Evaluation of new O-type lines of sugar beet resistant to root and crown rhizoctonia rot in the conditions of microplot artificial contamination

Root rot is a serious threat for sugar beet production and consequently sugar industry. The most important way to deal with it is to use resistant cultivars. In order to identify and grouping new O-type lines resistant the fungus that causes rhizoctonia and crown rot root in sugar beet, 83 O-type lines along with three resistant control (Novodro and line SB-709) and a susceptible (bulk 191) lines were evaluated in microplot in Hamedan in 2023. Artificial inoculation was performed by propagating the Rh133 isolate with AG2-2 anastomosing group on corn seeds and placing next to two months sugar beet seedlings. At the end of the growing season, roots were harvested and evaluated using 1-9 scale, and the disease and harvest indices were calculated accordingly. In the present study, the average number of roots, disease index, and harvest index for the evaluated genetic mass were 17.16, 4.05 and 17.18, respectively. O-types 5 (OT 010245), 32 (OT 010277) and 80 (OT HSF-010041) obtained the highest number of roots and harvest index and lower disease index compared with other genotypes. Based on the SIIG index, it was found that O-types 36 (OT 010282), 32 (OT 010277), 5 (OT 010245), 80 (OT HSF-010041), 28 (OT 010273), and 1 (OT 010240) were adjacent to the ideal O-types in terms of the number of roots, disease index, and harvest index. Results of the cluster analysis classified the evaluated O-types into four groups. O-types 5 (OT 010245), 80 (OT HSF-010041), 32 (OT 010277) and 36 (OT 010282) were placed in a cluster that had significantly lower disease index and higher harvest index as well as SIIG index closer to 1 compared with other three groups. Also, the biplot analysis based on the first two components showed that O-types 80 (OT HSF-010041), 1 (OT 010240), 28 (OT 010273), 5 (OT 010245), 32 (OT 010277) and 36 (OT 010282) were placed in a suitable position of the biplot in terms of resistance indicators. Finally, O-types 5 (OT 010245), 80 (OT HSF-010041), and 32 (OT 010277) were identified as resistant maternal lines for future breeding programs.