Effects of Pythium Root Rot, Seed Density, Fertilizer Concentration, and Bacterial Treatments on Amaranth Microgreens Grown in Hydroponic Systems

Abstract

Hydroponically grown microgreens are lucrative and nutritious, but are prone to root-rot disease, particularly garnet red amaranth (Amaranthus tricolor). To study root rot prevention in A. tricolor, seeds were sown on burlap in hydroponic trays (9.22 x 40 cm) with 2 ½ gallon reservoir tanks. Half of the reservoirs were infected with the phytopathogen Globiosprangium ultimum (Pythium ultimum), and half were treated with Hydroguard by Botanicare (Bacillus amyloliquefaciens). Foam covers were placed touching the seeds for 4 days to support germination. One non-infected tray showed symptoms of damping-off and root-rot (the pathogen can be transmitted by fungus gnats, which were present), eliminating the crop by day seven. Data indicated that higher seed densities (70.9 g/m2) significantly increased fresh weight yield (FWY) (p-value<0.001). Lower seed densities (35.4 g/m2) promoted black mold and resulted in less than half the average FWY (13.6 g), compared to higher seed densities (average FWY 31.8 g). Touching covers produced greater FWY and heights compared to non-touching, increasing the average by 5.9 g and 1.85 cm, respectively. There were no significant changes to FWY from higher sun exposures (262 mmol/m2s compared to 65.15), higher FC (2.5 mS/cm2 compared to 1.0), older seed age (2 years), cold storage, or Hydroguard treatments. Future studies should focus on sources of pathogen infections and treatments with products containing more diverse beneficial bacteria.