The tropical climate, agronomic practices and range of plant hosts in South-East Asia often provide ideal conditions for Phytophthora diseases to proliferate and be economically damaging. Despite this, there remain gaps in the data on the distribution of the genus, especially in least developed countries.
Throughout 2015, surveys were conducted on over 40 crops in Champasak province, with a focus on the Bolaven Plateau. This plateau is a fertile highland with volcanic soils and a major coffee, fruit and vegetable production area in the Lao PDR. Four species of Phytophthora were isolated directly from diseased plant tissue, and indirectly by soil baiting.
Phytophthora capsici and P. drechsleri were associated with chilli plants showing stem browning, root rot and wilt symptoms, growing in polyhouses on the Bolaven Plateau. Phytophthora palmivora was isolated from papaya trees showing root and collar rot symptoms in a garden in Pakse, as well as a papaya inter-row planted with citrus on the plateau. It was also isolated from the soil beneath durians with dieback on several small-holder farms. Phytophthora cinnamomi was associated with avocado dieback at a number of small-holder farms. Isolates of the four species were sent to the Centre of Phytophthora Science and Management at Murdoch University, Australia, where identification was confirmed through morphological and molecular markers, and where they were accessioned.
The results of this survey indicate the presence of important Phytophthora species in southern Lao PDR that are well known to occur in neighbouring countries. Workshops and in-field discussions have been held with small-holders to help with implementation of IDM strategies, including crop rotation where appropriate, the use of pathogen-free transplants and the use of phosphonate injections at avocado and durian farms. Another species, P. infestans, has become a serious problem in tomatoes on the plateau but has yet to be studied in detail.