Basal stem rot (BSR), caused by Ganoderma boninense, is a significant threat to the oil palm industry in Southeast Asia, with few effective control measures available beyond the removal of infected plants. This study explores the efficacy of soil pH modification through the application of ground magnesium limestone (GML) as a strategy for managing this disease. Over 32 weeks, oil palm seedlings were treated in a nursery setting with varying rates of GML (0, 1.6, 3.2, and 6.4 g per 4 kg of soil) and exposed to three G. boninense isolates of differing pathogenicity (T7, T10, and PER71).
Our results indicate that GML applications significantly reduced disease incidence (DI) and disease severity index (DSI), particularly at the 1.6 g and 3.2 g rates, across all isolates. The most aggressive isolate, T10, showed the most significant reduction in disease severity at the 3.2 g rate, suggesting an optimal lime application threshold for effective disease management. In contrast, the highest GML rate (6.4 g) did not correspond to lower disease levels, implying a plateau effect where further increases in lime may not enhance disease control and could potentially be counterproductive.
Growth measurements, including girth diameter, plant height, and leaf area, were slightly improved by GML treatments, with the most notable increase observed in leaf area, especially at mid-level GML rates. Biomass assessments showed variable responses, with generally higher fresh and dry weights in limed treatments.
In conclusion, modifying soil pH with GML can effectively reduce the incidence and severity of BSR in oil palm nurseries. However, the relationship between lime application rates and disease control is not linear, highlighting the importance of optimising lime dosages to maximise health benefits without inducing negative effects on disease resistance.