Biology and Identification of Fungi by Christine Balk, Chelsi Abbott, and A.D

CONTINUING EDUCATION UNIT Biology and Identification of Fungi By Christine Balk, Chelsi Abbott, and A.D. Ali will help you understand the complexities of fungi and Learning Objectives the importance of identification factors. • Discuss the complexities of fungi. Fungi (singular: fungus) are some of the most interest- • Describe how fungi can be both beneficial and detrimental. ing living organisms of the biological world. They are also • explain the general life cycle of a fungus. the most prevalent tree pathogens, when compared to • Describe what to look for when identifying fungal fruiting bodies. bacteria, viruses, etc. There are about 100 thousand dif- CEU(s) for this article apply to: A, T, L, Bs. ferent species currently identified, and there are still many more that are not yet identified—an estimated 5.1 million species (blackwell 2011). Fungi are eukaryotic organisms; that is, they are organisms that do have membrane- Biology bound organelles inside cells. Other examples of eukary- Trees in the urban environment are planted with good otic organisms are animals and plants. Fungi are closer in intentions but tend to have many problems. One biotic relation to humans than plants. Like humans, fungi are problem for trees is wood decay fungi. This group of heterotrophs, which means they need to consume organic organisms can be very difficult to understand and iden- matter to survive. Plants are autotrophs, meaning they tify. They are important to know for safety and for tree produce their own food (i.e., photosynthesis). It is because risk evaluations. This article, the first of a two-part series, fungi are heterotrophs that they are so crucial to the forest ecosystem. by decomposing organic matter, fungi recycle valuable nutrients back into the forest floor for plants to use. Other than the recycling of nutrients, some fungi form symbiotic relationships with plant roots. These fungi that form this mutualistic relationship are called mycorrhizae, and in this case, the fungus benefits by having direct access to carbohydrates, while in turn increasing the absorptive surface of the roots. Many fungi also provide food, antibiotics, and other resources for human use. It is true that there are some poisonous species, and species that are parasites, but overall, fungi are extremely beneficial, even though they have a generally negative connotation. The most common structure associated with fungi is the mushroom. we will examine the structure of the mushroom later in this article. It is often misconceived that the fruiting body of a fungus (i.e., mushroom) is the actual organism. However, the actual organism is made up of hyphae (singular: hypha) that grow underneath the surface where the fruiting bodies appear (Figure 1). Hyphae are long, thread-like structures. to the naked eye, they look like white to gray ‘fuzz.’ These hyphae rep- resent the vegetative structure of the fungus, while the fungal fruiting body is merely the reproductive structure Figure 1. Generalized diagram of mushroom anatomy. that releases spores (the dispersal stage of a fungus). The 12 | Arborist•News | www.isa-arbor.com CONTINUING EDUCATION UNIT hyphae (or collectively, mycelium) of the fungus grow throughout the soil wherever nutrients and space are available, whereas the fruiting bodies of fungi appear only when environmental conditions are right. These conditions include: cool, shady locations with high humidity (e.g., under trees), and a food source (e.g., dead plant material). Perfect environmental conditions are crucial for fruiting body growth and can explain the phenome- non of random mushroom sightings from year to year in the same spot. One exception to this rule are perennial conks, which are woody fruiting bodies. While there are many fungi that are beneficial to the landscape, what most concern arborists are fungi that are considered tree pathogens or parasites. Largely, these types of fungal organisms fall under two categories: basidiomycetes and ascomycetes. Basidiomycetes are generally considered the mushroom-forming fungi and typically encompass most wood decay fungi and rusts, the latter Figure 2. General life cycle of fungi (Luley and Ali 2009). produce non-traditional fruiting bodies. Ascomycetes encompass more of the foliar diseases on trees. The differ- ence between basidiomycetes and ascomycetes comes down to the number of spores and the structures on which the spores are borne. Basidiomycetes have four spores and are borne on a club (basidium), while ascomycetes have eight spores and are borne in a sac (ascocarp). Life cycles of fungi differ depending on the family. They are largely based on the spore type and whether it was reproduced sexually or asexually. Some fungal organisms, like rusts (basidiomycetes), have complex life cycles that require more than one host to complete, while others, like apple scab (ascomycete), have a simpler life cycle Figure 3. Foraged mushrooms, which display the vast variety of shapes, sizes, and require only one host to complete. In general, fungi textures, etc. of mushrooms/fungi. differ in reproduction and overwintering, but regardless of the fungal family, all fungi disperse via spores by wind, soil, vectors, or even through vegetative means, such as doesn’t bring about any new genetic modifications, but is rhizomorphs (e.g., Armillaria) (Figure 2). After dispersal, quick and best for the fast spread of fungi. Sexual repro- some fungi infect the plant indirectly, through wounds, duction takes more time and energy but allows for genetic and begin colonizing the plant tissue. However, certain adaption. This adaption is good for acclimating to new fungi can infect directly into the plant cell, without environments and obstacles that could get in the way of requiring a wound or outside help. These fungi use fungal growth. Without sexual reproduction, fungi would appendages termed haustoria (singular: haustorium), or die. arm-like structures that penetrate plant cells. Once the fungal organisms have entered and colonized the plant Morphology and Identification tissue, enzymes are released from the fungus to degrade Fungal identification can be very difficult. Every part of host tissue. Symptoms, or the plant’s reaction, to this the fruiting body needs to be observed. Regarding mush- degradation can show up within days to weeks to months, room-forming fungi, the mushroom or conk is consid- depending on the latency of infection and the overall vir- ered the fruiting body. There are many different shapes to ulence of the pathogen. Once the fungus can obtain mushrooms, so their cap shape, spore surface, gill attach- nutrients from the host, it will enter an overwintering ment (if present), consistency of the stem, and more, all stage until the environmental conditions are right to start need to be considered to arrive at an accurate identifica- the dispersal and infection process all over again. tion (Figure 3; Figure 4). Basidiomycetes and ascomycetes have both sexual and Here are some attributes to consider when trying to asexual reproduction capacities. Asexual reproduction identify mushroom-forming fungi: u CONTINUING EDUCATION UNIT L E D E I R KODI KODI ANTHONY WILLIAMS ANTHONY Figure 4. Compilation of fungal fruiting body differences. a) A mushroom Figure 5. a) Cedar quince rust on hawthorne; note also the orange spore with a porous spore surface, glossy cap and textured stem; B) gills of color on the leaf below swellings; b) the end result of a spore print. a Lactarius species, which secrete an exudate when cut (notice gill attachment); c) the porous underside of hen of the woods (Grifola frondosa); and d) side view of the northern tooth fungus, which has a tooth-like spore surface. • What is it growing on (in)? Deadwood, living G. lucidum, are wood-like, and don’t bruise when wood, bark, etc. touched. • At what time of year is it growing? • Does it have an odor or taste? If so, what does it • Where is it growing? Some mushrooms have smell like? For instance, Lactarius camphoratus can specific geographic range. smell sweet like honey maple syrup, and many • What is the host? For example, Ganoderma zonatum Russula species taste peppery. As a precautionary grows specifically on palms. note: Never attempt to taste mushrooms if you are • What color is the cap, stem, spores? Spore color not absolutely certain of the species in question. can be a crucial identification factor. Some can cause nausea, abdominal pain, halluci- • Does it have any defining characteristics such as a nations, and even death. veil (i.e., skirt) around the stem? • What is the spore color? A spore print is a great • What does the spore surface look like? Does it tool for identification. You can take a spore print have gills? Pores? Teeth? (Figure 3; Figure 4) by laying the spore surface (spore side down) on • Does it bruise easily? Some fungi bruise specific both black and white paper. Leave it overnight and colors, or have easily bruised flesh. For example, note the color of the spore print underneath the some Lactarius species bruise certain colors when cap the next day (Figure 5). touched. Whereas others, such as G. sessile (previously 14 | Arborist•News | www.isa-arbor.com CONTINUING EDUCATION UNIT Identifying mushroom-forming fungi can mostly be done without the use of magnifying equipment. Online resources are available to aid in identification (Fischer 2007; Gillman and Salzman 2011; Mushroom World 2018). However, when identifying non-mushroom forming fungi (like most foliar pathogens), a hand lens and microscope are required. This is because the fruiting bodies of these types of fungal organisms are microscopic, including structures like acervuli, pycnidia, chasmothecia (formerly cleistothecia), and others, which look like small black spots on the surface of the leaf (Figure 6). This means that they cannot be positively identified without a microscope. For example, the pycnidia of one fungal species can look almost identical to the pycnidia of another species.

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