Keywords :

DMC for agricultural management of pest and disease resistance

High nitrogen fertilization in conventional cropping systems fosters plant parasite pressure. The processes involved can be clarified by gaining insight into the mechanisms responsible for reducing plant disease resistance. This is helpful for designing and managing highly environment-friendly cropping systems conducive to ecological intensification. CIRAD, INRA and Montpellier SupAgro, through a project funded by ANR, the French research agency, focused studies on agricultural management of disease resistance through two study models:

• For plant/pathogen interactions: the rice-Magnaporthe oryzae interaction
• For cropping systems conducive to ecological intensification: direct seeding mulch-based cropping systems (DMC).

The prevalence of rice blast disease is associated with nitrogen fertilization practices in conventional rice cropping systems, whereas the incidence of this disease is lower under DMC at the same fertilization level. Within the framework of this project, in different environments in Madagascar, Brazil and Bolivia, tests were carried out to compare different levels of crop intensification under conventional and DMC cropping systems. The epidemiological status, the plant nitrogen status, the behaviour of a collection of cultivars having different resistance levels, and in-situ expression of resistance genes and nitrogen metabolism were monitored in the field according to the cropping systems. In parallel, complementary approaches were set up in the laboratory for an in-depth study of the expression of the genes involved, and especially to assess genetic control of nitrogen-induced sensitivity to rice blast. The expected results could provide hope for better use of partial plant disease resistance through cropping systems, such as DMCs, which are based on an agroecological approach and conducive to the intensification of natural regulation processes.