Oligochitosan (OC) is effective biostimulant on growth promotion and elicitation against disease infection for plants. However, the range of OC molecular weight that exhibits the most effective activity is not fully understood and requires further investigation. In this study, OCs with different weight average molecular weight (Mw) were prepared by gamma Co-60 irradiation degradation of chitosan in solution and the effect on growth promotion and enhancement of fruit yield of chili plant (Capsicum frutescens L.) by foliar application of OCs particularly with Mw of 7.8, 5.0, and 2.5 kDa was investigated. Chili plants, cultivated in a greenhouse were sprayed with OC concentration of 50 mg/L for three times. Results indicated that among treatments, OC with 2.5 kDa proved to be the best, which increased the shoot fresh weight by 71.5%, shoot dry weight by 184%, total chlorophyll content by 12%, and fruit fresh weight by 49.8% for the control. Thus, OC with low Mw (2.5 kDa) that can be suitably produced on large scale by gamma Co-60 ray irradiation degradation of chitosan solution is potentially promising to apply as a biostimulant to enhance chili fruit yield significantly.

Nanomaterials hold great promise of improved plant disease resistance, controlled release of agro-chemicals, enhanced plant growth, etc. In this study, the effect of nanosilica (10 -30 nm) prepared from rice husk on the growth promotion of chili plant in green house was carried out. The experiment of nanosilica treatment by foliar spraying was arranged in a factorial design with 3 replications at various nanosilica concentrations of 0, 40, 60 and 100 ppm. Plant growth characteristics and chlorophyll content were assessed. Results showed that the fresh weight, dry weight, and chlorophyll content increased with the treatment of nanosilica. The optimal concentration of nanosilica was found to be of 60 ppm. Thus, treatment of nanosilica was beneficial in enhancing the growth of the chili plants.

Oligochitosan (OC) with molecular weight Mw of 5000 g/mol was prepared by gamma Co-60 ray irradiation of chitosan solution. Nanosilica (nSiO 2 ) with the size of 10 -30 nm was synthesized by calcination of acid treated rice husk. The mixture of 1% OC -1% nSiO 2 was prepared by dispersion of nSiO 2 in OC solution. The morphology of nSiO 2 in the mixture of OC-nSiO 2 was measured from images of transmission electron microscopy (TEM). The effect of foliar application of the mixture of OC-nSiO 2 on the induction of resistance against anthracnose disease caused by Colletotrichum gloeosporioides fungus on chili fruits was investigated. Results indicated that foliar application of OC-nSiO 2 with the concentration of 60 mg/l -60 mg/l was found to be as the optimal treatment that reduced the disease severity on chili fruits to 22.2% compared with 90.0% of the control. Thus, OC-nSiO 2 hybrid material could be considered as an effective biotic elicitor to prevent anthracnose disease infection for chili fruits. Furthermore, the prepared OC-nSiO 2 hybrid material can also be used as an environmentally friendly agrochemical product for sustainable development of agriculture.

No abstract

No abstract