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Postharvest Pathology and Mycotoxins

Phytotoxicity of Fumonisins and TA-Toxin to Corn and Tomato. S. C. Lamprecht, Agricultural Research Council, Plant Protection Research Institute, Private Bag X5017, Stellenbosch 7599, South Africa; W. F. O. Marasas(2), J. F. Alberts(3), M. E. Cawood(4), W. C. A. Gelderblom(5), G. S. Shephard(6), P. G. Thiel(7), and F. J. Calitz(8). (2)(3)(4)(5)(6)(7)Medical Research Council, Programme on Mycotoxins and Experimental Carcinogenesis, P.O. Box 19070, Tygerberg 7505, South Africa; (8)Agricultural Research Council, Agrimetric Institute, Private Bag X5013, Stellenbosch 7599, South Africa. Phytopathology 84:383-391. Accepted for publication 22 December 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-383.

The phytotoxic effects of five fumonisin mycotoxins produced by Fusarium moniliforme, i.e., fumonisin A₁ (FA₁), A₂ (FA₂), B₁ (FB₁), B₂ (FB₂), and B₃ (FB₃), together with the aminopolyol hydrolysis products of FB₁ and FB₂ (AP₁ and AP₂, respectively) and tricarballylic acid (TCA) were compared with the host-specific phytotoxin TA-toxin (TA) produced by Alternaria alternata f. sp. lycopersici. A leaf assay was performed on detached leaves of the tomato genotypes Asc/Asc (tolerant to TA) and asc/asc (sensitive to TA) at four concentrations (0.1, 1, 10, and 100 µM) of each toxin. Seedlings of corn cultivars A1849W and PNR 473 and the two tomato genotypes were also used to assay TA, FB₁, FB₂, and FB₃. The fumonisins caused leaf necrosis identical to that caused by TA and FB₁, FB₂, FB₃, and TA caused significantly (P = 0.01) more necrosis compared with the other metabolites tested. Sterile distilled water (control) and TCA caused no necrosis. Significantly (P = 0.01) more necrosis was observed on the asc/asc genotype compared with the Asc/Asc genotype. There was no significant (P > 0.05) difference between necrosis caused by autoclaved metabolites and that caused by nonautoclaved metabolites. The fumonisins caused dose-dependent reductions in shoot and root length and dry mass of corn and tomato seedlings identical to those caused by TA. The results indicated that TA and FB₁ are more phytotoxic to seedlings than are FB₂ and FB₃. The effects of all four toxins were more pronounced on seedlings of the sensitive tomato genotype asc/asc than on the tolerant genotype Asc/Asc. No significant differences were recorded in the reaction of the two corn cultivars. The structural similarity of the fumonisin B mycotoxins and TA is therefore reflected by their phytotoxicity to detached tomato leaves as well as to corn and tomato seedlings.