Epidemiology of Pseudomonas syringae pv. syringae on Prunus laurocerasus
Pseudomonas syringae is a bacterial plant pathogen. Over 180 plant species have been identified as hosts for strains of pv. syringae. It is believed that pathovar syringae causes shot hole disease of cherry laurel Prunus laurocerasus. The nursery stock sector in Ireland has been valued at €40 million per annum and cut foliage from many shrub and tree species including Prunus laurocerasus are used as fillers in bouquets of flowers. Three particular cultivars of Prunus laurocerasus are grown by nurseries to supply this market. They include the Etna, Caucasica, and Novita cultivars. This pathogen can cause up to 30% losses in commercial nurseries and disease symptoms caused by this pathogen are usually exhibited as brown/black necrotic leaf spots with circular or irregular margins. Abscission zones can form around the leaf spots and finally the leaf tissue falls out. The leaves then display a ragged appearance, as if they have suffered damage from a shotgun. The current research being carried out includes: assessment of the effect of the pathogen on different cultivars, defense gene expression analysis and investigation of optimal growth conditions including temperature and humidity. At present Pss 7562 and a possible Ps isolate found at Belfield are being tested. This includes leaf inoculation experiments with both isolates on different cultivars to identify the possible expression of various abscission and wounding genes in the Prunus laurocerasus genome. Primers have been developed and tested to investigate these genes. Current results indicate a cultivar difference in the virulence of the isolates tested.