Effects of foliar versus soil water application on ecophysiology, leaf anatomy and growth of pineapple

Introduction - In the subtropics, pineapple [Anonas comosus (L.) Merr.] can be grown in plastic green-houses to avoid low temperature, which is the main limiting factor to production outside of the tropics. Foliar water application and subsequent evaporative cooling can help avoid excessive leaf temperatures in greenhouses during the hot seasons. The effects of foliar versus soil irrigation on ecophysiology, leaf anatomy and leaf temperature of pineapple in protected culture were tested to determine if the crop could receive sufficient irrigation to avoid plant stress solely from misting the foliage. Materials and methods - Relative water content, relative chlorophyll content, normalized difference vegetation index, membrane stability, and cross sectional leaf anatomy were measured at periodic intervals. Pineapple plants were subjected to soil irrigation, misting and drought. At the beginning and at the end of the experiment, total leaf area, plant biomass and assimilate partitioning to leaves, stems and roots were measured. Results and discussion - The normalized difference vegetation index revealed differences among treatments after fifteen days without irrigation. Pineapple plants endured thirty days of water stress without membrane damage. Plants irrigated by applying water only to the leaves did not receive adequate water amounts and showed similar signs of drought stress as those of the non-irrigated treatment. Conclusion - Based on ecophysiological, anatomical and growth responses, soil water application alone is sufficient for avoiding water stress and excessively high leaf temperatures of pineapple plants grown in protected culture in the subtropics, whereas only misting the leaves does not provide adequate water supply to prevent water stress.