Today the class was with Ms.Lisa Burton starts at 11.00 - 12.00pm and 1.00pm to 3.00pm.
The topic that she thought us was on Bacteria. Bacteria are very small one-celled plants. It like fungi they lack chlorophyll. Most bacteria are Saprophytes which are useful as they break down organic matter. Only a few bacteria are plant parasites. All the plant parasitic bacteria are facultative saprophytes. Bacteria cells about 0.001 mm long. It a great diversity in shape and flagella (tails).
How bacteria cause disease
It is small size allows bacteria to easily invade plant tissue via natural openings and. wounds. Aerial bacteria which infects plants through recent wounds, lenticels, stomata and fresh abscissions. Soil bacteria which infects roots or crowns, enter via small wounds caused by cultivation. Bacteria can easily infect young tissue, therefore seedlings and fresh growth are at risk.
How bacteria spread
Reproduction is by asexual cell division called fission. In favourable warm moist conditions the cell grow quickly and divide. Aerial bacteria form colonies inside infected plants, producing a slime which comes from the plant in wet weather and is spread by rain splashes, irrigation water insects and dirty tools. Soil bacteria are spread in surface water run-off, dirty tools and machinery. They can swim short distances in soil water. Bacteria infect the developing seed.
How bacteria survive
All plants-disease bacteria become inactive in dry conditions. Remain protected but inactive inside disease tissue, however will die if removed from the host plants. Soil-living disease bacteria live as saprophytes in absence of host plant and can last for many years.
Symptoms the pathogens concerned may cause completely different symptoms on other host plants. In many cases a similar symptoms on a different host is caused by a different pathogens.
Crown Galls - Abnormal swellings or outgrowths on a plant. The infested roots and crown develop large, rough galls. The roots and crown grow poorly which equal to stunned growth, reduced yield. Other parts of plants may show galls too.
Cankers and dieback - This disease areas are on the stems. Often have bacteria ooze. Plants dies above if canker girdles stem which equal to dieback. For example are blast and fireblight.
Leaf and fruit spots - They have various pattern and colours. Bacterial spot often look oily and may have a pale halo. As the tissue dies in spots it falls out giving a shortgun appearance.
Rots - This cause of the plant to decay. Water soaked appearance. and give leaves a shot hole appearances.
Controlling bacteria
- Control measures are different for soil borne and aerial bacteria.
- Timing is critical - lifecycle.
- Bacteria diseased are difficult to control ad usually require a combination methods.
- Mostly bactericides are protectant, bactericides are not systemic.
- Fungicides have little effect on bacteria with exception of copper-based sprays
- use resistant cultivar
- Plant only disease- free plants
- Use disinfected seed
- Disinfect the soil
- Use good crop hygiene practices
- Use careful growing practices, regular watering, feeding, care when cultivating
Viruses
It a very tiny particles that can only be seen under an electron microscope. All are parasitic and cause diseases in plants and animals.
How Viruses Cause Disease :
- Viruses interfere with the plants essential growth processes and energy systems.
- The virus particle cannot reproduce itself so it tricks the plant into making many more.
- The host cells use a lot of energy to reproduce the virus and the plant begins to loose vigour.
How Viruses Spread :
- Within the plant
- Carried from cell to cell in the cytoplasm through tiny tubes called plasmodesmata (very slow)
- through the plants sap stream in the phloem (rapid)
Between plants
- Must remain in plant sap, cannot spread on its own
- Wounds caused by pests, pathogens or environment
Viruses are difficult to control because they are not cellular, therefore we cannot use pesticides, as they are designed to disrupt the cellular organisation and they are protected inside the plant.
How do we prevent infection?
- keep viruses out of NZ by border controls
- Control insect vectors
- remove diseased plants
- Hygiene
- Propagate from virus free stock
- grow from seed and viruses don't normally spread to seed
- Use resistant tolerant cultivars
Mosaics - most common symptom, mottled light or dark green. Mottling may be in a defined pattern. In monocotyledons the mottling may occur as streaks along the veins.
Ring spots - These are chlorotic or necrotic rings which occur on leaves and sometimes the fruit and stems.
Chlorosis - They are yellowing of the green tissue due to a loss of chlorophyll. May appear as spots, inter-veinal spots and often about the leaf margins.
Necrosis - The spots of cells die with in the leaf, these may fall out giving a shot hole appearance. They can also show as streaks on the stems.
Distortion of leaves and fruits - The narrowing, rolling or crinkling of the leaf. The suppression of leaflets. Fruits misshapen and often have a crinkled surface.
Disorders - Plant disorders are typically caused by the following three factors such as unfavourable climatic conditions, nutrient deficiencies or toxicities and poor management.
1] Plant disorder due to climate such as light which is lack of light can cause poor growth and weak looking plants, typically etiolated, or stretched. Intense sunlight can cause sunburn in some plants and fruits.
Plants disorders or physiological disorders are the response by plants to unfavourable conditions caused by abiotic (non living) factors. No pathogen is involved in plant disorders.
Many crops have been severely damaged where poor interpretation has occurred, and incorrect treatments applied, particularly with nutrients disorders.
Temperature which are high can cause necrotic or dead patches on leaves. Low temperature can cause freezing and result in a range of damage symptoms including black burnt looking shoots, ring pattern on fruit and death of flowers. Extremely low temperatures can caused vertical cracking of bark on some trees. Russet is also a common damage.
Hail can obviously can cause tearing and bark damage, pitting of fruits and flowers. A risk of disease infection can follow hail.
Wind the symptoms is to damage can also vary from tattered leaves, wilted stressed plants, bruised fruits and flowers, wind rock and root damage.
Water excess and storage too much can result in wilt, dieback from the tips and the associated diseases of wet soils. The death of roots will cause drought-like symptoms such as dieback. Cracked fruits can result from over watering. A lack of water will result in wilt, shoot dieback, premature leaf-fall and eventual death.
2] Plant disorder due to nutrients and it always advisable to take leaf samples as a routine horticulture operations. It is highly recommended that you consider leaf sampling where nutrient issues are considered the problem.
- Nitrogen deficiency
- Phosphorous deficiency
- Potassium deficiency
- Sulphur deficiency
- Calcium deficiency
- Magnesium deficiency
- Zinc deficiency
- Manganese deficiency
- Boron deficiency
- Iron deficiency
- Copper deficiency
3] Plant disorders due to poor management and there are literally dozens of disorders that could result form poor management, and one could argue that poor climate management and nutrient status is also a management issue. For the purpose of this project we have tried to isolate climate and nutrients separately from the other management problems that can result.
Ms. Lisa Burton was reminding all students that there will be a test on disease on 13 June, 2013 and a assessment
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