Presentation on theme: "The Basics of Plant Diagnostics"— Presentation transcript:
1The Basics of Plant Diagnostics USAID IPM WorkshopOctober
2The Clemson University Plant Problem Clinic An Interdisciplinary ClinicDiagnosis of plant diseases and other problemsInsect identifications – DPR EntomologistPlant/Weed identifications – Botanist in Dept. of BiologySpecialists across campus assist with recommendations.Website:
3Plant Problem Diagnosis Diagnosis – process used to identify the cause of problems.Tools:Plant sciences, especially plant pathology, mycology and entomology.Arts of investigation and detective work.
4Consider the Possible Agents Biotic AgentsAbiotic AgentsDamage fromWeatherChemicalsMechanicalNutritional problemsCultural problemsPathogens or Pests:FungiBacteriaViruses, viroidsPhytoplasmasNematodesInsects and mites
5Patterns of Abiotic Damage Damage occurs suddenly.Many species of plants affected.Symptoms often distributed in a large area.Damage is uniform even if in small area.Cotton field with chemical damage
6Laboratory tests Diagnostic tests for abiotic causes Soil, water pH testingNutrient analysisSoluble salts analysisAnalysis for chemicalsPlant tissue tests
7Patterns of Biotic Damage Symptoms usually localized or scattered.Pattern is random.Symptoms develop gradually and get worse over time.Damage spreads to plants of same or related species.Fusarium wilt of tomatoR. BillingsLoblolly pine killed by southern pine beetle
8Consult literature resources APS Compendia seriesUS ARS Systematic Mycology and Microbiology websitePestnet Diagnostic Service:Other Online resources
9Identify symptoms and signs Symptoms - alterations of a plant’s appearance due to a disease, pest or disorder.Signs - actual pathogen, pest, parts orby-products seen on a host plant.
11Systemic SymptomsDiagnosis is often more difficult First pin point source Vascular disease Root Rots Nematode infestation Isolations or other techniques often needed to determine causal agent.
12Identification of Signs MyceliumDistinctive appearanceallows id. of some fungi.Advantageous if fungus produces no spores.Mycelium of Rhizoctonia sp.Mycelium of Phytophthora sp.
13Signs for Localized Symptoms Fungal fruiting bodies or sporesDowny mildewsPowdery mildewsSclerotiaBacterial oozeCercospora leaf spotof watermelon,Cercospoora citrulinaSouthern stem rot,Sclerotium rolfsiiDowny mildew of veronica, Peronospora sordida
14Laboratory tests Moist Incubation Goal – to induce sporulation. Important for obligate fungal pathogens.Avoid overly moist conditions.Moist chamber
15Identification of Signs Fungal signsFruiting bodiesMorphology of fruiting body aids in fungal identification.Spore-bearing myceliumMorphology of spores provides fungal identification
16Leaf Spot Diagnosis Yellow spots on leaves only. Spores (sign) form on leaf undersides.Microscopic mount reveals Fulvia fulva is causal.Can now diagnose visually
17Leaf Spot Diagnosis Leaves defoliating. Dark, water-soaked spots, more obvious when held up to lightMicroscopic mount shows bacterial flow.Doesn’t id. species, but control is same.Sally Miller
18Signs Bacterial signs “Streaming” from freshly cut stem “Stringing” from cut stems pushed together, then pulled apart.Bacterial oozeBacteria “flow” and morphology seen on compound microscope.Bacterial streaming from tomato stem infected by Ralstonia solanacearum.
19Laboratory tests Bacterial isolations Suspend infected tissue in sterile water.Streak suspension on bacterial medium.Can use selective media.Transfer single, isolated colony.Cultures of Ralstonia solanacearum
21Melon Vine Wilt Diagnosis Wilt of vine - look for symptoms and signs.GSB lesions have gumming and pycnidia; if not present may be Fusarium wilt.Fusarium wilt shows vascular discoloration
22Laboratory tests Fungal isolation Nutritive agar media, can be selective.Diagnostician can often id. to genus from appearance of cultureFungal culture.
23Isolate identification Fungal identification – Other methodsUtilizing keys in literature.Morphological comparison with drawings in literature.Literature sources for host diseases and disorders.Serological, molecular, other tests.
24Investigate Pathogenicity If symptoms match, but not a known host,Kochs Postulates may be next stepA lengthy process, rarely used in routine diagnoses.Problem arises when organism cannot be cultured.
25Koch’s PostulatesNote constant association of organism with diseased plants and consistent, observable symptoms.Isolate and characterize organism in pure culture.Inoculate healthy plant with organism, and observe the same disease and symptoms.Re-isolate same organism.
26Symptoms Viral Symptoms Mosaics Irregular patches of discolored tissue.Often with distortionRingspots or line patternsDistinct ring shaped lesions, various line patterns.Very few can be identified visually.
27Identification of non-culturable Pathogens MethodsSerological tests, e.g. ELISA .Electron microscopy.Staining for virus-induced inclusion bodies.Molecular tests, e.g. PCRDNA SequencingHost range testing.
28Pathogen Identification ELISA : a very pathogen specific serological testELISA uses animal antibodies to detect pathogens.Multi-well test for multiple samplesEnzyme-linked immunosorbent assay; a sensitive immunoassay that uses an enzyme linked to an antibody or antigen as a marker for the detection of a specific protein, especially an antigen or antibody.Individual test ELISA kit
29Plant Disease Diagnosis Steps 8. Final DiagnosisAll information compiled and analyzed.Organism identified, found to be pathogen of host ORLab tests or other information reveal an abiotic cause.9. Develop control recommendations and present to grower.