Bull. Spec. CORESTA Congress, Harare 1994, p. 130, PPOST 2

Cell wall components of non-pathogenic bacteria and hypovirulent Alternaria alternata responsible for induction of tobacco resistance to brown spot

Shandong Agricultural University, Dept. of Plant Protection, Taian, Shandong, China
Different components of cell walls of non-pathogenic Pseudomonas fluorescens P1 and hypovirulent TBA16 of Alternaria alternata were tested for inducing resistance to brown spot. Behaviors of virulent strain TBA28 of the pathogen on tobacco leaf surfaces were observed by SEM, to determine what alteration of pre-penetration of the pathogen into the plant was caused by the resistance induction. The powdered cell wall (0,1-1,0 µm size) of the TAB16 spores showed 89% resistance inductory effect, which was 52% and 56% higher than that showed by partly broken-down cell wall (BW) and the entire spore (ES) of the hypovirulent strain. Neither the BW nor ES of the virulent TBA28 gave resistance induction, but the AT-toxin produced by the virulent strain induced 100% resistance to infection of the TBA28 spores. The bacterium P1 was used as a resistance inducer in live and heat-killed cells, while LPS-free cells induced 57% resistance in tobacco to brown spot. LPS and EPS of the P1 were purified and used as the inducers, and induced over 95% resistance. The virulent TBA28 showed three types of alteration in the early pre-penetrating behavior on tobacco leaf surfaces caused through induction of TBA16 spore and P1 bacterium: (a) reduced spore germination and tube growth; (b) tube grows away from leaf surfaces; and (c) reduced production of adhesin by the tube. Studies are continuing on the biochemistry and function of an elicitor form of the adhesin.