Introduction to Stress Resistance Breeding
Stress refers to adverse conditions for crop growth and production imposed by either environmental factors or biological factors, thus stress is of two types, viz. 1) Biotic and 2) Abiotic. The stress that is caused by biological agents or factors, such as disease, insects and parasitic weeds, is known as biotic stress. When the stress is caused by environmental factors or non biological factors, it is referred to as abiotic stress. Abiotic stress is generally caused by factors like deficiency or excess of nutrition, moisture, temperature and light; presence of harmful gases or toxicants; and abnormal soil conditions such as salinity, alkalinity and acidity. All crop plants suffer from both biotic and abiotic stresses to varying degrees. This chapter deals with breeding for resistance to disease.