Interplay of apple volatile organic compounds with Neofabraea vagabunda and other post‐harvest pathogens

Abstract

Neofabraea vagabunda, causing bull’s eye rot, produces notable loss during cold storage of apples growing in cool humid regions. The infection initiates in the orchard, but the pathogen lives quiescently in fruit for some months before causing the symptoms of the disease. In vivo and in vitro assays were carried out to gain knowledge on the influence of fruit volatile organic compounds (VOCs) in N. vagabunda development and define volatile markers for pathogen detection, using SPME/GC‐MS, PTR‐ToF‐MS analysis and light microscopic observations. This study reports that: (i) the main VOCs of Cripps Pink apple (highly susceptible to bull’s eye rot) are degraded during the conidial germination of N. vagabunda, stimulating pathogen hyphal growth towards the host; (ii) first disease symptoms appear when fruit releases VOCs related to senescence, which also stimulate pathogen hyphal growth; (iii) VOCs typical of ripe‐senescent fruit are also emitted by infected fruit during N. vagabunda quiescence, and methanol and ethanol are the earliest markers of bull’s eye rot; and (iv) the in vitro volatile metabolism of Botrytis cinerea, Penicillium expansum and Colletotrichum fioriniae has similarities with that of N. vagabunda, but the volatile profile of each pathogen is distinguishable. Overall, this study provides novel knowledge on fruit–fungus interaction and insights for the development of tools for early disease detection in packing houses.

Characterization and Quantification of Postharvest Losses of Apple Fruit Stored under Commercial Conditions

“…production, ripening and eventually senescence of apples (DeEll et al, 2007;Lee et al, 2016), while resistance to fungal decay decreases as fruit begin to ripen and senesce (Neri et al, 2019;Nybom et al, 2020;Prusky et al, 2013). Fungal decay was the major cause of postharvest losses and the incidence increased during shelf life as reported previously (Neri et al, 2009).…”

New insight into morphological and genetic diversity of Phlyctema vagabunda and Neofabraea kienholzii causing bull's eye rot on apple and pear

“…The phenomenon of guttation usually involves release of water and bioactive compounds useful for maintaining a constant growth of aerial hyphae and the formation of fungal structures (Krain & Siupka, 2021); this suggests that the exudates of P. vagabunda and N. kienholzii may favour the growth of these pathogens. All isolates of P. vagabunda and N. kienholzii assayed in the present study sporulated more profusely on TA (a nutrient‐rich medium) than on PDA (a standard medium) (Neri et al, 2019). However, the Chilean isolates of P. vagabunda sporulated less on TA than the majority of the Italian isolates.…”

“…Fungi can use light as a source of information about their environment and those causing bull's eye rot possess negative phototropism (Olsson, 1965). These pathogens probably find an optimal habitat within fruit tissues, where they remain unnoticed for some months before switching to a necrotrophic lifestyle (Neri et al, 2019). The ability of PvM‐II isolates to live longer below the fruit skin and to form many conidiomata within fruit flesh suggests that the protection of fruit against this morphotype might require measures able to reach into and kill the pathogen in tissues far from the site of penetration.…”

“…Bull's eye rot, also known as lenticel rot, is one of the main postharvest diseases of pome fruits, producing notable economic losses during storage and shelf‐life (Cameldi et al, 2017; Den Breeyen et al, 2020; Henriquez et al, 2004; Neri et al, 2009; Soto‐Alvear et al, 2013; Spotts et al, 2009). Fruit infection initiates in the orchard, but the symptoms of disease appear after some months of cold storage, when the fruit have reached a certain stage of ripeness (Neri et al, 2019). The causal agents of bull's eye rot are fungal species belonging to the class of Leotiomycetes, which are currently assigned to the genera Neofabraea ( N. malicorticis , N. perennans and N. kienholzii ) and Phlyctema (Li et al, 2020).…”

Biocontrol Ability and Production of Volatile Organic Compounds as a Potential Mechanism of Action of Olive Endophytes against Colletotrichum acutatum

“…Thus, it is likely that the reduction in anthracnose incidence and severity observed in this treatment was not caused by one or a few VOCs, but instead by various components of the volatile blend that act synergistically. Curiously, on day 16 post-inoculation, 6-methyl-5-hepten-2-one was found to be positively associated with the C. acutatum treatment, and this compound was previously reported to be used by the pathogen Neofabraea vagabunda for conidial germination on the surface of apples [ 52 ]. 2-Nonanone was another compound highly associated with the Ca treatment and was previously reported as a biomarker for the identification of bacterial pathogens [ 53 ].…”