Introduction
Rice (Oryza sativa L.) is the main staple crop in the world. It is the primary source of food and calories for about half of world population 1. The demand of rice continues to increase as consumption is outstripping the current production 2, 3. Around 75% of the world rice supply comes from conventional flooded rice cultivation system. The present and future food security of Asia mostly depends on irrigated rice production system 4. The intensive cultivation of rice has large consequences to environment as rice is a luxurious water user crop and consumes about 80% of the total irrigated fresh water resources in Asia 5, 6. Lowland rice production uses immense quantities of water imparting an enormous stress on water resources 7. Therefore, researchers are concentrating to develop different water-saving rice cultivation systems for increasing yield without further environmental degradation.
A number of approaches have been reported to improve water use efficiency and sustain yield of rice under regulated irrigation condition 8 such as alternate waiting and drying irrigation, selective hormone under limited irrigation condition etc. 9. Malaysia is categorized in Zone-3 in terms of water scarcity in the 20th century with a need to increase water use efficiency in between 25-100% to meet up the demand of 2025 10. Zulkarnain et al. 11 tested three water regimes to choose one of the promising water saving technology keeping the morpho-physiological growth and yield unimpaired by using Malaysian commercial rice variety MR220. Their results suggested that it is not necessary to conventional flooding to obtain high rice yield as maintaining a saturated soil condition throughout the growing season reduce water input without a significant reduction in yield. However, to meet the ever increasing population demand of rice it is imperative to obtain higher yield under limited water use.
The use of hormones is highly effective in obtaining high yield. Cytokinins are plant hormones known as key regulator of plant growth and development, including cell division, chloroplast biogenesis, bud and root differentiation, shoot meristem initiation and growth, stress tolerance specially drought, organ senescence and nutrient mobilization 12, 13. Cytokinin played an important role in regulating tiller bud growth 14 and grain filling 9 in alternate waiting and drying irrigation system. However, very little is known about the effect of cytokinin application on rice growth and yield under limited water. Therefore, in this study an attempt was taken to investigate the effect of cytokinin on growth and yield of rice under limited water.