A New Method with a Pair of Polarizing Filters for Quantification of Luster of Corollas of Japanese Gentian Flowers for Determination of Growth Stage

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Japanese gentian (Gentiana triflora var. japonica) is one of the most important floriculture crops grown in Iwate Prefecture; it is grown mainly for cut flowers, but the flowers gradually deteriorate after harvest, and lose commercial value. To maintain the commercial value for as long as possible after harvest, various techniques for determining the growth stage of cut flowers have been studied. We previously reported that the spectral radiance of the corollas of older flowers was significantly lower than that of younger ones at wavelengths between 700 and 900 nm. We later reported that corollas of flowers that had just opened glittered significantly in the UV region when irradiated with UV light, and suggested that this glittering could be a useful guide for determining the growth stage of flowers. Because these studies did not examine the usefulness of information possibly contained in the luster of corollas, we developed a new, efficient, low-cost system to image luster by using a pair of polarizing filters, and propose a new method for quantifying luster as, for example, an index of smoothness. We then examined the relationship between this information and the growth stage of flowers. The index of smoothness showed a linear relationship with growth stage, and could distinguish fairly well between young flowers and old flowers.