production in Pythium -inoculated rice roots at 3 dpi. Black arrows indicate reddish-brown DAB precipitates, which seemed to slow down hyphal spread in the cortex of P. graminicola- and P. inflatum-infected rice roots. Blue arrows indicate an area of cell collapse in P. arrhenomanes-inoculated roots. Samples were taken in the middle of the primary root and infiltrated with DAB. After cross sectioning, samples (5 μm) were stained with trypan blue. Scale bars = 100 μm.