Nitrogen fertilization effects on wheat blast epidemics under varying field environmental conditions

Wheat blast, caused by the fungus Magnaporthe oryzae Triticum (MoT) pathotype, is one of the most important yield-reducing diseases of wheat, mainly in the tropical wheat-growing regions of South America. In this study, we assessed the effects of nitrogen (N) fertilization on wheat blast epidemics. Factorial experiments were carried out in Londrina (2015 and 2016) and Floresta (two sowings in 2017) with N rates (0, 40, 80 and 120kg/ha for the first experiment, and 0, 60 and 120kg/ha for the second) and wheat genotypes (three and six cultivars, for the first and second experiments, respectively) as factors. Wheat blast on spikes occurred only in two out of four experiments: 2015 in Londrina and first sowing of 2017 in Floresta. Nitrogen increased blast severity in the first crop of 2017 in Floresta, where blast severity on spikes ranged from 10 to 94% and yield ranged from 47 to 2823kg/ha, depending on N rate and genotype. Nitrogen did not affect wheat blast (except for genotype S1) in the 2015 Londrina trial, where blast severity on spikes ranged from 16.9 to 36.8%. Differences in blast severity among genotypes were likely due to different crop heading periods. Our results suggest that N fertilization and sowing time should be considered in a management strategy for reducing the risk of wheat blast epidemics.