Color analysis of rust symptoms caused by shiso rust mites

Abstract

To determine rust symptoms caused by shiso rust mites (Shevtchenkella sp.), perilla leaf color was quantified by image analysis, and symptomatic and healthy leaves were compared. On symptomatic leaves, the blue (B) value in the red, green, and blue (RGB) color system was lower on the back side of the leaf, whereas the red/green (a*) values in the L*a*b* color system were lower on both sides of the leaves, compared with those of healthy leaves. Complex color elements were investigated by principal component analysis to determine rust occurrence. Using the RGB system, less green (B) on the back indicated rust. Using the L*a*b* system, a* value on the front indicated rust and suggested that size may also contribute to the results.