University of Florida - IFAS Plant Disease General Concepts Signs Symptoms Etiology Epidemiology Pathogenicity 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

University of Florida - IFAS Signs vs. Symptoms Sign of Disease observation of the organism causing the disease (objective observation) Symptom 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

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

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

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

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

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

University of Florida - IFAS 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

University of Florida - IFAS 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

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

University of Florida - IFAS 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 111

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

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

Plant Pathology Terms Pathogenicity: the pathogen either does or does not cause a disease; a question with yes or no answer Virulence: relative capacity of pathogen to cause disease; range from minimal damage to dead plant Etiolgy: determining the cause of disease 17

Etiology and Pathogenicity Testing University of Florida - IFAS Consistent isolation of a pathogen from symptomatic host tissue Pathogen is grown in pure culture and its characteristics documented Inoculation of a healthy plant with the pure culture of the pathogen, and inoculated plant must then develop symptoms similar to those observed initially Recovery of the same pathogen used for inoculation purposes To confirm that a fungus is the actual cause of a disease, scientists must follow these steps. 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

University of Florida - IFAS Control F. oxysporum It was difficult to complete Koch’s postulates with older, juvenile palms, but we could complete Koch’s postulates with seedlings, as shown here. Of the three Fusarium species isolated from diseased palms, only the Fusarium oxysporum is pathogenic. F. incarnatum-equiseti F. proliferatum University of Florida - IFAS 21

But, how do pathogens enter the plant? Plant Pathology Terms Epidemiology: study of the factors influencing the initiation, development and spread of infectious disease But, how do pathogens enter the plant? 22

How do pathogens enter plant? University of Florida - IFAS 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) Stoma (plural=stomata) Plant Epidermis 24

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

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

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

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

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

Disease Development pathogen infects plant – penetration, can be 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 30

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

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

University of Florida - IFAS 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

University of Florida - IFAS 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