A combinatorial approach of Monarda citriodora essential oil (MEO) and linalool vapours to control fruit rot of Citrus limon caused by a new pathogen, Aspergillus foetidus, and its underlying mode of action
Nidhin PT, Pragya Rani, Mohini Sharma, Meenu Katoch- Applied Microbiology and Biotechnology
- General Medicine
- Biotechnology
Abstract
Aims
Citrus limon (lemon) is a widely cultivated citrus fruit. Significant postharvest losses due to fungi plague its production. Environmental and human health hazards have made the application of synthetic fungicides unsuitable. Despite the previous reports of antifungal activities of essential oil vapours, their synergistic combinations are understudied. Synergistic vapour combinations are advantageous due to less concentration of active components. This study aimed to isolate and identify postharvest fungal pathogens lemon and to evaluate the antifungal effects of synergistic MEO-constituent vapour combinations in vivo and in vitro.
Methods and results
Postharvest fungal pathogens of lemon (Citrus limon) were isolated from various infected samples. The most pathogenic isolate was identified through morphology and its ITS based rRNA gene sequencing as Aspergillus foetidus (O4). This is the first report of A. foetidus as a postharvest pathogen of lemon. The minimum fungicidal concentrations (MFC) of MEO vapours treatment against O4 was 1346.15 µL/L air. For carvacrol, hexanal, and linalool, MFC was same (96.16 µL/L air). Checkerboard assays demonstrated that 1/4 MFC of MEO (336.54 µL/L air) and 1/4 MFC of linalool (24.04 µL/L air) (M+L) were synergistic against O4. M+L vapours reduced the O4 growth on lemons during storage by 64±1.50% and preserved their quality (low weight loss per cent, unchanged pH, increased ascorbic acid content). Propidium iodide staining, ergosterol content analysis, calcofluor white staining and chitin content analysis revealed the integrity loss of the O4 plasma membrane and cell wall. 2′,7′-Dichlorofluorescin diacetate staining revealed accumulation of intracellular ROS, and SEM analysis exposed the M+L treated mycelia with malformations.
Conclusions
M+L vapours offer protection for lemons from A. foetidus and preserve their quality during storage.