Lsrc. Pinto et al., Symptomless infection of banana and maize by endophytic fungi impairs photosynthetic efficiency, NEW PHYTOL, 147(3), 2000, pp. 609-615
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.