Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/29/2005
Publication Date: 6/23/2005
Citation: Omer, M.A., Horst, L., Locke, J.C., Pitchay, D., Krause, C.R. 2005. Susceptibility of trailing petunia calibrachoa x hybrida to infection by foliar and root fungal pathogens. Phytopathology. 95(6):S77. Interpretive Summary: Trailing petunia is a popular, new annual crop that has been grown by the greenhouse industry since 1998. This plant is propagated by rooting cuttings taken from hybrid parent plants. Because trailing petunia is such a new crop in the marketplace, little is known about its susceptibility to common fungal pathogens found in the production greenhouse. Since it is closely related to the common petunia, speculation would implicate a number of potential diseases. This research reports the evaluation of the susceptibility of rooted cuttings to infection by commonly found greenhouse pathogens. Two water molds, Phytophthora and Pythium, were grown up and injected into the potting medium near the base of the test plant. After four weeks of growth in the greenhouse, plants were observed for visual symptoms and the roots removed from the medium for observation. All pathogen isolates tested caused some degree of disease. Challenged plants showed death of root tips and fewer secondary roots. Root fresh weight was also reduced by 12-90 percent compared to healthy, non-challenged plants. This research will be useful to researchers involved in developing management protocols for diseases of ornamental plants and will ultimately benefit commercial growers who must manage these potential diseases in their production facilities. With the increasing movement of propagative plant material, it has become important for growers to be aware of potential pathogens that may be associated with propagative plant material.
Technical Abstract: Calibrachoa (Calibrachoa x hybrida) is a relatively new herbaceous annual crop introduced in 1998 by the greenhouse industry. The plant is propagated vegetatively as patented hybrid plants. Because Calibrachoa is such a new crop, little is known about its susceptibility to various pathogens but since it is closely related to petunia, speculation would implicate a number of potential diseases. This research reports evaluation of susceptibility of Calibrachoa cuttings to infection by pathogens commonly associated with greenhouse production. For this study, rooted plugs of Calibrachoa x hybrida cv. Colorburst Violet were transplanted into 10 cm pots containing a peat-perlite mix (70:30 v/v). Two Phytophthora and two Pythium species were cultured on lima bean agar for two weeks and fungal propagules from each were suspended in distilled water. The suspension was injected into the soil 2.5 cm from the stem/soil interface of each plant. After four weeks of incubation on a greenhouse bench, plants were observed for aerial symptoms and removed from the growing medium to observe the roots. All isolates tested were pathogenic with varying degrees of symptom expression. Non-inoculated plants had healthy root systems with an abundance of primary, secondary and tertiary roots. Challenged plants showed necrotic root tips with fewer secondary and tertiary roots. We observed a decrease in root fresh weight from 12-90 % in challenged plants compared to the non-challenged plants. All isolates were recovered from infected plants and their identities were confirmed.