Survival of Pyricularia Oryzae on Rice Residues used in Manure Processes in Madagascar

Manure constitutes the principal fertilization of rice field in the Vakinankaratra region. Adding rice residues on the cattle excretion was recommended to improve manure composition. However, adding rice residues infected by Pyricularia oryzae, could play a role on the onset of rice blast disease in the field. To evaluate this risk, the survival of P. oryzae on rice residues used in different scenario of manure processes was monitored. Six treatments were tested where infected panicles were placed inside cattle excretion (CE) under anaerobic condition (T1), on CE (T2), inside CE (T3), inside CE with watering every week (T5), on the soil (T6) and infected panicles and CE were returned every two weeks (T4). No sporulation of P. oryzae was observed in the T1 (panicles placed in CE with anaerobic condition). However, the panicles with sporulating P. oryzae and spore of it were observed in the 5 other treatments at least after seven months. These results show that infected rice residues used in manure processes could be a potential primary inoculum source of rice blast. To minimize the risk of blast epidemic, we propose that only uninfected rice residues should be added to manure. Keywords: Manure, Pyricularia oryzae, rice blast, rice residues, survival