Effects of the triazole plant growth retardant BAS 111¨W on gibberellin levels in oilseed rape, Brassica napus

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Abstract
Three‐week‐old shoots of the spring oilseed rape cv. Petranova (Brassica napus L. ssp. napus) were found by combined gas chromatography‐mass spectrometry to contain GA1, GA8, GA15, GA17, GA19, GA20, GA24, GA29, 3‐epi‐GA1 and a previously uncharacterised C19 dicarboxylic acid that is probably structurally related to GA24. Shoots of the winter cultivar Belinda, harvested at the early flowering stage, contained the same GAs with the exception of the C19 dicarboxylic acid and, in addition, GA34 and GA51 were identified. All material contained higher levels of GA20 than of GA1; the ratio of GA1 to GA20 was highest in shoots containing the largest proportion of young immature tissues. Soil treatment of cv. Petranova seedlings with the growth retardant BAS 111¨W [1‐phenoxy‐5,5‐dimethyl‐3‐(1,2,4‐triazol‐1‐yl)‐hexan‐4‐ol] caused 80% reduction in height 18 days after treatment and the levels of all GAs were 20% or less that of control plants. Foliar treatment at the same dosage reduced height by 50% and caused an 85% or greater reduction in the concentrations of the GA1 precursors GA20, GA19 and GA44. However, the levels of GA1, GA8 and GA29 were affected to a much smaller extent. Foliar application of BAS 111¨W to cv. Belinda 1 month after sowing resulted in only a 20% height reduction at flowering, but no uniform decrease in the concentrations of endogenous GAs at this stage.