In researching Fungi, I have found that it is an interesting subject in and of itself. They are frequently the bane of C&S growers, but they demand grudging respect, at least. Fungi are heterotrophic plants, meaning they are only equipped to consume organic materials as food. In addition, they do not possess any chlorophyll, and so must obtain only pre-synthesised nutrients to survive. What this means for the host plant of a fungus, is that, in one way or another, the fungus robs the plant of the nutrients it has worked hard to produce. In some cases, Fungi have a symbiotic relationship with their hosts, but the species of concern to hobbyists are parasitic and remarkably destructive.
In general, over-watering and high humidity are major factors in the introduction of a fungus to a collection. Spores of different Fungi can travel in different ways, but almost all can be transmitted by wind and by water (including through splashing and spraying). Fungi can have one or more types of spores, all of which require moisture for germination. Sporangia, a Greek-derived word meaning seed vessel, are exactly as their name implies. They are small sacs, inside of which seeds are produced. Zoospores are formed inside sporangia, and are released under moist soil conditions. They are wall-less, asexual cells, equipped with two flagella, allowing them to travel by swimming. They can travel impressive distances through soil in this manner, until they find a possible host. They are attracted to wounds, and by the amino acids that roots discharge. Interestingly enough for us, they are also particularly attracted to succulent areas of roots. Upon making contact with a root, zoospores lose their flagellum, form a cell wall and germ tube, and begin growing and infecting their new host.
The third type of fungal spores are oospores. These are a type of resting cell, and they are sexual. Oospores remain dormant until conditions are optimal for their activation. They are encouraged by high calcium levels in the soil, and are inhibited by light. Chlamydospores are asexual resting spores, and they are formed within, or at the tips of, the hyphae (one of the thread-like elements that form the mycelium, or vegetative structure, of a fungus). Chlamydospores only germinate when soil is moist and warm, but they are capable for surviving for months in dry soil.
Most of the information in Cacti and succulent literature treats Fungi as a solitary issue. While there are some general truths about all Fungi, and how to deal with them, this treatment of the issue is overly broad. I found the specifics of some individual fungi very pertinent to my own experience.
