The Effect of Salicylic Acid on Growth and Flowering of Marigold (Calendula officinalis) Plant under High Temperature Stress

The need for improving heat tolerance of plants is increasing because of global warming. In order to investigate of foliar-applied salicylic acid (SA) on the growth and ornamental traits of common marigold (Calendula officinalis L.) under heat stress, a pot experiment was conducted in a factorial experiment based on randomized complete block design with four replications in 2015. Experimental treatments were consisted of two cultivars of calendula (‘Candyman’ and ‘Zen’) and four concentrations of SA (0.25, 0.5 and 1 mM, and control). The results showed that foliar application of SA under heat stress, improved most characteristics of all studied morphological characteristics with the exception of plant height, leaf number, days to first flower and flower dry weight. According to the results, among all concentrations, the highest mean in most of traits was obtained from foliar application of 0.25 mM SA. Compared to the control conditions, application of 0.25 mM solution of salicylic acid increased leaf area (21%), fresh and dry shoot weight (15% and 16%, respectively), flower number (42%), flower longevity (19%) and flower fresh weight (43%). The interaction effect between cultivar and concentration of treatment was not significant for all measured traits.