KINGDOM FUNGI
FUNGI range in size from microscopic organisms to larger mushrooms. They are heterotrophic in nature in that they cannot make their own food as they lack chlorophyll, and so they depend on other organisms as a food source. Some are saprophytes while others are parasites.
STRUCTURE: Unlike plant cells which contain the polysaccharide cellulose, fungal cells contain the polysaccharide chitin. Some fungi such as yeast are unicellular but most have the same basic structure consisting of hyphae which branch freely to form a mycelium.
REPRODUCTION: Fungi reproduce by producing spores, either sexually or asexually. A second form of asexual reproduction known as budding occurs in some fungi such as Rhizopus or bread mould. SIGNIFICANCE IN AGRICULTURE Beneficial Effects Some species of mushroom such as Agaricus are a successful food crop. Other fungi are used to flavour cheese.
Fungi are readily used in the production of antibiotics for example penicillin is isolated from the mould Penicillium.
Harmful Effects
DISEASE:
Fungi are responsible for diseases in animals including ringworm and fungal mastitis.
Fungi are also accountable for various diseases in plants including loose smut in barley, blight in potatoes and club root in turnips.
Economic Loss
Dry rot in timber which may be used in farm buildings is caused by a fungus.
Crops such as maize and silage may be subject to spoilage by fungi during storage, decreasing the nutritional value of the foodstuff.
CASE STUDY Phytophytora infestans
CAUSE: The fungus Phytophytora infestans, commonly known as potato blight, was responsible for the Irish Famine in 1846 and remains of great economic importance in Ireland today. Potato blight can affect the crop from June onwards and regular warnings from the meteorological services warn the grower if
climatic conditions that enhance the occurrence of the fungus are prevalent. Such conditions include light winds, moisture and temperature > 20oC.
SYMPTOMS: Brown spots appear on the leaves of the potato plant and eventually the entire plant will appear black and die off.
PREVENTION AND TREATMENT:
Clearing the soil of all tubers when digging potatoes every year is important as potato blight
spreads by fungal spores from old potatoes to new crops in summer. An effective spraying programme is essential to keep the disease at bay. Different spray types such as systemic and contact fungicides may be applied from mid-June onwards until the plant matures. Blight resistant varieties such as the Orla are more expensive to purchase but may be cost effective in the long run. Understanding the life cycle of the fungus may also help to understand the best methods of control.