Plant Disease and Defences

• Plants can catch diseases from a range of microorganisms including fungi, bacteria, and viruses, as well as from larger organisms like insects.
• Plants can also get deficiency diseases which can happen if they don't get enough essential minerals like nitrates or magnesium ions.
• Nitrates are needed for making proteins and therefore for growth, so plants without sufficient nitrates often get stunted growth where they don't grow as much as they should.
• Magnesium ions are needed for making chlorophyll which in turn is needed for photosynthesis, so plants with a magnesium deficiency often suffer chlorosis from lack of chlorophyll and have yellow leaves.
• Some other symptoms that diseased plants might have include abnormal growths or lumps, malformed stems or leaves, patches of decay or spots of discoloration on their leaves.
• To diagnose disease, the easiest thing to do is to take basic observations and try to match the symptoms that you see to a disease listed in a garden manual or a website.
• If that fails, then you could send a sample of the diseased plant to a plant pathologist who specializes in plant disease and will be able to do more detailed testing.
• The plant pathologist could take a tissue sample and look at it under a microscope, or they could look for unique antigens that come from particular pathogens using monoclonal antibodies or even better, they could run dna tests that look for pathogen dna.
• Plants have physical, chemical, and mechanical defenses to stop diseases from entering and spreading.
• Physical defenses active physically prevent the entry of pathogens and include a waxy cuticle which often covers the leaves and stems of plants, solos cell walls around each individual cell, and the layers of dead cells that some plants have around their stem like bark.
• Chemical defenses refer to actual chemicals that the plants can secrete, these could be antimicrobial substances which kill bacteria or fungi or poisons that deter or kill insects.
• Plants make so many different chemicals that a huge number of our drugs are derived from plant chemicals including the common painkiller aspirin which comes from the bark and leaves of willow trees.
• Mechanical defenses are similar to physical ones but have more of a function rather than just acting as a physical barrier, they include things like thorns and hairs that stop animals from eating or touching them, or leaves that curl or droop if insects land on them.