Grafted cactus, produced by grafting two different cactus speciesincluding photosynthetic stocks (mostly Hylocereus trigonus) andnon-photosynthetic scions (usually Gymnocalycium mihanovichiior Chamaecereus silvestrii), is one of the most popular exportingornamental plants, comprising about 70% of the world tradingmarket (Song et al., 2009a, 2009b). Since the grated cactus is culti-vated in greenhouses with warm temperature and high humidityduring the whole growing season, several diseases especially causedby fungi such as Bipolaris cactivora , Colletotrichum gloeosporioides(anamorph of Glomerella cingulata), Fusarium oxysporum, andAlternaria alternata are frequently found in the cactus farms inKorea (Chang et al., 1998; Choi et al., 2010; Hyun et al., 1998; Kimet al ., 2000).A stem disease of G. mihanovichii caused by a fungus wasobserved in 2010 in several greenhouses especially with highhumidity at Goyang, Gyeonggi province, the major cactus-growingarea in Korea. Its occurrence was not prevalent and found mostly inmature (old) cactus plants. Characteristic symptoms were initialblack or brown spots that were enlarged with time to becomeshrunken or water-soaked black lesions at advanced infection stages(Fig. 1A & B). Isolation of fungi and bacteria from the rotten stemsof G. mihanovichii was tried to, but it was fail the isolation of thepreviously known fungal and bacterial pathogens such as B. cacti-vora, C. gloeosporioides, F. oxysporum, A. alternata, and Pecto-bacterium carotivorum (Kim et al., 2007) except seven fungalisolates with identical morphological characteristics. The mycologi-cal characteristics of the fungal isolates were as follows. The fungusformed grayish brown colonies with the production of abundant flator irregular black sclerotia on potato-dextrose agar (PDA) (Fig. 1C).Conidiophores were upright, tall and slender, 8.0 −31.0 µm in width,determinate, hyaline or grayish, branched irregularly in upper portions,bearing clusters of conidia simultaneously on short denticles (Fig.1D). Conidia were one celled, colorless or pale brown, mostlyellipsoid or ovoid, and 8.5−12.3 × 6.3−11.2 µm in size (Fig. 1E).These morphological characteristics of the present isolates coincidewith those of Botrytis cinerea described by Ellis and Waller (1974).To confirm the identification of the fungus, the partial internaltranscribed space (ITS) region of rDNA from the present isolate wasamplified using the primers ITS1 and ITS4 as described by White etal. (1990) and sequenced. The resulting sequences were comparedto the GenBank database using the NCBI BLAST search program.A total of 798 base sequences determined from the ITS DNA were100% identical to those of several Botryotinia fuckeliana (teleo-morph of Botrytis cineria) strains of NCBI accession nos.HM849615.1 HM84, 9047.1 HQ1, 66517.1 and, FN812726.1 in, dicat-ing the causal fungus was confirmed to be B. cinerea . For pathogenicity test, one-year-old stems of G. mihanovichiiwere inoculated with spore suspension (1 × 10