Role of kaolin on drought tolerance and nut quality of Persian walnut

Abstract

Global warming has endangered crop production by reducing water availability and increasing temperature. Kaolin may protect plants against these conditions by reflecting the light and decreasing plant temperature. This study was conducted to evaluate the protective effects of kaolin spraying on kernel yield and quality of four walnut cultivars and genotype. The experiment was conducted as a split-plot factorial design in time factor with four factors including irrigation levels (100% and 50% of regular irrigation), kaolin solution concentrations (0, 2.5, 5 and 7.5%), walnut varieties (‘Chandler’, ‘Franquette’, ‘K72’ and ‘SG’) in two consecutive years (2012–2013). By increasing the kaolin concentration under well-watered irrigation, gas exchange, chlorophyll concentration, leaf potassium content, and kernel quality were improved. Moreover, increasing the kaolin concentration reduced sunburn and leaf temperature under different irrigation regimes. Based on results, genotypes ‘K72’ and ‘SG’ showed more severe sunburn symptoms. Water stress and no kaolin application had negative effect on the kernel color. Leaf temperature increased with reducing the irrigation and concentration of kaolin. Under water stress, ‘Chandler’ had the highest relative water content (58.25%) and ‘Franquette’ had the lowest RWC and therefore considered as the most drought sensitive cultivar. The lowest fruits sunburn in ‘Franquette’, was related to the thickness of its fruits’ husk. In general, the foliar application of kaolin 5% and 7.5% alleviated the negative effect of drought stress and improved the walnut kernels quality under water deficit condition by improving chlorophyll content, RWC, and gas exchange and reducing leaf temperature.