Effects of triazole fungicides on sterol biosynthesis during spore germination of Botrytis cinerea, Venturia inaequalis and Puccinia graminis f. sp. tritici

Abstract

With three plant pathogens, Botrytis cinerea, Venturia inaequalis and Puecinia graminis f. sp. tritici, the time course of sterol biosynthesis during spore germination was examined by labeling experiments along with the question whether this pathway could be inhibited by triazole fungicides. Conidia of B. cinerea and V. inaequalis are able to synthesize sterols immediately after the beginning of the germination process when the germ tubes have not yet emerged. On the contrary uredospores of P. graminis start sterol biosynthesis after 6 to 8 h germination time almost at the end of the germ tube phase, indicating that sterol reserves of the spores are likely to be used for the germ tube growth.The sterol C-14 demethylation appeared to be the rate limiting step within the sterol biosynthetic pathway: the half life of 24-methylenedihydrolanosterol was less than 1 h for B. cinerea. It was more than 1 h for V. inaequalis and 3 h for P graminis. Independent of these differences in the time course of sterol biosynthesis and in the C-14 demethylation rate, the synthesis of sterols in germinating spores was strongly inhibited by triazole fungicides in all three pathogens examined. In contrast to P. graminis, this inhibition could be demonstrated with B. cinerea and V. inaequalis even in ungerminated conidia, indicating that the fungicides were rapidly taken up and reached their target within 1 or 2 h. These results are discussed along with the question whether spore germination can be used as a bioassay for the estimation of sensitivities of triazole fungicides.

Activity of the novel fungicide SYP-Z048 against plant pathogens

“…For example, DMIs doesn't affect the urediniospore germination of Puceinia hemerocallidis 30 and conidium germination of Spilocaea oleagina 31 . But in some pathogens, it is effective on spore germination 32 33 . The behavior observed for DMIs in pathogens differs due to the stage of starting sterol biosynthesis.…”

“…The behavior observed for DMIs in pathogens differs due to the stage of starting sterol biosynthesis. Conidia of some species are able to synthesize sterols in the early stage of germination, whereas other initiate sterol synthesis at the very end of the germ tube phase 33 .…”

A test method based on microscopic assessments to determine curative and protectant fungicide properties against Septoria tritici

“…Triazoles belong to the group of sterol biosynthesis inhibitors, which have little effect on spore germination, as shown for epoxiconazole by Godwin et al (1994). Pontzen & Scheinpflug (1989) demonstrated with Puccinia graminis that sterol biosynthesis started 6-8 h after germination, almost at the end of the germ tube growth phase, and they concluded from this that sterol reserves are likely to be used for the germination process. Further, triazoles are highly systemic and the epidermal fungicide concentration decreases earlier than for non-systemic compounds such as kresoxim-methyl or chlorothalonil.…”

Is the emergence of fungal resistance to medical triazoles related to their use in the agroecosystems? A mini review

“…Triazoles are absorbed and translocated in the plant, where they act preventively (before infection) or curatively (in the presence of symptoms) by affecting germ tube and appressoria formation or haustoria development and/or mycelial growth. 26 , 27 By widening the window of protection beyond protectant fungicides, which act only preventatively and are not translocated, the advantages of triazoles represent a breakthrough in increasing the productivity of various crops affected by fungal diseases. 2 Around a third of all fungicides used for the protection of crop yields include triazoles, among which more than 99% are inhibitors of demethylation (DMI).…”