Influence of Beet necrotic yellow vein virus and Freezing Temperatures on Sugar Beet Roots in Storage.

Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) is a yield-limiting sugar beet disease that was observed to influence root resistance to freezing in storage. Thus, studies were conducted to gain a better understanding of the influence of BNYVV and freezing on sugar beet roots to improve pile management decisions. Roots from five commercial sugar beet cultivars (one susceptible and four resistant to BNYVV) were produced in fields under high and trace levels of rhizomania pressure and subjected to storage using five temperature regimes ranging from 0 to -4.4°C for 24 h. After cold treatment, eight-root samples were stored in a commercial indoor storage building (set point 1.1°C) for 50 days in 2014 and 57 days in 2015. Internal root temperature, frozen and discolored tissue, and moisture and sucrose loss were evaluated. The air temperature at 0, -1.1, and -2.2°C matched internal root temperature but internal root remained near -2.2°C when air temperature was dropped to -3.3 and -4.4°C. In a susceptible cultivar produced under high rhizomania pressure, the percentage of frozen tissue increased (P < 0.0001) from an average of 0 to 7% at 0, -1.1, and -2.2°C up to 16 to 63% at -3.3°C and 63 to 90% at -4.4°C, depending on year. Roots from the susceptible cultivar produced under low rhizomania pressure and those from the resistant cultivars from both fields only had elevated (P ≤ 0.05) frozen tissue at -4.4°C in 15 of 18 cultivar-year combinations. Frozen tissue was related to discolored tissue (r = 0.91), weight loss (r = 0.12 to 0.28), and sucrose reduction (r = 0.69 to 0.74). Consequently, BNYVV will not only lead to yield and sucrose loss in susceptible sugar beet cultivars but also to more frozen root tissue as temperatures drop below -2.2°C. Based on these observations, the air used to cool roots in nonfrozen sugar beet piles throughout the winter should not drop below -2.2°C to maximize sucrose retention.