Effect of iron concentration on growth and phylloclade edge yellowing of holiday cactus

Abstract

Production of holiday cactus has been limited by the common occurrence of marginal chlorosis of the phyllociade, which can lead to losses in crop quality. This work was conducted to determine if poor growth and phylloclade yellowing were correlated with applied Fe concentration, and if temperature and pH of the growing media affected Fe uptake. In two separate studies, rooted cuttings of Schlumbergera 'White Christmas,"Twilight Tangerine,"Christmas Charm,'and 'Lavender Doll'were placed in either a peat-based medium or solution culture, and fertilized with a modified Hoagland's solution, adjusted to a pH of 6, containing Fe as FE-EDTA at eithe@ 0, 10, 20, 30, or 40 mg,l-'. For solution culture studies, plants were placed in a growth chamber and grown under 16 hrs daylength for 16 weeks at 220C /1 80C day/night temperature. For the peatbased studies, plants were grown in a greenhouse under long day conditions (4 hrs night interruption) for 20 weeks at temperature set points of 250C /180C day/night temperature. Increased concentration of FE-EDTA was associated with increased symptom severity and higher phylloclade Fe concentrations. Fe concentrations in peat-based media increased over time, thus the cumulative effects of repeated Fe-chelate applications are an important factor in the occurrence of the Fe toxicity. There did not appear to be a critical concentration of Fe associated with symptom development, but was dependent on cultivar susceptibility. In two other separate studies, results indicate that temperature regimes and pH of the growing media used in this study do not affect the toxicity expression in holiday cactus.