HS SHETTY

Department of Studies in Applied Botany, University of Mysore, Mysore, India

Background
Developing countries have made spectacular progress in agriculture with the introduction of improved crop varieties during the early 1960s. Despite these achievements, the potential of the new cultivars is not realized in full, one of the reasons being major diseases on crops of economic importance, including new cultivars. It is estimated that 30% of such diseases are seedborne and can be managed through disease-free seeds. For many of these diseases, fungicides are either not available or not registered, and resistant cultivars are not available. Often, the use of disease-free seed may be the only means of plant protection and hence seed health tests are required. The demand and pressure for seed health testing in seed industries is increasing.

The sowing of contaminated or infected seeds for crop production can reduce germination and seedling vigour, and affect yield by transmitting pathogens from seed to plants. The most adverse effect of seedborne pathogens is contamination of previously disease-free areas. Primary infection foci are followed by secondary pathogen dissemination, leading to monocyclic or polycyclic diseases. Blast and brown spot of rice, white tip nematode, earcockle in wheat, bacterial leaf blight of rice, downy mildews, smuts, head mould, seedling rots, anthracnose, halo blight and some viral diseases are the major seedborne diseases and have become significant yield reducers in crops of cereals, oil seed, legumes and vegetables in developing countries. The economic significance of seedborne diseases and the changing global scenario in the light of the GATT and W70 are pressurizing the developing countries to give special attention to seed health testing. Programmes have been developed to manage seedborne diseases by exclusion of the inoculum through statutory, cultural and seed treatments. Trends are emerging for need-based seed treatments, and a shift from chemical treatments to biopesticides. Seed health has been recognized for statutory regulation in plant quarantine, seed quality tests and seed treatment programmes. Seed certification has been suggested as part of an integrated pest management system. Designated seedborne diseases, field standards and seed standards have been fixed for many crops. In this regard, national and international cooperation has been sought for effective seed health and crop protection.

Conclusions
Seed health testing needs to be understood in the light of the general evolution of the seed sector. Research and development priorities to facilitate seed health testing and future trends have been visualized. Estimation of losses attributed to seedborne inoculum, establishing predictive relationships between seedborne inoculum and disease incidence, developing reliable, effective, cheap and rapid detection methods, dialogue with the private sector on development of test procedures, and comparing data on advantages of seed health are the current issues. These considerations help the developing countries in evolving policies and methods for adoption of seed health testing as part of plant protection to increase crop yields.

In developing countries, seed pathology is not remaining as an academic discipline, but is also being used as a problem-solving exercise to prevent crop losses due to seedborne diseases. Although there is no legal requirement for seed health testing for some important pathogens as yet, serious consideration is being given to amending the seed act and making testing obligatory.