KINETICS OF PHYTOALEXIN ACCUMULATION IN POTATO-TUBERS OF DIFFERENT GENOTYPES INFECTED WITH ERWINIA-CAROTOVORA SSP ATROSEPTICA

The time-courses of rotting and phytoalexin accumulation in tuber soft rot tissue of two cultivars of Solanum taberosum subspecies tuberosum were examined from 1-7 days after inoculation with Erwinia carotovora sap atroseptica. In extracts of infected tissue, rishitin. solavetivone, phytuberin, hydroxysolavetivone, phytuberol, dehydroxyphytuberol, solanascone and various fatty acid ethyl esters were detected. This paper describes a new and convenient method of extracting phytoalexins and analysing complex extracts with fused silica capillary gas chromatography. Low concentrations of phytoalexins were correlated with extensive rotting. Thus, tubers incubated anaerobically rotted rapidly and extensively and no phytoalexins were detected. When tubers were incubated aerobically, stored mature tubers accumulated considerable amounts of rishitin and smaller amounts of solavetivone and phytuberin, and exhibited less extensive rotting. In the tubers of cultivar Grata, rishitin accumulated more rapidly than in those of cv. Irmgard, but the differences in susceptibility were not significant. Aerobically incubated immature unstored tubers rotted extensively and no phytoalexins were Found in the rot, which demonstrated the influence of physiological age on the resistance. The selected accessions of Solanum tuberosum um spp andigena showed the most pronounced correlation between high concentrations of phytoalexins in the tissue and low susceptibility.