Investigations into Phytophthora dieback of alder along the river Lagan in Belfast, Northern Ireland

Abstract

Common alder (Alnus glutinosa) is an important tree species, especially in riparian and wet habitats, it is very common across Ireland and Northern Ireland, and provides a wide range of ecosystem services there. Alder suffers from Phytophthora induced decline in many parts of Europe, and this research set out to identify the presence and scale of the risk to alder health from Phytophthora and other closely related oomycetes in Northern Ireland. This was done through surveys along the river Lagan in Belfast, Northern Ireland and revealed that of the tree vegetation along an 8.5 km stretch of the river, 166 alder trees were counted. Of these,28 were severely defoliated/diseased and nine were dead. Sampling and a combination of morphological and molecular testing of symptomatic plant material and river baits identified the presence of three Phytophthora species, including Phytophthora lacustris -the first time it has been recorded as disease-causing in Ireland. Inoculation studies using potted alder saplings demonstrated that P. lacustris was able to cause disease (under bark lesions), and Koch’s postulates for this pathogen-host combination were completed, which suggests a future risk to alder health from P. lacustris in Northern Ireland.