Potential Spread of Phytophthora cactorumfrom Tailwater Ponds and Irrigation Sources

Abstract

Strawberry fields in Florida are severely affected by Phytophthora crown rot, an important disease caused by Phytophthora cactorum. A current trend in Florida agriculture to conserve water is to irrigate with surface runoff water (tailwater) recovered in retention ponds and canals. However, dissemination of plant pathogens in irrigation water may be aggravated by the increasing use of recycled water. We investigated whether the use of recycled water could increase the incidence of Phytophthora crown rot in commercial fruiting fields. Selective media for growth of P. cactorumand storage temperature for pathogen survival were tested prior to the collection of water from four different strawberry farms. Each sample was filtered and plated into P5ARPB media. Out of 2000 colonies isolated, 1000 colonies were selected and transferred to new P5ARPB media. From those, 85 colonies that resembled P. cactorumwere selected for molecular characterization. DNA extractions, PCR amplifications, and enzymatic digestions were made, but the presence of the pathogen could not be confirmed. Our results support previous reports in which the main source of contamination of strawberry with P. cactorumis thought to be infected transplants from the nurseries rather than recycled irrigation water.