Spathe Color Variation in Anthurium andraeanum Hort. and Its Relationship to Vacuolar pH

The relationship between vacuolar pH in Anthurium andraeanum (Hurt.) and spathe color, cultivar, developmental stage, spathe location, spathe surface differences, and time after harvest was investigated with the overall long-term objective of developing a methodology for engineering blue-colored spathes. Chromospectral analysis of the pigmentation was also studied. Six experiments were conducted involving 23 cultivars of anthurium with each experiment arranged in a randomized complete block design with five replications. Spathe color was associated with vacuolar pH with the whites and greens having the highest pH (average 5.65) followed by corals (5.38), pinks (5.20), reds (5.10), and oranges (4.5). In general, there was correspondence between the lightness of the pigmentation (L*) and the pH values with the lighter colors having higher pH values. There were, however, significant differences among cultivars within the color groups. Whereas spathe pH decreased with aging, there was no difference in the spectral data, suggesting that factors other than anthocyanin content may be contributing to the pH difference. There were no differences in pH between locations sampled on the spathe nor between the spathe surfaces provided there were no differences in color intensity (L*). The pH increased with vase life in two of three cultivars tested with pH values showing an association with increases in a* and b* (chromospectral data) reflecting a bluing effect. The importance of the results to engineering blue-colored spathes in anthurium is discussed.