Abstract
Evidence is presented which indicates that certain fluorescent spots observed in raw cotton under ultraviolet light are associated with the prior growth of microorganisms on the fiber. A striking and characteristic type of spot which fluoresces bright greenish- yellow was noted frequently in classers' samples from the 1954 cotton crop grown around Yuma, Arizona, and Brownsville, Texas. It was also, but less frequently, noted in samples from other regions of Texas and occasionally in samples from other states. Spots of this particular type have been shown to be associated with growth on the fiber of the fungus Aspergillus flavus, three principal lines of evidence having been obtained : (1) the very common occurrence of A. flavus in the fluorescent spots; (2) the production of a fluorescence of similar appearance by A. flavus growing on cotton fiber in pure culture; and (3) the similarity of the fluorescent substances from field- and A. flavus -incubated fiber in chromatographic behavior and absorption spectrum. The fluorescent fiber in commercial samples exhibited abnormally high swelling in alkali and decreased strength.
A white-fluorescent spot, less striking and less easily recognized than the above, has been found to be associated with certain isolates of the fungus Alternaria sp. Several other common types of microbial growth on cotton prior to harvest were not accom panied by distinct differences in fluorescence as compared with uninfected fiber, indi cating that under the conditions here employed ultraviolet examination is not a general tool capable of detecting all of the types of microbial infection present in commercial cotton.
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