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 1st 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 Group 1 pathogen: Black- colored Rhizoctonia sclerotia of -causes many, many diseases -mostly soilborne Rhizoctonia solani on a potato Damping-off of alfalfa Lesion caused by caused by Rhizoctonia Rhizoctonia spp. Rhizoctonia Hyphae branch at right angles No asexual spores 3 Other diseases of Group 1 basidiomycetes: Turf diseases: Gray Red snow thread mold 2nd 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-to- root 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 3rd 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 Spores from diseased infected seed leads to heads infect healthy flowers diseased plants in next crop 10 Common bunt (covered smut) of wheat - Infection of emerging coleoptiles via soil infestation or contaminated seed Spores on healthy seed (or in soil) infect cloud of smut spores 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 4th 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) teliospores Overwintering stage basidium basidiospores spermagonium spermatia aecium aeciospores urediniospores Repeating uredium stage telium teliospores 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 Teliospores Germinate to bearing teliospores produce basidiospores cedar apple rust in spring Telia on which basidiospores were produced Telia are produced en mass on the fleshy galls rose rust 17.