plant diseases

• examples of plant pathogens?


  Fungi, bacteria, viruses, insects
• how can plant diseases be identified?

  tobacco mosaic virus- green leaves turn to a yellow/white mosaic pattern, can also make leaves crinkle or curl up

  rose black spot- causes black and purple spots on roses leaves
• what are deficiency diseases?

  Deficiency diseases are diseases caused by a lack of essential vitamins or mineral ions. 
• what does nitrate deficiency do to a plant?

  Without nitrates, the amount of chlorophyll in leaves reduces. This means leaves turn a pale green or yellow colour. This reduces the plant's ability to photosynthesise and grow properly, which reduces the farmers' crop yield.
• how can we treat nitrate deficiency?


  Farmers or gardeners can add chemical or natural fertilisers, such as manure to increase nitrate levels.
• why do plants use nitrates?

  Plants use nitrates as a supply of nitrogen, which is needed to make proteins for healthy growth. Plants absorb nitrates in water through their roots. Nitrates are present in high levels in plant fertilisers.
• what happens when a plant has magnesium ion deficiency?

  Plants use magnesium ions to make chlorophyll in their leaves. Like in nitrate deficiency, the plant is limited in terms of its photosynthetic ability and the plant growth is compromised. Magnesium is a limiting factor in healthy plant growth.
• how do farmers identify plant diseases?

  Farmers use books and the internet to identify plant diseases. They can also take a small cutting of an infected plant to a local garden centre, which have staff that can often help identify and treat the disease. For diseases that are more difficult to identify, cuttings of the plant may be analysed by scientists in laboratories using testing kits containing monoclonal antibodies.
• how do plants physically defend themselves?

  Many plants are covered with a thick bark. This is an external layer of dead cells which forms a physical barrier against infection. In this way it is very much like our skin. Beyond bark, each plant cell has a cellulose cell wall which acts as another barrier against infection. Leaves are covered with a waxy cuticle which also stops their cells from becoming infected.
• how do plants defend themselves chemically?

  Some plants such as mint and witch hazel produce antibacterial chemicals. These limit the spread of bacteria that were not stopped by physical defences. These chemical defences are now used in antiseptics for humans.

  Other plants, like stinging nettles, have developed poisons to stop themselves being eaten by herbivores. These do not defend plants from infection by pathogens.
• what are three mechanical defences plants have?

  1. Thorns and hair- these adaptations protect the plant from damage and keeps vital water stores safe
  2. Drooping leaves- the mimosa podia plant has evolved to close its leaves and then point its stems towards the ground when touched by an insect
  3. Mimicry- some plants can mimic what is around them, Passion flowers grow yellow spots on its leaves so that butterflies don't lay eggs on them and caterpillars cannot eat the leaves