ABSTRACT
Admittedly, due to ignorance of the nature of plant disease, crop losses have been profound in earlier years. Many investigations to assess disease intensity and consequent losses were later taken up (Horsfall and Cowling, 1978). The term phytopathometry was introduced by Large (1953). Phytopathometry is the measurement of disease and constitutes the basis for reliable assessment of crop losses, since the magnitude of loss is directly related to disease severity. Disease severity represents the extent of pathogen invasion in the host plant and amount of host tissue that has been destroyed or made nonfunctional/less functional by the pathogen, resulting in adverse effect on the productivity of crop plants. When a pathogen infects susceptible host plants, injury is caused to the different tissues involved in photosynthesis, absorption and transport of water and nutrients, translocation of photosynthates to storage organs such as grains, roots, tubers and fruits. Injury to the crop may be defined as the visual or measurable symptoms induced by plant pathogens. Injury to the tissues leads to damage resulting in decrease in quantity or quality of the produce (Gaunt, 1995a,b).
