Differential deposition of suberin phenolic and aliphatic domains and their roles in resistance to infection during potato tuber (Solanum tuberosum L.) wound-healing

Rapid suberization of wounded potato tubers is critical in avoiding infection by Erwinia carotovora subsp. carotovora (a causal organism of bacterial soft rot) and Fusarium sambucinum ja causal organism of fungal dry rot) in cut seed and stored potatoes. However, until now the reason for the differential development of resistance to bacterial and then fungal penetration during suberization has not been shown to be related to the differential deposition of the two major suberin components (phenolic and aliphatic domains during wound-healing. Tubers of four varieties of diverse generic background were wounded and inoculated with E. carotovora subsp. carotovora throughout a 5-day time course and F. sambucinum throughout an Ii-day time course during wound-healing (18 degrees C and 98 % RH). During wound-healing, the tubers were examined at the cellular level for deposition of suberin phenolic and aliphatic domains. The percentage of inoculated tubers which became infected was determined for each wound-healing time point and was related to the deposition of suberin phenolic and aliphatic domains. Total resistance to infection by E. carotovora subsp. carotovora occurred after the completion of phenolic deposition on the outer tangential wall of the first layer of cells (2-3 days). However, this suberin phenolic matrix offered no resistance to fungal infection by F. sambucinum even after phenolic deposition was complete on adjoining radial and inner tangential cell walls of the first layer of cells. Resistance to fungal infection did not begin to develop until after deposition of the suberin aliphatic domain was initiated. Total resistance to fungal infection was attained after completion of deposition of the suberin aliphatic domain within the first layer of suberizing cells (5-7 days). These results indicate that the suberin phenolic domain provides resistance to infection by E. carotovora subsp. carotovora bur not infection by F, sambucinum. They further suggest that deposition of the suberin aliphatic domain is responsible for final resistance to infection by F. sambucinum. This is believed to be the first evidence indicating separate depositional patterns, at the cellular level, for the two major domains of suberin and separate roles for each of these domains in the development of resistance to bacterial and fungal infection during suberization. (C) 1998 Academic Press.