Effects of Kaolin Application on Leaf Chlorophyll Content and SPAD Values in Some Walnut Cultivars

This study evaluated the effects of kaolin particle film application on leaf chlorophyll content and SPAD values in various walnut (Juglans regia L.) cultivars grown under Mediterranean climatic conditions. The plant material included Bilecik, Kaplan86, Malatya1, Şebin, Şen1, Tokat1, Yalova1, Yalova3, Yalova4, Yavuz, and 77H1. Compared with control trees, kaolin-treated trees had higher chlorophyll a, chlorophyll b, total chlorophyll, and SPAD values in most genotypes. On average, chlorophyll a increased from 0.85 to 1.18 mg/g FW , chlorophyll b from 0.38 to 0.53 mg/g FW, total chlorophyll from 1.23 to 1.72 mg/g FW , and SPAD values from 38.24 to 40.91 under kaolin treatment, indicating that kaolin particle film can effectively mitigate heat and light stress by preserving photosynthetic pigments and chlorophyll status. These results revealed that kaolin is a practical cultural strategy for walnut-growing regions where thermal and radiation stress during the summer months can reduce physiological performance.