First Report of Brown Rot (Monilinia fructicola) on the Dogwood, Cornelian Cherry (Cornus mas)

Abstract

Cornelian cherries (Cornus mas), also called cornels, are members of the dogwood family (Cornaceae), and are not true cherries. Cornelian cherry is primarily grown as an edible landscape ornamental in the United States. Brown rot, caused by fungi in the genus Monilinia, is one of the most important diseases of stone fruit worldwide. In the United States, M. fructicola is the most commonly observed Monilina species, although M. fructigena and the European brown rot pathogen, M. laxa, may also infect stone fruit. M. fructigena is the only Monilinia species reported to infect cornelian cherry, but there is only a single report of it occurring in the United States (1,4). All three species have similar morphology and are commonly misidentified (1,3,4). In August of 2010 and 2013, in one location, brown rot was observed on fruit of the cornelian cherry cultivar Elegans. In both instances, only ‘Elegans’ fruit was infected while neighboring ‘Sunrise’ exhibited no symptoms in the field, and lesions did not appear to develop into shoot blight. In 2013, single-spore isolates from the diseased fruit were cultured on potato dextrose agar (PDA) incubated at 25°C for 5 days. Colony morphology was consistent with M. fructicola and was rapidly growing, gray, producing concentric rings, and developing smooth colony margins. Conidia were hyaline, 10 × 15 μm, and formed in branched, monilioid chains of varying lengths (1). Molecular-based species identification was performed on the 450-bp amplified ribosomal internal transcribed spacer (ITS) sequences, using primers ITS1 and ITS4. BLAST searches of the ITS sequences in GenBank showed the highest similarity (100%) with sequences of M. fructicola isolates from Italy (FJ411110), China (FJ515894), and Spain (EF207423). Pathogenicity was confirmed by inoculating surface-sterilized, mature ‘Sunrise’ fruit with mycelial plugs of the isolate identified with the ITS sequence. Mycelial plugs (3 mm in diameter) were removed from the periphery of a 5-day-old colony and placed upside down into five fruit that were wound-inoculated with a 3-mm cork borer, petiole hole-end inoculated, or unwounded but inoculated; control fruit for each treatment received sterile plugs of PDA as a control. All fruit was stored in a moist chamber for the duration of the experiment. Wound-inoculated fruit developed symptoms within 2 days; sporulating lesions developed within 5 days. Symptoms of infection via the petiole developed in 4 days; by day six, three of the five inoculated fruit were infected, and four of the five were infected by day eight. Unwounded, inoculated fruit showed symptoms on day six; three of the five fruit were infected by day eight. None of the control inoculations showed Monilinia infection. Pathogens were re-isolated from the inoculated fruit and confirmed to be M. fructicola on the basis of morphological characteristics. To our knowledge, this is the first fulfillment of Koch's postulates demonstrating that M. fructicola can infect cornelian cherry. A previous report by Höhnel in 1918 described infection by Lambertella corni-mas of a cornelian cherry in Austria; however, the taxonomic details presented are consistent with M. fructigena (2). References: (1) M.-J. Côté et al. Plant Dis. 88:1219, 2004. (2) T. H. Harrison and A. F. El-Helaly. Brit. Mycol. Soc. Trans. 19:199, 1935. (3) C. R. Lane. EPPO Bulletin 32:489, 2002. (4) E. M. Sagasta. EPPO Bulletin 7:105, 1977.