Genetic Variability in Post‐harvest Respiration Rates of Sugarbeet Roots1

Post‐harvest respiration rates were measured on whole sugarbeet (Beta vulgarisL.) roots from 97 inbred and hybrid breeding lines to determine the magnitude of the genetic variability. Measurements were made between 50 and 160 days of storage at 5 C on 19 hybrids and inbreds grown at two locations; on eight hybrids and inbreds in 2 successive years; and on 76 inbreds. A high correlation (r=0.90**) existed between the loss of sucrose and respiration rate. The respiration rate of the entries varied between years and between locations, but relative rankings remained consistent (rs=0.87** and 0.81**, respectively). The Spearman's coefficient for respiration rates between locations was similar to those for yield (rs=0.77**) and sucrose content (rs=0.89**). Single‐cross hybrids respired at a lower rate than the midparent mean and, in several cases, lower than the lowest component inbred. A range of 2.5‐fold in respiration rate was found within the 76 inbreds. No correlation existed between sucrose content or root size and respiration rate. Sufficient genetic variability exists within sugarbeet genotypes to sustain a breeding program designed to develop low‐respiring breeding lines.