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

Abstract

The effects of varying irrigation intervals (I) and foliar application of salicylic acid (M) on morphological and physiological traits of <em>Catharanthus roseus </em>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 <em>Catharanthus. roseus </em>L.