The Use of Colors as an Alternative to Size in Fusarium graminearum Growth Studies

Abstract

Size-based fungal growth studies have limitations. For example, the growth in size stops in closed systems once it reaches the borders and poorly describes metabolic status, especially in the stationary phase. This might lead mycotoxin studies to unrealistic results. Color change could be a viable alternative, as pigments result from a mold’s metabolic activity. This study aimed to verify the possibility of using gray values and the RGB system to analyze the growth of Fusarium graminearum. It consisted of color and area measurements using ImageJ software for specimens grown in yeast extract agar (YEA). The results suggest the utility of color and gray values as reliable tools to analyze the growth of F. graminearum.

RGB Imaging as Tool to Analyze the Growth of <em>Fusarium graminearum</em> in Infected Oats (<em>Avena sativa</em>) and Rice (<em>Oryza sativa</em>)

“…The only source of light was a round LED attached to the bucket's lid. The photos were then processed on the ImageJ software (FIJI edition, National Institutes of Health, Bethesda, MD, USA), developed by the National Institutes of Health [15] using the method described by Cambaza, et al [8]. ImageJ allowed the determination of average intensities of the RGB components from the photos.…”

“…The predictability of color change in F. graminearum as it grows as already been demonstrated in yeast extract agar [8] but not yet in food matrices. Therefore, the current study aims to verify if oats and rice infected with F. graminearum present predictable patterns of color variation if incubated for 16 days at different aw settings.…”

“…radius or diameter) as a growth measure assuming that the organism matures as it becomes larger, by the same logic used for plant animals and other types and organisms. However, this approach has several limitations because it provides little information about the organism's metabolism and it may result in misinterpretations if the mold grows irregularly or if the mold attains the maximum size in a closed system [8,9]. A viable alternative to this issue is digital imaging combined with statistics, an approach nowadays gaining relevance in studies of FHB because of their potential to monitor the extent and severity of Fusarium infection in grains [10,11].…”

“…When F. graminearum is grown in yeast extract agar in a Petri dish, the so-called stationary phase starts when it reaches the plate's border and stops expanding, keeping the same size until it eventually depletes the nutrients and its spores endure in a state of dormancy [8,13]. However, phases like lag and stationary, represented by size-based models as apparently less active, are exactly the circumstances at which the fungus has to employ the highest effort to ensure its survival, in the former because the organism needs to adapt to a new medium and in the latter because the medium becomes exhaust.…”

“…However, phases like lag and stationary, represented by size-based models as apparently less active, are exactly the circumstances at which the fungus has to employ the highest effort to ensure its survival, in the former because the organism needs to adapt to a new medium and in the latter because the medium becomes exhaust. Besides the well-known fact that molds produce secondary metabolites during the stationary phase [14], a previous experiment demonstrated that F. graminearum keeps changing its surface color (and the color of the agar medium) even during the stationary phase [8].…”