Plant Diseases Level 2 – Plant health problems

Introduction Organisms causing diseases are called pathogens and their study is plant pathology. Diseases may be caused by: Organisms causing diseases are called pathogens and their study is plant pathology. Diseases may be caused by: a] Fungi a] Fungi b] Bacteria, b] Bacteria, c] Viruses c] Viruses

Fungi Fungal Diseases Fungal Diseases Fungi, of which there are over 100,000 species, are plant-like but lack chlorophyll so they have to obtain, their food and energy from other dead or living matter. Fungi affect their hosts in different ways and may be:- Fungi, of which there are over 100,000 species, are plant-like but lack chlorophyll so they have to obtain, their food and energy from other dead or living matter. Fungi affect their hosts in different ways and may be:-

Fungi 1] Parasitic - these are the main horticultural fungal diseases. They attack and damage or kill living plants. 1] Parasitic - these are the main horticultural fungal diseases. They attack and damage or kill living plants. 2] Saprophytic - fungi living on dead and dying tissues and organic matter. Many are responsible for initiating the decay of dead plants and breaking them down into organic matter and eventually humus as in a compost heap. 2] Saprophytic - fungi living on dead and dying tissues and organic matter. Many are responsible for initiating the decay of dead plants and breaking them down into organic matter and eventually humus as in a compost heap.

Fungi 3] Symbiotic - fungi living in close and mutually beneficial association with plants eg. mycorrhizal fungi which are found on the, roots of many woody plants in particular. 3] Symbiotic - fungi living in close and mutually beneficial association with plants eg. mycorrhizal fungi which are found on the, roots of many woody plants in particular.

Fungi The majority of fungal diseases are caused by microfungi. These are very small but usually visible to the naked eye eg mildews, grey mould, rust, fungal leaf spots. The majority of fungal diseases are caused by microfungi. These are very small but usually visible to the naked eye eg mildews, grey mould, rust, fungal leaf spots. The larger macrofungi are identified by typical toadstools many of which are specific to particular plants. There are no methods of biological control. The larger macrofungi are identified by typical toadstools many of which are specific to particular plants. There are no methods of biological control.

Fungi Both types of fungi have similar structures and life cycles. A fungus is composed in most species of microscopic tubular threads called hyphae which form a loose 'root- like' structure called the mycelium which ramifies into living or dead matter. Both types of fungi have similar structures and life cycles. A fungus is composed in most species of microscopic tubular threads called hyphae which form a loose 'root- like' structure called the mycelium which ramifies into living or dead matter. The hyphae of most fungi can produce spores by which they reproduce, spreading by wind or water. The hyphae of most fungi can produce spores by which they reproduce, spreading by wind or water. They often produce tough resting spores called sclerotia which can remain dormant for some years and then infect a new crop. They often produce tough resting spores called sclerotia which can remain dormant for some years and then infect a new crop.

Bacterial Diseases Bacteria are much less significant horticultural pathogens compared to fungi [only 1,600 species]. Most bacteria are involved in decomposition. Bacteria are much less significant horticultural pathogens compared to fungi [only 1,600 species]. Most bacteria are involved in decomposition. They are structurally simpler than fungi consisting of a single microscopic cell which reproduces by simple division into two cells, a very rapid process in warm conditions like a compost heap. They are structurally simpler than fungi consisting of a single microscopic cell which reproduces by simple division into two cells, a very rapid process in warm conditions like a compost heap. Symptoms and effects are very similar to fungi. Many infections occur initially through injured tissues and may be spread by rain splashes, insects, animals and pruning tools. They are difficult to control. Symptoms and effects are very similar to fungi. Many infections occur initially through injured tissues and may be spread by rain splashes, insects, animals and pruning tools. They are difficult to control.

Virus Diseases Extremely small organisms - sub microscopic. Viruses enter plant cells and take over the organization of the cell nucleus and produce many more virus particles. Infection is systemic in plants although symptoms may be local. There is no method of chemical or biological control. Extremely small organisms - sub microscopic. Viruses enter plant cells and take over the organization of the cell nucleus and produce many more virus particles. Infection is systemic in plants although symptoms may be local. There is no method of chemical or biological control. Viruses can cause substantial loss of yield and unacceptable appearance. Viruses can cause substantial loss of yield and unacceptable appearance.

Virus Transmission Transmission methods include:- Transmission methods include:- a] Vectors such as peach potato aphid, leaf hoppers, thrips, white fly. a] Vectors such as peach potato aphid, leaf hoppers, thrips, white fly. b] Vegetative propagation methods b] Vegetative propagation methods c] Mechanical transmission by hand and on tools eg. tomato mosaic c] Mechanical transmission by hand and on tools eg. tomato mosaic

Virus Symptoms Symptoms may include:- Symptoms may include:- a] Leaf mosaic, a yellow mottling eg, tomato mosaic a] Leaf mosaic, a yellow mottling eg, tomato mosaic b] Leaf roll eg. potato leaf roll b] Leaf roll eg. potato leaf roll c] Stunting_ eg. Chrysanthemum stunt c] Stunting_ eg. Chrysanthemum stunt d] Flower colour break eg. tulip break virus d] Flower colour break eg. tulip break virus

Virus - Control Control is primarily by cultural methods including:- Control is primarily by cultural methods including:- a] Using virus free certified plants. eg. potatoes, strawberries, raspberries a] Using virus free certified plants. eg. potatoes, strawberries, raspberries b] Using virus resistant plants eg. Tomatoes resistant to TMV b] Using virus resistant plants eg. Tomatoes resistant to TMV c] Rotation to minimise soil borne viruses transmitted by eelworms c] Rotation to minimise soil borne viruses transmitted by eelworms d] Controlling vectors especially aphids d] Controlling vectors especially aphids e] Rogueing and burning infected plants e] Rogueing and burning infected plants