Bacterial canker of cherry trees, Prunus avium, in South Africa

In the 1980’s the causal agents of bacterial canker of cherry trees in South Africa was reported to be Pseudomonas syringae pv. syringae and Pseudomonas syringae pv. morsprunorum. Subsequently, no further studies were undertaken on the disease or causal agents. The aim of the current study was to conduct field surveys to determine the current situation pertaining to bacterial canker in the major cherry producing areas of South Africa. Following isolations from infected trees, strains were characterized using biochemical as well as multilocus sequence analyses (MLSA). Pathogenicity tests were undertaken with immature cherry fruit as well as three different cherry cultivars. Although symptoms of bacterial canker were present in all areas surveyed, P. syringae isolates were only isolated from three sites in the Western Cape Province. The isolates collected in this study showed a hypersensitive response on tobacco leaves and were pathogenic on immature cherry fruit and cherry trees. The phenotypic tests and MLSA using four genes (cts, gapA, gyrB and rpoD) showed phenotypic and genetic identity with Pseudomonas syringae pv. syringae. Selected strains induced a hypersensitive response on tobacco leaves and were pathogenic on immature cherry fruit and green cherry tree shoots. The current study shows that P. syringae pv. syringae is responsible for bacterial canker in the Western Cape Province, South Africa.