ASHS 2015 Annual Conference

The ability to detect, identify, and measure plant pathogens that are living inside of plant tissue is a critical component of research involving chemical treatments to induce disease resistance in nursery plants. Visual assessment for pathogen symptoms in inoculated plants may not be accurate because partial inoculations may be non-symptomatic due to low infection rates.  In this study a PCR method was evaluated to positively identify a wilt bacterium in plant tissue using its DNA barcode. The same PCR method was also used to semi-quantify the concentration of the bacterium inside the plant tissue. A study was conducted at Colorado State University in 2014 to test chemicals for inducing disease resistance in kidney bean seedlings inoculated with Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), a vascular wilt disease. ElectroBiocide and Actigard were applied to seedlings to stimulate the natural plant defenses against the pathogen.  At plant harvest the stem sap was collected on chemically-treated cards (FTA^®cards) to extract the DNA from both the plant and the bacteria. The cards were then analyzed at the University of Alabama. Card extract samples from a pure Cff bacteria culture and from non-inoculated plants were also collected to validate the DNA profile for each species. The results show that the PCR methods could readily distinguish the DNA profile of the Cff bacteria from the kidney bean tissue. The DNA analysis verified that all the inoculated kidney bean plants were successfully inoculated with the Cff wilt, while the non-inoculated plants showed only a trace level of Cff wilt DNA.  Finally, the bacteria DNA was ranked, among the four chemical treatment combinations for the inoculated plants. These DNA results indicate that the chemicals did not induce disease resistance to the wilt disease, as the DNA ranking for the four treatments was equivalent to the inoculated control treatment.  Induced disease resistance is primarily focused on foliar, chemical defense mechanisms. In this study the plants were stem inoculated, thereby side stepping the primary foliar defenses against the vascular wilt disease.  Also, the FTA card extraction had varying amounts of sap applied for each sample, which resulted in a crude estimate off Cff bacteria inside the plant.