Indian Phytopath. 52 (1) : 1-9 (1999) Pathogen diversity and plant disease

I express my deep sense of gratitude and apprecia-tion to the Executive Council of the Indian Phytopatho-logical society (IPS) for nominating me to present this prestigious Jeersannidhi Award Lecture for 1998. By bestowing this honour, the IPS has put me in the select group of plant pathologists of India. I happen to be the 15th speaker of this important lecture ofIPS. The topic for my presentation, "Pathogen diversity and plant dis-ease management", is probably more relevant today than ever before. Every plant species, wild or cultivated, has one or more diseases naturally associated with it. Plant dis-eases are normal part of every natural and semi-natural community, but their impact and role in these commu-nities are usually unnoticed and unappreciated. In arti-ficial cropping systems (particularly monocultures), plant diseases often cause death and destruction leading to yield loss. In natural ecosystems (biologically diverse), they are an unseen influence on both plant community and the evolution of individual species. In natural com-munities, plant diseases are in balance with their hosts; some host plants die, but enough survive to maintain the species. Plant pathogens, through the diseases they cause, influence the distribution of individual species, the genetic variation of that species with respect to disease resistance, the balance between sexual and asexual reproduction in the host plant, and interaction with other organisms. According to a recent publication of the first IUC