An isolate of Fusarium moniliforme (Sheldon) (JW #1) was discovered on greenhouse-grown jimsonweed in Mississippi, U.S.A., in 1990. Applications of aqueous suspensions of spores/mycelia (>1 × 107 propagules ml−1) grown on potato-dextrose agar to the potted soil in which 2- to 4-wk-old jimsonweed plants were grown caused local lesions or mosaic-like patterns on the leaves and inhibited growth. Application of lesser doses to the leaves only produced no visual effects. When the fungal suspensions were applied at higher dosages (>1 × 107 propagules ml−1) either by soil drench or subirrigation, symptoms such as local lesions or a mosaic-like pattern on the leaves appeared and plant growth was inhibited. When the fungus was grown on an autoclaved rice medium and the ground mixture applied to jimsonweed plants, the plants wilted within 24 h and died after 48 h. Crude and cell-free filtrates of the fungal-rice culture also killed 1- to 2- and 3- to 4-week-old plants after 24 to 72 h. A major toxin identified was fumonisin B1, isolated from fermented rice at 400 μg g−1. Fumonisin B1 applied in water at 2.5 μg 100 μl−1 to excised jimsonweed leaves caused the same symptomology (i.e., soft rot diffusing along leaf veins) within 24 h as the cell-free extract or the crude culture filtrates. Similar damage occurred to intact plants treated with crude or cell-free filtrates or purified aqueous fumonisin B1 solutions.

Very little is known about the physiological interactions between plant hosts and symptomless endophytic fungi despite their widespread occurrence. We investigated the impact of two such fungi, Colletotrichum musae and Fusarium moniliforme, upon the photosynthetic capacity of two crop plants, banana and maize, respectively. Endophyte-free plants were obtained first and then infected with the fungi. Measurements of total chlorophyll content revealed very little difference between endophyte-free and infected plants of banana, whereas in maize they showed 50% reductions in the endophyte-infected plants. The maximum photochemical capacity (Fv/Fm ) 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 Fv/Fm to plants typical of nonstressed conditions, whereas the endophyte-infected plants showed a reduction of approx. 15%. Unlike banana, infected maize plants displayed values of Fv/Fm similar to those of control and endophyte-free plants, indicating that the maximum photochemical 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 μmol m−2s−1 whereas the control and endophyte-free plants were saturated at much higher photon flux densities. In banana the effect seemed to be due to an impairment of electron transport in the thylakoid membranes. By contrast, reduction of the photosynthetic capacity in maize was due to a reduction in chlorophyll content, leading to a decrease in the electron transport components and a consequent reduction in carbohydrate synthesis. It is possible that the reduction in the maximum yield of photosynthesis in both crops was caused by toxins produced by the fungi. Nevertheless there were no major macroscopic effects on the plants to indicate disease symptoms.