Abstract
Chitosan with an initial molecular weight (Mw) of approximately 193 kDa was degraded into about 11.4 and 14.8 kDa by γ-ray irradiation of the solution containing 5% chitosan in 0.2 M acetic acid at 75 kGy and the solution of 5% chitosan in 0.2 M acetic acid supplemented with 1% H2O2 at 10 kGy, respectively. The synergistic degraded chitosan sample with Mw ~14.8 kDa was separated into 5 fractions by using ultrafiltration membranes. The analysis results from UV, FTIR, and NMR spectra indicated that the combined treatment of low irradiation dose and low H2O2 concentration did not cause any change in the molecular structure of degraded chitosan fractions. Separated chitosan fractions with Mw > 1 kDa inhibited the growth of Colletotrichum capsici in vitro. While all separated chitosan fractions remarkably enhanced fresh biomass (11–56%) and chlorophyll content (20–92%) of capsicum seedlings. In the field test, the treatment with oligochitosan fractions with Mw in a range of 1–3 kDa (F2) to 3–10 kDa (F3) gained 9.0–11.4% of the fruit yield and reduced 64.8–67.2% of the rate of anthracnose disease outbreak fruits caused by C. capsici. Thus, the F2 and F3 fractions in degraded chitosan product are the key fractions for the enhancement of both the growth promotion effect and defense respond activity against the infection of pathogenic Colletotrichum fungi causing anthracnose disease in capsicum.
Highlights
Chitosan is the second abundant natural polymer after cellulose
The enzymatic hydrolysis of chitosan has been performed by chitosanase, hemicellulase, lysozyme, etc., but some difficulties are still remaining for large-scale industrial production [9]
According to Qin et al [5], the treatments of chitosan with H2O2 led to a decrease in the molecular weight (Mw) of chitosan, but this method resulted in some changes in the chemical structure
Summary
Chitosan is the second abundant natural polymer after cellulose. This copolymer consists of β-D-glucosamine and β-N-acetyl-D-glucosamine in molecules and has been applied in agriculture as an antimicrobial agent [1,2,3,4]. International Journal of Polymer Science degradation method using γ-ray irradiation in combination with hydrogen peroxide treatment has been found as a very efficient way for the preparation of low Mw of polysaccharides: alginate, chitosan, etc., with a low dose [15,16,17,18,19,20,21,22]. The synergistic degraded method using γ-ray irradiation in combination with hydrogen peroxide treatment was performed to reduce the irradiation dose as well as to enhance the bioactive fractions in degraded product for plant growth stimulant and defense respond activity against the infection of pathogenic Colletotrichum fungi causing anthracnose disease in capsicum. The bioactive fractions prepared by the synergistic degradation method may apply as a natural elicitor and growth promoter for red pepper production
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