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The figure below shows the change in cumulative number of living accessions in INVAM since it was transferred to West Virginia University in 1990. The greatest number of additions occurred during the first two years, in part because an extensive collection already present at WVU was merged with the collection from Florida. From 1996 onward, new accessions have been deposited at a relatively constant rate, consisting of an eclectic mix of inoculum types: (i) spores mailed in folded filter paper, (ii) "whole" inocula of single species, (iii) "whole" inocula of species mixtures, (iv) trap pot cultures (one or more generations removed from field soil), and (v) on rare occasion, mycorrhizal roots. The plateau, and even a slight decline, in total number of accessions is the result of many deposits consisting of trap cultures from exotic areas (saltwater wetlands, tropical sites with high organic matter, and desert sites with naturally low inoculum potentials), and monospecific cultures that failed to establish or were unable to persist for more than 2-3 generations in our greenhouse environment. Attrition of established cultures (propagated at least four generations) has been very low, cumulatively less than 7%. When losses occurred, causes varied but the most common was susceptibility to microbial decay or degradation during prolonged storage (often species in Acaulospora, Glomus, and Scutellospora whose spores are larger and moderately to darkly pigmented).
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