Nonphytotoxic aluminum-peat complexes suppress Phytophthora parasitica

ABSTRACT Amendment of peat-based potting media with Al2(SO4)3 suppresses damping-off of Vinca (Catharanthus roseus) caused by Phytophthora parasitica. The species of aluminum (Al) responsible for disease suppression have not been identified. The objective of this study was to determine the effects of amount and pH of Al2(SO4)3 amendment solutions on survival of P. parasitica. In separate experiments, peat was amended with Al2(SO4)3 solutions adjusted to pH 4 or 6 at either 0.0158 or 0.0079 g of Al per gram of peat. Amended peat was placed in Buchner funnels maintained at -2.5 kPa matric potential. Peat was infested with P. parasitica by placing zero, two, or five colonized Vinca leaf disks in each funnel, and 15 Vinca seeds were placed in each funnel. After 24 h, the matric potential was brought to 0 kPa to induce zoospore release and returned to -2.5 kPa after 24 h. Pathogen populations and stand counts were assessed after 2-week incubation. Al amendment solutions at both pH 4 and 6 reduced pathogen popu...