Use of natural bioactive agents obtained from radiation processed polysaccharides as growth promoting substances is an emerging technology to exploit full genetic potential of crops in terms of growth, yield, and quality of plants. A pot experiment was carried out to investigate the effects of foliar application of depolymerised form of gamma irradiated (520 kGy) irradiated carrageenan (IC) on growth (shoot and root lengths, leaf area, fresh and dry weights of plants), physio-biochemical attributes (content of chlorophyll and carotenoid, nitrate reductase and carbonic anhydrase activities and leaf -N, -P and –K content) and the alkaloid production in Catharanthus roseus (L) G. Don, a medicinal plant. Aqueous solutions of different concentrations (0, 10, 50 and 100 ppm) of IC were sprayed seven times on foliage, using unirradiated carrageenan (UC) and deionized water as control. Application of 50 ppm IC significantly increased the growth and the physio-biochemical characteristics. The IC (50 ppm) treatment also increased the total alkaloid content in leaves and roots by 36.8% and 38.8%, respectively. This technique of foliar spray of IC may be employed to improve the performance of plant including the alkaloid production which is of great medicinal values.
