Abstract:
Phosphorus is an essential nutrient for growth and development of rice. Receiving insufficient level of phosphorus below its critical concentration will result in reduced growth tillering and yield of rice. Therefore, the root system has to quickly adapt morphologically in order to increase root surface so that sufficient phosphorus can be absorbed by the root system. At different growth stage, rice has a difference in phosphorus requirement, as well as that the minimum phosphorus requirement or critical level of phosphorus for each rice cultivar is different. The objectives of this study are to investigate the response of root systems of different rice cultivars to phosphorus deficiency, and to find a critical concentration of phosphorus where rice displays deficiency responses during seedling stage when studied under nutrient solution system. Two experiments were conducted in this study. Experiment 1 was divided into two parts whereby part 1.1 was setup in a 4 x 4 factorial in CRD (the first factor are 4 rice cultivars and the second factor are 4 levels of phosphorus concentration). Part 1.2 was setup in a 4 x 5 factorial in CRD (the first factor are 4 rice cultivars and the second factor are 5 levels of phosphorus concentration). Rice plants were grown until 28 days for part 1.1 and 15 days for part 1.2 to evaluate responses of rice root system of different cultivars to phosphorus deficiency. Experiment 2 was setup in a CRD to find a critical concentration of phosphorus for growth of rice cultivar KDML105 by testing in seven different phosphorus concentrations and evaluate root system during the 30 days of seedling growth. It was found that when receiving phosphorus below 100 ?M, all tested rice cultivars displayed elongated root at 7 days post germination. From 9 days post germination, number of roots per plant and root dry weight started to reduce while root:shoot ratio increased. When comparing responses of rice from different ecosystems, it was found that upland rice was able to extend their root longer, had more root dried weight, and had higher root:shoot ratio than lowland rice. However, Lowland rice was able to produce more roots per plant than upland rice, especially in cultivar KDML105, whose root system responses were directly proportional to phosphorus concentration. Evaluation of critical phosphorus concentration for root system responses to phosphorus deficiency during seedling stage for cultivar KDML105 suggested that critical concentration for phosphorus responses in both root and shoot was 60 ?M. However, responses were detected at different growing stages, whereby root system responses were visible from 15 days post germination while shoot responses were present from 27 days post germination. Consequently, it is necessary that during seedling stage of cultivar KDML105, phosphorus availability of at least 60 ?M is needed in order to ensure optimum growth.