Plant Disease General Concepts Signs Symptoms Etiology Epidemiology

Plant Disease General Concepts Ø Signs Ø Symptoms Ø Etiology Ø Epidemiology Ø Pathogenicity Ø Virulence Photos used from various UF/IFAS Extension Publications or provided by UF/IFAS faculty and staff, unless otherwise stated. University of Florida - IFAS 1

Signs vs. Symptoms ØSign of Disease • observation of the organism causing the disease (objective observation) ØSymptom of Disease • observation of how the host is manifesting infection by a pathogen and disease development due to a pathogen University of Florida - IFAS 2

Signs vs. Symptoms of Guinea worm disease or dracunculiasis Dracunculus medinensis - nematode Photos from The Carter Center University of Florida - IFAS Symptoms of Ganoderma Butt Rot Ganoderma zonatum - fungus 3

Bacteria oozing from leaf Rust spores on leaf Signs of Disease University of Florida - IFAS Rust spores on leaf (Puccinia ) Mycelia (cottony growth) 4

Fungal sclerotia inside stem Powdery mildew mycelia Fungal mycelia and sclerotia Signs of Disease University of Florida - IFAS Fungal mycelia 5

Pycnidia (fungal structures with spores) on branch Pycnidia (fungal structures with spores) on orange skin Signs of Disease Fungal mycelia on roots (microscopic view) Pythium oospores on roots (microscopic view) University of Florida - IFAS 6

Plant Organs Disease And Symptoms Functions University of Florida - IFAS 7

Types of Symptoms • spot – small, distinct lesion on leaf, fruit. . . • blight – spots that have coalesced or merged together; more tissue being affected University of Florida - IFAS 8

Types of Symptoms • rot – tissue is breaking down (fruit, roots); usually mushy, but can be dry • wilt – plant droops due to water stress; can be systemic (xylem) or due to root rot University of Florida - IFAS 9

Types of Symptoms • canker – sunken lesions; usually on stems or woody tissue; but can occur on fruit University of Florida - IFAS 10

Types of Symptoms • gall – masses of undifferentiated growth; usually on stems or woody tissue (branches) but can be on roots S. Browning, University of Nebraska, Lincoln http: //hortupdate. unl. edu/peach-leaf-curl University of Florida - IFAS 11

Types of Symptoms • patches, decline – terms often used in association with grasses (turf, grain crops) University of Florida - IFAS 12

Symptoms Caused by Bacteria • leaf spots and blights – water soaked, greasy • soft rots of fruits • wilts (systemic – xylem) • cankers • gall (overgrowths/cell proliferation) University of Florida - IFAS 13

Symptoms Caused by Fungi/Oomycota • leaf spots and blights (including rust and powdery mildew) • soft or dry rots of fruits, bulbs. . . • root rots • wilts (systemic – xylem) • overgrowths/cell proliferation – clubroot, galls, warts, witches’-broom • scabs, cankers, patches and decline University of Florida - IFAS 14

Symptoms Caused by Viruses • dwarfing or stunting to some degree • mosaics – light green, yellow or white areas intermingled with green – leaves or fruits • ring spots – chlorotic or necrotic rings – leaves, fruits or stems University of Florida - IFAS 15

Symptoms Caused by Viruses Dwarfing Mosaic Ringspot University of Florida - IFAS 16

Etiology and Pathogenicity Testing 1) Consistent isolation of a pathogen from symptomatic host tissue 2) Pathogen is grown in pure culture and its characteristics documented 3) Inoculation of a healthy plant with the pure culture of the pathogen, and inoculated plant must then develop symptoms similar to those observed initially 4) Recovery of the same pathogen used for inoculation purposes This is general scheme; non-culturable plant pathogens have special rules. University of Florida - IFAS 18

Etiology and Pathogenicity Testing Example: Fusarium Wilt of Queen Palm The “potential” pathogen isolated consistently from symptomatic tissue was Fusarium. University of Florida - IFAS 19

Etiology and Pathogenicity Testing Example: Fusarium Wilt of Queen Palm Isolated Three Fusarium Species (sometimes from the same tissue piece) 1) F. incarnatum-equiseti species complex (6 isolates) isolated from Fusarium wilt symptomatic palms in Australia 2) F. oxysporum (43 isolates) known Fusarium wilt pathogen of palms worldwide 3) F. proliferatum (9 isolates) known pathogen of palms; can cause wilt symptoms 20

Control F. oxysporum F. incarnatum-equiseti F. proliferatum University of Florida - IFAS 21

How do pathogens enter plant? • Viruses and Viroids and Fastidious Bacteria most require vectors; a few mechanical entry • Bacteria – most enter through natural openings or wounds • Fungi & Oomycetes – enter through natural openings, wounds; by mechanical pressure or enzymes they produce; a few by vectors • Nematodes – stylets used to gain entry University of Florida - IFAS 23

How do pathogens enter plant? Plants have natural openings: stoma or stomata (plural) Plant Epidermis Stoma (plural=stomata) 24

How do pathogens enter plant? Leafhopper (insect vector) Use mouth parts to penetrate 25

How do pathogens enter plant? Leafhopper Bacteria (insect vector) on water film, Use mouth parts to enter penetrate through stoma 26

How do pathogens enter plant? Leafhopper Bacteria (insect vector) on water film, Use mouth parts to enter penetrate through stoma Fungal Spore entering through stoma 27

How do pathogens enter plant? Leafhopper Bacteria (insect vector) on water film, Use mouth parts to enter penetrate through stoma Appressorium fungal structure from Fungal Spore entering spore for direct through stoma penetration 28

How do pathogens enter plant? Leafhopper Bacteria (insect vector) on water film, Use mouth parts to enter penetrate through stoma Appressorium fungal structure from Fungal Spore entering directly spore for direct through stoma penetration Fungal Hyphae can grow between cells or penetrate cells 29

Disease Development • pathogen comes in contact with plant • pathogen infects plant – penetration, can be direct or indirect; with or without vector • incubation period – time between penetration and first appearance of symptoms • pathogen increases within plant, uses host to grow and reproduce • symptoms observed continue to increase 30

Disease Development Environmental conditions influence each and every step in disease development process!! Susceptible Host Favorable Environment DISEASE Pathogen 31

Disease Development Susceptible Host Nematode Fungus W. Deacon, Univ. of Edinburgh Vector required for some pathogens! DISEASE Favorable Environment Pathogen Mite Insect USDA/ARS University of Florida - IFAS 32

How do plant pathogens move from plant to plant if they are not moved by a vector? • Wind dispersal of spores • Splash dispersal of spores – rain, irrigation • Physical movement of soil-borne pathogens that don’t produce spores – ex: soil tillage • Nematodes swim or move with soil • Seed associated – internal or external • Plant associated – cuttings, grafting University of Florida - IFAS 33

How do plant pathogens move from plant to plant if they are not moved by a vector? Time to have some fun! Cheap, easy way to demonstrate spore dispersal without water or spores! University of Florida - IFAS 34

Splash Dispersal of Spores University of Florida - IFAS 35

SPORE Asexual, not requiring the union of sexual parts to be produced • Conidia

SPORE • Sexual, requiring union of sexual parts to be produced • Basidiospore, ascospore, oospore…

SPORE Where do you see spores when a plant is infected? • Leaf surface • Appears as mold (powdery mildew)

SPORE Where do you see spores when a plant is infected? • Fungal fruiting bodies • Spore producing pockets • Sporodochium, acervulus, pycnidium…

HYPHAE Hyphae is what germinates out of the spore • Branches out into tubular filaments

HYPHAE Mycelium refers to all the hyphae as a whole, as the fungal body • Inside the plant, or outside the plant under high moisture

PLANT INVASION Fungus enters plant through any of the following • Wounds • Mechanical, pruning or handling

PLANT INVASION Wounds • Insects, vectors or egg laying

PLANT INVASION Wounds • Naturally occurring Secondary roots rupture the main root when emerging • Leaf scars •

PLANT INVASION Fungus enters plant through any of the following • Natural openings • Lenticels

PLANT INVASION Fungus enters plant through any of the following • Direct penetration • Pushing through tissue • Resistance can come in the form of thicker cuticle or hairy leaf