ABSTRACT
           The present study was carried out at Antoniades Research Branch, Horticulture Research Institute, A.R.C. Alexandria, Egypt during the two successive seasons of 2017 and 2018 to study the effects of different concentrations and application methods of Diphenylamine (DPA) on the flower longevity of Aster New York plants (Symphyotrichum novi-belgii). Four concentrations of  DPA (0, 25 , 50 and 100 ppm)  and three application methods ( pulsing , foliar spray and holding  solution ) were used in this experiment . The results showed that the highest significant vase life was obtained after application 50 ppm DPA as pulsing treatment for one hour ,  this treatment caused the lowest significant loss of flower fresh weight percentage (LFFW %), highest significant flower fresh weight/flower dry weight ratio (FWR), the highest  relative fresh weight (RFW )  value  and  the  highest significant  reducing sugar content . Moreover, foliar spray treatment of DPA caused the highest significant increase of chlorophyll a and b content along the experiment period.