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. solavetivo ne, phytuberin, hydroxysolavetivone, phytuberol, dehydroxyphytuberol, solanascone and various fatty acid ethyl esters were detected. This pa per describes a new and convenient method of extracting phytoalexins a nd analysing complex extracts with fused silica capillary gas chromato graphy. Low concentrations of phytoalexins were correlated with extens ive rotting. Thus, tubers incubated anaerobically rotted rapidly and e xtensively and no phytoalexins were detected. When tubers were incubat ed aerobically, stored mature tubers accumulated considerable amounts of rishitin and smaller amounts of solavetivone and phytuberin, and ex hibited less extensive rotting. In the tubers of cultivar Grata, rishi tin accumulated more rapidly than in those of cv. Irmgard, but the dif ferences 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 ag e on the resistance. The selected accessions of Solanum tuberosum um s pp andigena showed the most pronounced correlation between high concen trations of phytoalexins in the tissue and low susceptibility.