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
Apple is 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. Comparison of Rusts & Smuts
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