Rhizoctonia Root Rot on Sugar beet Cultivars Having Varied Degrees of Resistance

Abstract

To address a concern that yield losses may be greater in resistant than in susceptible sugarbeet cultivars, five cultivars, including a susceptible and two moderately resistant commercial varieties, a resistant three-way experimental hybrid, and a highly resistant breeding line, were tested in the field in 1989, 1990, and 1991 for their reaction to inoculation with Rhizoctonia solani (AG-2-2). Generally, rankings of the cultivars for percent decreases (inoculated versus noninoculated) in root and recoverable sucrose yield and percent sucrose and percent purity tended to be proportional to disease severity indices. With the exception of percent purity in 1990, positive significant or highly significant coefficients of linear correlation between disease index differences (inoculated versus noninoculated) and percent decreases in yield and purity parameters each year indicated that there were no hidden losses to Rhizoctonia root rot in resistant germplasms