eChapter Name: Introduction and Importance of Plant Pathology in Agriculture
9789390083466
eBook Name: PLANT PATHOGENS AND PRINCIPLES OF PLANT PATHOLOGY
by Dr. Sanjeev Kumar
Plants make up the majority of the earth’s living environment as trees, grass, flowers, etc. Plants are the only higher organisms that can convert the energy of sunlight into stored, usable chemical energy in carbohydrates, proteins and fats. Directly or indirectly, plants make up all the food on which humans and all animals depend. Plants however also gets sick, grow and exhibit various types of symptoms and sometimes whole plant die. It is not known whether diseased plant feel pain or discomfort. If a plant is looking different from its community then it is equal to be disease one. Any biotic or abiotic agents which induce the disease in plant is referred as the cause of diseases.The causative agents of disease in plants are pathogenic such as fungi, bacteria, viruses, protozoa and nematodes and environmental conditions such as lack or excess of nutrients, moisture, light, etc to presence of toxic chemicals in air or soil. These biotic constraints can, at times, seriously compromise food security, For example, potato late blight, caused by Phytophthora infestans, struck Europe like ‘a bolt from the blue’ in the 1840s. In Ireland, about a million people died of starvation and more than a million attempted to emigrate. The reasons for this calamity were the arrival in Europe of a virulent strain of the pathogen, the high dependence of much of the Irish population on potato for sustenance, the lack of resistance in the plant to the pathogen, and weather conditions favorable to epidemic development. There have been other disasters caused by plant diseases such as the Great Bengal Famine of 1943 and the southern corn blight epidemic of 1970-71 in the USA, to name but two. In the former, an estimated 2 million people died owing to the high dependence of most of the population on a single crop, rice, which was attacked by the fungus Cochliobolus miyabeanus. In the USA, by contrast, although in some genus, Cochlobolus heterostrophus, alternative sources of nutrition were plentiful so no one died, although the effect on the agricultural economy was severe.
The first two of these heartbreaking examples demonstrate with brutal clarity that in areas of the world where a large proportion of the population is dependent on a single crop or a few crops, they are at risk should that crop fail owing to one or more devastating diseases. At the present time, the threat is partially great in developing countries, where populations are growing fastest, poverty is endemic , the population depends upon on locally produced staples, and the infrastructure of extension and R&D is often poorly resourced. The losses due to weeds, disease and insects have been estimated to around 40% in the developing and underdeveloped countries. If the post harvest losses (15-20%) are also added , the situation becomes even more alarming.
