Basidiomycetes in lab tomorrow Quiz (Lab manual pages 7-13 Isolation of fungal pathogens and 51-57 Ascos III, and intro pages for Basidiomycetes (pp. 59-61) and Race I.D. of Wheat Stem Rust (p. 109). Look at Basidiomycete diseases signs and symptoms emphasis is understanding disease cycles and knowing the types of spores present on the host tissues Inoculate wheat cultivars with rust isolates Basidiomycetes (the club fungi) Septate hyphae Dikaryotic (paired haploid) nuclei (n + n) Cell wall made of chitin Sexual reproduction: basidiospores produced externally on a club-like one or four celled basidium 1
Diseases caused by Basidiomycetes Four major pathogen groups Root rots & web blights ( sterile fungi ) Root and heart rots of forest and fruit trees Smuts of cereals Rusts of grasses, pines, rose family, coffee, etc 1 st Group: Root rot and web blight pathogens (Facultative parasites) In herbaceous plants, diseases caused by sterile fungi --- (some produce a teliomorph, but only rarely) Produce sclerotia (or other vegetative survival structure) but generally no asexual spores 2
Blackcolored sclerotia of Rhizoctonia solani on a potato Group 1 pathogen: Rhizoctonia -causes many, many diseases -mostly soilborne Damping-off of alfalfa caused by Rhizoctonia Lesion caused by Rhizoctonia spp. Rhizoctonia Hyphae branch at right angles No asexual spores 3
Other diseases of Group 1 basidiomycetes: Turf diseases: Red thread Gray snow mold 2 nd nd Group: Rots of trees (Facultative parasites) Example: Armillaria root rot Life strategy: Facultative parasite Fruiting body (basidiocarp) is a mushroom Fungus spreads from tree to tree via root-toroot contact or rhizomorphs Large host range: oak, grape, pine,fruit trees Aggressive colonizer of dead wood 4
Mushrooms of Armellaria In the gills of the mushroom: basidiospores basidium from a mushroom or conk 5
Rhizomorphs are aggregated, mycelium strands used by Armilleria to grow along roots and from root to root. Rhizomophs R h i Mushroom fairy ring in golf green. In the woods, Armillaria fairy rings can have diameters of many miles, giving this pathogen the nickname, Humungous Fungus. 6
Another Example: Heart rots In living trees, decay of older, central wood (heartwood) Caused by large fleshy fungi Basidia are produced on basidiocarps (conks or mushrooms) Ken s house in grad school The tree fell on Ken s bedroom He narrowly escaped the work of a plant pathogen 7
The fallen poplar tree had heartrot Fruiting bodies (conks) of the heartrot pathogen 8
Pore of conk producing basidiomycete Basidium with basidiospores Number of basidiospores produced in a conk Billion spores per day 9
3 rd group: Smuts Obligate parasites known as replacement diseases because fungal teliospores replace normal seeds of plant Two kinds of spores: 1) teliospores (overwintering) that germinates to form a 2) basidium bearing basidiospores (infective) Host tissue infected initially helps to understand disease cycles of smut fungi: seed via flowers - leading to systemic infection emerging coleoptiles in soil -systemic infection very young, growing tissues -local infections Loose smut of barley -Seed infection via flower Healthy appearing but infected seed leads to diseased plants in next crop Spores from diseased heads infect healthy flowers 10
Common bunt (covered smut) of wheat - Infection of emerging coleoptiles via soil infestation or contaminated seed cloud of smut spores Spores on healthy seed (or in soil) infect next crop after seed is planted Common corn smut - Local infection In Mexico, immature smut balls are considered a delicacy 11
Long-lived Resting spores Teliospores of Smut Fungi Germination of teliospores (n+n) of smut fungi to produce basidiospores (n) Two basidiospores (n) must fuse to form an infective hyphae (n+n) 12
4 th group: Rusts Obligate parasites Attack leaves and stems Produce pustules (masses of yellow, orange or rusty spores that erupt through the epidermis) 13
Rusts cont d Many rust fungi produce 5 types of fruiting structures and 5 types of spores (= macrocyclic rusts) Other rusts, like smuts, produce only teliospores and basidiospores (= microcyclic rusts) Some rust produce only urediniospores (= asexual rust) basidium spermagonium aecium uredium telium teliospores basidiospores spermatia aeciospores urediniospores teliospores Overwintering stage Repeating stage 14
Rusts cont d. Some rusts complete their life cycle on a single host = autoecious e.g. rose rust Other rust fungi require two different plant hosts to complete their life cycle = heteroecious e.g. stem rust of wheat (polycyclic on wheat) uredia and telia on wheat spermagonia and aecia on barberry e.g. cedar-apple rust (monocyclic) telia on cedar (no uredial stage) spermagonia and aecia on apple basidiospores of a rust fungus basidium teliospore 15
Spermagonia (n) and aecia (n+n) Upper surface or lesion center Lower surface or lesion edge Infection by basidiospore leads to spermagonium Aecia on apple fruit aecium Pustule with uredia and urediniospores repeating stage/ summer spore 16
telia and uredia (black) (orange) For many rusts, late in the season, the uredium converts to a telium Telial galls bearing teliospores cedar apple rust Teliospores Germinate to produce basidiospores in spring Telia on which basidiospores were produced Telia are produced en mass on the fleshy galls rose rust 17