Purpose : Excessive transpiration of water from plant leaves can damage crop productivity during droughts, but commercial antitranspirants are expensive. The aim of this research was to characterise extracted wax from brassica leaf waste, and determine its antitranspirant efficacy and economics.
Methods : Yield of wax extracted with dichloromethane from six types of brassica waste was measured and the highest yielding waste was selected for bulk extraction with supercritical CO 2 . Wax was compared with a commercially-available terpene antitranspirant (di-1- p -menthene) for efficacy in reducing leaf water vapour loss, measured as stomatal conductance, in three experiments on rapeseed and in one experiment on wheat. Cost of wax under different production scenarios was calculated.
Results : Cauliflower leaf waste gave the highest wax yield, with the concentration varying from 1.31% (m/m) to 5.85% (m/m) in different batches of dried leaves. Nonacosane was the main component of the wax. In two of the three rapeseed experiments and in the wheat experiment, stomatal conductance was significantly reduced to similar extents by wax and by di-1- p -menthene, despite the wax being formulated and applied at a much lower concentration. Economic analysis showed that a high wax concentration in the cauliflower leaves would be needed to produce a commercially-viable leaf wax antitranspirant.
Conclusion : The results demonstrate biological efficacy as an antitranspirant of extracted cauliflower leaf wax. Further research is needed on variation in wax yield to reliably source high wax concentration leaves and reduce cost of production, and also to understand the greater efficacy of wax than di-1- p -menthene.