The conidial release of Pyricularia grisea in upland rice (Oryza sativa) in vegetative and panicle developmental phases was studied in field experiments, under both conventional planting and direct drilling methods, over a period of two years (1998/2000). The conidia of P. grisea were collected with a volumetric Rotorod spore sampler. For quantifying viable conidia that posseses potential for causing infection in new leaves, plastic trays containing 25-day old rice plants of cultivars Carajas and Primavera were exposed in the field as live spore traps. The increase in conidial production and release was linear with time from dough to mature growth stages, during the 1998/99 rice growing season. In 1999/2000, the quantity of conidia increased exponentially starting from terminal booting until semimature growth stages. The number of conidia colleted with the volumetric spore sampler decreased in an exponential manner with an increase in the amount of rainfall, with reduction of leaf blast severity in live traps in cultivars Carajas and Primavera. Conidial production and release was lower under direct drilling than in the conventional method of planting in both the vegetative and grain formation phases of panicle.
Magnaporthe grisea; Oryza sativa; epidemiology; spore traps; tillage system
