First Report of Colletotrichum fioriniae and C. godetiae Causing Apple Bitter Rot in Slovenia

Bitter rot is a common disease of apple (Malus domestica Borkh.) in several apple growing regions worldwide. The disease affects the fruit pre-harvest in orchards and/or post-harvest in storage, resulting in considerable economic losses. The most frequently reported causal agents belong to Colletotrichum acutatum and C. gloeosporioides species complexes. Apple bitter rot was observed in Slovenia in 2011 and 2012 at harvest in three commercial apple orchards near Ljubljana. Symptoms were observed on approximately 10% of fruits in the orchard, and included circular, brown, slightly sunken necrotic lesions on fruit surface. When placed in high humidity, acervuli with orange conidial masses developed on the lesions. Eleven isolates were obtained from symptomatic apples by culturing pieces of necrotic tissue on potato dextrose agar (PDA). Single spore isolates were prepared and grown at 21°C and a 12-h photoperiod for 10 days. Total DNA was extracted and fragment of the β-tubulin-2 gene (exons 2-6) was amplified with primer pair T1 (3) and Bt-2b (2), and was sequenced (Macrogen, The Netherlands). BLAST analysis showed that six isolates had 100% identity to C. fioriniae (Marcelino & Gouli) R.G. Shivas & Y.P. Tan (4) including the ex-holotype strain CBS 128517. The remaining isolates showed 100% identity to sequences reported for C. godetiae Neerg. (1), including the ex-type strain CBS 133.44. One sequence of each species was deposited in GenBank (KJ650030 and KJ650029). Morphological characteristics of two isolates per species were recorded after 10 days of incubation on PDA at 21°C. C. fioriniae colonies were white to light gray on the upper side and brownish pink to vinaceous with black spots on reverse. Average growth rate was 56.5 mm in 7 days. Conidia were cylindrical to fusiform, pointed at both ends, and measured 7.5 to 16.7 μm (mean 13.1 μm) × 3.5 to 4.9 μm (mean 4.1 μm). C. godetiae colonies were light gray on the upper side and gray with black spots on reverse. Average growth rate was 48.5 mm in 7 days. Conidia were cylindrical to fusiform, pointed at one or both ends, and measured 7.9 to 18.1 μm (mean 12.2 μm) × 3.4 to 4.9 μm (mean 4.2 μm). Pathogenicity of both species was tested by inoculating surface-sterilized 'Gala' and 'Golden Delicious' apples with 10 μl of a conidial suspension (10⁵ conidia ml^-1) obtained from single spore cultures. Five mature apples were wound-inoculated with one isolate of each species and sterile distilled water was used for controls. After 10 days of incubation at 23°C and 100% relative humidity, symptoms, identical to those observed initially, developed around the inoculation point, while controls showed no symptoms. C. fioriniae and C. godetiae were re-isolated from inoculated apples. To our knowledge, this is the first report of apple bitter rot associated with C. fioriniae and C. godetiae in Slovenia. The disease can pose a threat to our apple production and cause substantial losses during storage. References: (1) U. Damm et al. Stud. Mycol. 73:37, 2012. (2) N. L. Glass and G. Donaldson. Appl. Environ. Microbiol. 61:1323, 1995. (3) K. O'Donnell and E. Cigelnik. Mol. Phylogenet. Evol. 7:103, 1997. (4) R. G. Shivas and Y. P. Tan. Fungal Divers. 39:111, 2009.

First Report of Brown Rot Caused by Monilinia fructicola Affecting Peach Orchards in Slovenia

Monilinia fructicola, the causal agent of brown rot, is a destructive fungal pathogen that affects mainly stone fruits (Prunoideae). It causes fruit rot, blossom wilt, twig blight, and canker formation and is common in North and South America, Australia, and New Zealand. M. fructicola is listed as a quarantine pathogen in the European Union and was absent from this region until 2001 when it was detected in France. In August 2009, mature peaches (Prunus persica cv. Royal Glory) with brown rot were found in a 5-year-old orchard in Goriška, western Slovenia. Symptoms included fruit lesions and mummified fruits. Lesions were brown, round, rapidly extending, and covered with abundant gray-to-buff conidial tufts. The pathogen was isolated in pure culture and identified based on morphological and molecular characters. Colonies on potato dextrose agar (PDA) incubated at 25°C in darkness had an average daily growth rate of 7.7 mm. They were initially colorless and later they were light gray with black stromatal plates and dense, hazel sporogenous mycelium. Colony margins were even. Sporulation was abundant and usually developed in distinct concentric zones. Limoniform conidia, produced in branched chains, measured 10.1 to 17.7 μm (mean = 12.1 μm) × 6.2 to 8.6 μm (mean = 7.3 μm) on PDA. Germinating conidia produced single germ tubes whose mean length ranged from 251 to 415 μm. Microconidia were abundant, globose, and 3 μm in diameter. Morphological characters resembled those described for M. fructicola (1). Morphological identification was confirmed by amplifying genomic DNA of isolates with M. fructicola species-specific primers (2-4). Sequence of the internal transcribed spacer (ITS) region (spanning ITS1 and ITS 2 plus 5.8 rDNA) of a representative isolate was generated using primers ITS1 and ITS4 and deposited in GenBank (Accession No. GU967379). BLAST analysis of the 516-bp PCR product revealed 100% identity with several sequences deposited for M. fructicola in NCBI GenBank. Pathogenicity was tested by inoculating five mature surface-sterilized peaches with 10 μl of a conidial suspension (10⁴ conidia ml^-1) obtained from one representative isolate. Sterile distilled water was used as a control. Peaches were wounded prior to inoculation. After 5 days of incubation at room temperature and 100% relative humidity, typical brown rot symptoms developed around the inoculation point, while controls showed no symptoms. M. fructicola was reisolated from lesion margins. Peach and nectarine orchards in a 5-km radius from the outbreak site were surveyed in September 2009 and M. fructicola was confirmed on mummified fruits from seven orchards. The pathogen was not detected in orchards from other regions of the country, where only the two endemic species M. laxa and M. fructigena were present. To our knowledge, this is the first report of M. fructicola associated with brown rot of stone fruits in Slovenia. References: (1) L. R. Batra. Page 106 in: World Species of Monilinia (Fungi): Their Ecology, Biosystematics and Control. J. Cramer, Berlin, 1991. (2) M.-J. Côté et al. Plant Dis. 88:1219, 2004. (3) K. J. D. Hughes et al. EPPO Bull. 30:507, 2000. (4) R. Ioos and P. Frey. Eur. J. Plant Pathol. 106:373, 2000.

First Report of Phytophthora citricola Occurring on Fagus sylvatica in Slovenia

During 2005 and 2006, eight declining, mature Fagus sylvatica trees with severe crown dieback were encountered at two stands near Ljubljana and Kamnik in central Slovenia. Bleeding cankers were seen mostly in the lower parts of the stem. Fresh cankers showed orange brown necroses of the inner bark and cambium. Older cankers were dark brown and surrounded by cracks and shedding bark. Small pieces of marginal tissue were excised from fresh necrotic lesions and incubated in the dark at 20°C on P₅ARP and cornmeal (CMA) agar plates. Soil samples collected from around the base of these declining trees were submerged in sterile distilled water. Leaves of Rhododendron catawbiense were used as bait to test for the presence of Phytophthora spp. Several similar isolates were obtained from trees and soil from both stands. Colonies were narrowly petaloid, slow growing on P₅ARP, and fast growing on CMA. The colonies produced abundant sporangia when submerged in pond water. Semipapillate, noncaducous sporangia were ovoid to obpyriform, but were occasionally distorted, and 30 to 69 (49) μm long and 23 to 44 (34) μm wide. Neither hyphal swellings nor chlamydospores developed. Isolates were homothallic showing paragynous antheridia, spherical oogonia of 22 to 31 (25) μm diameter, and plerotic oospores of 20 to 27 (23) μm diameter. The morphological characters resembled those described for Phytophthora citricola (1). ITS rDNA, spanning ITS 1 and 2, plus the 5.8S rDNA were generated using primers ITS4 and ITS5. Isolates from symptomatic trees and the soil yielded identical sequences and were the same as various sequences deposited for P. citricola at GenBank. The ITS rDNA of one representative strain was deposited at GenBank (Accession No. EF423556). Mycelial plugs from one of the P. citricola strains grown on CMA were used to inoculate stem wounds of seven potted seedlings and wounds made on four freshly cut, healthy branches of F. sylvatica. Sterile agar plugs were used as controls. The test was carried out over 4 weeks at 20°C. Extensive necrotic lesions developed around inoculation points on seedlings and branches, whereas the controls showed no symptoms. P. citricola could also be reisolated from margins of these lesions. During the past decade, declining F. sylvatica trees were observed in an increasing number of stands in Germany (2). Several Phytophthora species appeared to be involved in this decline, but P. citricola was the most frequently recovered species (2,3). To our knowledge, this it the first report of P. citricola found associated with a decline of European beech in Slovenia. References: (1) D. C. Erwin and O. K. Ribeiro. Pages 282-287 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (2) T. Jung. Forst Holz. 60:131, 2005. (3) T. Jung et al. Mycologist 19:159, 2005.