Postharvest Storage Losses Associated with Aphanomyces Root Rot in Sugarbeet

Because of its persistence in the soil and the ineffectiveness of control measures, Aphanomyces cochlioides (causal organism of Aphanomyces root rot) is one of the more problematic pathogens attacking sugarbeet (Beta vulgaris). As a consequence, diseased roots often are included in storage piles; however, information on the consequences of storing roots with Aphanomyces root rot is lacking. Roots from six commercial fields with chronic root rot problems were divided into groups based upon root rot severity. Prior to measuring storage respiration rate, sucrose concentration, and extractable sucrose concentration, a root rot index (0 = no rot to 100 = completely rotted) was determined for each sample. Regression analyses were used to characterize relationships among root rot index, postharvest respiration rate, and extractable sucrose losses during storage for 120 days. Below rot indices of 35, Aphanomyces had little or no effect on respiration rate or extractable sucrose loss during storage. Sucrose losses associated with rot indices of 65 and 80 were 1.8 and 2.8 times those associated with a rot index of 35, respectively. Aphanomyces root rot has the potential to significantly increase losses during storage; however, field by Aphanomyces severity interactions and variability in the observed response patterns indicate that accurately predicting these losses prior to harvest will be difficult. This report provides information that will assist in determining the Aphanomyces root rot severity that would justify not harvesting a field or if roots from diseased fields should be processed early in the campaign.