Rapid deposition of lignin in potato tuber tissue as a response to fungi non-pathogenic on potato

Potato tuber slices were inoculated with a pathogen (Fusarium roseum f.sp. sambucinum)and with pathogens of other plant species (Cladosporium cucumerinum and F. roseum). Growth of all three fungi on the tuber tissue surface was similar through the first 12 h; after this time, the pathogen, but not the non-pathogens, began to penetrate into the tissue and caused a gradual softening and darkening of the tissue. The non-pathogens caused a yellow discoloration in the host cell walls, first detected 8-10h after inoculation. These yellow areas of the cell walls stained positively for lignin. Positive staining for lignin was not observed in the pathogen-challenged tissues until 18-20 h. Tissues inoculated with the non-pathogens and treated with thioglycolic acid gave a ligninthioglycolate in much greater yields than did control tissues or tissues inoculated with the pathogen. Ligninthioglycolic acid yields increased in the non-pathogen-challenged tissues by 9 h and in pathogen-challenged tissues by 18 h after inoculation. Cupric oxide oxidation of alkali pre-treated tissues also provided evidence for the formation of lignin. Alkali pre-treatment had no effect on ligninthioglycolic acid yields or on histochemical staining, which is further evidence for the production of lignin. Pre-treatment of the tissue with a-aminooxyacetic acid, a competitive inhibitor of phenylalanine ammonia lyase, or abscisic acid induced a state of "susceptibility" in the tissue to C. cucumerinum, and this was associated with a lack of lignin deposition. © 1984.