Effect of Salcylic acid (SA) on the photosynthesis, dry weight and canopy temperature in the cowpea (Vigna unguiculata) vegetative growth stage

Salcylic acid (SA) as a plant growth regulator. It has major effects on some of plant traits. The cowpea (Vigna unguiculata) also as one of the source of protein supplies is consequential. To study effect of SA on some physiological traits and to obtain the best concentration of this substance in the cowpea plant, an experiment was carried out in the field research of University of Zanjan. There were five treatments including: control, four treatment of spray application of SA (150, 300, 450 and 600 µM). The experiment was laid out in randomized complete block (RCB) design having three replications. Results showed that in photosynthetic parameters such as photosynthesis speed rate, transpiration rate, intercellular CO2 concentration, Chlorophyll Content Indexin the treatment with 150 µM SA, had the highest effect and significant difference was observed at 5% level.Total dry weight, stem dry weight, leaf dry weight in also treatment with level 150µM SA more average have shown ratio control treatments and were significant difference in level 5% in compare with control. Also with increasing levels of SA, canopy temperature also was significantly increased. In addition positive correlation was observed between dry weight of plant with photosynthetic rate, rate of transpiration, chlorophyll, leaf dry weight and stem dry weight.