Satureja montana L. (winter savory “Repandens”) is an evergreen shrub. In late summer 2010, blight was observed on a farm near Albenga (northern Italy) on 3% of 500 potted 2-month-old plants. Semicircular, water-soaked lesions appeared first on stems then on leaves. As the disease progressed, blighted leaves turned brown, withered, clung to the shoots, and matted on the surrounding foliage within 5 to 6 days. Stem fragments taken from the margin of the diseased tissues of 10 plants were disinfected for 10 s in 1% NaOCl, rinsed with sterile water, and plated on potato dextrose agar (PDA) amended with 100 μg/liter streptomycin sulfate. A fungus with morphological characters of Rhizoctonia solani was consistently isolated. Three isolates of R. solani obtained from affected plants were successfully anastomosed with R. solani isolate AG 1 (ATCC 58946). Three pairings were made for each tested strain. Hyphal diameter at the point of anastomosis was reduced, the anastomosis point was obvious, and death of adjacent cells was observed. Results were consistent with other reports on anastomosis reactions (2). Isolates from winter savory were paired with R. solani isolates AG 2, 3, 4, 6, 7, or 11 and examined microscopically. Anastomosis was not observed in any of the pairings. Tests were repeated once. Mycelium of 10-day-old isolates from winter savory appeared light brown, compact, and radiate. Numerous, dark brown sclerotia, 1 to 4 mm in diameter (average 1.7), developed within 20 days after transfer of mycelia to PDA in 90-mm-diameter petri dishes and incubated (11-h daylight, 13-h dark) at 21 to 24°C. Descriptions of mycelium and sclerotia were typical for subgroup IA Type 2 (3). The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and sequenced. BLASTn analysis (1) of the 696 bp showed a 99% homology with the sequence of R. solani. The nucleotide sequence has been assigned GenBank No. JQ313811. For pathogenicity tests, inoculum of R. solani was prepared by growing the pathogen on wheat kernels autoclaved in 1-liter glass flasks (30 min at 121°C and 1 atm) for 15 days. One of the isolates assigned to the anastomosis group AG 1 IA was tested. Five 90-day-old plants of S. montana were inoculated. Each plant grown in 2-liter pots in a steam disinfested peat/pumice/pine bark/clay mix (50:20:20:20:10) was inoculated with 10 g of infested wheat kernels placed at the base of the stem. Five plants inoculated with noninfested wheat kernels served as the control. Plants covered with plastic bags were arranged randomly in a growth chamber at 20 ± 1°C with 12-h light/dark for 5 days. Symptoms, similar to those observed in the farm, developed 4 days after inoculation. Ten colonies of R. solani were reisolated from infected leaves and stems of each inoculated plant. Control plants remained healthy. The pathogenicity test was carried out twice. Symptoms caused by R. solani have been recently observed on S. hortensis in Poland (4). This is, to our knowledge, the first report of blight of S. montana caused by R. solani in Italy.
References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) D. E. Carling. Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. Kluwer Academic Publishers, The Netherlands, 1996. (3) R. T. Sherwood. Phytopathology 59:1924, 1969. (4) B. Zimowska. Herba Polonica 56:29, 2010.