Fasciation (or cresting) is a relatively rare condition of abnormal growth in vascular plants in which the apical meristem (growing tip), which normally is concentrated around a single point and produces approximately cylindrical tissue, instead becomes elongated perpendicularly to the direction of growth, thus, producing flattened, ribbon-like, crested, or elaborately contorted tissue.
While radiation from the Fukushima disaster in 2011 certainly has had an impact on the plant life in the surrounding area, the above-displayed photograph doesn't necessarily show the mutation of daisies due to nuclear radiation. It is much more likely that this image simply displays an example of fasciation.