I. Completion. (24 pts)
1. Pathogens that kill host cells, often in advance of their colonization, and live off the breakdown products of dead cells are_____________________________.
2. Plant pathogenic nematodes are equipped with a ______________________, a specialized feeding structure that is not present in saprophytic forms.
3. Long distance transport of viruses in a plant occurs in the ___________________.
4. The asexual spore bearing structure in the Oomycetes is the ___________________.
5. The ___________________________ is a small, mushroom-shaped sexual fruiting body in the Ascomycetes.
6. A foreign substance which when injected into a warm blooded animal elicits an immune response is a(n) _______________________________.
7. The life cycle strategy, _____________________________________, is typical of the female clover cyst nematode who tunnels inside a root and establishes a permanent feeding site at which she will feed for the remainder of her life.
8. Plant pathogenic bacteria gain entry into a host through ____________________________ and ______________________________.
9. Nematode sensory structures are located on the ______________________________.
10. Bacteria reproduce by _____________________________.
11. Viruses gain entry into their hosts primarily through ___________________________.
II. Name four plant functions that are disrupted by a plant disease and name the primary symptom associated with the dysfunction. (10 pts)
Select one of your answers and describe the pattern (fingerprint) of symptoms on an individual plant
III. Below is an article on a disease of a fruit tree grown in Southeast Asia. After you read this article, please answer the following questions.
Durian (Durio zibethinus Murr.) is a popular fruit tree grown extensively in Southeast Asia for its highly valued fruits. A stem canker was found on many durian trees in an orchard in Sungai Liang, Brunei Darussalam. This disease, commonly known as patch canker, is widespread in other countries in this region. Although symptoms were found in the main trunk near the base and on lower branches, they were prominent at the point of branching between the main trunk and lateral branches. The symptoms were characterized by a reddish brown discoloration of the outer bark, areas of necrosis on the bark, and a reddish brown discoloration in the outer sapwood. Disease symptoms of the tree canopy ranged from gradual defoliation to dieback of twigs from the top of trees. Cultures of a single fungus derived from infected bark from canker margins were grown on potato dextrose agar and tap water agar. Abundant sporangial production by the fungus occurred on these media and the fungus was identified as Phytophthora palmivora (E. J. Butler) E. J. Butler. This is the first published report of patch canker of durian caused by P. palmivora in Brunei Darussalam. The disease could pose a threat to the durian industry in this country.
1. Name of the disease is ______________________________________. (2 pts)
2. Cause of the disease is ______________________________________. (2 pts)
3. Host of this disease is ______________________________________. (2 pts)
4. The pathogen belongs to the fungal class _____________________________. (2 pts)
5. What primary symptoms were observed? (2 pts)
6. What secondary symptoms were observed? (2 pts)
7. Differentiate between primary and secondary symptoms? (4 pts)
8. Necrosis was observed. Define necrosis. (2 pts)
9. The fungus was cultured on two agar media, potato dextrose agar (sugar + potatoes) and tap water agar. Would either of these media be selective or differential in nature? Explain your answer (4 pts).
IV. Match the pathogen group in the left hand column with the terms in the right hand column (20 pts).
| _____ eukaryote
_____ extracellular enzyme
V. Below is a schematic diagram outlining replication by viruses in plant cells. Briefly describe the parts of the replication process that are indicated by the numbered arrows (11 pts).
What are the major proteins responsible for replication, movement and assembly of a virion?
VI. Three patterns of diseased plants are seen in forests, crop land, and landscapes. Name and describe the patterns. (6 pts)
VII. Name the three components of the plant disease triangle. (3 pts)
VIII. Bacteria gain nutrition from a plant by three ways. What are they? (3 pts)