Molecular identification and pathogenicity of Rhizoctonia spp. from tobacco growing areas in northwestern Argentina Guadalupe E. Mercado Cárdenas 1 & Marta Z. Galván 1,2 & Viviana A. Barrera 3 & Marcela S. Rodriguero 4 & Marcelo A. Carmona 5 & Guillermo J. March 6 & Ana C. Ramallo 7 & H. David Shew 8 Received: 7 October 2014 /Accepted: 27 January 2015 # Sociedade Brasileira de Fitopatologia 2015 Abstract In Argentina, more than 60 % of the tobacco crops are grown in the northwestern part of the country and where Rhizoctonia solani leads to a reduction in crop yield and qual- ity. In this study, 35 isolates of Rhizoctonia were obtained from 32 tobacco fields in northwestern Argentina and charac- terized by both morphological and molecular approaches. Based on the variability in the ITS region, isolates were iden- tified as R. solani (80 %), Waitea circinata var. zeae (Rhizoc- tonia zeae) (8 %) and binucleate Rhizoctonia (8 %). Most isolates of R. solani belonged to the anastomosis groups (AGs) AG 4 HG-I (44 %), AG 2-1 (41 %) and AG 4 HG-III (13 %). Isolates of binucleate Rhizoctonia belonged to AG-F and AG-P of Ceratobasidium sp. Morphological variability was higher within isolates of AG 2-1 and AG 4 HG-III than within those of AG 4 HG-I. Aggressiveness of the isolates towards tobacco seedlings was assessed in the greenhouse. Isolates of AG 2-1 were the most aggressive on leaves, caus- ing target spot, whereas isolates of AG 4 HG-I were the most aggressive on stems and roots, causing damping-off. Keywords Nicotiana tabacum . ITS . Anastomosis group (AG) . Vegetative compatibility Introduction Tobacco (Nicotiana tabacum L.) is commercially produced in more than 128 countries worldwide. Argentina is among the ten main producers of unmanufactured tobacco, with over 60 % of the tobacco grown in northwestern region of the country (FAO 2012). The crop is grown mainly in the prov- inces of Salta and Jujuy, where it achieves a mean yield of 2000 kg/ha. The main constraints for tobacco production in Argentina are root and stem diseases caused by the soilborne pathogens Rhizoctonia solani, Ralstonia solanacearum, Fu- sarium oxysporum f. sp. nicotianae, and Phytophthora nicotianae. Among the Rhizoctonia species pathogenic to tobacco, multinucleate species such as the teleomorphs Thanatephorus cucumeris (Rhizoctonia solani) and Waitea circinata var. zeae ( Rhizoctonia zeae ), and binucleate species such as Ceratobasidium spp. have been reported (Lucas 1975; Nicoletti and Lahoz 1995; Shew and Melton 1995; Garcia et al. 2009; Gurkanli and Ozkoc 2011). In tobacco, these path- ogens cause several symptoms including target spot, stem rot and damping-off in transplants and target spot and sore shin in field plants, resulting in crop losses of up to 15 % (Lucas 1975; Shew and Lucas 1991; Csinos and Stephenson 1999; Tarantino 2007; Gonzalez et al. 2011). Under wet conditions, especially rainy weather, target spot epidemics may lead to severe losses. However, these conditions are not frequent in Section Editor: Adalberto Café-Filho * Guadalupe E. Mercado Cárdenas mercado.guadalupe@inta.gob.ar 1 Instituto Nacional de Tecnología Agropecuaria (INTA) EEA Salta, Ruta Nac. 68 Km 172 (4403) Cerrillos, Salta, Argentina 2 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), CCT-Salta. Av. Bolivia 5150 (4400), Salta, Argentina 3 IMYZA, INTA Castelar, Buenos Aires, Argentina 4 Laboratorio de Genética Evolutiva, Departamento de Ecología, Genética y Evolución, UBA, Buenos Aires, Argentina 5 FAUBA, Buenos Aires, Argentina 6 IPAVE, INTA, Córdoba, Argentina 7 UNT, Tucumán, Argentina 8 Department of Plant Pathology, North Carolina State University, Raleigh, NC 27695, USA Trop. plant pathol. DOI 10.1007/s40858-015-0035-7