Symptomless infection of banana and maize by endophytic fungi impairs photosynthetic efficiency

Very little is known about the physiological interactions between plant hos ts and symptomless endophytic fungi despite their widespread occurrence. We investigated the impact of two such fungi, Colletotrichum musae and Fusari um moniliforme, upon the photosynthetic capacity of two crop plants, banana and maize, respectively. Endophyte-free plants were obtained first and the n infected with the fungi. Measurements of total chlorophyll content reveal ed very little difference between endophyte-free and infected plants of ban ana, whereas in maize they showed 50% reductions in the endophyte-infected plants. The maximum photochemical capacity (F-v/F-m) was measured in order to determine if the plants had any photoinhibitory effect caused by biotic or abiotic factors. After 45 d of growth, endophyte-free banana plants had similar values of F-v/F-m to plants typical of nonstressed conditions, wher eas the endophyte-infected plants showed a reduction of approx. 15%. Unlike banana, infected maize plants displayed values of F-v/F-m similar to those of control and endophyte-free plants, indicating that the maximum photoche mical capacity was not affected by infection. The light response curves of both species showed that the photosynthethic capacity was severely reduced in endophyte-infected plants, reaching saturation at c. 400 mu mol m(-2) s( -1) whereas the control and endophyte-free plants were saturated at much hi gher photon flux densities. In banana the effect seemed to be due to an imp airment of electron transport in the thylakoid membranes. By contrast, redu ction of the photosynthetic capacity in maize was due to a reduction in chl orophyll content, leading to a decrease in the electron transport component s and a consequent reduction in carbohydrate synthesis. It is possible that the reduction in the maximum yield of photosynthesis in both crops was cau sed by toxins produced by the fungi. Nevertheless there were no major macro scopic effects on the plants to indicate disease symptoms.