What organism causes the deadly “sudden oak death disease”?

Question

BlackTom AI · Accepted Answer

Phytophthora ramorum is the organism that causes sudden oak death.

1) Relevant knowledge points and concepts
- Phytophthora ramorum is an oomycete (a water mold), not a true fungus; members of Phytophthora produce sporangia and motile zoospores that spread in water and on plant surfaces.
- Sudden oak death describes a disease syndrome characterized by bleeding cankers on trunks and rapid crown dieback in oak and tanoak species, first recognized in California and Oregon in the 1990s.
- Distinguishing a causal organism (pathogen species) from disease names or unrelated taxa is essential for correct identification.

2) Step-by-step reasoning process
- Identify the scientific name associated historically and repeatedly with the sudden oak death outbreaks: Phytophthora ramorum.
- Match disease symptoms and epidemiology (waterborne zoospores, leaf and twig infections on many hosts, lethal trunk cankers on oaks) to properties of Phytophthora species.
- Compare each answer option against known biology and nomenclature.

3) Intermediate evidence (no numeric calculations needed)
- Phytophthora ramorum produces sporangia/zoospores that infect many hosts (tanoak, oaks, ornamentals), explaining rapid spread in cool, moist climates and the characteristic bleeding cankers on oak trunks.
- Molecular analyses (DNA sequencing) and isolations from symptomatic trees have repeatedly confirmed P. ramorum as the causal agent.

4) Why the correct answer is correct
- Only Phytophthora ramorum is the scientifically identified pathogen proven by isolation, pathogenicity tests, and molecular diagnostics to cause sudden oak death. Its life cycle and host range match the disease pattern.

5) Why other options are incorrect
- Phycobillin rizhobium: not a recognized pathogen of oak or likely a fictitious name.
- Rhizobium quercus: Rhizobium are nitrogen-fixing bacteria associated with legumes, not oak trunk canker pathogens.
- Cocus nucifera: refers to coconut (Cocos nucifera) or is a mistaken plant name, not a pathogen.
- Anthracnose disease: a disease syndrome (caused by various fungi) rather than a specific organism; does not specifically denote the sudden oak death pathogen.

6) Conclusion
Phytophthora ramorum is the correct causal organism for sudden oak death, confirming the provided answer: Phytophthora ramorum.

What organism causes the deadly “sudden oak death disease”?单项选择题

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