Basidiomycota

1. Basidiomycota Rusts & Smuts

2. Pucciniomycotina- Rusts • Economically very important as parasites of crop plants • Obligate parasites of vascular plants (ferns, gymnosperms, angiosperms) • Each species has very narrow host range • Generally do not kill host, but weaken and greatly reduce yields of seeds and fruits • Produce intercellular hyphae with haustoria

3. Rusts • Very large group of Basidiomycota - ~8400 spp. • Example – Puccinia graminis – stem rust of wheat – tremendous problem in wheat growing areas, Romans made sacrifices to the rust god – Robigus • Rust can exhibit the most complex life cycles in fungi

4. Rust life cycles • Long cycle or Macrocyclic rusts produce five different types of reproductive stages (spores and spore bearing structures), may alternate between two hosts • Short cycle or microcyclic rusts, one or more of these stages are lacking • Examine the different stages and then examine a life cycle

5. Stage 0 - pycnium • Pycnium (spermogonia) produces pycniospores (spermatia) • Haploid • Stage in which plasmogamy occurs • Vary in shape – flask shaped, flat or globose • Pycnium produces receptive hyphae – function as female structures • Pycniospores function as male gametes

6. Pycnia • Rusts are typically heterothallic • Plasmogamy occurs between pycniospore of one mating type and receptive hypha of another

7. Stage I - Aecium • Aecium produces aeciospores • Dikaryotic stage • Infects different host

8. Stage II - Uredinium • Uredinium produces urediniospores • Dikaryotic • Serves as the asexual (anamorphic) stage, since it infects same host

9. Uredinia • Form a pustule (acervulus) that breaks through the epidermis of host • Urediniospores are generally reddish in color – hence the common name - rusts

10. Uredinia

11. Stage III - Telium • Telia produce teliospores • Begin as dikaryotic cell, site of karyogamy so become diploid • Telium is a sorus on host plant

12. Telium • Teliospore is overwintering spore

13. Teliospores • Great variation in size, shape and color of teliospores in different species

14. Teliospore • Teliospore functions as probasidium – site of karyogamy and gives rise to basidium • Teliospores germinate and give rise to phragmobasidia (metabasidium – site of meiosis)

15. Stage IV - Basidium • Basidium produces basidiospores

16. Life cycles • A given rust species may produce all 5 stages or only some of these stages • Some produce only uredinia –could be classified in Deuteromycota • Some species require two hosts – heteroecious rusts • Produce pycnia and aecia (Stages 0 & I) on one host, uredinia and telia (Stages III & IV) on second host • Hosts are not closely related • Some only require one host - autoecious

17. Puccinia graminis • Stem rust of wheat – macrocyclic heteroecious rust • Teliospores overwinter, germinate in spring (karyogamy and meiosis) to form basida and basidiospores • Basidiospores can only infect and grow on alternate host – barberry bush • Gives rise to pycnia

18. Puccinia life cycle • Pycnia secrete nectar to attract insects to carry pycniospores • Pycniospores fuse with compatible receptive hyphae – plasmogamy • Hyphae from pycnia have formed aecial initials, once plasmogamy takes place, aecia develop (n + n)

19. Puccinia life cycle • Aeciospores are dispersed by wind, can only infect primary host – wheat • Dikaryotic mycelium develops in wheat stem and leaves and gives rise to uredinia with urediniospores

20. Puccinia life cycle • Urediniospores are dispersed by wind, continue to infect wheat throughout the summer • As wheat begins to ripen, uredinia gradually shift to producing teliospores, become telia (red sori become black sori)

21. Puccina life cycle • Teliospores overwinter, germinate next spring by forming basidia and basidiospores • Complex life cycle – took a number of years to work out that the forms on barberry was the same organism that was on wheat

22. Puccinia life cycle

23. Puccinia life cycle • In 1600’s, it was observed that barberry plants increased incidence of wheat rust, no one knew why • In 1800’s, Anton deBary discovered that all the stages were of the same fungus • deBary called father of modern mycology, worked with plant diseases, rusts and smuts, wrote the first text on mycology

24. Wheat rust • With the discovery of the life cycle of wheat rust, erdication programs were began to get rid of barberry • Practical importance of importance of understanding life cycles • However, this did not eliminate wheat rust • If winters are not too cold, urediniospores can overwinter and establish on wheat in spring

25. Wheat rust • In U.S. wheat belt, urediniospores overwinter in Texas and then migrate northward on winds through the great plains states into Canada • Also discovered that genetic recombination was not eliminated since rusts have a parasexual cycle operating so that they can carry out genetic recombination in absence of meiosis

26. Cedar apple rust • Gymnosporangium juniperi-virginianae • Appleis alternate host – produces pycnia and aecia • Junipers are primary host but there is only a telial stage no uredinial stage so that elimination of either host is effective in controlling the disease

27. White pine blister rust • Cronartium ribicola • White pine is alternate host – produces pycnial and aecial stages • Gooseberries and currents are the primary host – produce uredinial and telial stages • Asexual stage is not on economically important host so eliminating it is effective

28. Ustilaginomycotina - Smuts • Smuts – so called since they form black dusty spore masses on hosts that they infect ~1200 spp. • Commonly infect the reproductive structures of non woody angiosperms (grasses) – anthers, ovaries, embryos • Grow in culture as yeast like cells

29. Smuts • A number of economically important plant pathogens – corn smut, Ustilago maydis, loose smut of oats, Ustilago avenae, bunt and stinking smut of wheat, Tilletia spp.

30. Smut life cycle • Haploid phase is limited • Plasmogamy takes place between compatible cells – basidiospores, conidia, yeast cells or combinations • Dikaryotic mycelium grows intercellularly in plant host • Some species form conidia for asexual reproduction

31. Smut life cycle • When dikaryotic mycelium reaches sporulation stage, it consist of short dikaryotic cells • Cells round up, form thick walls and differentiate into teliospores • Teliospores are the overwintering spores • Teliospores germinate to produce basidia

32. Smut teliospores • Teliospores may be individual or grouped in spore balls

33. Smut basidia • Ustilago Tilletia

34. Ustilago life cycle

35. Tilletia life cycle

36. Urediniomycetes Terminal teliospores 4 basidiospores produced on sterigmata Plasmogamy – specialized cells May require 2 hosts Obligate biotrophs Hosts include angiosperms, gymnosperms, ferns Ustomycetes Intercalary teliospores Variable number basidiospores, no sterigmata Plasmogamy – no specialized cells Never require 2 hosts Facultative biotrophs Hosts include angiosperms only Comparison of Rusts & Smuts