Samantha L. Thomas, Landon H. Rhodes, and Michael J. Boehm
Department of Plant Pathology, The Ohio State University, Columbus, OH
Answers to Follow-up Questions
- Give two examples of how aseptic technique was used in this experiment. Why do you think this was important?
Examples: Sterilize forceps tips, surface-sterilized seed, sterilize probe tip or sterile toothpicks, sterile wooden stick
Rationale: To reduce the chance that tubes or seeds may become infected or colonized by a contaminant.
- Were there differences in the rate of root infection and perithecial development between creeping bentgrass and wheat?
Please note that this will vary depending on the isolate!! With our work we have found that some isolates prefer to produce perithecia on wheat and some on bentgrass; this is why we suggest that the experiment be performed prior to using with students.
Generally, similar rates of root infection and perithecial development occur. However, infection will be more noticeable to the inexperienced student on wheat roots first, as they are larger and fewer in number. Also, due to the fact that the creeping bentgrass has to germinate, there will some delay between wheat and bentgrass.
- What was the purpose of including non-inoculated tubes? Were there any differences observed between the non-inoculated and the inoculated tubes? If so, what were they?
The purpose of the non-inoculated tubes was to provide an untreated control-that is, a non-infected plant to compare with the infected plant. This permits one to assess the effect of disease on growth and development of the host plant.
The non-inoculated wheat tube will lose more water over time as compared to the inoculated tube as all of its roots remain functional throughout the duration of the study. Other differences are: plants in inoculated tubes tend to become chlorotic sooner (the control plants will eventually become chlorotic to the lack of available nutrients); and plants in inoculated tubes will have roots with vascular discoloration.
- Describe where the perithecia were produced on each host. Given their location, what role do you think perithecia play in the disease cycle?
Again, perithecial location will vary depending on the isolate. Generally perithecia produced in wheat tubes are embedded in root or lower stem tissue. Perithecia produced in bentgrass tubes are generally produced in the medium surrounding the roots-not embedded, probably due to differences in the root mass available. For either example, the majority of perithecia are formed below the surface of the rooting medium. Given this location, perithecia may act as overwintering structures (associated with crop residue).
- From your observations, how do you think the fungus is affecting water uptake of the plants?
Observations: Dark hyphae should be noticed growing from the agar plug towards host roots followed by the production of infection points, which are slightly darkened areas where the hyphae penetrate the host root (usually associated with the hyphae either disappearing into the root or the beginning of ectotrophic growth along the root). Dark ectotrophic hyphae are often produced abundantly (again, depending on the isolate). Once an infection point is noticed, it is generally no more than 3-4 days before a discoloration of the stele appears. The appearance of vascular discoloration is quite apparent after 10-14 days. The vascular discoloration is the effect of the fungus colonizing the area plus the effect of any plant defenses induced to stop the spread of the pathogen.
Answer: Given these observations, the fungus is plugging the vascular system of the roots, and water and nutrient uptake by these roots is severely reduced. Only unaffected roots will remain capable of translocating the nutrients and water necessary for continued plant growth.
