Pomegranate: Postharvest Fungal Diseases and Control

Abstract

Due to well-known nutraceutical properties, pomegranate (Punica granatum L.) cultivation is recently increasing in various areas of the world including Italy. Fungal diseases are the major causes of postharvest yield and economic losses. Most of the fungi infect pomegranates in the field during the blooming stage remaining latent until fruit ripening, others infect fruit during harvest and postharvest handling through rind injuries. Main postharvest fungal diseases of pomegranates are gray and blue molds caused by Botrytis spp. and Penicillium spp., respectively, black heart and black spot due to Alternaria spp., anthracnose related to species ascribable to Colletotrichum genus, and Coniella rot, due to Coniella granati. Few fungicides are allowed for pre- and postharvest treatments, making it extremely difficult to control fungal infections. In this scenario, especially in organic fruit production, alternative control means may be a desirable solution to reduce pomegranate losses during the production chain. This chapter focuses on the most important postharvest diseases of pomegranates and possible strategies and means to reduce spoilage.

Postharvest Diseases of Pomegranate: Alternative Control Means and a Spiderweb Effect

“…Indeed, pomegranates are chiefly available from September to February in the northern hemisphere and from April to July in the southern one; therefore, pomegranates are globally scarce in March and August [ 20 ]. Morphological features of pomegranate fruit, such as the persistence of the calyx, remains, and senescent stamens, allow for the setting of latent infections [ 11 , 12 , 21 ], as reported for strawberries and table grapes [ 22 , 23 ]. Indeed, this is one of the leading causes of pomegranate losses, as described by Opara et al [ 24 , 25 ], who analyzed the South African pomegranate trade.…”

“…The same research highlighted the importance of avoiding abiotic stresses, pests, and fungal infections in the field and fruit damage during harvesting, postharvest handling, and transport to reduce the incidence of secondary fungal infections [ 8 , 26 ]. Most of the fungal infections of pomegranates occur in the field during the blooming and early fruit-growing stages, remaining latent until optimal conditions for pathogen growth [ 11 , 12 ]. As latent infections are difficult to control, specific strategies must be implemented for prevention [ 7 , 11 ].…”

“…These facts are also confirmed by our data: incidence and severity of postharvest rots, generally, are significantly reduced by repeated treatments in the field. Being registered as a postharvest fungicide and effective in reducing crown rots caused by latent and wound pathogens [ 12 , 30 , 31 ], in our trials, fludioxonil was selected as positive chemical control, and its efficacy was fully confirmed. D’Aquino et al [ 30 ] analyzed chemical residues of fludioxonil postharvest application, highlighting their absence in the edible portion of the fruit; furthermore, in the USA, the Environmental Protection Agency (EPA) gave a complete registration tolerating residues of 5 ppm [ 32 ].…”

“…Chitosan is a D-glucosamine linear polymer, mainly obtained by alkaline deacetylation of chitin extracted from different sources [ 12 ], indeed classified as a basic substance [ 35 ]. Such factors as pH, deacetylation degree (60 to 100%), molecular weight (3800 to 20,000 Da), origin, and active ingredient concentration affect its solubility in water, bio-adhesive properties, and above all, antifungal properties [ 36 , 37 ].…”

“…In Italy, despite the growing economic importance of this crop, few fungicides or alternative compounds are authorized to control fungal diseases. Until last year, as needed, employment of conventional and alternative fungicides was locally and yearly allowed according to regional legislation [ 12 ]. Among chemical compounds, in 2023, field and postharvest application of boscalid and fludioxonil, respectively, has been approved; similarly, among alternative control means, essential oils (geraniol, thymol, eugenol) and beneficial microorganisms ( Coniothyrium minitans , Trichoderma species) have been allowed [ 13 ].…”