SILICA SPRAYS REDUCE THE INCIDENCE AND SEVERITY OF BRACT NECROSIS IN POINSETTIA

Silica sprays (Na2SiO3 or SiO2 . nH(2)O) markedly reduced the incidenc e and severity of bract necrosis (BN) of Euphorbia pulcherrima Willd. cv. Supjibi Red compared to plants not sprayed with silica. BN has bee n associated with low Ca concentrations or high K : Ca ratios in tissu es of bract margins. Silica had no effect on Ca or K concentrations in bract margin tissues, and BN was not associated with the macro- or mi cronutrient composition of bract margin tissues. Sixteen days after in itial anthesis, nontreated and deionized-water-sprayed poinsettias dev eloped a higher incidence of BN than did plants sprayed with Na2SiO3 o r CaCl2. However, sprays of 3.56, 5.34, and 7.12 mM Na2SiO3 were as ef fective as 9.98 mM CaCl2 sprays in protecting against BN of 'Supjibi R ed' and 'Angelika White' bracts for up to 30 days after initial anthes is. 'Supjibi Red' developed a higher incidence of bract necrosis than did 'Angelika White', but both cultivars showed a similar response to the treatments and similar symptoms of necrosis. In both cultivars, in itial symptoms appeared as small necrotic lesions on bracts at the loo ped ends of lateral veins that displayed a closed-vein pattern after t he plants reached initial anthesis.