PLANTS' INNATE DEFENCE MECHANISMS AGAINST PHYTOPATHOGENS

Plants are affected by a number of severe conditions including damages caused by phytopathogens, which ultimately reduce productivity. Overtime, plants have evolved different mechanisms for defence against and resistance to invading pathogens, such as bacteria, viruses and fungi in different pathosystems. Defence mechanisms in plants could either be innate or artificial. Innate defence is said to occur when plants are naturally able to limit the development of a specific pathogen or the damage it may cause based on properties inherent in the plant without human intervention. This defence strategy could be divided into pre-existing and induced defence mechanisms. The pre-existing defence strategy comprises defence gardgets endogenously present in the plant even before pathogen colonization. It include the use of superficial structures (such as thick walled tissues, waxes and cuticle), biochemical substances (such as inhibitors released by plant into its environment) and defence through lack of essential factors (such as lack of host receptors and sensitive sites for toxins). The induced defence mechanism only becomes active in response to pathogen attack. It consists of defence through the formation of structures (such as cytoplasmic and cellular defence structures) and through biochemical reactions or the production of certain substances (such as pathogenesis related proteins and phenolics). Proper understanding of plant defence mechanisms against pathogens is important in developing new and improved disease resistant varieties.