Microscopic Identification of Turfgrass Diseases

Microscopic Identification of Turfgrass Diseases Horticulture In-service Training, September 30, 2005 The Inn at Virginia Tech, Blacksburg, VA

Purpose of session • Learn procedure for disease identification • Locate and identify fungal structures • Help confirm/eliminate a field diagnosis based on symptoms • Possibly eliminate fungicide applications

Diagnosing turfgrass samples • Disadvantage: • plants are small • many microorganisms in soil • Advantage: • plants are small • verification of initial field diagnosis • quicker treatment if necessary

Tell a story with pictures

Useful equipment • Dissecting microscope (4 – 40X) • Compound microscope (40 – 1000X) • Digital camera (Sony, Nikon) • Universal adapter • Lab supplies • Scapula, forceps, probing needle, distilled water or stains, slides & covers, etc.

Dissecting microscope • Useful for observing mites, insects, and some fungal structures • Helps pinpoint problematic areas • Not powerful enough for fungal ID

Compound microscope • Difficult to pinpoint if starting blind • Useful for distinguishing fungal hyphae, spores, fruiting bodies, and other structures

Digital camera • Can be mounted on microscope • Provides documentation for archives • Rapid sharing of information • Tell a story

Factors affecting disease diagnosis • Turf species and cultivar • Weather patterns, time of year • Cultural and chemical inputs • Symptoms and signs

Diagnostic procedure • Collect information • Examine plant under dissecting scope • Identify problematic regions • Make wet mount from diseased tissue • Examine under compound scope

Diagnostic procedureCompound microscope • 4x- focus and find fungal structures • 10x- to pinpoint spores, hyphae, etc. • 40x- identify fungus based on spore and hyphae characteristics

What to look for • Spores • Hyphae • Fruiting bodies • Plant parasitic nematodes

Hyphal characteristics • Septation • Branching • Pigmentation • Consistency

Spore morphology • Shape • Number of cells • Spore origin

Moist Chamber • Promotes disease development, mycelial growth, sporulation • Sample placed in plastic container with moist paper towel & checked daily

Rhizoctonia species on turf • Rhizoctonia solani • Rhizoctonia blight • “warm weather” brown patch • Rhizoctonia cerealis • Yellow patch • “cool season” brown patch • Rhizoctonia zeae • Rhizoctonia leaf and sheath spot • “hot weather” brown patch

Rhizoctonia characteristics • Right angle branching • Septate (cross walls) • Uniform hyphae • Septae near branching • Constricted hyphae at branching point

Pythium species • Pythium blight • Pythium root rot

Pythium characteristics • Coenocytic (no cross walls) • Small, thin filamentous hyphae • Oospores • Sporangia • Non-pigmented 250x 540x

Dollar spotSclerotinia homoeocarpa • Clear hyphae • Variation in size • Often branches in V • Granular cytoplasm

Gray Leaf SpotPyricularia grisea (oryzae) • Spores (conidia) are hyaline • Pyriform shaped • Bowling pins, pear, ice cream cone • 2- to 3-celled conidia borne on slender stalks (conidiophores)

AnthracnoseColletotrichum graminicola • Acervulii w/ setae on leaf and crown tissue U. Of Guelph

Microscopic Identification of Turfgrass Diseases