Intraspecific variation in the ultraviolet colour proportion of flowers in Brassica rapa L.

In Brassica rapa L., intraspecific variation in the ultraviolet (UV) colour proportion invisible to humans but visible to insect pollinators, was investigated by UV-photographing. After digitization of each photograph, the UV-absorbing area (UVA) and total flower area (FA) were evaluated by means of image analysis. The ratio of UVA to FA represented the UV colour proportion (UVP). Nested anova indicated that the proportion of the variance caused by the genotypic effect was largest for UVP, and anova indicated that the F-value for UVP was larger than that for FA. These results indicate that UVP is very stable within a genotype. That is, there was almost no additional variation caused by plants and branches. In contrast, UVP varies widely between genotypes with respect to FA. The large differences in the UVP of B. rapa flowers are likely to be distinguishable by insect pollinators, which might use these differences as visual cues in their foraging flight.