First report of Asiatic brown rot (Monilinia polystroma) and Brown rot (Monilinia fructicola) on pears in Italy

Brown rot caused by Monilinia spp. is an important fruit postharvest decay causing severe losses in stone and pome fruits with a significant economic impact. In Italy, three Monilinia species (M. laxa, M. fructicola, and M. fructigena) are the causal agents of blossom and twig blight and brown fruit rot in stone fruit. M. polystroma has been observed on peaches in Italy (2) and has been reported in Czech Republic and Hungary (3), Poland (4), Serbia (5), and Switzerland (1) on pome fruits and apricots. In September 2013, stored var. Abate Fetel pears showing brown rot symptoms were observed in Emilia Romagna region. In 20% of the symptomatic pears, circular and brown to black decay spots were observed, covered by a large number of yellowish or buff-colored stromata, while decayed tissues remained firm, resembling M. polystroma symptoms. In another 13% of stored pears, the decayed tissues remained firm, and decay lesions were covered with numerous grayish pustules containing spores. Putative pathogens were isolated on potato dextrose agar (PDA) and incubated at 25°C in darkness for 5 days. The colonies grown on PDA were yellowish, with irregular black stromatal crusts at the edges of the colonies after 10 to 12 days of incubation. Some colonies developed, at their margins, sporogenous tissue slightly elevated above the colony surface that was buff/pale luteous (4). Conidia developing from such cultures were one celled, ovoid or limoniform, smooth and hyaline, measuring 12.2 to 20.4 × 8.4 to 12.3 µm when grown on V8 juice agar (V8) at 22°C, and matched the description of those for M. polystroma. Other colonies, which developed a gray mass of spores in concentric rings with the reverse side black, were morphologically identified as M. fructicola. The colony margins were smooth edged, and the conidia were one-celled, limoniform, hyaline, and measuring 12.1 to 17.4 × 8.1 to 11.2 µm on V8 at 22°C. Isolate identificaton was obtained using the universal primers for Monilinia spp. (3). Pathogenicity was confirmed using surface-sterilized mature var. Abate Fetel and William pears wounded with a sterile needle, and inoculated with 20 µl of an M. polystroma or M. fructicola conidial suspension (103 spores/ml). After 7 days of incubation at 20°C, typical symptoms of Asiatic brown rot or brown rot developed on both the wounds of all inoculated pears, while controls remained symptomless. Mean colony diameters measured after 7 days were 47.3 mm for Asiatic brown rot and 44.1 mm for brown rot, and there were no significant differences in colony diameter after 7 days between M. polystroma and M. fructicola (α < 0.05). After 14 days, yellowish exogenous stromata appeared on the surface of pears infected by M. polystroma, whereas numerous grayish pustules containing spores appeared on pears inoculated with M. fructicola. Control pears still remained symptomless. The fungus isolated from inoculated fruit exhibited the same morphological features as the original isolates, and PCR/sequencing analysis using primers ITS1 and ITS4 confirmed the results of the universal primers (3) (GenBank Accession Nos. GU067539.1 and HQ893748.1). Although the presence of M. polystroma and M. fructicola has been documented in Italy, this is the first time these two species were observed on Italian pears. This report suggests a broader impact since M. polystroma and M. fructicola have not been previously reported on pears in Europe. Because of the importance of pears in the Italian fruit industry, knowledge about the occurrence of new pathogens will facilitate the adoption of adequate control strategies to reduce postharvest losses.