Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 20, 2003
Publication Date: March 10, 2004
Citation: Gracia-Garza, J.A., Blom, T.J., Brown, W., Roberts, D.P., Schneider, K., Freisen, M., Gombert, D. 2004. Increased incidence of erwinia soft-rot on calla lilies in the presence of phosphorus. European Journal of Plant Pathology. 110:293-298.
Interpretive Summary: Erwinia carotovora subsp. carotovora is a soilborne plant pathogenic bacterium that causes serious soft-rot disease that results in economic losses on calla lily and other crops. Effective control measures are limited for control of this pathogen on calla lily. This research was performed to determine the influence of certain cultural practices on severity of disease caused by E. carotovora subsp. carotovora on calla lily. It was found that superphosphate incorporated into the planting medium significantly enhanced soft-rot by this bacterium. In contrast, phosphate added in nutrient solution did not increase soft-rot severity. It was also found that phosphate added in nutrient solution met the phosphorous nutritional needs of calla lily plants. Therefore, growers can supply phosphorous in nutrient solution to meet the phosphorous nutritional needs of calla lily and limit soft-rot disease losses. This information will be useful to scientists and growers.
Erwinia soft-rot is an important disease of many ornamental crops. In particular, it is one of the most limiting factors on greenhouse calla lily production. In preliminary experiments, it was observed that addition of phosphorous to the soil-less mix used for greenhouse forcing of tubers of calla lilies, increased the severity of the disease caused by Erwinia carotovora subsp. carotovora (Ecc). A series of experiments was conducted to test the effect of phosphorous added to soil-less mix or to nutrient solutions used for irrigation, and to study the effect that phosphorous has on calla lily tubers and on the pathogen. Soft-rot incidence was significantly increased when superphosphate was added to the soil-less mix (51%) in comparison to regular soil-less mix (no superphosphate added) (31%). In tests conducted in a commercial greenhouse with a larger sample size, similar results were obtained. In laboratory experiments to determine the effect of phosphorous on tuber root development, no statistical differences were found between tubers sprayed with water (control) or with a 0.5 mM solution of KH2PO4. In other experiments, tubers were sprayed with either water, a bacterial cell suspension (Ecc), a solution of KH2PO4, or a suspension of Ecc in KH2PO4. The results from these tests showed a significant increase of soft-rot development in tubers treated with the suspension of Ecc prepared in a solution of KH2PO4. Further laboratory tests indicated that enzymatic activity (polygalacturonase and pectate lyase) of Ecc increased when grown in the presence of phosphorous.