Morphology and pathogenicity of Rhizoctonia solani Kühn associated with potato black scurf in Nariño (Colombia) by Betancourth-García, Carlos A., Castro-Caicedo, Bertha Lucía, Quiroz-Ojeda, Claudia, Sañudo-Sotelo, Benjamin, Florez-Casanova, Carlos, Salazar-González, Claudia