Fungal pathogens causing postharvest decay of pomegranate fruit in Spain

Abstract

Spain is the largest European Union exporter of entire pomegranates (Punica granatum L.) for fresh consumption. The most important cultivar in the country is 'Mollar de Elche' (syn.: 'Mollar'), an autochthonous cultivar of yellowish rind and excellent sensory properties cultivated mainly in Alacant province (València region, eastern Spain). However, foreign intense red cultivars such as 'Wonderful', 'Acco' or 'Smith' are increasingly being planted in northern areas in the region (València and Castelló provinces) due to their good adaptability and good acceptation in EU markets, especially for the industries of juices and minimally processed arils. Research work has been conducted and is still in progress to identify and characterize fungal pathogens causing fruit postharvest disease in local environmental conditions. 'Mollar de Elche' pomegranates from different orchards were used in different seasons to assess both latent and wound fungal pathogens causing decay after harvest. In addition, disease was also assessed on fruit packed and stored in commercial conditions. In red cultivars, postharvest symptoms consisting of internal black rot of arils and membranes were increasingly observed in the last seasons. Affected fruit with light to moderate internal lesions are very difficult to sort at harvest and during packaging, which is very detrimental for consolidation of export markets. In all cases, fungi from symptomatic fruit were isolated, purified and identified by means of macroscopic and microscopic observation and molecular techniques. Pathogenicity (Koch's postulates) and disease development at ambient and low temperatures were tested with pomegranates artificially inoculated with the fungi. Main fungi causing latent and wound infections on 'Mollar de Elche' pomegranates were Botrytis cinerea (gray mold) and Penicillium spp. (blue/green mold), respectively. These pathogens were also the most frequently found on symptomatic cold-stored pomegranates. Other relatively frequent pathogens on fruit stored at 20 and 5°C were Aspergillus niger (black rot) and Pilidiella granati (syn.: Coniella granati; dry rot), respectively. In red cultivars, heart rot was caused by Alternaria alternata. This disease was not observed on 'Mollar de Elche' pomegranates.