Abstract
Postharvest apple diseases are mainly caused by fungal pathogens entering fruits through wounds during harvesting, handling, storage, transport, and marketing. Penicillium spp., Botrytis spp., Rhizopus spp., and Mucor spp. are common wound pathogens. Other pathogens are characterized by latent infections in field and symptom development during the postharvest phase. Latent pathogens are increasingly relevant on Italian apples during postharvest. Neofabraea alba syn. Phlyctema vagabunda and N. kienholzii cause bull's eye rot, infecting late-harvested cultivars as 'Cripps Pink' via lenticels. Propagules of N. alba are found in rainwater collected from apple orchards. Another pathogen infecting lenticels is Ramularia mali, agent of dry lenticel rot, common on 'Golden Delicious' and 'Ambrosia' apples. White haze, able to reduce fruit quality, is attributed to various basidiomycetous genera, such as Entyloma, Golubevia, and Tilletiopsis species being common in northern Italy. New species like E. mali sp. nov. and G. mali sp. nov. have been recently identified. Fruit microbiome analysis showed that the agents of white haze are only epiphytic and they occur on the fruit skin just before harvest. On the contrary, R. mali first appears as an endophyte at least 3 months before harvesting, but it becomes epiphytic starting from September and during storage. Changes in microbiota assembly and composition over time are crucial for understanding postharvest pathogen epidemiology. A SYBR Green qPCR assay detects and quantifies R. mali in apples, revealing its presence on asymptomatic fruits. R. mali was found early in the season in the aerial microbiome analysed from spore traps placed in apple orchards. Also, other latent pathogens are emerging on apples in Italy, such as Colletotrichum spp., causal agents of bitter rot. Fruit and aerial metabarcoding are valuable tools for the assessment and prediction of postharvest diseases, and to design targeted crop protection strategies.