[PhD defence] 12/11/2025 - Meriem HAMRANI: "Development of alternative and innovative strategies for sustainable and resilient management of biotic and abiotic stresses in citrus fruit" (UPR ERIT PSII)

Ms Meriem HAMRANI will publicly defend her thesis entitled: "Development of alternative and innovative strategies for sustainable and resilient management of biotic and abiotic stresses in citrus fruit", supervised by Mr Jawad AARROUF and Ms Rabea ZIRI (co-supervision with the "Université Ibn-Tofail" -Morocco), on Wednesday 12 November 2025.

Laboratory

UPRI - ERIT PSII - Plant Science, Interactions and innovation

Composition of the jury

Mr Jawad AARROUF	Avignon University	Thesis supervisor
Mr Driss HMOUNI	Ibn Tofail University	Rapporteur
Ms Valérie LEGUÉ	University of Clermont Auvergne	Rapporteur
Mr Jamal IBIJBIJEN	Moulay-Ismaïl University	Rapporteur
Ms Miloudia SLAOUI	Mohamed V University, Rabat	Examiner
Mr Olivier FAURE	Jean Monnet University, Saint-Étienne	Examiner
Mr Mohammed EL GUILLI	French National Institute for Agronomic Research	Thesis co-supervisor
Ms Rabea ZIRI	Ibn Tofail University	Thesis co-director

Summary

Citrus plays a major role in Morocco's agricultural economy. However, they are facing increasing constraints linked to abiotic and biotic stresses throughout the production chain. The main problems are soil salinisation, water stress and increased pressure from fungal diseases and pests. Intensive use of chemical products and refrigeration treatment, although effective, lead to the emergence of fungal resistance and chilling injury, compromising quality and post-harvest preservation. These constraints, exacerbated by climate change, underline the need to implement sustainable, environmentally-friendly practices. This study assesses three innovative and complementary strategies aimed at strengthening the resilience of the citrus industry: (1) The application of UV-C light flashes to the aerial part of the Citrange carrizo rootstock (Citrus sinensis×Poncirus trifoliata) to check the activation of systemic signalling to the roots, thus preparing the plant to tolerate salt stress; (2) Pre- and/or post-harvest application of silicates to reduce cold damage and post-harvest rot; (3) Post-harvest use of GRAS (Generally Recognized As Safe) feed salts against resistant isolates of Penicillium spp. The results show, for the first time, that hormetic doses of UV-C trigger systemic signalling down to the roots, associated with the accumulation of metabolites such as γ-aminobutyric acid, azelaic acid and 4-hydroxybenzoate, which are involved in adaptation to abiotic stresses. UV-C attenuated the deleterious effects of salt stress and also stimulated rhizogenesis, thus confirming the transfer of foliar signals to the root system. In addition, pre-harvest applications of Green Silk® (0.5 %) and potassium silicate (1 %) significantly reduced chilling injury indices (0.77 and 0.71 compared with controls 1.83), while reducing fruit losses by more than 40 %. This effect is attributed to the accumulation of phenolic compounds and silica in the tissues. Finally, GRAS salts were able to limit post-harvest rot by stimulating defence enzymes, offering a promising alternative to fungicides. These approaches pave the way for an integrated, sustainable and multifactorial management strategy for the citrus industry.

Keywords Citrus, salt stress, chilling injury, fungal diseases, UV-C flashes, GRAS salts, silicates, systemic signalling, metabolites.