Soil Properties Influence the Prevalence of Soilborne Pathogens in Robusta Coffee and Black Pepper Systems in Vietnam's Central Highlands

Monoculture and intensive fertiliser use in the cultivation of Robusta coffee (Coffea canephora var. Robusta) and black pepper (Piper nigrum L.) have led to soil degradation and increased disease pressure in Vietnam's Central Highlands. To identify key factors driving soilborne diseases and threatening sustainable production, a soil and root survey was conducted across three provinces: Gia Lai, Dak Lak, and Dak Nong. Soils were characterised by high clay content (51.2-62.0 %), moderate silt (35.5-46.0 %), and low sand (2.5-2.8 %), with a notably low cation exchange capacity (7.72-8.04 cmolckg-1). The soils were strongly acidic, with average pH values of 4.51 in coffee farms and 5.45 in pepper farms. Despite sufficient levels of nitrogen (N), phosphorus (P), and potassium (K), soilborne pathogens were widespread. Fusarium spp. were detected in all samples, Phytophthora spp. in 64-76 % of black pepper farms, and plant-parasitic nematodes in 67-84 % of farms, with Meloidogyne spp. predominant. Fusarium density increased with soil acidity in coffee plantations. In coffee, nematode density was positively correlated with N input, while in black pepper, N was negatively correlated with Phytophthora. Organic matter and available K were negatively associated with Fusarium in coffee but positively with Phytophthora in black pepper. These findings underscore the need for integrated management of nutrients and pathogens to sustain perennial crop production in the region.