Chytrids
Phylum Chytridiomycota
Chytrids are an ancestral group of fungi, that are mostly aquatic parasites or saprotrophs. They are known for causing plant diseases such as brown spot on corn, crown wart on alfalfa, and black scab on potatoes, which can be significant for farmers, particularly during rainy summers. This group is interesting, evolutionarily, since their parasitic nature and ancestral position in the fungus kingdom may indicate that the earliest fungi on Earth were aquatic and parasitic (and zoosporic), and later became terrestrial and saprotrophic, and eventually mutualistic with plants.
Ecology and Form
Usually siphonous or coenocytic (=tubes without cross walls)
Mostly aquatic and with zoospores (flagellated spores)
Parasites and saprotrophs
Life cycle
Chytrids exhibit a haplo-diplontic lifecycle, unlike other fungi
The sporophyte produce spore cases (sporangia) which create flagellated spores (zoospores) through meiosis
Zoospores are dispersed and germinate into gametophytes
Gametophytes mature to produce male and female sexual structures (gametangia)
Gametangia produce motile male and female gametes which fuse in the water to produce zygotes
Symbioses
Plant pathogens
Brown spot (corn)
Crown wart (alfalfa)
Black wart/black scab (potato)
Diversity
~790 spp. e.g. Synchytrium, Batrachochytrium
Geologic Age
Mesoproterozoic (~1.5 billion years ago) - present
Macro-fossils from the Devonian
Most ancestral true fungi
Above: Lifecycle of chytrids
Above: Black wart (Synchytrium endobioticum) in potato
Below: brown spot (Physoderma maydi)
Questions for Thought
How are the chytrids similar to the mucuromycetes?
How are chytrids similar to the slime molds?