Application interval and concentration effect of gamma degraded chitosan on mulberry plant

Abstract

Gamma radiation is one of the established tools to induce chain-scission of chitosan for low molecular weight chitosan preparation. The introduction of various radiation doses to chitosan powder produces degraded chitosan with various molecular ranges. They indicate different physicochemical and biological properties which are very important in product development. This study aimed to produce low molecular weight chitosan with an average molecular weight below 20 000 Da by exposing chitosan powder to gamma radiation at doses of 25, 50, 75 and 100 kGy. Then, to observe its growth-promoting activity on mulberry plants. The gamma-degraded chitosan was characterized by size exclusion chromatography-multi-angles laser light scattering (SEC-MALLS) and Fourier-Transform infrared (FTIR) to determine its weight-average molecular weight and molecular composition changes, respectively. After that, the gamma-degraded chitosan powder was dissolved in an acidic solution before spraying into mulberry. In the field, the mulberry plants were treated with 40, 80 and 100 ppm of degraded chitosan by foliar application. Each treatment consisted of 5 replicates of 2- 3 months-old mulberry plants which were randomly picked from the nursery. The control plants were treated with commercial growth promoter at concentration of 100 ppm which was applied weekly according to the farmer's practice. The study was carried out for 4.5 months at 2 different application intervals which were every two- and four-weeks’ time. The mulberry plants treated with 80 ppm and 100 ppm degraded chitosan every two- and four-weeks showed better results on an average number of leaves and fruit, respectively compared to control.