DURATION: 3 HOURS TOTAL MARKS: 150. External Examiner: Dr K.S. Yobo Internal Examiner: Mr C. Becker/ Prof M.D. Laing

Transcription

1 DURATION: 3 HOURS TOTAL MARKS: 150 External Examiner: Dr K.S. Yobo Internal Examiner: Mr C. Becker/ Prof M.D. Laing NOTE: THIS PAPERS CONSISTS OF FIVE (5) PAGES, PLEASE SEE THAT YOU HAVE THEM ALL. QUESTION 1 1.1) Give five examples of agricultural practices that affect the spread of disease. Discuss each example briefly. (15) 1.2) Use annotated diagrams to differentiate between simple, multiplepored and dolipore septa. (6) 1.3) Give the common name and host plant for the diseases caused by the following pathogens: i) Sphaerotheca pannosa f. sp. rosae ii) Fusarium oxysporum f. sp. lycopersici iii) Plasmodiophora brassicae iv) Tilletia caries (4) QUESTION 2 2.1) Define plant disease. (2) 2.2) Explain how to differentiate between biotic plant disease and abiotic plant disease. (2) 2.3) Give two examples of biotic causes of plant disease and two examples of abiotic causes of plant disease. (4) 2.4) Explain the concept of a disease cycle and state the primary events that occur during a disease cycle. (6) 2.5) Outline the 8 primary steps in the production of button mushrooms. (8) 1

2 2.6) Discuss the event of parasexuality that occurs in some fungi. What is its significance? (3) QUESTION 3 3.1) Discuss the vesicular hypothesis of hyphal tip growth. Use annotated diagrams to explain the hypothesis. (8) 3.2) You are asked for help from a local nurseryman who is experiencing disease problems with his grapes. You suspect that the pathogen causing the disease is Plasmopara viticola. i) What fungal subdivision does P. viticola belong to? (1) ii) What is the common name of this disease? (1) iii) Recommend three methods that the farmer could use to achieve control of the disease. (3) 3.3) In which fungal subdivision do clamp connections occur? (1) 3.4) Perithecia and pycnidia appear similar to the naked eye and can be difficult to tell apart. Use annotated diagrams to illustrate how they differ internally. (6) 3.5) Discuss the role that insects play in the spread of viral diseases. (5) QUESTION 4 4.1) Give the names of three types of plant parasitic nematodes and use an illustrated diagram to show where each type would be found feeding on a plant root. (6) 4.2) Name the pathogen that causes black rot of crucifers. Explain three measures that can be used to control the disease. (6) 4.3) Natural/wild pathosystems are less likely to suffer from plant disease epidemics than crop/manmade pathosystems. Discuss this statement using diagrams to illustrate your answer. (5) 2

3 4.4) Name the four types of conidiomata that are produced by the Deuteromycetes. (4) 4.5) Define the following terms: i) Chlamydospore ii) Chitosome iii) Heterokaryotic iv) Prosenchyma (4) QUESTION 5 5.1) There are no treatments that can cure plants infected with viruses. It is important to use preventative measures to prevent infection from occurring. Explain how the following measures can be used to control viral diseases: i) Avoidance (2) ii) Eradication (2) iii) Protection (2) 5.2) Complete the following table: Differences between ectomycorrhizae and endomycorrhizae (9) Characteristic Ectomycorrhizae Endomycorrhizae Types (a) (b) Presence of sheath on outside of root (yes/no) (c) (d) Inter- or intracellular hyphal growth (e) (f) Hosts (g) (h) Presence of root hairs (yes/no) (i) (j) Appearance of roots (k) (l) Increased nutrient uptake (m) (n) Presence of arbuscules and vesicles (o) (p) Fungal subdivision (q) (r) 5.3) What is the scientific name of the mushroom species that is involved in a symbiotic relationship with termites? To which fungal subdivision does this species belong? (2) 5.4) What are the names given to the three phases of sexual reproduction in fungi? (3) 5.5) Discuss the methods by which nematodes are disseminated. (5) 3

4 QUESTION 6 6.1) Not all fungi are harmful and many can be found as partners in symbiotic relationships with other organisms. Lichens are an example of symbiosis between algae and fungi. Explain what each partner provides the other in this symbiotic relationship. (5) 6.2) The Ascomycetes can be divided into five classes based on the type of ascocarp they possess. Name each group and state the name of the ascocarp found in each group. (10) 6.3) Define the following terms: i) Crozier ii) Clamp connection iii) Heterotrophic iv) Gametangium (4) 6.4) Give the scientific name of the organisms that cause the following diseases: i) Ergot of rye ii) Boil smut of maize iii) Bacterial wilt of potato iv) Grey mould of strawberries (4) 6.5) Discuss what you understand by the terms lumpers and splitters in taxonomy. (2) QUESTION 7 7.1) When a pathogen is discovered, various steps need to be followed to confirm that the pathogen is the causal organism of the disease. What is the name given to these steps? State each step. (5) 7.2) Rust fungi are notorious for their spore polymorphism. Name the five different spore types and the five distinct fruiting bodies in which they are found. (10) 7.3) Use annotated diagrams to discuss the formation of the asci and ascospores of the Ascomycetes. (8) 4

5 7.4) What is the difference between macro- and microelements when referring to the nutrition and growth of fungi? Give one example each of a macro- and micro-element. (2) 5