Bull. Spec. CORESTA Congress, Harare 1994, p. 133, PPOST 5

Induction of contact recognition as related to host-induced resistance in tobacco brown spot

Shandong Agricultural University, Dept. of Plant Protection, Taian, Shandong, China
Tobacco leaf surfaces which had been pretreated with non-pathogenic bacteria, viruses, and hypovirulent strains of brown spot pathogen ( Alternaria alternata ), or a virulent strain of A. alternata showed seven types of abnormal pre-infection behavior : (1) delayed germination of spore; (2) continuous sporulation; (3) reduced or defective production of adhesin; (4) germ tube growth away from leaf surfaces; (5) swollen tip of germ tube with defective or reduced infection; (6) tight anchoring of germ tube on leaf surfaces, with defective or reduced infection, and (7) zigzag germ tube, vasculated or emptied tip of germ tube. The induced abnormalities were related to decrease in pathogenicity of the pathogen, indicated by 55 - 94% reduction of brown spot in the induced tobacco. It is suggested that the induced abnormalities interfere with host-pathogen contact recognition.