Lime,molybdenum, and cultivar effects on molybdenum deficiency of poinsettia

Poinsettia (Euphorbia pulcherrima Willd. ex Klotz) cultivars ‘Annette Hegg Brilliant Diamond’ (AH), ‘Gutbier V‐14 Glory’ (GG), and ‘Eckespoint C‐1 Red’ (ER) were grown in a peat‐perlite potting medium to study lime and Mo effects on the occurrence of Mo deficiency. Two rates of dolomitic limestone, 0 and 3 kg/m³of growing medium, and weekly applications of micronutrient solutions containing 0.0 or 1.0 ppm Mo were made in factorial combination. Lime, Mo, or both prevented Mo deficiency symptoms in all cultivars. Without both lime and Mo, Mo deficiency symptoms appeared on AH and GG, but not on ER. Lime and/or Mo reduced NO₃‐N content, increased Mo content and increased nitrate reductase enzyme activity (NRA) in the upper recently matured leaves of all cultivars. Lime and Mo interacted to affect these parameters in all cultivars. Comparing the three cultivars without both lime and Mo, NO‐‐N content was lowest and NRA highest in ER. However, the Mo content of ER leaves was equal to or less than that of AG and GG which showed Mo deficiency symptoms.