Chitosan (CHN), a deacetylated derivative of chitin, was shown to be efficient in promoting plant defense reactions. CHN oligomers of different molecular weight (MW) and degree of acetylation (DA) triggered an accumulation of phytoalexins, trans- and cis-resveratrol and their derivatives epsilon-viniferin and piceid, in grapevine leaves. Highest phytoalexin production was achieved within 48 h of incubation with CHN at 200 mug/ml with an MW of 1,500 and a DA of 20% (CHN1.5/20), while oligomers with greater MW were less efficient, indicating that a specific MW threshold could be required for phytoalexin response. Treatment of grapevine leaves by highly active CHN1.5/20 also led to marked induction of chitinase and beta-1,3-glucanase activities. CHN1.5/20 applied together with copper sulfate (CuSO(4)) strongly induced phytoalexin accumulation. CuSO(4) alone, especially at low concentrations also elicited a substantial production of phytoalexins in grapevine leaves. Evidence is also provided that CHN1.5/20 significantly reduced the infection of grapevine leaves by Botrytis cinerea and Plasmopara viticola, and in combination with CuSO(4) conferred protection against both pathogens.
Chitosan (b-1,4-linked glucosamine oligomer) derived from crab shells conferred a high protection of grapevine leaves against grey mould caused by Botrytis cinerea. Under controlled conditions, it was shown to be an efficient elicitor of some defense reactions in grapevine leaves and to inhibit directly the in vitro development of B. cinerea. Treatment of grapevine leaves by chitosan led to marked induction of lipoxygenase (LOX), phenylalanine ammonia-lyase (PAL) and chitinase activities, three markers of plant defense responses. Dose-response curves show that maximum defense reactions (PAL and chitinase activities) and strong reduction of B. cinerea infection were achieved with 75-150 mg l )1 chitosan. However, greater concentrations of chitosan did not protect grapevine leaves with the same efficiency, but inhibited mycelial growth in vitro. Present results underlined the potency of chitosan in inducing some defense responses in grapevine leaves which in turn might improve resistance to grey mould.
We evaluated the potential of chitosan both to stimulate plant development and to induce protection from Botrytis cinerea in Vitis vinifera L. plantlets. The presence of 1.75% (v/v) chitogel in the culture medium was the optimal concentration for in vitro grapevine plantlet growth, as determined by measurements on enhancement of root and shoot biomass. Photosynthesis and related parameters were also stimulated in chitogel-treated plantlets. Chitogel reduced the development of Botrytis cinerea and induced cytological alterations to the pathogen. When challenged with the fungus, a significant decrease in disease incidence was observed in plants growing on medium supplemented with chitogel. Furthermore, exogenous foliar applications of chitogel to plantlets growing on chitogel-free medium sensitized them so as to be protected against Botrytis cinerea attack. Our results indicate that chitogel can be used in the vineyard as a means to attain protection against Botrytis cinerea and that its application may counteract the wide use of chemical pesticides.
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