3.7.46
ETIOLOGY OF CANKER AND DIE-BACK OF PEACH AND SWEET CHERRY TREES IN SOUTH AFRICA

WA SMIT, C LINDE, MG FOUCHÉ and L SMIT

Department of Plant Biotechnology and Pathology, ]nfruitec Centre for Fruit Technology, ARC-Research Institute for Fruit, Vine and Wine, Private Bag X5013, Stellenbosch 7599, South Africa

Background and objectives
In 1997, a die-back of peach and sweet cherry branches associated with cankers was noted in several commercial orchards in the eastern Free State and Western Cape Province, South Africa. Perithecial stromata were present on the cankers and single-ascospore isolates were identical in colony morphology to isolates obtained from infected host tissue at the canker margins. Though producers had generally attributed the symptoms to pathovars of Pseudomonas syringae

  • , examination of dead and dying branches in severely affected peach and sweet cherry orchards showed that the bacterium was not associated with active cankers. This suggested a fungal pathogen, such as Leucostoma, as the cause of infection.

    Leucostoma canker of Prunus spp., caused by either Leucostoma cincta (anamorph Cytospora cincta) or Leucostoma persoonii (anamorph Cytospora leucostoma) is common in many parts of the world [1,2]. Leucostoma canker, also called perennial or Valsa canker, is frequently misdiagnosed as bacterial canker, since many of the early symptoms are indistinguishable and perithecia and pycnidia may not readily form in infected bark tissue [2].

    The principal objective of this study was to identify the primary pathogen causing the cankers and die-back that have led to the widespread decline of peach and sweet cherry trees in the eastern Free State and Western Cape Province of South Africa.

    Results and conclusions
    This study has shown that the causal agent of the canker disease of peach and sweet cherry in South Africa is a species of Leucostoma. Canker and die-back symptoms were found in most orchards throughout the major peach and sweet cherry production areas of the eastern Free State and Western Cape Province. Leucostoma canker is considered as the principal canker disease occurring in those orchards. Bacterial canker, caused by P. syringae, was not found in our survey of orchards where canker and die-back were endemic. Recognition of Leucostoma canker as the major canker disease in peach and sweet cherry orchards in South Africa could lead to the development and implementation of improved control practices.

    References
    1. Biggs, AR, 1989. Plant Disease 73, 869-874.
    2. Regner, KM, Johnson, DA, Gross, DC, 1990. Plant Disease 74, 430-433.