My class was with Ms.Lisa Burton at 1pm. The topic that she thought us was Plant Diseases caused by micro-organisms that can live on, or inside, our plants causing damage to them. the three main types of micro-organisms are fungi, bacteria and viruses.
Physiological Disorder that when any environmental factor is affecting plant growth in a negative way. For example climate factors may be too much sun, frost soil factors due to lack of nutrients.
All living organisms require energy to grow, including micro-organisms. They gain this energy from consuming other organisms such as plants. Some are parasites - they feed on living tissue. Some are saprophytes which they feed on dead tissues.
Which type of micro-organism do we want and why? When a parasite lives on a plant it effects the growth of the plant.
Which type of micro-organism do we not want and why? When the parasites lives on a plant it effects the growth of the plant. When the parasite causes distinct disease symptoms we call the parasite a pathogen.
A pathogen is a general term for an organism capable or causing death. The sign are any part of the pathogen we can see e.g. the body of the organism itself. The symptoms are plant reaction to being attacked by a pathogen @yellowing.
Causes of Diseases - the caused by bacteria, fungi and viruses. Fungi cause the greatest number of diseases. Diseases mainly occur when a pathogen alters one or more of the plants internal processes. This will result in the plant displaying various symptoms and / or displaying visible signs of the disease.
Ms. Lisa taught us on Fungi. What is Fungi? Fungi are very small organisms which are often only visible through a microscope. Fungi are either parasites or saprophytes, so they can not make their own food, and therefore do not contain chlorophyll, the green pigment in other plants.
Structure of Fungi it is important to understand the structure and behaviour of fungi in order to understand how they affect plants. The body of a fungus is made up of fine strands called hyphae. Some hyphae have "walls" dividing them, others will be continuous strands. A tight mat of hyphae is called mycelium.
Nutrients Uptake by Fungi -
- Fungi absorb nutrients by penetrating the food source with their mycelium
- Individual hyphae of saprophytic fungi secrete enzymes which break down the food source into nutrients it can absorb
- Parasitic fungi obtain nutrients from within living cells producing special sac-like structures called haustoria, which form at the ends of hyphae that have entered living cells. Haustoria absorb nutrients from the cytoplasm.
How Fungi Infects Plants -
1. Once dispersed, the spores which land on a host plant will lay dormant until conditions are
favourable.
2. Spores require certain temperature and humidity conditions to germinate.
3. The exact conditions will vary according to the fungi species.
4. On germination, the spores produce a small hypha called a germ tube, which will eventually form the
mycelium.
5. Fungi enter the plant tissue via wounds, natural openings, through the cuticle and epidermis.
6. Once inside the plant, the fungi will disrupt normal cell activities by removing nutrients and secreting
toxic substances.
How fungi Spread through spores over large distances and depending on the type and it spread by air, water, insects, birds, people tools and seeds.
Signs and symptoms of Fungal Diseases:-
Blights - First shows as large irregular, water soaked areas on soft leaves and stems; can spread to fruit. Can spread rapidly and quickly ruin a crop.
Cankers & diebacks - Lesions on stem of trees and shrubs. Plant will die out above the canker if it girdles the stem.
Damping-off - Infected seedlings collapse, fall over and die. Pythium and Phytopthora (wet soils). Rhizoctonia spp. (dry soils)
Downy Mildews - Pale areas on the upper leaf surface, often watery appearance. Corresponding "downy" growth on lower surface. Requires humidity and leaf wetness.
Galls - Abnormal swellings or nodules on a plant. Can occur all plants part depending on the infection.
Leaf spots - spots of various patterns and colours on fruits and leaves. Size, colour margins, signs, habit will all assist identify fungi.
Moulds and Rots - Plants parts decay. Mycelium shows on moulds but absent with rots. Some moulds will not cause decay - sooty mould contained on plant surface. Root rots cause wilting.
Powdery Mildew - Discoloured and distorted leaves. Upper leaves surface covered in white mycelium. Spores borne on chains on upright hyphae. Require high humidity and temperature but not wet.
Rusts - Postules which raised lumps on underside of leaves are fruiting bodies. Corresponding yellowing on upper side of leaf. May change colour during season as spore type changes.
Wilts fungi e.g Phytopphthora - loss of water from plants. More obvious in herbaceous plants. Woody plants produce short unhealthy shoots, yellowish leaves, wilting and eventually dieback from tips. Collar rot on deciduous trees.
Several fungal symptoms don't fit into previous groups are Turf which has brown patches, fairy rings and red thread. Fruits symptoms are peach leaf curl, bladder plum, verrucosus and flowers symptoms are tulip fire.
No comments:
Post a Comment