Phenylalanine ammonia lyase activity and fungitoxic metabolites produced by potato cultivars in response to Fusarium tuber rot

The specific activity of phenylalanine ammonia lyase (PAL), glycoalkaloid and sesquiterpene accumulation were measured in potato tubers (Solanum tuberosum L.) at 48, 96, and 168 h following wounding or inoculation with a spore suspension of the dry rot pathogen Fusarium roseum var. sambucinum. Activity of PAL was higher in inoculated than in wounded tissues and remained higher up to 168 h after inoculation in both resistant and susceptible cultivars. PAL activities in inoculated tissues of four clones of divergent genotype varied threefold but very high resistance shown by the breeding clone BR6316-7 was not related to its PAL activity. Challenge with the nonpathogen Fusarium reseum resulted in less stimulation of PAL activity than did inoculation with the virulent Fusarium roseum var. sambucinum or with the relatively weak pathogen Alternaria solani.