Assessing anti-transpiration potential of beeswax waste on Calendula officinalis under drought stress conditions

Beeswax waste, as a novel biostimulant, may be involved in anti-transpiration process in plants exposed to drought stress. Therefore, the aim of this study was to investigate the anti-transpiration effect of beeswax waste in comparison with chitosan, a known anti-transpiration substance. The treatments consisted of two drought stress conditions [no stress, 90% field capacity; and stress, 40% field capacity (FC)] together with four exogenous foliar applications [control (water), beeswax waste extract (BWE), chitosan, and BWE +chitosan]. Plants sub-jected to irrigation with 40% FC displayed a significant reduction in plant yield and physiological traits. In drought stress, foliar application with BWE and BWE + chitosan increased shoot dry weight, flower number and weight, net photosynthesis (Pn), essential oil percentage and yield, and decreased membrane permeability compared with water and chitosan spraying. Under drought stress, foliar treatment with BWE and chitosan decreased stomatal conductivity by about 8% and 31%, and transpiration (Tr) by 7% and 22%, respectively compared with water spraying. Under these conditions, the leaves sprayed with BWE and BWE + chitosan exhibited a lower temperature compared with water and chitosan treatments. Furthermore, foliar spraying with BWE + chitosan, BWE and chitosan increased the water use efficiency (WUE) by 104%, 92% and 56%, respectively, compared to control. Foliar application with BWE, chitosan and BWE + chitosan improved ascorbate peroxidase (APX) and catalase (CAT) activity and osmoregulation parameters (increased proline, proteins and soluble sugars) as plant adaptive mechanisms to drought. In conclusion, BWE can mitigate the drought stress similarly to chitosan, a better known anti-transpiration agent.