Integrated effect of host plant resistance and fungicidal seed treatment on rice blast control in Brazil

A field experiment was conducted in two successive years at Goiania, GO, Brazil, to study the effect of seed treatment with pyroquilon fungicide (4.0 g a.i. per kg of seed) on rice blast in cultivars that differed in their level of resistance. Leaf and panicle blast progress was monitored in the newly released, early maturing upland rice cultivar Guarani and the advanced line CNA 4136, and compared with disease progress in the susceptible commercial cultivars IAC 165 and IAC 25 in plots with treated and untreated seed. Seed treatment suppressed leaf blast until 62 and 47 days after seeding in 1987 and 1988, respectively when averaged across cultivars. The slow blasting nature of Guarani and CNA 4136 increased the level of disease control when environmental conditions favored blast development in 1988. Under high disease pressure the correlation between leaf blast and panicle blast severity in the field plots was negative (r = -0.5, P = 0.01). Leaf blast severity at 47 days after seeding was negatively correlated to grain yield (r = -0.709, P = 0.001). Guarani exhibited an increase in grain yield over the untreated control of 28%, corresponding to 826 kg/ha.