The Role of Leaf Nutrients in Vascular Streak Dieback Disease in Cocoa Plants (Theobroma cacao L.)

Background: Vascular streak dieback (VSD) is an important disease in cocoa and a decrease in nutrient supply is indicated to increase the severity of this disease. This study aimed to analyze the direct and indirect effects of nutrients that play a role in protecting cocoa plants from VSD. Methods: The research location was selected based on criteria such as being a smallholder cocoa plantation area, having 5-10-year-old plants and the presence of VSD disease. A sampling technique for observing disease severity was systematically conducted, with the main sample being farmers’ plantations. Cocoa leaf samples were taken from branches at one-third of the plant height, specifically from the upper canopy (leaves 3-4), which were physiologically mature, healthy and dark green. The variables observed were disease severity and cocoa leaf nutrient contents. The influence of N, P, K, Mg, Ca, Fe, Mn, B, Cu and Zn on VSD severity was analyzed using path analysis. Result: The results showed that disease severity was related to nutrient content in the leaves. The cocoa leaf nutrients that have a direct influence on the increase in VSD disease severity are K, Ca, Mn and Cu, while nutrients N, P, Mg, Fe, B and Zn have a direct influence on reducing VSD disease severity. Nutrients N and P have a significant direct influence, whereas nutrient K has a significant indirect influence through its interaction with nutrients N and P in reducing VSD disease severity.