Toxins alternaria

The Alternaria black spot fungi A. brassicae and A. brassicicola produce host-selective toxins as well. While A. brassicicola produces brassicicolin A (11) as the major host-selective phytotoxin [28], A. brassicae produces destruxin B (12) (Fig. 9.4) [29]. Consistent with the virulence of these phytopathogens, both brassicicolin A (11) and destruxin B (12) appeared to be more phytotoxic to the susceptible cruciferous species B.juncea than to the tolerant B. napus. 

Other cyclic tetrapeptides have also been isolated by Japanese workers and AM toxins I, II, and III, isolated from Alternaria mail., are extremely toxic to certain plant species (9.10). These are constructed of L- i-hydroxyisovaleric acid, L-alanine, c-amino-acrylic acid and, in AM toxin I, L-6(-amino- -( .-methoxyphenyl)-valeric acid. The phenyl residue in AM toxin II is L-t(-amino-S-phenylvaleric acid, while in AM toxin III, it is L-ol-amino-( .-hydroxyphenyl)valeric acid (Figure 2), All the AM toxins produce leaf spot, or necrosis, in apple but as might he expected slight change in substitution (R-group) on the phenyl ring radically alters the specific activity of the molecule. Both AM toxin I and III induce interveinal necrosis in the "Indo" apple cultivar, which is also highly susceptible to A. mail. at concentrations as low as 0.1 pph within 18 h after treatment. In contrast, the resistant apple cultivar "Jonathan" is only affected by 1 ppm of AM toxin I and 10 ppm of AM toxin III. 

Whilst the ACRL Toxin I totally synthesized in this way is the main and most toxic component of the toxins produced by the phytopathogenic fungus Alternaria citri (68), other synthetic work has concentrated on a minor, essentially non-toxic component, i. e. ACRL Toxin Illb (63) (69, 70) - a task considerably easier as lack of a stereocenter in the pyranoid ring greatly facilitates the joining of the acyclic and pyranoid fragments. 

As pointed out above, bioassay choice is extremely important since different sensitivities and different responses are observed that are dependent on the bioassay specimen. For example, comparison of four bioassay methods for detection of destruxin B, a host-specific toxin produced by Alternaria brassicae, indicated a lack of rapid electrolyte leakage and insensitivity of host protoplasts. However, leaf and pollen bioassays were sensitive to low toxin levels. Pollen germination was the most rapid, sensitive and quantitative bioassay for the toxin. Significant inhibition of Brassica campestris pollen germination and pollen tube growth occurred only 30 min after incubation with 2.5 pg mL 1, and 7.5 pg mL 1 caused total inhibition.3... 

Bains, P. S. 1990. Purification, chemical characterization, host-specificity, bioassay, mode of action, and herbicidal use of the toxin produced by Alternaria brassicae. Dissertation Abst. Internat. 50, 2708-B... 

Gardner, J. M., Kono, Y., and Chandler, J. L. 1986. Bioassay and host-selectivity of Alternaria citri toxins affecting rough lemon and mandarins. Physiol. Molec. Plant Pathol. 29, 293-304... 

AAL-Toxin. Stem canker of tomato is caused by the fungal pathogen Alternaria alternata f. sp. Ivcooersici (21). Concentrations of less that 10 ng/ml of AAL-toxin [14], a host-specific toxin, can produce disease symptoms. Two phytotoxic fractions have been isolated from fungal culture filtrates that reproduce disease symptoms in susceptible plants. These fractions are termed T ... 

Alternaria solani, the causal organism of early blight disease of tomato and potato produces several metabolites whose structures have been clarified. It was pointed out that the fungus also secretes host-specific toxins which induce necrotic symptoms typically associated with the disease [50]. Five phytotoxins were isolated, solanapyrones A (67), B (68), C (69), D (70) and E (71), Fig. 17. The diastereomeric... 

Scott (2001) summarized the available literature on the natural occurrence of Alternaria toxins in fruits. The most frequently detected toxins were alternariol, alternariol methyl ether, and tenuazonic acid in apples, mandarin, melon, and alternariol and its methyl ether in red currant, raspberry, strawberry, gooseberry, and blackberry. Stinson et al. (1980) were able to detect Alternaria toxins after the authors isolated Alternaria strains from blueberries, broke the skin, and inoculated the berries after steam disinfection. In contrast, Tournas and Stack (2001) did not detect Alternaria toxins after infection of blueberries with A. alternata. As discussed earlier in this chapter, fruits become more susceptible to mold invasion during ripening, and this may be a crucial point for inoculation experiments. 

Scott, P.M. and Kanhere, S.R. 2001. Stability of Alternaria toxins in fruit juices and wine. Mycotoxin Res. 17, 9-14. 

HC-Toxin and victorin are produced by Helminthosporium carborum, which is a pathogen on maize, whilst another peptide, AM-toxin, is produced by Alternaria alternata, which causes a blotch disease on apples. The peptabiols, produced by Trichoderma harzianum, affect the development of other fungi. 

It is also possible to use toxins isolated from fungi. The cyclic tetrapeptide, tentoxin, from Alternaria species causes severe chlorosis in many problem weeds without... 

Johnson RD, Johnson L, Itoh Y, Kodama M, Otani H, Kohmoto K. Cloning and characterization of a cyclic peptide synthetase gene from Alternaria alternata apple pathotype whose product is involved in AM-toxin synthesis and pathogenicity. Mol Plant-Microbe Interact 13 742-753, 2000. 

Another group of toxins called the AAL-toxins was fotmd to have a structural relationship to the fumonisins, since they have only one tricarboxylic acid (TCA) moiety. AAL-toxin TAi (265) and TA2 (266) (Fig. 5.2) are produced by the fungus Alternaria alternata f. sp. lycopersici and can lead to phytotoxic effects on several crops such as tomatoes and weeds (200). Due to the toxic effects of long alkyl-chain pyridinium compounds, this new class of fumonisins is of high interest (201). 

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