Abstract
In in vitro assays, a chitosan polymer caused differential growth inhibition of the following pathogens isolated from tobacco: Phytophthora parasitica Dastur var. nicotianae (Ppn), Pythium aphanidermatum (Edson) Fitzp, Rhizoctonia solani Kühn, and Sclerotium rolfsii Sacc. The most sensitive were P. aphanidermatum and S. rolfsii, the growth of which was fully inhibited at a chitosan dose of 1.5 g/L; the growth of Ppn was fully inhibited at 2 g/L. In vivo assays involving plants grown from seeds immersed in chitosan, as well as plants sprayed with this product, were performed to detect the induction of defence response markers in the leaf and consequent resistance to disease. Although defence/resistance marker enzyme activities varied, activation was greater in the chitosan-treated plants than in controls. Marker enzyme activities in the sprayed plants were generally equal to or stronger than those recorded in the seed immersion-treated plants, except for phenylalanine ammonia-lyase activity at the lowest immersion concentration tested. Although there were no statistical differences among treatments with respect to resistance against Ppn, the greatest protection was afforded by the spray treatments, in which the infection index was reduced between 17 and 19% compared to the controls. In conclusion, this chitosan polymer directly inhibited the growth of several tobacco pathogens and caused the induction of defence enzymes in leaves, but was not able to protect tobacco plantlets against Ppn infection via the activation of induced resistance. This work demonstrated the potential of chitosan in protecting tobacco plants against soil-borne pathogens.
Highlights
Tobacco (Nicotiana tabacum L.) is a crop of great economic importance worldwide
The aim of this work was to evaluate the potential antimicrobial effect of a low acetylation level chitosan polymer against different soil-borne phytopathogens isolated from tobacco, and to determine its capacity to induce the production of defensive response markers in tobacco seedlings and their consequent resistance to disease
An antifungal assay was performed on potato dextrose agar (PDA) plates amended with chitosan at different concentrations following the method of Falcón et al (2004)
Summary
Tobacco (Nicotiana tabacum L.) is a crop of great economic importance worldwide. Protection in the nursery is essential for obtaining healthy plants. During this phase, the plantlets suffer the attack of many soil-borne pathogens which need to be controlled by chemical means (Erwin and Ribeiro, 1996). Current thinking is focused on reducing crop production costs by cutting those associated with the use of agrochemicals, and on the use of more ecologically sound management systems (García and Andino, 2002; García et al, 2002). Several soil-borne pathogens have developed resistance to the chemicals usually used to control them (Jaarsveld et al, 2002), making alternative protection systems necessary
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