Plant Pathology Fungi as Disease Organisms Slime Moulds

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 – 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 – 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 1. 2. 3. 4. 5. 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 • Basidiomycetes • Smuts and Bunts (Ustilaginales) – Ustilago, Tilletia • Rusts (Urediniales) – Puccinia, Uromyces • Rots of roots, crowns, and stems – Armillaria, Rhizoctonia, Scloerotium

Smut Diseases • Important cereal diseases – 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 “Mycelia Sterilia” – White and brown

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 A few Various, unknown A few

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