Metabolism of Terbacil in Strawberry (Fragaria × ananassa) and Goldenrod (Solidago fistulosa)

Terbacil (3-tert-butyl-5-chloro-6-methyluracil) metabolism was evaluated as a possible basis of tolerance in two species, strawberry (Fragaria × ananassa Duchesne) and goldenrod (Solidago fistulosa Miller). Reported cultivar variation in strawberry tolerance to terbacil was examined by comparing herbicide metabolism patterns in an established tolerant cultivar, 'Sunrise’, with those of the reported susceptible cultivar, ‘Guardian’. A terbacil-sensitive plant, cucumber (Cucumis sativus L. ‘Chipper’), was also used as a basis for comparison. Using gradient elution high performance liquid chromatography (HPLC), two terbacil metabolites were separated and quantitated from methanol extracts of the three species treated with 14C-terbacil via roots in solution culture. The minor metabolite was identified as the non-phytotoxic derivative, 3-tert-butyl-5-chloro-6-hydroxymethyluracil, based on its co-migration with authentic 3-tert-butyl-5-chloro-6-hydroxymethyluracil in two chromatographic systems. The major metabolite was a glycoside, which yielded the hydroxylated derivative upon β-glucosidase hydrolysis. In all species, metabolites accumulated more rapidly and extensively in roots than in leaves. Metabolism was greater in the two tolerant species than in cucumber. However, the greater tolerance of goldenrod to terbacil compared to that of strawberry was apparently unrelated to differences in herbicide metabolism.