Recovery of Rhizoctonia solani AG-5 from Tobacco in Italy. R. Nicoletti, Istituto Sperimentale per il Tabacco, Scafati 84018, Italy. E. Lahoz, Istituto Sperimentale per il Tabacco, Scafati 84018, Italy. Plant Dis. 79:540. Accepted for publication 26 April 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0540B.
Rhizoctonia solani Kuhn is known to cause damping-off, sore shin, and leaf spot of tobacco. Isolates belonging to anastomosis groups (AGs) AG-1, AG-2-2, and AG-4 have been described as pathogens of tobacco. Also, isolates with affinity to AG-3 were found to cause taget spot on tobacco leaves. During the summer of 1994, plants with symptoms of crown rot were received from a number of field sites in the tobacco-growing area in Southern Italy (Campania). Rhizoctonia solani was isolated from infected tissues on 2% water agar. Two of the isolates recov ered were identified by anastomosis with two AG-5 isolates, GM-10 and 441, obtained from Ogoshi. On potato-dextrose agar (PDA), young colonies were cream-colored, appressed to the surface of the medium, and showed some zonation later on, they turned tan with production of aerial mycelium. Sclerotia were absent or scattered toward the edge of the dish. The growth of isolates was thiamine-dependent when tested on Czapek-Dox medium. Pathogenicity was evaluated by placing plugs from PDA cultures near the crown of 20-day-old plants. Cortical lesions developed 10 days after inoculation, but symptoms were less severe than those induced by a highly virulent AG-4 isolate from tobacco (RT 16). Reisolation from inoculated plants yielded colonies that anatomosed with both AG-5 tester isolates. To our knowledge this is the first report of R. solani AG-5 on tobacco.