Pest control and mitigation of the heat stress with kaolin may also lead to save water in Mediterranean environments

Kaolin-based particle film technology (Pft) employs a multi-functional, environmentally friendly material that provides effective insect control, mitigates heat stress, and contributes to production of high-quality fruit and vegetables. These characteristics make kaolin suitable also for organic farming, especially in arid and semi-arid environments. The presence of mineral particles on leaves and fruit surfaces interferes with physiological processes, mainly with heat and radiation balance and gas exchange. Several experimental findings show that the Pft, as well to limit the damage from some insects, changes the radiative and thermal regime of the different organs of the plant that may result in a significant reduction in stress from high temperatures, mainly sunburn, as widely proven on apple, pear, pomegranate and tomato. The Institute of Sciences of Food Production, CNR, for several years is carrying out research to test the effects of kaolin on the control of the heat stress and some insects of fruit trees and vegetables. In addition, is evaluating the effects on gas exchange, water and salt stress. In the latter area, was assessed the gas exchange, evapotranspiration and water use efficiency (WUE) of tomato, orange and bean. In addition, we studied the effects on transplanting stress of seedling of tomato, pepper, eggplant and zucchini. In this paper we report some significant results that highlight the positive effect of kaolin on the reduction of evapotranspiration, water use, water and saline stress, and improvement of WUE. The water and salinity stress has caused the reduction of the leaf water potential, stomatal conductance, leaf net photosynthesis and transpiration and the increase of leaf and canopy temperature of tomato plants. The kaolin has resulted in an improvement of the water status of the plant, the reduction in stomatal conductance, net photosynthesis and transpiration under well watered or low salinity conditions. Instead, under drought or salt stress, the kaolin was effective to limiting the reductions in net photosynthesis and to reduce leaf and canopy temperature, resulting respectively in a 15 and 20% in WUE increase. The leaf and canopy temperature was slightly affected by kaolin, in different ways in different water/salt stress treatments. In particular, while in non stressed plant it was 0.2-0.8 °C higher in the kaolin-treated plants, the situation was reversed in stressed plants. In fact, in the latter situation, the kaolin has determined 0.2-1.5 °C reduction in canopy temperature, especially at noon time. The variations of the canopy temperature show that the kaolin influences the thermal balance of vegetation mainly for the dual effect of reflection of the incoming radiation and partial occlusion of the stomata. Kaolin has reduced by 13% the crop evapotranspiration of bean and has resulted in a 6% increase in the yield-WUE. In well watered orange tree kaolin led to a reduction of 16% in transpiration rate and 11% increase in WUE. Kaolin has proved effective in limiting transplant stress. Indeed, during the rooting of seedlings, resulted in an increased accumulation of dry biomass and height of seedlings of 17 and 39% respectively. The results are in agreement with other works reporting a reduction of stomatal conductance and, consequently, evapotranspiration. The reduction in stomatal conductance and water loss indicates that kaolin can be efficiently utilized as an antitranspirant to alleviate effects of drought and salinity and to save water in dry regions.