EFFECT OF FLUCTUATING ROOT-ZONE TEMPERATURES IN PLANT PLANE HYDROPONIC ON LEAF PROLINE LEVEL AND CUTTING YIELD OF CHRYSANTHEMUM STOCK PLANTS

The stress effect of highly fluctuating temperatures in the root zone of the cultivation system plant plane hydroponic on chrysanthemum (Den dranthema-Grandiflorum-hybrids) stock plants was investigated by measu ring the proline level in leaves as an indicator of stress and by eval uating the yield of cuttings. In two greenhouse experiments stabilizat ion of root zone temperatures, fluctuating between 43.3 and 8.3 degree s C in the summer and 27.8 and 8.5 degrees C in the winter, close to 2 0 degrees C resulted in consistently lower proline levels in leaves. B ut even in the case of stabilized root zone temperatures different pro line levels were determined for the two experiments and a large tempor al variation was observed during the winter experiment. Correlation an alyses indicated, that the higher proline levels for the fluctuating r oot zone temperatures in the summer were mainly caused by low night te mperatures. The chilling stress potential of the low temperatures beca me evident in a short-term experiment, where a continuous relative inc rease of proline level up to 300 % of the control (20 degrees C) was o btained after a cold treatment of roots (10 degrees C) for two days. S tabilization of root zone temperatures slightly increased the cutting yield only in the winter experiment. Mean proline levels and mean numb ers of cuttings per harvest date of both experiments combined with the data of earlier experiments followed a consistent non-linear dose rel ationship indicating a mean proline threshold range for the reduction for the investigated cultivar. Proline levels and yields suggested tha t in addition to the fluctuating root zone temperatures other stress f actors affected chrysanthemum stock plants in the low-buffered root zo ne.