Cytokinin and its precursors for improving growth and yield of rice

Phytohormones are well known for their regulatory role in plant growth and development and cytokinins represent one of the five well-established classes of phytohormones. A field experiment was conducted to evaluate the effect of a synthetic cytokinin (kinetin) and its physiological precursors (adenine + isopentyl alcohol) on growth and yield of rice. Five levels (10(-2)-10(-6) M) of each, kinetin and adenine (ADE) plus isopentyl alcohol (IA) were used, in addition to an untreated control. Treatments were applied by dipping roots of rice seedlings in solutions of cytokinin or its precursors for an hour just before transplanting. The precursors were more effective in comparison with pure cytokinin. The plant height was increased by 6.5% over control when treated with 10(-5) M ADE + IA. The application of ADE + IA at the rate of 10(-4) M significantly increased the number of tillers (34.7%), number of panicles (38.5%) and paddy yield (21.6%) compared to control. Moreover, nutrient (NPK) contents were also significantly improved by 83.1, 36.4 and 26.0% in straw and 53.2, 27.7 and 10.8% in grain, respectively, as compared to control. The findings support the hypothesis that exogenous supply of cytokinin or its precursors in the root zone could improve the growth and yield of treated plant. However, it is difficult to conclude in this study that the precursors were metabolized into cytokinins outside the roots by rhizosphere/rhizoplane microorganisms before being absorbed by the plant roots or converted into cytokinins within the plant tissues. The greater effectiveness of precursors compared to kinetin could be attributed to a gradual conversion of ADE plus IA into cytokinins resulting in a continuous supply over a period of time. (C) 2001 Elsevier Science Ltd. All rights reserved.