POINSETTIA BRACT NECROSIS IS AFFECTED BY SCION ROOTSTOCK COMBINATIONSAND ARRESTED BY A BENZYLADENINE SPRAY/

Poinsettia (Euphorbia pulcherrima Willd, ex. Klotzch) cultivars vary w idely in susceptibility to bract necrosis, a disorder that has been as sociated with localized calcium deficiency. When 'Supjibi Red' (SR) po insettia shoots were grafted on 'SR' stocks, a higher incidence of bra ct necrosis was observed (26.4% of bracts) 28 days after initial anthe sis than on corresponding 'SR' shoots grafted on 'Annette Hegg Dark Re d' (AH) stocks (13.8% of bracts).'AH' shoots developed few bract necro sis symptoms, regardless of rootstock. Calcium (Ca) concentrations wer e higher in whole bracts of 'AH' than of 'SR', but were unaffected by rootstock, In a second study,'SR' shoots were grafted on a double root stock of one 'AH' and one 'SR' to determine if removing either rootsto ck, at the start of flower initiation or at anthesis, affected bract n ecrosis. At 28 days after initial anthesis, 'SR' scions on only 'AH' r oots from the beginning of flower initiation, or on 'AH' roots from ti me of initial anthesis, had less bract necrosis (12.3% and 14.9%,respe ctively), than 'SR' scions grafted on only 'SR' roots from the onset o f the study (24.2%), At harvest (36 days after anthesis), Ca concentra tions in bract margin tissues were highest on 'SR' shoots grafted to ' SR' roots throughout the study [0.17% of dry mass (DM)I, and lowest on shoots grafted to only 'AH' from the time of flower initiation (0.15% of DM) or from time of initial anthesis (0.14% of DM), There was no s ignificant correlation between Ca concentrations in bract margin tissu e and bract necrosis. A single spray of benzyladenine to bracts, after bract necrosis symptoms first began to appear (at initial anthesis), totally arrested the further development of bract necrosis for up to 3 4 days. Similar treatment with daminozide increased the incidence of b ract necrosis, This evidence suggests a new concept of bract necrosis etiology that includes a role for endogenous hormones. Chemical names used: N,N,dimethylaminosuccinamic acid (daminozide), N-6-benzylaminopu rine (benzyladenine).