6-deoxy-6-amino chitosan: a preventative treatment in the tomato/ Botrytis cinerea pathosystem

Naadirah Moola; Anwar Jardine; Kris Audenaert; Mohamed Suhail Rafudeen

doi:10.3389/fpls.2023.1282050

6-deoxy-6-amino chitosan: a preventative treatment in the tomato/ Botrytis cinerea pathosystem

Front Plant Sci. 2023 Oct 10:14:1282050. doi: 10.3389/fpls.2023.1282050. eCollection 2023.

Authors

Naadirah Moola¹, Anwar Jardine², Kris Audenaert³, Mohamed Suhail Rafudeen¹

Affiliations

¹ Laboratory of Plant Stress, Department of Molecular and Cell Biology, Faculty of Science, University of Cape Town, Cape Town, South Africa.
² Department of Chemistry, Faculty of Science, University of Cape Town, Cape Town, South Africa.
³ Laboratory of Applied Mycology and Phenomics, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.

Abstract

6-deoxy-6-amino chitosan (aminochitosan) is a water-soluble chitosan derivative with an additional amine group at the C-6 position. This modification has improved aqueous solubility, in vitro antifungal activity and is hypothesized to have enhanced in vivo antifungal activity compared to native chitosan. Gray mold disease in tomatoes is caused by the fungus, Botrytis cinerea, and poses a severe threat both pre- and post-harvest. To investigate the optimal concentration of aminochitosan and its lower molecular weight fractions for antifungal and priming properties in the tomato/B. cinerea pathosystem, different concentrations of aminochitosan were tested in vitro on B. cinerea growth and sporulation and in vivo as a foliar pre-treatment in tomato leaves. The leaves were monitored for photosynthetic changes using multispectral imaging and hydrogen peroxide accumulation using DAB. Despite batch-to-batch variations in aminochitosan, it displayed significantly greater inhibition of B. cinerea in vitro than native chitosan at a minimum concentration of 1 mg/mL. A concentration-dependent increase in the in vitro antifungal activities was observed for radial growth, sporulation, and germination with maximum in vitro inhibition for all the biopolymer batches and lower MW fractions at 2.5 and 5 mg/mL, respectively. However, the inhibition threshold for aminochitosan was identified as 1 mg/mL for spores germinating in vivo, compared to the 2.5 mg/mL threshold in vitro. The pre-treatment of leaves displayed efficacy in priming direct and systemic resistance to B. cinerea infection at 4, 6 and 30 days post-inoculation by maintaining elevated F_v/F_m activity and chlorophyll content due to a stronger and more rapid elicitation of the defense systems at earlier time points. Moreover, these defense systems appear to be ROS-independent at higher concentrations (1 and 2.5 mg/mL). In addition, aminochitosan accumulates in the cell membrane and therefore acts to increase the membrane permeability of cells after foliar spray. These observations corroborate the notion that aminochitosan biopolymers can exert their effects through both direct mechanisms of action and indirect immunostimulatory mechanisms. The contrast between in vitro and in vivo efficacy highlights the bimodal mechanisms of action of aminochitosan and the advantageous role of primed plant defense systems.

Keywords: Botrytis; aminochitosan; antifungal activity; plant-pathogen interaction; priming; systemic resistance; tomato.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported by the National Research Foundation under Grant No. (114330). The authors acknowledge the financial support from the Hercules Foundation of the Flemish Government for the multispectral imaging platform (AUGE/15/17).