Dissolved oxygen limitation and Pythium root rot in strawberry NFT systems: mechanisms, research gaps, and prospects...

Strawberry (Fragaria × ananassa Duch.) production faces growing pressure to reduce reliance on peat and coconut coir substrates, driven by documented life cycle liabilities including carbon losses from peat extraction and embodied transport emissions from coir. Nutrient film technique (NFT), a substrate-free recirculating hydroponic system, eliminates growing media entirely and reduces material inputs across successive crop cycles, making it an environmentally attractive candidate for controlled environment strawberry production. Despite early commercial adoption in Europe during the 1970s, NFT was largely abandoned for strawberry production by the 1980s following systematic failures whose physiological basis remains incompletely characterized. This review synthesizes evidence from hydroponic systems engineering, plant physiology, and oomycete pathology to examine the two structural constraints underlying NFT's historical rejection: dissolved oxygen depletion dynamics within recirculating nutrient solution, and exceptional susceptibility to Pythium spp. root rot. We demonstrate that these constraints are coupled rather than independent, sharing a common pathway through root-zone oxygen status. Progressive root mat development over a six-month fruiting cycle degrades passive film aeration and creates hypoxic conditions that impair root membrane integrity, alter rhizosphere exudate profiles, and facilitate Pythium zoospore encystment and necrotrophic transition. This interaction is compounded by strawberry's exceptional oxygen sensitivity and absence of adaptive aerenchyma formation, rendering thresholds established for tomato and cucumber inapplicable to this species. We identify two prerequisite research gaps that must be resolved before NFT can be rationally reconsidered for commercial strawberry production: characterization of root mat effects on channel hydraulic performance, and establishment of a strawberry-specific dissolved oxygen threshold under NFT-relevant conditions.