Management of blast disease of rice caused by Magnaporthe oryzae B.C. couch through the use of differential varieties

Cultivation of blast resistant cultivars is by far the only viable solution for disease control with no addition to the cost of cultivation and without any deleterious effects on environment. However, resistance, often breaksdown within twoor three years due to the build- up and appearance of new virulent races of the pathogen, thereby indicating the dynamic nature of the pathogen and prevalence of its tremendous pathogenic variability. Differential rice lines for determining pathotypes were commonly developed to suit local populations because International differential sets were largely unsuitable for tropical populations. Two sets of NILs with single major resistance gene against P.oryzae were introduced via repeated backcrosses in the genetic background of broadly and highly susceptible "indica" and "japonica" rice cultivars, Co-39 and Lijiangxintuanheigu (LTH), respectively.Thus, unambiguous pathotypes were assigned to isolates based on their reactions to the NILs following a gene- for-gene concept.