Aeromycobiota profile in apple warehouses: a report on apple cell wall degradation by postharvest fungal pathogens

Aerospores are one of the main components of aeromycobiota that can cause fungal diseases in fruits. Their presence in warehouses limits the storage time of apples and affects their organoleptic properties. Our study was based on previously identified airborne fungi collected from apple warehouses in Tunisia. Fifteen species: Penicillium allii, P. chrysogenum, P. citrinum, P. expansum, P. italicum, P. polonicum, P. solitum, P. steckii, P. sumatraense, P. viridicatum, Aspergillus europaeus, A. flavus, A. niger, A. pulverulentus and Alternaria alternata with different level of pathogenicity were tested for their carbon and nitrogen requirements. The tested compounds were selected for their abundance in apple cell wall: polygalacturonic acid, arabinan, arabinogalactan, fructose, galactose, arabinose, maltose, xylose, sucrose, sorbitol, xylan, cellulose microfibril and cutin. Assimilation tests proved that only P. expansum and P. polonicum, with the highest pathogenicity, were able to assimilate all types of carbohydrates and nitrogen sources present in the apple cell wall. This could be a mean to annotate virulence mechanisms of highly pathogenic fungi during apple colonization.