Soilborne pests and diseases affecting both coffee and black pepper in Central Highlands in Vietnam: a complex consortium of pathogenic fungi, oomycetes, and nematodes

Vietnam is the world's 1st and 2nd largest exporter of black pepper and coffee robusta, respectively. However, due to intensive management practices, soil health has gradually reduced, resulting in production of both commodities being seriously affected by Soil Borne Pests and Diseases (SBPDs). About 300,000 ha of coffee plantations must be renewed, but all attempts to replant them have failed due to high populations of SBPD (mainly attributed to nematodes) in severely degraded soils. During the early years after its introduction, black pepper yields have exceeded the Vietnamese government's expectations even in areas with poor soils. However, farmers now observe a decrease in pepper yield. Pathogenic oomycetes including Phytophthora capsici and P. tropicalis were previously considered to be the only agents responsible for reduced pepper yields in the region. In the frame of the V-Scope project funded by the Australian Centre for International Agricultural Research (ACIAR), our team investigate SBPDs responsible for destruction of plantations of both black pepper and coffee in 3 Provinces 20 (Gai Lai, Dak Lak and Dak Nong). Our results show that in addition to Phytophthora, other groups such as Pythium, Phytopythium and Fusarium are also causing damages in black pepper plantations. Nematodes (Meloidogyne and Pratylenchus) were also found to affect both commodities and analysis of secondary data suggests that the populations of nematodes may be increased when coffee trees are intercropped with jackfruit and black pepper. Moreover, by using quantitative PCR, we found that Phytophthora and Fusarium were also present in black pepper plantations showing no symptoms, suggesting complex interactions between soil health, pathogen presence and plant damages. Overall, understanding the complex relationship between agricultural management practices and the consortium of SBPDs is crucial to restore soil health, control the SBPD populations and improve yields of coffee and pepper.