamins, minerals) Selective ( fungicides, limited carbon source) Serological Nucleic Acid Detection (PCR) Fatty Acid Analysis Carbon Source Utilization (Biolog) Conventional Tests (See Flow Charts)
Fatty Acid Analysis Based on Fatty Acids in bacterial cell membranes and lipoplysaccharides Analyzed by Capillary Gas Chromatography for length, structure and amount Computerized library to compare to known samples Best Match Statistically Calculated
Viral Disease Diagnosis Plant Symptom Expression Mosaic and Mottle (irregular mixing of yellow and green usually on leaves) Ring Spots (sweet potato ring spot virus) Vein Clearing (transparency in leaf veins) Vein Banding (light discoloration outlining bands) Stunting Malformations Rough textured leaves, color break in petals, leaves curling or cupping, abnormal growth Overgrowth (proliferation of buds, roots, tumors or galls)
Virus Disease Diagnosis inclusion body structure developed within a plant cell as a result of infection by a virus, often useful in identifying the virus (pinwheel inclusion bodies formed by soybean mosaic virus in soybean leaves) Virus Inclusion Bodies Electron Microscopy Transmission to Indicator Plant Nucleic Acid Detection (PCR) Serology dsrna (only viruses produce high molecular weight in plant tissue)
Defining the Diagnosis Presence of pathogen does not necessarily mean that it is causing plant problem Is the diagnosis reasonable? References and Literature checked Crop Protection Reference, UF publications, web Other Specialists
Disease Triangle Host Man Pathogen Environment
Control Methods for Plant Diseases http://www.plant-care.com/lawn-fungus-identification-and-treatment.html
Control Methods for Plant Regulatory Diseases Quarantine, Inspection, Certification, Registration Cultural Start with healthy plant materials Activities of man Sanitation, Improve growing conditions, crop rotation
Biological Control Methods for Plant Beneficial organism, Cross protection Physical Heat treatment, soil sterilization, hot water treatment Chemical Diseases
Chemical Control Protectant must be present on surface of plant to prevent infection by pathogen Copper Compounds Denatures proteins and enzymes Systemic chemical can be translocated internally throughout host plant and can kill or prevent fungal reproduction Benomyl, mefenoxam Inhibit enzymes, replication, sterol-inhibitors
Integrated Crop Management Total plant management system which uses a wide variety of interdisciplinary methods to maintain pest populations at levels below those causing economic injury
Integrated Crop Management Optimal Cultural Practices Disease Resistance Exclusion Chemical Control Biological Control Crop Rotation
Biological Control Optimal Cultural Practices Environment Crop Rotation Pathogen Plant Disease Resistant Plants Chemical Control Exclusion