Leaf and Fruit Responses to Kaolin Particle Film Applied onto Mature Olive Trees

Abstract

Hot dry summers with high irradiance levels and low precipitation are typical in Mediterranean areas where olive trees are cultivated. Kaolin particle films (PF) are used with various crops to alleviate heat stress under these conditions. In this study, the effect of kaolin PF application on leaf physiological characteristics and functions of mature field-grown ‘Konservolea’ olive trees was investigated. Deficit irrigated [around 50% of crop evaportraspiration (ETc)] trees were studied during the 2009 and 2011 fruit growth periods (‘on’ years) in central Greece. Repeated applications of kaolin PF resulted in a white coating highly reflective in photosynthetically active radiation (PAR) on olive leaf surfaces found to significantly decrease the available PAR on leaf surface underneath the coating. The physiological characteristics of kaolin-treated leaves did not change to support any shade effect, but showed changes related to ameliorating heat stress. Kaolin applications improved leaf gas exchange functions under mild climatic conditions early and late in the season. In midsummer with high vapour pressure deficit and heat and water stressed olive trees, kaolin did not improve leaf gas exchange. However, overall, olive leaves from kaolin-treated trees seemed to manage better their water status and had more stable physiological characteristics and less negative midday stem water potential through the experimental period. Kaolin-treated-trees had similar fruit production, yield variables, fruit and fruit oil content were of similar maturity with control trees, but olive oil from kaolin-treated trees had lower free acidity and peroxide index compared to oil from control trees showing decreased oxidative stress.

Keywords: Olea europaea, heat stress, photosynthetic rate, stomatal conductance, chlorophyll, fruit quality