PHENOLIC CONTENT OF DAYLIGHT-EXPOSED AND SHADED FLOATING LEAVES OF WATER LILIES (NYMPHAEACEAE) IN RELATION TO INFECTION BY FUNGI

Under suboptimal growing conditions (e.g. a lack of sunshine), floatin g leaves of Nymphaea alba and Nuphar lutea can become heavily infected with the fungi Colletotrichum nymphaeae and Pythium F, respectively. These fungi normally act as decomposers of senescent leaves. Mature le aves of Nymphaea alba and Nuphar lutea contain high concentrations of phenolics, secondary substances known for their fungistatic properties . The production of these compounds requires energy and primary metabo lites. The hypothesis that suboptimal growing conditions reduce the ab ility of nymphaeids to maintain a sufficiently high level of phenolics , thereby making them more vulnerable to infection by fungi, was teste d. Outdoor mesocosm experiments were used to examine the response of f loating leaves of Nymphaea alba and Nuphar lutea to reduced light avai lability. Shading significantly reduced the phenolic content of the le aves. This was accompanied by higher disease severity. The outcome of this experiment is also discussed in relation to the higher nitrogen c ontent measured in shaded leaves.