Identification and characterisation of a novel chitosan
formulation in its ability to induce resistance against Botrytis
cinerea
We tested the water-soluble chitosan-based commercial formulation
ChitoPlant, from hereafter termed chitosan, in its capacity to induce
resistance against the fungal pathogen B. cinerea . Treatments of
chitosan demonstrated that this elicitor successfully triggers
resistance in tomato (Fig 1a), Arabidopsis (Fig 1b) and aubergine (Fig
S1) against B. cinerea . In tomato, chitosan significantly
decreased necrotic lesion size in all concentrations compared with
control plants (Fig 1a). The resistance phenotype induced by chitosan
had a dose-dependent effect at the two high concentrations (1% and
0.1%), however, the lowest concentration (0.01%) induced a level of
resistance in between 0.1% and 1% treatments. In Arabidopsis, chitosan
treatment resulted in induced resistance in a concentration-dependent
manner, with 1% having the strongest effect (Fig 1b). In aubergine,
chitosan treatment resulted in differences in lesion diameter in all
concentrations compared to water-treated control plants (Fig S1),
however, post-hoc analysis demonstrated that 0.1% was the most
effective concentration.
We then tested whether chitosan induces callose deposition in a similar
manner to other chitosan formulations (Luna et al., 2011). Plants were
treated with increasing concentrations of chitosan one day before
aniline blue staining. In both plant species, treatments with chitosan
resulted in a direct induction of callose. The lowest concentrations of
0.001% and 0.01% in tomato and Arabidopsis, respectively, triggered
the strongest effect (Fig 1c and d).
To determine any antifungal effect of chitosan, different concentrations
were tested on B. cinerea hyphal growth in vitro and
compared to different concentrations of the fungicide Switch
(Syngenta). Whereas all concentrations of Switch arrested
pathogen growth, only 0.1% concentration of chitosan or higher had an
antifungal effect (Fig S2). However, the lowest concentration of
chitosan tested (0.01 %) had no antifungal effect compared to the
control. This shows a concentration threshold for chitosan-direct
antifungal activity against B. cinerea . Since 0.01% chitosan had
no antifungal effect, but reduced B. cinerea lesions and induced
callose formation, this concentration was selected for more in-depth
analysis.