Genetic diversity and virulence of Rhizoctonia spp. associated with black root rot of strawberry in Türkiye

Black root rot , caused by Rhizoctonia spp., is a significant limiting factor for strawberry production globally. This study aimed to identify Rhizoctonia spp. and characterize their anastomosis groups (AGs) and virulence from strawberry-growing regions in Mersin, Bursa, and Konya. A total of 122 Rhizoctonia spp. isolates were recovered from strawberry plants exhibiting black root rot symptoms in 173 strawberry fields. Morphologically, all isolates except three were identified as binucleate Rhizoctonia spp. The internal transcribed spacer region of ribosomal DNA was sequenced to identify AG groups, and a dendrogram was constructed to assess the phylogenetic relationships among these groups. In total, 81 isolates were identified as AG-A, 20 as AG-G, 9 as AG-K, 7 as AG-Fa, one each as AG-V, and AG-W. Additionally, three isolates belonged to R. solani AG-4 HG-I. Pathogenicity testing revealed that 117 isolates, excluding five, exhibited varying degrees of virulence on strawberry plants. Binucleate AG-Fa demonstrated the highest virulence with an average lesion length of 14.85 mm, followed by AG-A and AG-G, respectively. Notably, binucleate AG-Fa, AG-V, AG-W and multinucleate AG-4 HG-I were identified as novel strawberry black root rot pathogens in Türkiye, with AG-V and AG-W being reported for the first time globally. • Binucleate Rhizoctonia AG-Fa, AG-V, AG-W, and R. solani AG-4 HG-I were reported for the first time on strawberry in Türkiye. • The isolates of binucleate AG-V and AG-W were identified globally for the first time as black root rot pathogens. • Binucleate AG-A was dominant in Türkiye, followed by AG-G and AG-K in strawberries. • Multiple AG groups highlight the need for improved local disease management methods.