Fungi as Disease Organisms Plant Pathology Fungi as Disease Organisms

Slime Moulds Most not pathogenic to plants highly conspicuous fungi that often seem to "magically" appear on mulch, plants, and turf overnight the rapid appearance of these nuisance fungi is frequently a cause for misdirected alarm.

Clubroot of Crucifers (Cabbage, cauliflower) Widely distributed around world Can cause severe damage Pathogen remains in soil indefinitely Plasmodiophora brassicae

Oomycete Diseases Soil pathogens Aboveground Roots, lower stems, tubers, seeds, fleshy fruits lying on soil Aphanomyces, Pythium, Phytophthora Aboveground Leaves, young stems, fruits Phytophthora, Pythium,

Diseases Downy mildews White rust Pythium Damping off Root rots

Sudden Oak Death Ramourm blight

Olpidium Parasitic on algae, fungi, mosses, pollen grains, flowering plants Zoosporangium Resting sporangia

Zygomycetes Rhizopus Mucor Weak parasites Soft rot of fruits and vegetables Mucor Soft rot Weak parasites Mostly grow on dead or processed plant products

Rhizopus Rot

Diseases Caused by Ascomycetes Leaf and fruit spots / blights Fruit decay and rots Vascular wilts Root and stem rots Stem and trunk cankers

Powdery Mildews Attack many hosts White to grayish patches on plant tissues Chlorosis, tissue distortions, necrosis Obligate parasite Causes yield reductions

Apple Scab Very important disease Scabby lesions on leaves and fruit Fruit stunting, and drop, defoliation Requires cool springs and summers

Basidiomycetes Smuts and Rusts Smuts and Bunts (Ustilaginales) Ustilago, Tilletia Rusts (Urediniales) Puccinia, Uromyces Rots of roots, crowns, and stems Armillaria, Rhizoctonia, Scloerotium

Smut Diseases Important cereal diseases Smuts (Ustilago spp.) Barley, wheat, oats, corn Smuts (Ustilago spp.) Bunts (Tilletia spp.) Causes reduced yields, quality

Smut Diseases Monocyclic diseases Systemic growth Corn smut – Ustilago maydis Loose smut – U. tritici (wheat) - U. nuda (barley) - U. avenae (oats) Common bunt – Tilletia spp (wheat) Karnal bunt – T. indica (wheat)

Basidiomycete Rots Rhizoctonia Sclerotium Armillaria Wood Rots White and brown “Mycelia Sterilia”

Control Quarantines and Inspection Pathogen Free Propagating material Host eradication Crop rotation Sanitation Vector control Biological control agents Chemicals Foliage sprays Seed treatment Soil treatment

Site / mode of action Comments Nucleic acid synthesis Some that control Oomycetes Microtubules A few systemics Protein synthesis A few Lipids and membranes Affect phospholipids or biosynthesis or membranes Sterol biosynthesis Many important fungicides affect sterol pathways Melanin synthesis Various, unknown

Some Examples Ridomil – specific for Oomycetes Score – systemic for almost any crop against wide range Tilt – rusts and leaf spot Unix – for some difficult to control pathogens