The CITRUSBUSTERS team presented its work on citrus-derived biofractions as plant immunity inducers at the II Meeting on Plant Biotic Interactions. The event took place in Logroño in Spain on 27-28 May 2026.

The oral presentation was delivered by Miguel Ángel Torres, a researcher at the Centro de Biotecnología y Genómica de Plantas (CBGP), part of the Universidad Politécnica de Madrid (UPM). Titled “Citrus-derived biofractions with DAMP activity as immunity inducers against HLB and CBS”, it presented progress from Work Package 2 (WP2) of CITRUSBUSTERS, carried out together with Gemma López, Meriem Aitouguinane, Antonio Molina and Lucía Jordá.

Turning citrus waste into a signal

Every year, the citrus industry produces vast quantities of peel waste from juice processing. Often discarded or used as low-value animal feed, this waste contains chemical compounds with untapped potential. When processed correctly, they can be transformed into signals that switch on the plant’s own immune system.

The CBGP-UPM team has developed a method to do exactly this. Citrus peel by-products, both fresh and dried, are processed through milling, subcritical water extraction and controlled enzymatic digestion. The result is a set of complex biofractions enriched in oligosaccharides from plant cell walls.

These molecules act as Damage-Associated Molecular Patterns (DAMPs). They are generated when plant tissues are damaged and serve as natural alarm signals that warn the plant of danger, triggering immune responses before a patogen can become established.

To test the biofractions’ elicitor activity, the team uses Arabidopsis reporter lines that monitor calcium influxes as an early immune-signalling event. Calcium bursts inside plant cells are among the first signs that a plant’s defence system has been activated.

The results have been consistent. Extracts obtained from both fresh and dried peels show stable and reproducible immune-inducing activity, dependent on the extraction and processing conditions used. To elucidate the biochemical nature of the active components, the team combines several analytical approaches: HPIC profiling, proteinase K digestion, thin-layer chromatography (TLC), and genetic assays using receptor-impaired mutant plant lines.

The next step is real citrus

The most active biofractions are now being evaluated in protection assays under controlled laboratory conditions. The next stage will be validation in citrus infection systems against Huanglongbing (HLB), caused by the bacterium Candidatus Liberibacter asiaticus, and Citrus Black Spot (CBS), caused by the fungus Phyllosticta citricarpa.

The aim is straightforward but ambitious: if the biofractions can be produced at industrial scale, this approach could contribute to the future development of sustainable plant protection solutions based on citrus processing by-products. Over time, this could reduce chemical treatments, minimize waste, and build a more resilient citrus sector that transforms its own residues into tools for crop protection.

The citrus industry’s waste, turned into the citrus industry’s shield.

 

Contact: Miguel Ángel Torres (CBGP-UPM), miguelangel.torres@upm.es