Treatment with Glyphosate Induces Tolerance of Citrus Pathogens to Glyphosate and Fungicides but Not to 1,8-Cineole

Abstract

During the postharvest period, citrus fruits are exposed to Penicillium italicum, Penicillium digitatum, and Geotrichum candidum. Pesticides such as imazalil (IMZ), thiabendazole (TBZ), orthophenylphenol (OPP), and guazatine (GUA) are commonly used as antifungals. Glyphosate (GP) is also used in citrus fields to eliminate weed growth. The sensitivity of fungal pathogens of citrus fruit to these pesticides and 1,8-cineole was evaluated, and the effect of GP on the development of cross-resistance to other chemicals was monitored over a period of 3 weeks. IMZ most effectively inhibited the mycelial growth and spore germination of P. digitatum and P. italicum, with minimum inhibitory concentrations (MICs) of 0.01 and 0.05 mg/mL, respectively, followed by 1,8-cineole, GP, and TBZ. 1,8-Cineole and GP more effectively inhibited the mycelial growth and spore germination of G. candidum, with minimum inhibitory concentrations (MICs) of 0.2 and 1.0 mg/mL, respectively, than OPP or GUA. For the spore germination assay, all substances tested showed a total inhibitory effect. Subculturing the fungal strains in culture media containing increasing concentrations of GP induced fungal tolerance to GP as well as to the fungicides. In soil, experiments confirmed that GP induced the tolerance of P. digitatum to TBZ and GP and the tolerance of P. italicum to IMZ, TBZ, and GP. However, no tolerance was recorded against 1,8-cineole. In conclusion, it can be said that 1,8-cineole may be recommended as an alternative to conventional fungicides. In addition, these results indicate that caution should be taken when using GP in citrus fields.

Modes of Action of 1,8-Cineol in Infections and Inflammation

“…Further, 1,8-Cineol was suggested as an alternative to conventional fungicides against different Penicillium species. Data revealed that fungal citrus pathogens developed a tolerance to glyphosate and conventional fungicides but not to 1,8-Cineol [ 53 ].…”

1,8-Cineol Attenuates Checkpoint Molecule PDL-1 and Adhesion Molecule CX3CR1 in Circulating Monocytes in Otitis Media Patients

“…Moreover, it has recently been shown that 1,8-Cineol contributes to a synergistic anti-microbial and also anti-fungal activity within a novel substance based on Melaleuca alternifolia leaf oil, which showed inhibitory effects against the pathogenic yeast Malassezia furfur , which is involved in the dermatological disease, Seborrheic dermatitis [ 37 ]. In this context, 1,8-Cineol may be a potential alternative to conventional fungicides, since different fungal citrus pathogens have been shown to develop tolerance to conventional fungicides but not to 1,8-Cineol [ 38 ].…”

Molecular Targets of Herbicides and Fungicides─Are There Useful Overlaps for Fungicide Discovery?

“…79 The mechanism of resistance was not determined from this apparently evolved case of glyphosate resistance in a fungus. Resistance to glyphosate was quickly selected for in several citrus postharvest fungal pathogens, 80 and glyphosate-resistant Fusarium verticillioides was isolated from an agricultural soil that had been treated with glyphosate for multiple years. 81 Thus, one can expect resistance to evolve if a fungicide that targets EPSPS is widely used.…”