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1. Is it always necessary to identify species in a study?
2. Are there any keys available to identify species of glomalean fungi?
3. Why aren’t you willing to identify species from field-collected samples?
8. When you make an identification, what kinds of specimens do you need?
1. Is it always necessary to identify species in a study?
No, but like in all scientific studies, the more information collected to characterize components of an experimental system, the better. At the very least, when dealing with native fungi to conduct an experiment, we think it is important to estimate the number of species present (by separating into classes based on major differences in spore appearance).
2. Are there any keys available to identify species of glomalean fungi?
All of the published keys (Schenck, Trappe, Hall) are based on published descriptions, and as everyone knows, many of these are vague in crucial diagnostic criteria or don't have enough information based on what we know today. Others lack so much critical information that they are virtually useless. INVAM and BEG have been trying to collaborate for far too many years now to develop a computerized database and ID system for CD, but we can't free ourselves of all our other responsibilities at the moment to do all the necessary work (and keeping up with operating systems compatible with "expert systems" is a bit frustrating). At the present time, we have generated a genus-level key based on four morphological character sets, but it shouldn't be long before we have descriptions of the most common (geographically or as experimental fungi) species based on living reference cultures.
3. Why aren't you willing to identify species from field-collected samples?
The short answer: the spores are either too deteriorated, too parasitized, or too old to reliably identify them. Remember that spores are single cells with ALL of the morphological properties that identify a species present in only one structure: the cell wall. This cell wall is easily modified, so its true properties are obtained only from new healthy spores. These can be obtained in the field where samples are lucky enough to capture newly-formed spores, but we don't see this happening often enough in our experience. Based on personal experience and that of other scientists, sand dunes are a habitat that seems to impact least on spore properties, probably because they are the closest environment to uncontainerized pot cultures.
4. It seems like no matter what preservative is used to store spores long-term, all cause significant changes in spore morphology. What can be done?
This is a tough one. Some preservatives can have direct effects on spore structures, but unfortunately, they all do one thing which causes inevitable changes: they kill the cells. With cell death, some structural disintegration occurs regardless of the environment in which spores are stored. When we want to maintain healthy looking spores for up to 6 months, we store them in a solid sterile substrate (usually coarse sand) slightly moistened with sterile distilled water. Spores stay alive and hence retain much of their structure. This applies even to Gigaspora spores, which discolor quickly as a result of any physical manipulation. We ship carefully selected spores for molecular studies in such an environment. We now are also looking at lyophilization, not only for long-term storage of inocula, but to preserve spores as well.
5. Can you briefly indicate one or two properties of spores which will separate them into different genera?
This information now is available in a genus-level diagnostic key, which separates all genera according to (i) mycorrhiza morphology, (ii) mode of spore formation, (iii) subcellular structure of spores, and (iv) mode of spore germination.
6. The hardest genus in which to identify species seems to be Glomus. The differences between them don't seem to be that great. Are there other characters that can be used for this genus?
Not that are morphological. The problem here is that the differences between species are narrowing as more species are found. This trend should not be surprising if the hypothesis that both parental and descendant species have remained alive through geologic time (most large gaps between species or groups of species are the result of extinction events). For example, there are only five species of Gigaspora, yet the differences between them are few and small. Species in other genera seem to have bigger differences because of complexity with inner wall structure, but many of these properties don't help to define species. In reality, the differences between Acaulospora and Scutellospora species aren't any greater than that amongst Glomus species. That is why such care must be taken to fully characterize the variation within an isolate and between isolates of the same species to define truly heritable distinctions between a species and all others.
7. I isolate a fungus and manage to establish it in a monospecific culture. It resembles a described species, but I can't be sure based on the description. What can I do to confirm its identity?
First, look on this website for a description of the species from a living reference culture. Compare the traits of your fungus with those in this description. If that is not sufficient, or if the photos you see cause confusion, then write to us and request the loan of voucher slides of the reference isolate to examine specimens with your particular microscopic equipment.
8. When you make an identification, what kinds of specimens do you need?
In general, I require a sample of the pot culture contents so that I can follow all stages in the transition of healthy spores under a stereomicroscope to mounted spores fully cured in the mounting medium. When only slides are sent, they usually are more than one month old (sometimes years), and details of spores can disappear or become faint compared to when they were first mounted.