Preface Agriculture in India has come a long way to modern times through pre Green Revolution, Green Revolution and post Green Revolution stage and now we are making efforts for the Second Green Revolution. To realize this dream it is necessary to keep effective checks on the losses of agricultural produce by various agencies including plant diseases. Although integrated strategies of disease management are being advocated for their effectiveness and economic potential yet application of chemical pesticides have been the most relied upon tool to prevent losses from diseases in crops. In this context, it is worthwhile to mention that indiscriminate use of chemical pesticides has resulted in several complications with a particular reference to our environment. Plant diseases take a heavy toll of agricultural produce every year even after considerable improvements in the strategies for their management. One of the reasons behind this irony is improper identification of many of a plant disease which not only dictates invalid measures for their management but also contributes to pesticidal load in the environment through use of illogical pesticides in fairly injudicious amounts. It has, therefore, become necessary to spread awareness among the people involved in education, extension and practice of agriculture of proper characterization of plant diseases with the most appropriate management strategy for the disease. In this context, students, extension workers and farmers stand the major clients who must be armed with information on proper identification method and management of a given plant disease.

A disease is characterized by the sum total of symptoms as expressed by the host plant and the signs of the pathogen involved. As stated earlier, it is the core part of disease diagnosis because in every diseased plant there are some symptoms/signs of the problem regardless of the ease in their visibility. Even in latent infections there are certain clues or at least presence of the pathogen inside the host serves as sign of the pathogen. However, the term, ‘disease’ itself refers to an uncomfortable situation of the concerned host. It reflects in the form of reduction in the vitality and performance of the host to varying degrees depending on the quality and quantity of the factors involved in production of the disease. Study of the characteristics of disease is, therefore, important for its quick and accurate identification.

2.1 Loose Smut of Wheat The disease is prevalent in all the wheat growing areas in the world. However, it is a serious problem in humid and sub-humid areas. The incidence of the disease is comparatively more in cooler and humid parts of northern India as compared to the drier and tropical parts of the country. Being a simple interest disease epidemiologically, this is a threat to the cultivation of wheat for seeds. The disease is therefore, dreaded by seed growing agencies who have to treat the seeds with costly chemicals.

3.1 Damping-off Disease of Seedlings The disease is quite common in nurseries or seedbeds all over the world. It is virtually a serious threat to almost all the nursery crops of vegetables and other crops including tomato, chillies, cauliflower, cabbage, brinjal, cucurbits, tobacco and a number of other crops. The economic importance of the disease is more because it takes the toll of precious seedlings in the very initial stages of the crop cultivation. The seed can become infected with a fungus which may cause darkening and softening of the seed leading to its decay. Similarly, seedlings may also be infected while sprouting or even after emergence. The disease is more serious in heavy soils with poor drainage. Abundant soil moisture with 90-100% humidity and temperature around 200C is favourable for the disease.

In this section we shall discuss diseases that do not involve any parasitic etiology. Such diseases are now more appropriately called ‘Disorders’. The disorder may be of many kinds but all of them have adverse effects on the normal physiology and total performance of the crop host. They are therefore, more often called ‘Physiological disorders’. Lack of proper soil and environmental conditions, nutrient status, irrigation factors and other parameters for successful crop cultivation may result in such disorders.

Suggested Readings Agarwal, V.K. and Sinclair, J.B. (1993). Principles of Seed Pathology, Vol. I and II. CBS Publishers & Distributors, New Delhi India. Agnihotri, V.P. (1988). Perspective of Mycopathology. Mehrotra Publishing House, New Delhi, India. Agrawal, S.C. (1993). Diseases of Greengram and Blackgram. International Book Distributors, Dehradun, India. Agrawal, S.C. (2003). Diseases of Pigeonpea. Concept Publishing Company, New Delhi, India. Agrios, G. N. (2005). Plant Pathology, 5th Ed., Academic Press, New York, USA. Alexopoulos, C. J., Mims, C. W. and Blackwell, M. (1996). Introductory Mycology, 4th Ed., John Wiley and Sons, Inc., New York, USA. Alford, D. (2000). Pest and Disease Management Handbook. British Crop Protection Council (BCPC) Publications, UK.  Anderson, H.W. (1956). Diseases of Fruit Crops. McGraw-Hill Book Company, New York, USA. Atkins, P.C. (1972).  Mushroom Growing Today.  Faber and Faber Ltd., London, UK. Bahl, N. (1988). Handbook on Mushroom, 2nd Ed., Oxford and IBH Publishing Company, New Delhi, India. Baker, K.F. and Cook, R.J. (1974). Biological Control of Plant Pathogens. American Phytopathological Society, ST Paul, MN 55121, USA.  Barnett, H. L. (1976).  Fundamentals of Mycology, 2nd Ed., Edward Arnold, London, UK. Barnett, H.L. and Hunter, B.B. (1998). Illustrated Genera of imperfect Fungi. American Phytopathological Society, ST Paul, MN 55121, USA.   Bawden, F.C. (1964). Plant Viruses and Virus Diseases. Ronald Press, New York, USA. Biddle, A. (2001). Seed Treatment, Challenges and Opportunities. The BCPC Publications, UK.  Blanchard, R.O. and Tattar, T.A. (1981). Field and Leknely Geide to Tree pathology, Academic Press. Londan.