MULCH SURFACE COLOR AFFECTS ACCUMULATION OF EPICUTICULAR WAX ON DEVELOPING LEAVES

— Leaf waxes are important to plant growth because they impede water loss and may influence entry of light. Leaf wax quantity and composition were studied in Capsicum annuum plants in trickle-irrigated field plots covered with white, black or red plastic mulches. The quantity of reflected blue light (BL) was greatest over white and about the same over black versus red surfaces; and reflected far-red to red ratios (FR/R) were about the same over white versus black and higher over red. The greatest quantity of total epicuticular wax developed on leaves of plants grown over white mulch (443 μg/cm2) while plants grown over black and red mulches had 229 and 227 μg/cm2, respectively. When individual lipid classes were expressed as percentages of the totals, esters constituted the highest percentages over white and black surfaces while secondary free fatty alcohols dominated over red. The higher ester content of epicuticular wax on plants grown over black (versus red) was almost exactly equalled by increased contents of free fatty alcohols and free fatty acids in the epicuticular wax of plants grown over red mulch. We conclude that the total wax concentration on leaves of field-grown plants was influenced by quantity of BL, and the percentage of individual components was influenced by the FR/R ratio.