Formation of root air spaces (aerenchyma) and root growth of lowland rice (Oryza sativa L.) varieties under different water regimes

Anaerobic stress is a serious practical problem causing severe economic losses in the rainfed lowlands of Asia as well as in many regions of the world. This is the rationale behind much research dealing with the possible causes of death of anoxic cells. This study was conducted to determine the effect of-different Water regimes on the aerenchyma cell and root growth of rice. Flooded, intermittent, and upland water regimes were imposed 21 DAS on nine rice varieties, composed of TRVs, HYVs and Hybrids, planted in 17.8 x 17.8 x 35.6 cm black plastic bags. Data were collected at tillering and panicle initiation growth stages. Regardless of variety, rice plants had the capacity to adjust to early flooding without significant changes in root anatomy. However, as the plants mature, the different water regimes exerted significant impacts on the mean area and number of aerenchyma cells. There was compensation in these two components of total aerenchyma cell area, i.e. the bigger the mean area per aerenchyma cell, the less number of aerenchyma cells that developed. Water regimes affected the root growth and morphology with flooded water regime resulting to higher root length, root dry weight and root-shoot ratio at both growth stages. Further studies on the adaptability of rice root system to different soil-water status with regards to aerobic-anaerobic conditions are needed to determine their relationship to growth. and activities of aerial parts and yield of rice plants. Such studies should be valuable in crop management for obtaining higher yield.