In planta detection used to define the distribution of the European lineages of Phytophthora ramorum on larch (Larix) in the UK

UK distribution of Phytophthora ramorum evolutionary types provided by new testing method

By developing a new molecular-based testing method based on PCR techniques, Forest Research scientists have been able to examine the distribution of the two main lineages of Phytophthora ramorum responsible for the major epidemic on larch (Larix spp.) in the UK. In a paper published in the journal Plant Pathology (doi: 10.1111/ppa.12345), Kevin King, Anna Harris and Joan Webber describe the new protocol and use it to test the lineage of 134 UK samples collected during 2013-14. Lineage testing was also applied to over 300 P. ramorum isolates cultured from a wide range of hosts between 2002-12.

In the UK there are two genetically distinct lineages of P. ramorum; EU1 which is widespread, and the recently identified EU2, which has been reported only from Northern Ireland and a small area in south west Scotland. P. ramorum is difficult to isolate from infected larch tissue and as existing methods to determine lineage require pure cultures of the pathogen, there has been only limited information available as to the extent and severity of the spread of the EU2 varient.

The group’s findings showed that there was no evidence that EU2 had spread into England and Wales where only the EU1 lineage was found. However, the EU2 was more widely distributed in southern and eastern parts of Scotland than previously reported.  EU1 and EU2 were detected less than 10 km apart in larch plantations suggesting that convergence of the two populations might be a possibility. This study provided the first reports of natural EU2 infection on European larch (Larix decidua), hybrid larch (Larix x. eurolepis), beech (Fagus sylvatica), noble fir (Abies procera) and western hemlock (Tsuga heterophylla).

Read In planta detection used to define the distribution of the European lineages of Phytophthora ramorum on larch (Larix) in the UK.

Plant Pathology (2015) doi: 10.1111/ppa.12345

K. M. King, A. R. Harris and J. F. Webber

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