Morphological and Physiological Traits of Catharanthus roseus L. at Different Irrigation Intervals as Affected by Salicylic Acid Application

The effects of varying irrigation intervals (I) and foliar application of salicylic acid (M) on morphological and physiological traits of Catharanthus roseus L. were studied in a factorial experiment based on a randomized complete design with three replications. The experimental treatments consisted of four irrigation intervals [2 days (I1), 4 days (I2), 6 days (I3) and 8 days (I4)] and foliar application of 200 mg L-1 salicylic acid (SA) at three frequencies [0 (M0), one (M1) and two (M2) times]. Among the morphological traits, treatment I2M2 resulted in the greatest number of flowers (25.66 flowers), the fewest leaf abscissions (3.8), and the highest root fresh weight (1.181 g); I1M0 resulted in the highest plant height (154 cm), leaf number (36 leaves), internode length (9.243 mm), shoot fresh weight (8.636 g), and shoot dry matter (26.20%); and I1M2 resulted in the largest flower diameter (1.176 mm), node number per plant (16.66 nodes), plant fresh weight (9.366 g), and root dry matter (30.03%). Among physiological traits, I1M0 was related to the highest chlorophyll b, total chlorophyll, and petal anthocyanin. The highest and lowest proline contents were obtained from I3M2 and I2M0, respectively. The lowest MDA content of 1.42 nmol g-1 fresh weight (FW) was observed in I4M1 and the highest SOD activity of 88 IU g-1 FW was obtained from I3M0. POD activity was lowest in I2M0 and highest in I4M2. In total, given the detrimental impacts of water deficit stress at irrigation intervals of 6 and 8 days, it is recommended that SA be applied to improve the growth of Catharanthus roseus L.