Evaluation of resistance of sugar beet commercial cultivars to Rhizoctonia root rot in greenhouse and field conditions

Rhizoctonia root rot mainly caused by Rhizoctonia solani AG 2-2 and R. solani AG-4 is a sugar beet disease in Iran. In this study, the resistance of foreign and domestic commercial cultivars, available to farmers, against both pathogenic groups of AG 2-2 and AG 4 was evaluated in greenhouse and field conditions. Under greenhouse condition, 18 cultivars were planted in pots along with a control cultivar (Jolgeh) and after 8-weeks, seedlings were inoculated with corn seeds infected with R. solani AG 2-2 and R. solani AG 4 isolates. Six weeks after inoculation, the intensity of contamination on the roots of each plant was measured based on a nine-point scale (1 to 9). For field evaluation, cultivars were planted in a contaminated field in 50-m-long rows with three replications and the intensity of root infection was evaluated at harvest. Results showed that there was a significant difference between cultivars and susceptible control and also among cultivars in both greenhouse and field conditions. Also, the general response of cultivars to both pathogenic groups was similar. In total, Ekbatan, Iris, Aigrette, Novodoro, Ivano, Novella, Tourelle, Modex, Efesos and Cadet cultivars had the lowest infection under different trial conditions.