Respiration Rate (ml/Kg fresh weight)
Cultivars tested did not respond similarly under the conditions of this experiment. For `Centennial', there was an overall tendency for storage roots treated with SO2 and CO2 + SO2 to have higher respiration rates (Table 1A).
The control and CO2 treated roots had higher respiration rates just after curing with no difference among treatments for months 1, 2 and 3. For months 4 - 7, the control and CO2 treated storage roots had lower rates of respiration when compared to the CO2 + SO2 treatment. Respiration rates for the control and the CO2 treated roots were also lower than those treated with SO2 for months 5 - 7. The increase in respiration during the last months of storage was much greater for the SO2 and CO2 + SO2 treated storage roots. The value obtained for SO2 and CO2 + SO2 treatments were 190.67 and 110.67, respectively, at month 7. The highest values recorded for the control and CO2 (78.0 and 70.0 ml/Kg respectively) were for the period just after curing.
The trends in respiration for `Jewel' were similar to those found for `Centennial', however, the increase in the rate of respiration was much lower (Table 1B). The highest rate of respiration for the control and the CO2 treated storage roots were obtained just after curing. These values were greater than those found for the SO2 and the CO2 + SO2 treated storage roots for this sampling period. The control and CO2 treated storage roots did not show a difference over the seven month storage period.
The SO2 treated storage roots had respiration rates higher than the control for months 1, 3, 6 and 7 and were not lower than the control except just after curing. When the storage roots were treated with CO2 + SO2, respiration was increased for months 2, 3, 6 and 7 compared to the control. A lower rate of respiration was recorded just after curing only.
In general, `Beauregard' storage roots seemed to have lower respiration rates over the storage period tested (Table 1C). The highest rate of respiration for `Beauregard' roots did not exceed 40 ml/Kg for any treatment during the experiment. On a per month basis, the SO2 and the CO2 + SO2 treatment showed a trend toward increased respiration. The SO2 treatment had higher respiration compared to the control for months 4, 5 and 6. Treatment with CO2 + SO2 increased respiration just after curing and during month 5, 6 and 7. When the storage roots were treated with CO2 + SO2, the roots did not have lower respiration compared to control for any sampling period. The CO2 treatment did reduce respiration just after curing compared to the control. The CO2 treated roots did not differ from the control for any month tested.
Storage roots of `Hernandez' were only slightly responsive to the treatments used in this experiment. Each treatment differed from the control for two measurement periods. The CO2 treatment had higher rates of respiration for month 1 and 6. Treatment with SO2 differed from the control only for month 7, giving higher rate of respiration. The CO2 + SO2 treated roots also differed from the control only during one month, yield a higher rate for month 4. All treatments and the control exhibited an inconsistent trend of increased respiration with time in storage.
Many researchers have reported variable respiration rates for sweetpotato cultivars (Ahn et al., 1980; Appleman et al., 1943; Chang and Kays, 1981; Kushman and Pope, 1972; Kushman and Deonier, 1959 and Picha, 1986d). The data in this research suggests that the variability is not restricted to respiration. The treatments imposed were selected because of the possibility that they would effect respiration and these effects would alter metabolism and therefore, increase storage.
The curing treatments that contained SO2 (SO2 and CO2 + SO2) showed a tendency to increase respiration in storage roots of `Centennial', `Jewel' and `Beauregard'. However, the treatment effect in `Hernandez' was inconsistent and did not differ greatly from the control. The CO2 treatment differed less from the control than the other two treatments.