BIOLOGICAL EFFECTS OF CHITOSAN IN FUSARIUM SOLANI AND PISUM SATIVUM

The cell walls of Fusarium solani and many other fungi contain polymers of (beta)-1,4-linked glucosamine called chitosan. Hexosamine-containing oligomers are released from the fungal cell wall during the interaction between pea tissue and formae speciales of F. solani. These oligomers both penetrate into the plant cell where they activate the host's disease resistance response and accumulate within the fungal cells thereby inhibiting fungal growth. The mode by which chitosan can both induce plant genes and suppress fungal growth is not completely understood. Two studies were made on the mode of action of chitosan in the Pisum sativum-F. solani host-pathogen interaction.; I. Cell death and membrane leakage are not associated with the induction of disease resistance in peas by chitosan or F. solani f. sp. phaseoli. Host cell viability was reduced more rapidly in the compatible interaction (F. solani f. sp. pisi). Changes in conductivity due to release of electolytes from damaged plant tissue likewise did not correlate with disease resistance. Fungal cell viability in the presence of chitosan was related to both the chitosan concentration and the length of the exposure.; II. No correlation was found between the chitosan or F. solani-induced disease resistance response in pea pod tissues and fluctuations in Ca('2+) , inhibition of calmodulin, blockage of Ca('2+) channels or release of UV-absorbing material.; This study additionally showed that cell wall-derived chitosans (CWC) from the above mentioned formae speciales of F. solani differed biologically and structurally when assayed in the pea-F. solani host-pathogen system. The biological activity of the F. solani f. sp. pisi CWC differed from that of both F. solani f. sp. phaseoli CWC and shrimp chitosan; while the CWC of F. solani f. sp. phaseoli mimicked that of shrimp chitosan (eg. antifungal action, induction of pisatin formation and induction of resistance to F. solani f. sp. pisi in pea tissue). Gel filtration separations showed that the CWCs of F. solani f. sp. pisi contained smaller oligomers than F. solani f. sp. phaseoli. This difference in cell wall composition may be at least partially responsible for the differences in the pea tissue response to the two fungi.