Foliar application of the triazole fungicide, epoxiconazole, retarded the growth of Galium aparine L. (cleavers). GC-MS and GC analysis clearly indicated that phytosterol biosynthesis in stem and leaflet tissue was significantly affected by this treatment. For example, in leaflet tissues, 125 g al ha(-1) (field rate) caused reductions in campesterol and sitosterol of 81% and 75% respectively. C14-methyl phytosterols such as 14 alpha-methylergost-8-enol, obtusifoliol and dihydroobtusifoliol were detected in treated tissues indicating that epoxiconazole inhibits the cytochrome P-450 dependent obtusifoliol 14 alpha-demethylase. In addition, ratios of campesterol to sitosterol were reduced. Stigmasterol was not detected in control or treated tissues. Preliminary determination of photosynthetic characteristics of isolated thylakoids from treated plants indicated that electron transport and oxygen evolution were impaired by epoxiconazole and these effects were dose-related. Ten days after treatment, oxygen evolution from thylakoids (determined as electron flow from water to ferricyanide) isolated from control plants was 24.2 mu mol mg(-1) chl h(-1), whilst treatment with 125 g and 250 g ai ha(-1) reduced this rate to 15.2 mu mol and 8.2 mu mol mg(-1) chl h(-1), an inhibition of 37 and 67% respectively. These results suggest that epoxiconazole influences thylakoid integrity and function in addition to phytosterol biosynthesis in G. aparine.
