Enhanced Yield and Physiological Performance of Mediterranean Grapevines through Foliar Kaolin Spray

Abstract

Future climate in the Mediterranean grapevine (Vitis vinifera L.) growing regions will be characterized by more severe summer conditions, with lower water availability, increased temperature and elevated solar irradiance, which may bring relevant changes in grapevine performance. Although grapevines have several survival strategies, the amounting evidence for significant climate change in the upcoming decades urges short-term adaptation measures to be taken. With this in mind, the potential protective role of 5% foliar kaolin (KL), a white and inert clay mineral, was examined in the Port Wine Region over a two year period (2012 and 2013). The results revealed that leaves treated with KL showed higher light reflectance, lower leaf temperature and greater water potential, namely at midday period. As a consequence, net photosynthetic rates increased, particularly due to a lowering of mesophyll limitations, which include lesser perturbations in PSII photochemistry processes. In fact, sprayed KL plants had higher accumulation of active PSII reaction centres (RC) and capture efficiency of excitation energy by open RC, maximum and effective quantum efficiency of PSII, and electron transport rate. Moreover, KL application reduces the oxidative damage on cell membranes by lipid peroxidation. Altogether, these results and the delays in leaf senescence of grapevines sprayed with KL inhibited scorching of clusters and, consequently, lead to a higher yield per plant. Thus, kaolin is a very promising and cost- effective compound to alleviate the negative effects of summer stress in Mediterranean grapevines. In addition, since KL is a natural product can be used in organic farming.