14.2 A few examples of headline crop diseases

There are too many plant pathogenic fungi for us to list here, so we will limit our examples to a few that illustrate specific general points that we will develop in more detail later in this Chapter.

Generally, ‘disease’ is any physiological departure from the normal health of a plant. Disease may be caused by living (biotic) agents (fungi, bacteria, viruses) or by environmental (abiotic) factors, for example nutrient or water deficiency, anoxia, excessive heat, high ultraviolet radiation, or pollution. To protect themselves from damage, plants have developed a wide variety of constitutive and inducible defences.

Constitutive defences include many preformed barriers such as cell walls, waxy epidermal cuticles, and bark. These substances not only provide the plant with a barrier to invasion, they also give the plant strength and rigidity.

In addition to preformed barriers, virtually all living plant cells can detect invading pathogens and respond with inducible defences that include production of toxic chemicals, pathogen-degrading enzymes, and deliberate cell suicide. Plants often wait until pathogens are detected before producing such defences because of the high energy costs and nutrient requirements associated with their production and maintenance (Freeman & Beattie, 2008; Faulkner & Robatzek, 2012).

The pages that immediately follow give only a brief description of a mere handful of the numerous fungal diseases of plants. If you would like to get more information on plant diseases we suggest you look at the URLs shown in Resources Box 14.1.

Resources Box 14.1

Where to find more information about crop diseases, crop losses, plant pathogens and food and agriculture statistics

We have a page giving references to scientific papers and hyperlinks to online resources.

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Updated July, 2019