What is plant pathology? History of plant pathology. History of plant pathology. Irish potato famine ( ) 10/31/2013

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1 MG Training: Basic plant pathology and the art of the diagnosis. Richard J Buckley, PDL Director Soil Testing and Plant Diagnostic Services What is plant pathology? Plant pathology is the study of: living entities and environmental conditions that cause disease in plants mechanisms by which these factors result in disease interactions between disease agents and hosts disease prevention and management History of plant pathology Theophrastus (c. 300 B.C.): Greek philosopher who believed that God controlled the weather and brought about disease; diseases were the manifestation of the Wrath of God Concept of spontaneous generation: diseases (human and plants) develop spontaneously Even after advent of the microscope, the microbes observed were thought to be the result of the disease, not the cause of it History of plant pathology In 1845, late blight of potato epidemics occurred in Belgium, Holland, Germany, Switzerland, France, Italy, England, Ireland, and Scotland Completely destroyed the potato crop in Ireland in (Irish potato famine) Anton debary: the father of plant pathology In controlled experiments, proved that a fungus causes late blight (1861) Fungus was named Phytophthora infestans (Phyto = plant; phthora = destroyer) Irish potato famine ( ) Gave birth to the science of plant pathology Changed the course of human history Introduces: The political aspects of the food supply Risks of genetic uniformity in crops Problems when new crops are distributed throughout the world Anton debary (APS) 1

2 Plant Pathology 101 Plant Pathology 101 Plant Disease: any disturbance of a plant that interferes with its normal structure, function, or economic value, or any condition of a plant that is contrary to grower expectations Plant Disease: a condition of abnormal physiology in a susceptible host plant that is a result of the plants constant association with a disease causing agent within a set of favorable environmental conditions. Plant Pathology 101 Host Plant Condition Most plants resist or tolerate attack Plant must be susceptible to attack Resistance and susceptibility different degrees of the same thing influenced by genetics influenced by environment Immunity is absolute Two types of causal agents: 1. Biotic (infectious) organism (pathogen) grows, multiplies, and spreads to other plants 10% of diseases reported 2. Abiotic (non-infectious) environmental conditions that impact plant development (physiogens) much more common: 90% of diseases reported (injury not disease) 2

3 Abiotic Causal Agents - Physiogens Physical factors temperature moisture Chemical factors air pollutants pesticides fertilizers and salts Mechanical factors everything else Biotic Causal Agents - Pathogens Fungi (largest group of plant pathogens) Prokaryotes (no nuclear membrane) bacteria mollicutes (phytoplasmas, spiroplasmas) Nematodes (round worms) Viruses (nucleic acid with a protein coat) Viroids (naked RNA with no protein coat) Parasitic plants Algae Protozoa Insects and mites Fungi Pythium Disease Complex Cottony mycelium of Pythium Systematic study of fungi is 250 years old Mycology is Greek for mycos (fungus) + -logy (study of) Manifestations of this group of organisms is thousands of years old (e.g., wine and leavened bread) Most important as agents of decay Can attack wood products, leather goods, fabrics, petroleum products, foodstuffs Infect animals and plants: most common (or important) of plant pathogens Bacteria Bacteria 1600 species are known, most are saprophytic Important as decomposers and in nitrogen recycling Cause human, animal (e.g., tuberculosis, pneumonia, typhoid fever), and plant diseases Actinomycetes produce antibiotic compounds Shapes: rod, spherical (cocci), spiral, or filamentous Reproduce by fission (they divide in two) Xylella fastidiosa - a single-celled bacterium with rippled cell walls 3

4 Bacteriology 101 Bacteriology Bacteria are found in every ecological niche Large colonies form a biofilm: an extracellular polysaccharide ooze Illustration by Samatha Bozak Pathogenic bacteria are found on their hosts Infection occurs through natural openings or wounds Large populations overwhelm plant defenses and invade xylem tissues Plant tissues are killed and digested by toxins and enzymes Virus Tobacco Mosaic Virus entity that contains genetic material within a protein coat that can only reproduce using the metabolic processes of a suitable host cell Structure Protein coat = capsid Nucleic acid core (DNA or RNA) = nucleocapsid Size Ultramicroscopic = too small for microscope Must use electron microscope Shape Rod, filamentous, isometric May have more than one particle satellites Nematode Kingdom Animalia; non-segmented roundworms Several thousand species Most live in fresh or salt water, feeding on microorganisms and microscopic plants and animals Numerous species attack animals Several hundred species feed on living plants (roots or foliar tissue), obtaining food with stylets Annual losses on crops such as grains, legumes, banana, cassava, coconut, potato, sugar beet, sugarcane, and sweet potato are approximately 11% Plant parasite Plant parasitic nematodes have a stylet 4

5 Biotic Causal Agents Parasitic Plants Epiphyte orchid, spanish moss Hemi parasite mistletoe True parasite dodder, witchweed, dwarf mistletoe dodder Causal Agent Pathogen must be present Pathogen must be pathogenic Pathogen must be virulent influenced by genetics influenced by environment Environmental Condition Provides pathogen opportunities influences host plant condition increases pathogen virulence Predisposing conditions site weather management Photo: Dr. Peter Dernoeden, UMD 5

6 Symptom descriptions Recognizing Diseases Symptoms - observable condition of abnormal physiology in the plant Signs - physical presence of the causal agent or clear evidence of abiotic stress factors leaf spot, blight, tip blight, dieback, flagging, chlorosis, necrosis, canker, wilt, root rot, witches broom, mottling, interveinal necrosis, epinasty, scorch, crown rot, defoliation, boring phyllody, leaf blotch, rust, damping off, soft rot, mummification, stem pitting, gall, shot-hole, bleeding, slime flux, blast, scald, bronzing, staghead, tumefacation, fasciation, hairy root, knots, enation, shoestring, erinos, stipple, notching, chewing, skeletonization, rugose, puckering, edema, intumescence, russet, scab, callus, leafroll, leaf curl, croziers, dwarfing, stunting, rosetting, atrophy, etiolation, spiralism, hyperelongated, bunchy, cresting, dead Blight, dieback Aster yellows Photo: Dr. Ann Gould, NJAES Symptoms: stunting chlorosis phyllody witches broom Photo: Sabrina Tirpak, NJAES Photo: Dr. Joe Peterson, Rutgers Pine Bark Beetle Wilt symptom = cause? larvae leave distinct galleries 6

7 Signs Symptoms Caution Not the be all end all Simple starting point Don t jump to conclusions Need more information Fruiting body, sporocarp, cliestothecia, pycnidia, mushroom, hyphae, stroma, spores, conidia, sclerotia, conidiophore, perithecia, apothecia, synnema, cyst, egg, cast skin, nematode, insect, plasmodium, sporodochia, acervulus, aecium, oospore, zoospore, cirrhus, basidiocarp, ascus, sporangium, teliospore, uredium Cedar Apple Rust Dogwood Anthracnose Photos: Dr. Ann Gould, NJAES telia on Eastern red cedar The fungus moves into small stems and causes dieback Discula destructa Signs Photos: Dr. Ann Gould, NJAES Caution Not the be all end all Simple starting point Don t jump to conclusions Need more information Acervulus with conidia 7

8 Gray Leaf Blight Winter injury Pestalotiopsis spp. Photos: Richard Buckley, NJAES Photos: APS Press Winter desiccation March 2010 Basic Diagnostics Identify the plant 2. Observe the symptoms 3. Evaluate the predisposing conditions 4. Identify the sign 5. Synthesize the information Step 1: Identify the plant Understand the needs of the plant What are the horticultural requirements? Provides a list of pathogens Key plant / key pest concept Volutella Stem Blight Fungus - Volutella buxi Zoysia turns brown in winter in stark contrast to the perennial ryegrass Host - Boxwood 8

9 Know your plant materials! Step 2: Observe symptoms Proper identification is key Understand the needs of the plant What are the horticultural requirements? Photos: Richard Buckley, NJAES Define the problem Examine the entire plant Examine the plant community Recognize patterns Observe symptom progression Recognize classic symptom expression Step 2: Observe symptoms Examine the entire plant Define the problem Examine the entire plant Photo: University of California Lesser Peachtree Borer Evaluate the entire plant Botryosphaeria Canker Photos: Richard Buckley, NJAES Photos: Debbie Miller, Davey Tree Don t be afraid to cut it up! 9

10 Photos: Richard Buckley, NJAES Define the problem! Step 2: Observe symptoms Define the problem Examine the entire plant Examine the plant community Identify dysfunctional plant part or plant system What kind of symptoms do you see? Symptom Expression Similar symptoms on unrelated plants are likely due to a non-living (abiotic) cause Similar symptoms on related plants are likely due to a living (biotic) organism Photo: University of California Step 2: Observe symptoms Define the problem Examine the entire plant Examine the plant community Recognize patterns Drop Spreader Disease Recognize Patterns Uniform - abiotic Random - biotic What can you say about this? 10

11 Close shearing Crown and Root Rot Drought stress Bacterial Leaf Scorch Photo: Dr. Ann Gould, NJAES Photo: Dr. Ann Gould, NJAES Step 2: Observe symptoms Define the problem Examine the entire plant Examine the plant community Recognize patterns Observe symptom progression Observe symptom progression Progressive biotic Non-progressive - abiotic 11

12 Crown and Root Rot Heat stress All plants rapidly decline after a week above 100 o F Step 2: Observe symptoms Define the problem Examine the entire plant Examine the plant community Recognize patterns Observe symptom progression Recognize classic symptom expression Typical symptoms of fungal pathogens Fungi cause most plant diseases Fungi attack all plant parts and cause all possible symptoms Central infection point Rounded, even borders Discolored margins Dry rot Signs frequently produced Entomosporium Leaf Spot Fungus Entomosporium mesculi Photos: Richard Buckley, NJAES Crown and Root Rot Host 60 species in the rosaceae particular pathogens attack particular plant parts Note: dry rot, discolored cambium, even border 12

13 Maple Anthracnose Fungus Aureobasidium apocrypta Nectria Canker Central Infection Point Concentric circles Rounded border Discoloration of sapwood Photos: Sabrina Tirpak, NJAES Host sugar and red maples Note: the gelatinous amber colored acervuli Dry rot Signs Photo: Dr. Ann Gould, NJAES Typical symptoms of bacterial pathogens Photo: Sabrina Tirpak, NJAES Bacterial Leaf Spot Bacteria attack all plants, but are most common on herbaceous hosts Infection through natural opening or wound Angular borders Chlorotic halo Water soaked rot Tissue blight Rotten smell Fire Blight Fire Blight Bacteria ooze from natural openings on infected trees Pollinators carry bacteria to nectar cells in flowers, which results in spur blight 13

14 Fire Blight Fire Blight Spur blight progresses to branch blight Severe disease Erwinia Soft Rot Bacterial Blight of Cucurbit Rose Mosaic Virus Typical symptoms of viral pathogens Virus attack many plants and cause unusual symptoms Abnormal growth Abnormal color Look for the vector Latent / symptomless host Photos: APS Press 14

15 Rose Mosaic Virus Rose Mosaic Virus Photos: APS Press Photos: APS Press Impatiens Necrotic Spot Impatiens Necrotic Spot Photo: Sabrina Tirpak, NJAES Impatiens Necrotic Spot Western flower thrips adult larva Virus Vectors Photos: APS Press Photo: Dr. Ann Gould, NJAES Photos: APS Press 15

16 Typical symptoms of physical injury Photo: Ann Gould, NJAES Drought stress Tip and edge scorch On individual plant parts On entire plant canopy Intervienal necrosis Loss of older needles Early fall color Premature defoliation Loss of turgor first symptoms of drought Tip and edge scorch Photo: University of California Drought stress Photos: Bruce Clarke, NJAES Drought stress Tip and edge scorch due to drought Needles wilt and scorch too Heat stress Photos: Richard Buckley, NJAES tip and edge scorch over entire plant Drought stress Photo: University of California Severe scorch after high heat stress top - down injury 16

17 Heat stress Typical symptoms of chemical injury Symptom follows application pattern Patterns match application technique Cause and effect clearly evident Symptom expression relates to product: Toxic contact with exposed plant parts Uptake and translocation of toxic concentrations Damage is more severe on tough sites July 11, 2010 Typical symptoms of chemical injury Necrosis of exposed plant parts due to direct contact with toxin Abnormal growth and color due to growth-regulator effects due to imbalances of nutrients Top-down, outside-in, tip-edge due to uptake of toxin on individual plant parts on entire plant canopy Ozone toxicity Ozone causes tan, gray or metallic spots on upper leaf surfaces during hot, sunny days in summer Sulfur dioxide toxicity Oil phytotoxicity Photo: Sabrina Tirpak, NJAES Sulfur dioxide is absorbed through the stomates in toxic concentrations; damage was due to a poorly functioning heater and the plants recovered Burn from horticultural oil application on cloudy day 17

18 Herbicide phytotoxicity Herbicide phytotoxicity Photos: Richard Buckley, NJAES Photo: Sabrina Tirpak, NJAES Injury to new growth due to Imprelis; Do not apply under the drip-line! dicamba distorts flowers and causes upward cupping of leaves; this sample injured by drift Salt phytotoxicity Salt phytotoxicity Photos: A&L Services De-icing salt damage burn by contact Sodium and chloride are absorbed and moved to the leaf tips where they build to toxic concentrations Boron toxicity Phosphorous deficiency Irrigation with high boron content water is also problematic P deficiency rare in most NJ soils; symptoms include purple discoloration 18

19 Iron deficiency Liquid fertilizer overdose Photos: Richard Buckley, NJAES High ph binds Fe in the soil and causes deficiency symptoms Typical symptoms of mechanical injury Lightning strike Breaks Bruises Punctures Cracks Chewing Girdling Root pruning Winter Injury Winter Injury Photo: A&L Services Heavy snow breaks branches and knocks stuff over Ice will do it too January

20 Root damage Root damage Photo: Ann Gould, NJAES Damage to the rootzone = damage to the canopy Do no construction under the drip line String girdling Stop sign Photo: Ann Gould, NJAES Step 3: Evaluate the predisposing conditions Analyze the site condition Record the weather condition Evaluate management program Step 3: Evaluate the predisposing conditions Analyze the site Drainage Shade and exposure Air movement Contour Soil chemical properties Soil physical properties 20

21 Wet feet Wet feet Photo: University of California Some wet sites are obvious Note the white pine performs poorly on wet sites Taxus does poorly on wet sites Winter injury Pachysandra Stem Blight Damage most severe on exposed surfaces (NE side) Black Layer Weed indicators of site conditions Black layer smells like a swamp, must be a swamp High ph = plantain Low ph = sorrel 21

22 Step 3: Evaluate the predisposing conditions Record the weather condition Temperature Relative humidity Rainfall Evapotranspiration rates Air quality Time of year Entomosporium Leaf Spot severe disease on photinia Nectria Canker Brown Patch Rhizoctonia solani Predictive Model Warm nights Soil temperature >61 o F Air temperature >59 o F Extended leaf wetness 95% RH for >10 hours 0.1 rain or irrigation in preceding 36 hours Photo: University of California Heat stress Frost damage Cold temperatures damage new growth Cause and effect clearly evident Leaf scorch and drop after high heat July 11,

23 Wet Feet and Wind Step 3: Evaluate the predisposing conditions Evaluate management program Pruning Fertility Irrigation Cultivation Pesticide input Note the lack of root biomass and the poor drainage Wet feet Excessive mulch Photo: Bruce Clarke, NJAES Wet roots turn black Photo: University of California Physical injury Herbicide phytotoxicity Photo: University of California Photos: Richard Buckley, NJAES Cupressaceae very hard hit by heat (Poor planting technique, crummy mulch, and excess irrigation didn t help much) Distorted growth = phenoxy herbicide damage 23

24 Chemical Injury What fungicides, insecticides, and herbicides were used on site? How much and when? Specific chemicals cause specific problems Can the materials used cause the symptoms you see? Step 4: Identify the sign Macroscopic observation Insect traps Microscopic observation Pathogen stimulation Pathogen isolation Antibody based test kits Special tests Bagworm Red Thread pseudosclerotia Red threads form on leaf tips epidemic Photos: Richard Buckley, NJAES Juniper Tip Blight Macroscope 10 to- 60x magnification Phomopsis spp. pycnidia 24

25 Oriental beetle, Exomala orientalis Nematodes from turf soil Raster patterns indicate scarab species Copper Spot Gloeocercospora sorgii Compound microscope 40 to- 400x magnification Note: sporodochia produce copious numbers of whip-like conidia Bacteria Bacterial streaming Pink Snow Mold Microdochium nivale incubate plugs to stimulate fungus Photo: Sabrina Tirpak, NJAES 25

26 Cyclamen Wilt Bacteriology 101 Photo: Lane Tredway, NC State Bacteria laden sterile water is then streaked on media: Which one is the pathogen? Bacteriology 101 Plant Pathology 101 selective media Isolates are subjected to a battery of biochemical tests only allows target to grow Photos: APS Press Photo: Sabrina Tirpak, NJAES differential media makes target look different Antibody-based test kits effective for Pythium Plant Pathology 101 Detection Step 5: Synthesize the information Put it all together Evaluate the symptoms (host) Photo: Dr. Ann Gould, NJAES PCR ELISA Photo: Sabrina Tirpak, NJAES Consider the predisposing factors (environment) Identify the sign (causal agent) 26

27 !!!! Caution!!!! Fungi don t read the book Don t jump to conclusions Keep an open mind Expect the unexpected Accumulate information Educate yourself Act on your hunches Soil Testing and Plant Diagnostic Services 27