Lesson 5 Nursery Diseases and Mycorrhizas Flashcards
What are the two types of seedlings that are produced for regenerating forests?
“Bare root” seedlings are grown in “normal soil”, much like you would see in any other agricultural production of plants. Containerized seedlings are grown in more controlled environments, where the soil is often synthetic and fumigated to reduce pathogens. Bare root soil can also be fumigated too but is less common.
Describe some abiotic injuries typically suffered in forest nurseries.
Mostly due to weather conditions, most notably low temperature, and heat/moisture stress. Other types of abiotic injuries include poor nutrition, herbicide injuries (chemical), and watering issues (over or under).
What are the typical types of diseases affecting seeds, roots, and the root collar area of seedlings?
“Dampening off” is the most notable disease affecting both seeds and seedlings. Preemergence dampening off is where the pathogen kills the seeds before they are visible. Postemergence dampening off affects newly emerged seedlings.
Root rot is another common nursery disease caused by Fusarium, Pythium, and Cylindrocarpon spp. These fungi attack the seedling roots as the emerge from the seed in various ways.
What are pre- and post-emergence damping off?
“Dampening off” is the most notable disease affecting both seeds and seedlings. Preemergence dampening off is where the pathogen kills the seeds before they are visible. Postemergence dampening off affects newly emerged seedlings.
Explain why containerized seedlings might have different disease problems than bareroot seedlings.
Containerized seedlings are usually protected from most abiotic diseases since they exist in more controlled environments such as greenhouses where they can be protected a gains low temperatures or irrigation. Because bareroot seedlings are in traditional soils, it is more difficult for managers to fumigate the soil, and they are therefore more susceptible to biotic agents such as fungi or nematodes.
Soil fumigation with methyl bromide is widely used throughout the world to control soil borne nursery diseases. Discuss the pros and cons of this practice?
The most notable downside of using this chemical is the environmental issues it presents. When it breaks down, it creates bromine, which depletes ozone. It has since been phased out in the USA and CAN since 2005.
The pro of using this chemical is that it is a broad-spectrum pesticide that can effectively eliminate many pathogens and disease-causing agents such as nematodes, insects, weeds, and rodents.
What alternatives are available for managing seedling diseases other than soil fumigation?
Nonchemical alternatives to this method include biological controls, soil pasteurization, and cultural practices, seed treatment with fungicides.
What are the two basic types of mycorrhizas formed with forest trees? What are their features?
Ectomycorrhizas: dominate commercially important tree genera. Characterized by a sheath of fungal tissues, and a hartig net that externally latch onto the plant root.
Endomycorrhizal/Arbuscular mycorrhizas: produce arbuscular or branched hyphae-like trees. They are the most abundant mycorrhiza and found in every taxonomic group of plants. They form their relationship within the cells of the plant roots.
What types of mycorrhizas occur on pines, firs, hemlocks, spruces, and cedars?
Ectomycorrhiza form on these species. The are most associated with commercially important species in BC.
Also Endomycorrhiza.
What are the functions and roles of mycorrhizal fungi?
Mycorrhizae
Mycorrhizae form symbiotic relationships with their host. The fungus provides water and nutrients, extends the reach of the roots, protects against drought and pathogens. In exchange the plant provides carbohydrates for the fungi.
