LOCALIZED ACCUMULATION OF CONDENSED TANNINS ASSOCIATED WITH POINSETTIA BRACT NECROSIS

The early onset of bract necrosis in poinsettia (Euphorbia pulcherrima Willd. ex. I(lotzch) is characterized by small dark-stained spots tha t precede the development of enlarged necrotic lesions. Electron micro graphs of adaxial epidermal and subepidermal tissues with early sympto ms of necrosis revealed large, electron-dense deposits in cell vacuole s. These spherical bodies resembled condensed tannins observed in the epidermal tissues of peach and apple fruit. Chemical analysis of bract tissues confirmed the presence of condensed tannins. Furthermore, the re were higher concentrations of condensed tannin in bract samples wit h 2-mm-diameter lesions than in samples with lesions <0.5 mm (equivale nt to catechin concentrations of 59 and 13 mg . g(-1) fresh mass, resp ectively). No tannin bodies were observed in parallel samples of healt hy-appearing bracts in which only trace concentrations of condensed ta nnins were measured (0.2 mg . g(-1) fresh mass). The evidence suggests an association between condensed tannin accumulation in localized are as of the bract and the early appearance of bract necrosis symptoms.