L-phenylalanine (Phe) is a metabolic precursor in the phenylpropanoid pathway that gives rise to phenolic and flavonoid compounds commonly associated with enhanced plant resistance. The authors evaluated exogenous Phe across multiple crops and pathogens. When applied as either spray or drench at concentrations consistently effective at ≥4 mM, Phe reduced disease severity in a broad set of pathosystems including necrotrophic and biotrophic fungi, oomycetes, bacterial pathogens and a virus. Experiments encompassed greenhouse and commercial-like conditions in both mono- and dicotyledonous species. The preprint reports frequent parity with chemical fungicides, occasional synergistic interactions with certain fungicides or adjuvants, and improved efficacy for a commercial formulation relative to non-formulated Phe. Application timing affected protection, with treatment 5 days before inoculation providing better control than 0, 3, or 7 days before infection.
The study expanded earlier observations in petunia, chrysanthemum and determinant tomato to a wider set of hosts and pathogens. Dicot crops and hosts included tomato (determinant and indeterminate cultivars), sweet basil, cucumber, lettuce and other dicots; the monocot evaluated was wheat. The pathogens suppressed by Phe spanned multiple taxonomic and lifestyle groups. Notable necrotrophs and generalist fungi included Botrytis cinerea and Sclerotinia sclerotiorum. Powdery mildew species targeted on different hosts comprised Leveillula taurica and Oidium neolycopersici on tomato, and Podosphaera xanthii on cucumber. Wheat foliar pathogens assessed included Blumeria graminis f. sp. tritici, Zymoseptoria tritici, Puccinia triticina, and P. striiformis f. sp. tritici. Oomycete pathogens tested were Pseudoperonospora cubensis (cucumber leaves) and Pythium aphanidermatum (root pathogen). Bacterial targets included Pseudomonas syringae pv. tomato and Clavibacter michiganensis subsp. michiganensis. A viral pathogen, Tomato brown rugose fruit virus (ToBRFV; a tobamovirus), also showed reduced activity following Phe treatment.
Across the experiments reported in the abstract, Phe applied either as a foliar spray or as a drench consistently showed disease suppression at concentrations of ≥4 mM. The compound was effective on both young and mature leaves. The abstract does not provide detailed dosing schedules, exact volumes, or full protocol parameters; those experimental specifics were not reported in the provided source text.
Under the conditions described, Phe often performed comparably to conventional chemical fungicides. Combining Phe with other fungicidal compounds rarely produced improved control, with one exception noted: combining Phe with pyrimethanil enhanced activity against B. cinerea in tomato. These observations suggest additive or occasionally synergistic potential in specific pairings, though broad enhancement with fungicides was uncommon in the reported trials.
Formulation influenced efficacy. A formulated product, NaturaFend 550 SP, was reported to be more effective than non-formulated Phe against B. cinerea on tomato and P. xanthii on cucumber. Synergistic effects were observed when Phe was combined with an adjuvant in trials against tomato powdery mildews, indicating that formulation chemistry and adjuvant selection can modify field-relevant performance.
Application timing had a measurable effect on disease control in the reported results. Treatment administered 5 days before infection provided superior control relative to applications given at 0, 3, or 7 days before infection. This finding indicates a temporal window in which pre-treatment with Phe confers stronger protection, although the abstract does not include mechanistic detail or time-course data beyond the relative differences noted.
The reported dataset spans a wide taxonomic range of pathogens and multiple crop species, demonstrating that exogenous phenylalanine can suppress diverse plant diseases under greenhouse and commercial-like conditions. The abstract emphasizes consistent activity at or above 4 mM and documents effects on fungi (necrotrophs and biotrophs), oomycetes, bacteria and a virus. Observations include comparable performance to chemical fungicides in many tests, occasional synergistic outcomes with specific fungicides or adjuvants, and improved results for a formulated product.
Limitations in the provided source text include absence of detailed methods, quantitative efficacy metrics, statistical analyses, phytotoxicity assessments, environmental persistence data, and long-term field trial outcomes. Because the article is a preprint, the findings have not been peer reviewed; further validation and reporting of experimental detail would be required to assess practical deployment and regulatory implications.
The authors declared no competing interests. The preprint is posted on bioRxiv and is made available under a CC-BY-NC-ND 4.0 International license. The article has not been certified by peer review.