B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Forest Pathology and Disease Management 3 — Questions and Answers
Question 1: Annosus root disease, caused by Heterobasidion irregulare in eastern North America, is best managed in pine stands by applying which material to fresh stumps after thinning?
- Copper sulfate solution
- Borax or urea (Correct answer)
- Lime-sulfur spray
- Neem oil emulsion
Correct answer: Borax or urea
Applying borax or urea to freshly cut pine stumps prevents infection by Heterobasidion spores that land on the cut surface and spread root-to-root.
Question 2: Which of the following forest pathogens is classified as an oomycete rather than a true fungus?
- Armillaria ostoyae
- Ganoderma applanatum
- Phytophthora cinnamomi (Correct answer)
- Neonectria ditissima
Correct answer: Phytophthora cinnamomi
Phytophthora species are oomycetes (water molds) in the kingdom Stramenopila, evolutionarily distinct from true fungi despite similar morphology.
Question 3: What is 'littleleaf disease' of shortleaf pine, and what organisms are involved?
- A viral disease spread by aphids that stunts needle growth
- A disease complex involving Phytophthora cinnamomi and poor soil drainage causing fine root death (Correct answer)
- A nutrient deficiency caused by soil acidification from acid rain
- A mycoplasma disease transmitted by leafhoppers causing reduced leaf size
Correct answer: A disease complex involving Phytophthora cinnamomi and poor soil drainage causing fine root death
Littleleaf disease is a complex involving Phytophthora cinnamomi infecting fine roots, compounded by poorly drained, compacted soils that reduce root function.
Question 4: In the context of biological control of forest pathogens, Peniophora gigantea (Phlebiopsis gigantea) is used to control which pathogen?
- Phytophthora ramorum on tanoak
- Heterobasidion annosum on pine stumps (Correct answer)
- Cronartium ribicola on five-needled pines
- Ophiostoma novo-ulmi on American elm
Correct answer: Heterobasidion annosum on pine stumps
Phlebiopsis gigantea is a commercially available biological control agent applied to pine stumps to competitively exclude Heterobasidion annosum before it can colonize.
Question 5: Which ecological process explains why mature trees in old-growth forests often have greater tolerance to Armillaria root disease than plantation trees?
- Old-growth trees produce more resin that kills Armillaria mycelium
- Structural root buttresses physically block rhizomorph penetration
- Diverse mycorrhizal communities and complex soil food webs suppress pathogen activity (Correct answer)
- Old-growth trees lack the cambium layer that Armillaria requires to colonize
Correct answer: Diverse mycorrhizal communities and complex soil food webs suppress pathogen activity
High diversity of ectomycorrhizal fungi and complex soil food webs in old-growth forests suppress Armillaria by competing for resources and stimulating microbial antagonists.
Question 6: What is the significance of 'somatic incompatibility' in Armillaria species identification?
- It is the mechanism by which Armillaria resists fungicide treatments
- It is used to distinguish between different biological species by pairing mycelial cultures and observing interaction zones (Correct answer)
- It describes the inability of Armillaria to infect conifers versus hardwoods
- It refers to the pathogen's resistance to host chemical defenses
Correct answer: It is used to distinguish between different biological species by pairing mycelial cultures and observing interaction zones
Somatic incompatibility reactions—visible as barrage zones where two cultures meet—are used to distinguish among the many cryptic biological species of Armillaria.
Question 7: The 'zone of inoculum potential' concept is important in managing which group of forest root diseases?
- Foliar rust diseases of pine
- Soilborne root rot pathogens like Armillaria and Phytophthora (Correct answer)
- Canker diseases caused by Neonectria and Cytospora
- Vascular wilt pathogens like Dutch elm disease
Correct answer: Soilborne root rot pathogens like Armillaria and Phytophthora
Inoculum potential describes the energy available for infection by soilborne pathogens per unit area of host root surface, which is key to predicting outbreak risk for root rot fungi.
B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Forest Pathology and Disease Management 3
Annosus root disease, caused by Heterobasidion irregulare in eastern North America, is best managed in pine stands by applying which material to fresh stumps after thinning?