Abstract
Root-associated decline, suspected to involve Phytophthora species, is considered one of the major constraints to duku (Lansium domesticum Corr.) production in Indonesia. Although the disease primarily affects roots and basal stem tissues, prolonged stress may also influence physiological processes in leaves. This study examined whether several leaf biochemical parameters associated with antioxidant and phenylpropanoid metabolism could differentiate healthy and diseased duku trees under orchard conditions. Guaiacol-reactive POD-like oxidative activity, total flavonoid content, and tannin levels were analyzed in leaf samples collected from healthy and diseased trees using spectrophotometric methods. Statistical analyses showed no significant differences between the two health categories for all measured parameters (p > 0.05). Health categories were defined based on field-observed root-associated decline symptoms, and pathogen identity was not directly confirmed in the present study. Considerable overlap among individual samples was also observed. The POD-related measurement should be interpreted as an exploratory guaiacol-reactive oxidative indicator rather than as a direct estimate of native POD enzyme activity. The results suggest that leaf biochemical responses remained relatively stable despite prolonged root-associated stress. Under field conditions, these parameters were not sufficiently sensitive to distinguish between healthy and diseased trees when measured at a single sampling period. The findings suggest phenylpropanoid-related compounds in duku leaves mainly reflect long-term physiological adjustment rather than short-term inducible defense responses. Consequently, single-time-point biochemical measurements in leaves have limited value for diagnosing prolonged root-associated decline in perennial fruit trees.