Identification and Pathogenicity Assay of Rhizoctonia Anastomosis Groups Associated with Tomato in Iğdır Province, Türkiye

Root rot caused by Rhizoctonia spp. is a serious threat to tomato production worldwide. This study was carried out to determine the anastomosis groups (AGs) and pathogenicity of Rhizoctonia spp. that cause root rot on the tomato plants in Iğdır province, Türkiye. Isolations were performed obtained from 305 diseased tomato plants from 26 different locations, and 93 Rhizoctonia isolates were obtained from tomato plants. The isolates were characterized according to their morphological properties and anastomosis groups (AGs). As a result on the comparison with the tester isolates, 95.7% were classified as multinucleate (MN) Rhizoctonia solani, while 4.3% were identified as binucleate (BN) Rhizoctonia (Ceratobasidium sp.). Based on ITS1‑5.8S-ITS2 rDNA sequencing, 18 Rhizoctonia isolates were confirmed by molecular analysis and were determined to belong to MN Rhizoctonia AG 3 (2), AG 4 HG-I (7), AG 4 HG-III (5), and AG 5 (2). BN Rhizoctonia isolates were also confirmed as AG-A (1) and supported further putative classification to subgroup AG-Fb (1). In the pathogenicity test, we determined the differences in the virulence of these isolates on tomato plants (cv. Hazera 5656 F1) (p < 0.05). The AG 4 isolates (HB-15, HB-66, and HB-81) had the highest disease severity in this study. BN Rhizoctonia isolates (AG‑A HB-18, HB-40, and AG-Fb HB-100) were found to have the lowest disease severity. Growth parameters such as plant height, root length, fresh weight, and dry weight were measured for all plants and it was determined that there was significant difference between isolates (p < 0.05). To our knowledge, this is the first report of MN AG 4 HG III and BN Rhizoctonia AG-Fb on tomato plants in Türkiye. Understanding the genetic diversity of Rhizoctonia may help to understand and will also facilitate the control of black root rot disease. Therefore, the results of the study are crucial for tomato growers and researchers.