First report of the downy mildew Peronospora lamii on Salvia officinalis and Rosmarinus officinalis in the UK

D.R. Humphreys-Jones ¹, A.V. Barnes ² and C.R. Lane ^2*

¹ Consultant Plant Pathologist, 25 Jumper Drive, Ely, Cambridgeshire, CB7 4TT, UK
² Central Science Laboratory, Sand Hutton, York, YO41 1LZ, UK

*c.lane@csl.gov.uk

Accepted for publication 08/12/06

In May 2004 samples of Salvia officinalis and its variegated form S. officinalis ‘Icterinia’ infected with downy mildew were received from a herb-propagating nursery based in the south of England.  Both cultivars were grown under protection, in a cool, damp polythene tunnel.  The infection first appeared as pale green patches on the upper surfaces of the leaves, that later became yellowish and then brown (Fig. 1).  A dense layer of dingy, purple-coloured sporangiophores, with ovoid to ellipsoid sporangia (mostly 20-24 x 17-18 µm), were found on the lower leaf surface below the brown patches.  Thick-walled golden yellow oospores (mostly 30-38 µm) developed between veins on some dead leaves.  Specimens and photographs of both infected cultivars were sent to CABI Biosciences at Egham, Surrey where Dr JC David confirmed the identification as Peronospora lamii.  Isolates from Salvia officinalis (IMI392138) and S. officinalis Icterinia (IMI392139) were added to the reference collection.  In October 2005 the same fungus was found affecting Salvia sp. and Rosmarinus officinalis (rosemary) grown under cover on a commercial herb-production nursery in Southern England.  The pathogen was causing a severe foliar blight with a profuse downy growth on the under leaf surface.  Sporangia were ovoid to ellipsoid with a mean diameter of 21.7 to 18.3 µm (17.5-25 µm x 17.5-23 µm), again conforming to the published description of P. lamii (Francis, 1981).

Figure 1: Peronospora lamii damage to Salvia officinalis 'Icterinina'

P. lamii has a broad host range affecting several members of the mint family (Labiatiae) (Francis & Waterhouse 1988; Preece, 2002) but there are no UK records on S. officinalis or R. officinalis.  The pathogen has been intercepted on a number of occasions on Salvia spp., but mainly on sage from Israel and not on Rosmarinus.  The mildew at times has been very damaging, with up to 90% of plants infected preventing harvesting of the crop.  Due to the presence of the organism in the UK no statutory action was warranted.  This is the first record of P. lamii causing damage to sage (S. officinalis) and rosemary (R. officinalis) in the UK.

Acknowledgements

The authors wish to thanks Dr JC David of the Royal Horticultural Society, Wisley, UK (formerly at CABI Bioscience UK) for assistance in identifications on sage and Mr Terry Thorpe for photographic work.

References

Francis SM, 1981. Peronospora lamii. CMI Descriptions of Pathogenic Fungi and Bacteria Number 688. Egham, UK: CABI Biosciences.

Francis SM, Waterhouse G, 1988. List of the Peronosporaceae reported from the British Isles. Transactions of the British Mycological Society 91, 1-62.

Preece TF, 2002. A checklist of the Downy Mildews (Peronosporaceae) of the British Isles. Kew, UK: British Mycological Society.

The British Society for Plant Pathology