V. dahliae

Akhunov et al. (2008) purified chitin-specific PO with fungicidal activity from cotton and observed the increase of its activity in plants, penetrated by Verticillium dahliae. Golubenco et al. (2007) showed the presence of the chitin-binding PO isozyme in Hibiscus trionum, which activated dramatically after inoculation by V, dahliae. The plants of Nicotiana tabacum overexpressing the anionic PO (chitin-specific according to our data) were more resistant to Helicoverpa zea and Lasioderma serricorne as compared with the wild-type (Dowd et al., 2006). 

Tjamos EC (1984) Control of Pyrenochaeta lycopersici by combined soil solarization and low dose of methyl bromide in Greece. Acta Hort (ISHS) 152 253-258 Tjamos EC, Fravel DR (1995) Detrimental effects of sublethal heating and Talaromyces flavus on microsclerotia of Verticillium dahliae. Phytopathology 85 388-392 Tjamos EC, Paplomatas EJ (1987) Effect of soil solarization on the survival of fungal antagonist of V. dahliae. Bull OEPP 17 645-653... 

Fig. (2). Different mechanisms to detoxify tomatine by fungal pathogens. 1 F. oxysporum, A. alternate , C. coccodes, F. solani, G. pulicaris, S. botryosum, S. solani, V. dahliae. 2 A. solani, V. albo-atrum. 3 B. cinerea. 4 A. solani.

Reducing agents that stabilize dHG have been shown to reduce significantly its toxicity to V, dahlias. Thus, the dHG free radical is implicated as an essential element in the mechanism of cytotoxicity. Phytoalexins, such as the pterocarpans, are postulated to operate by a similar mechanism. 

Dissolves in water buffered to the pH of infected xylem vessels at concentrations significantly higher than those required to kill V. dahliae conidia and mycelia. 

Present in vivo at the site of infection and in contact with V. dahlias mycelia. 

The phytoalexin dHG is rapidly absorbed by V, dahliae conidia, 75% of the dHG in a 6.5 /ig/ml solution being absorbed from the bioassay media by V, dahliae conidia (5 X 10 cells/ml) in one minute. Each V, dahliae cell would therefore contain 3.2 X 10 molecules of dHG. When these cells were washed repeatedly with media, -70% of the dHG was removed in six washes subsequent washes removed smaller and smaller amounts. 

We hypothesize dHG is rapidly absorbed by V, dahliae conidia and mycelia. An initiator (e.g. HO ) begins a chain reaction in which a series of highly reactive, cytotoxic free radicals are generated. One or more of these radicals reacts with vital processes in cell membranes (probably the plasmalemma) leading ultimately to death of conidia and mycelia. 

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