Genotypic variation in root growth among rice (Oryza sativa L.) cultivars of different ecosystems

Development of rice cultivars with efficient root system requires that genetic resources of desired root traits to be identified. Pot experiment was conducted in PhilRice CES to evaluate root and shoot growth and yield of rice (Oryza sativa L.)cultivars under aerobic and anaerobic conditions. The experiment was in split plot design with three replications with aerobic and anaerobic as the main plots and 11 cultivars (japonica new plant type (NPT), indica NPT, IR64, PSB Rc14, PSB Rc18, PSB Rc82, PSB Rc90, PSP Rc92, IR73018, IR43649 and Azucena) as the subplots. In aerobic conditions, soil was maintained moist but aerated while in anaerobic condition, it was submerged. Pots (20 cm diameter and 50 cm height) were filled with soil with 50-30-30 mg N-P-K added per kg soil. Six pre-germinated seeds were sown in each pot and thinned to 3 seedlings 10 days later. At plant maturity, the shoot and roots were harvested separately. The soil cores were cut in layers (0-5, 5-10, 10-20 and below 20 cm) and roots were collected and measured for root volume (RV) and root dry weight (RDW). The results indicated that the cultivars were significantly different for root and shoot growth and yield with more vigorous growth and yield in anaerobic condition. Azucena produced highest RV (32.8 ml/pot) and RDW (4.89/pot) and IR64 produced the least RV (15.1 ml/pot) and RDW (2.098 g/pot). The roots were mostly contained in 0-10 soil surface (73%). Shoot growth was positively correlated with root growth, but grain yield correlated mainly with number of panicles and number of grains per panicle. In general upland cultivars had greater root and shoot growth but lower harvest index and yield. More studies are needed to evaluate the impact of heavy and deep rooting system on yield under conditions of soil fertility and water stress.