Phytopathogens in the Tap Water?! Using Amaranthus tricolor Microgreens to Study Pythium Induced Root Rot in a Hydroponic Greenhouse

Abstract

Hydroponic systems offer advantages over traditional agricultural practices; however, the moist, recirculating environment promotes Pythium-induced root rot, which can reduce yield. An unknown Pythium species was isolated from infected roots and cultured in vitro, then used to inoculate roots in mini hydroponic tanks growing Amaranthus tricolor microgreens. Throughout ten trials over two years, control tanks unexpectedly presented root rot symptoms. In the most recent trial, all tanks and equipment were disinfected with sodium hypochlorite diluted to 1700 ppm chlorine for at least 8 minutes. Three different sterilization methods were used together to sterilize the municipal tap water: 0.22 µm syringe filter, pressure cooking for 15 minutes, and deionization. Control tanks remained free of root rot, suggesting that municipal tap water could be a source of Pythium contamination. Frequently in past trials, even seemingly healthy crops produced shriveled, dead microgreens throughout, decreasing the quality and profitability of the harvest. In this trial, minimal amounts of shriveled plants were present in crops, suggesting that sterile water contributed to preventing symptoms. These findings suggest that the source of irrigation water is a major variable in hydroponic disease management. While distilled water was effective at excluding the pathogen, it is not practical at large scales and is susceptible to pH instability. Hydroponic growers using municipal tap water may benefit from investing in UV sterilization, reverse osmosis, ozone filters, or other water sterilization methods to eliminate phytopathogens at their source for higher quality yields.