SSF had no effect in the first crop cycle, but it reduced the
severity of the disease in the second. In the second crop cycle the
dispersion of P. cactorum propagules through the crop row either
through root to root contact or through the movement of zoospores
in the free water may have been reduced by the high microbial
activity of the reused growth medium. This high microbial activity
is possibly associated with high accumulation of plant exudates and
plant decomposition residues from the first crop cycle (Martínez et
al., 2009). Hardy and Sivasithamparam (1991) proposed that the
lytic activity of a large population of microorganisms suppresses or
kills Phytophthora spp. propagules. In this regard, the transmission
of P. parasitica was very low when potting mixwas not pasteurized
in an ebb-and-flow subirrigation system (Strong et al., 1997).