TOXICITY IN PLANTS (PHYTOTOXINS)    

The genus Fusarium is known to produce many mycotoxins that attack plant cells.  These are called phytotoxins (substances that are toxic to plants), and they may break down the cell walls of the host plant, or help dissolve and release nutrients (in the case of the combination of fusaric acid and lycomarasmin).   If these fungi did not contain such toxins, they would not be able to attack the cells of the plant to gain entry into the plants -i.e. they would not be toxic to plants. It is also true that but most of these phytotoxins are also toxic to humans, animals and other living organisms. 

We will look at the following phytotoxins that have been reported from Fusarium species, especially F. oxysporum:

Fusaric Acid: 1, 2

Lycomarasmin: 1, 2

Lycomarasmic Acid: 1, 2

Nep ? (24kDA protein): 1, 2

Fusaric Acid.  

"Fusaric acid is a well-known phytotoxin that is produced by several Fusarium species, particularly pathogenic strains of F. oxysporum causing wilt diseases of a great variety of plants (Gaümann, 1957; Kern, 1972). Although fusaric acid is not generally regarded as a mycotoxin, some attention will be given here to fusaric acid production by F. oxysporum because fusaric acid as well as certain other phytotoxins such as lycomarasmin and lycomarasmic-acid produced by F. oxysporum (Gaümann & Naef-Roth, 1950; Kern, 1972) are chelating agents and may be involved in certain diseases of abnormal bone development in animals (see F. moniliforme, abnormal bone development). In addition, fusaric acid is toxic to mice (intraperitoneal LD50 80 mg/kg) and death caused by the lethal dose has been attributed to its hypotensive effect (Hidaka et al., 1969). The ability of fusaric acid to cause significant decreases of blood pressure has also been observed in cats, dogs, rabbits, and rats and has been attributed to the inhibition of dopamine-3-hydroxylase (Bilai et al., 1975; Hidaka, 1971; Hidaka et aI., 1969). Fusaric acid has been administered to humans in clinical trials as an antihypertensive agent (Matta & Wooten 1973), in the treatment of Parkinson's disease (Hidaka, 1971; Matta & Wooten, 1973), and at dosage rates up to 1200 mg/day in the treatment of drug addiction (Pozuelo, 1976).

A positive correlation between pathogenicity to plants and the amount of fusaric acid produced has been found for many strains of F. oxysporum (Kern, 1972). The production of fusaric acid in Richard's medium incubated at 21°C for 21 days has been reported for a weakly pathogenic (IMI 166917) as well as a virulent (IMI 186539) strain of F. oxysporum f. sp. carthami by Chakrabarti et al. (1976) and Ghosal et al. (i977b), respectively. However, Chakrabarti & Basu-Chaudhary (1980) found that an unspecified virulent strain of this fungus produced three times more fusaric acid (60-80 mg/e) than an unspecified "mild" strain (20-30 mg/e).

Surico & Graniti (1977) reported that unspecified virulent isolates of F. oxysporum f. sp. a/bed/n/s isolated from Bayoud diseased date palms (Phoenix dacty/ifena L.) in Algeria produced an average of 41 5 mg/e of fusaric acid and small amounts of anhydro-aspergillomarasmin B. We have identified one of these strains as F. oxysporum (Strain ii .8). Recently Mutert et al. (1981) detected moderate amounts (12-290 mg/e) of fusaric acid by HPLC in culture fluid of F. oxysporum f. sp. ap// CBS 184.38 and an isolate of F. oxysporum f. sp. p/si."quoted from Toxigenic Fusarium Species by Marasas et alia, Penn State U, 1984

Nep ? (24kDA protein)

This compound is a large protein (24 kiloDaltons) that was shown to be toxic to many species of plants.  Its human toxicity has not been tested, but some of the most powerful animals venoms (Black widow spider venoms, snake venoms, etc) are also large proteins.

Also see: FUSARIUM, TRIGO Y CEBADA, RIESGOS - (URUGUAY) (02)