Recent Scientific Advances in Epidemiology
The world knowledge-base on epidemiology and management of P. savastanoi has increased dramatically over the last 5-7 years mainly due to the contributions of plant pathologists in Spain and Italy. The efflux of progress from European researchers is not surprising, particularly because Spain boasts over 6 million acres of olives, representing approximately 25% of the world's cultivated area and producing almost half of the world's olive oil (4). A brief summary of major recent findings include:
- Epiphytic (on twig/leaf surfaces) pathogen populations serve as primary innoculum (2).
Implication: pruning galls does not eliminate pathogen from orchard. Lack of historic disease incidence does not denote reduced risk of future infection.
- The pathogen may be introduced to orchards on asymptomatic plant materials (1).
Implication(s): The pathogen may move over large geographic areas on asymptomatic nursery stock. Presence of old galls may not serve as primary determinate of risk in
- Pathogen populations may vary over geographic regions and even within orchards or individual trees (3).
Implication: Disease management research must include diverse isolates.
- An interaction between specific bacterial strains and olive cultivars determines susceptibility.
Implication: Future studies on cultivar susceptibility must be conducted with a range of pathogen isolates from CA orchards. Published cultivar susceptibility data from other
geographic areas may not be applicable to CA orchard systems because pathogen population may differ from test populations in published literature.
- Pathogen may move locally through xylem vessels; however, translocation isn't systemic at whole-plant level (4).
Implication: Pathogen may reside inside the plant, even in asymptomatic tissues. Epiphytic bacterial populations may be more susceptible to suppression by topical sprays than populations residing inside the plant.
1. Quesada, J.M., Garcia, A., Bertolini, E., López, M.M., Penyalver, R. 2007. Recovery of Pseudomonas savastanoi pv. savastanoi from symptomless shoots of naturally infected olive trees. International Microbiology 10:77-84.
2. Quesada, J.M., Renyalver, R., Pérez-Panadés, J., Salcedo, C.I., Carbonell, E.A., López, M.M. 2010. Dissemination of Pseudomonas savastanoi pv. savastanoi populations and subsequent appearance of olive knot disease. Plant Pathology 59:262-269.
3. Marchi, G., Viti, C., Giovannetti, L., Surico, G. 2005. Spread of levan-positive populations of Pseudomonas savastanoi pv. savastanoi pv. savastanoi, the causal agent of olive knot, in central Italy. European Journal of Plant Pathology. 112:101-112.
4. Penyalver, R., García, A., Ferrer, E., Bertolini, E., Quesada, M.M. Salcedo, C.I., Piquer, J., Pérez-Panadés, J., Carbonell, E.A., del Río, C., Caballero, J.M., López, M.M. 2006. Factors affecting Pseudomonas savastanoi pv. savastanoi plant inoculations and their use for evaluation of olive cultivar susceptibility. Phytopathology 96:313-319.