Two ways fungal spores can affect cotton color

Authors: Chun, David; Rodgers Iii, James

Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2011
Publication Date: 5/1/2011
Citation: Chun, D.T., Rodgers III, J.E. 2011. Two ways fungul spores can affect cotton color. Journal of Cotton Science. 15:52-60.

Interpretive Summary: When cotton is stored under very humid or wet conditions, the fiber will often become discolored, usually becoming more gray or yellow. Because of the recent historical interest in byssinosis, many studies looking at the bacterial relationship with cotton were done. So now when microbial damage occurs to cotton, a bacterial agent is often initially sought. Yet historically, fungi are usually attributed to causing graying and yellowing in the field due to weathering. In our own work here dealing with excessive moisture content of cotton during storage, a mycological influence is often found. For a long time, we have wondered if the ever ubiqueously present fungal spores could cause discoloration since early workers have suggested that cottons under high humidity will often become grayer and more yellow during storage. Yet under conditions of cotton storage, moisture content should be too low for bacteria to be active. However, fungi are capable of activity under much lower water pressures. Since it is known that fungi can germinate under lower moisture conditions than bacteria can grow in, we have long speculated that perhaps when spores germinate, the production of a germ tube which increases the overall size of the fungus many times greater than the area of the original spore, that this increased size may be picked up as color changes. A study was initiated where fungal spores were applied to the surface of cotton and permitted to germinate. Since it has been suggested that the higher sugar content associated with stickiness would favor microbial activity, resulting in lower Rd and higher +b readings, cottons with different levels of stickiness will be used. The color results of this study, by both HVI and a spectrophotometer, will be reported. The work done in this study demonstrates that the presence of the spores alone can account for color changes; and further color change can occur if the conditions permit the spores to germinate. This work has considerable value in helping to interpret and predict cotton condition under improper storage of cotton in seed modules and in warehouses.

Technical Abstract: For a long time, we have observed that cotton can undergo color change when moisture conditions of the cotton sample would not be expected to support bacterial activity which normally requires free water. Several fungi can grow under low moisture pressures. It has been speculated that the spores present on cotton can occasionally germinate when moisture or nutrient conditions are favorable. When spores germinate, germ tubes are produced. These extensions from the spore may be several times the size of the original spore so that even if conditions stop fungal growth, it might be possible for this larger fungal body to influence the cotton color. The results from the study demonstrate that a heavy spore presence itself can influence color change. If the conditions permit growth, the heavy spore presence may produce limited growth that is detected as color changes.