Abstract:
To determine suitable molecular weight (Mv) of chitosan for plant growth promotion. Low molecular weight chitosan was prepared by gamma radiation degradation and molecular weight fractionation. The degradation of chitosan sample was performed by successive gamma irradiation of chitosan powder with radiation dose of 100 kGy and then 10%(w/v) of the chitosan in 2.5% acetic acid was further irradiated at doses of 20, 40, 60, 70 and 80 kGy to obtain 68, 26, 12, 8 and 4 kDa respectively as determined by viscosity method. Chitosan with M [subscript v] of 20 was prepared from selective precipitation of 26 kDa chitosan using 0.75% NaOH solution. Chitosan at M [subscript v] of 4, 8, 12 and 20 kDa were selected for investigation the effect of chitosan molecular weight on the plant growth promotion. The study was done by measuring the height of three kinds of seedling with 200 ppm chitosan at each molecular weight in a nutrient solution after 26 days. It was found that chitosan at M [subscript v] of 4 and 8 kDa possessed the highest rate of growth for kale (Brassica albloglabra). Chitosan of 20 kDa gave the highest growth for lettuce (Lactuca sativa Linn) and M [subscript v] of 8 and 12 kDa gave the highest growth for Chinese spinach (Amaranthus tricolor Linn).