ETIOLOGY OF VASCULAR DISCOLORATION IN CASSAVA ROOTS AFTER HARVESTING - DEVELOPMENT OF ENDOGENOUS RESISTANCE IN STORED ROOTS

The susceptibility of cassava roots, Manihot esculenta Crantz, to vascular discoloration beneath two types of injury site, transverse cuts and periderm injuries, was compared for freshly harvested and stored roots. Susceptibility beneath transverse cuts changed rapidly, so that roots stored at ambient temperature for 5–9 days were largely resistant to vascular discoloration beneath this type of injury. Susceptibility to localized deterioration beneath periderm injuries changed more slowly, but significant decreases were observed in roots stored at ambient temperature for 10–16 days. Changes in susceptibility were observed in all cultivars tested, seven in Colombia and one in Jamaica. These changes were retarded but not prevented by storage at 2°C and by storage in sealed polyethylene bags. Pruning plants 1 to 3 weeks prior to harvesting, which has been shown to reduce the rate of post‐harvest deterioration of roots, was also found to reduce the susceptibility of roots to vascular discoloration beneath injuries made immediately after harvesting. Water loss through injuries caused a respiratory response as well as vascular discoloration. This respiratory response was as large in stored (resistant) roots as in freshly harvested (susceptible) ones. The potential of cassava roots to develop endogenous resistance to vascular discoloration either before or after harvesting is discussed in relation to the problems of storage of harvested cassava roots. Copyright © 1979, Wiley Blackwell. All rights reserved