| Response of 38 rice (Oryza saliva L.) cultivars to low phosphorus environment was preliminarily evaluated by means of a controlled system with insoluble phosphorate source(Ca3(PO4)2) in liquid phase. Xianyou63 ,Xianyoul61 and Namcheung ,which were the typical varieties screened from the preliminary experiment as mentioned above, as well as 13 other rice genotypes from the IRRI were further identified at the low P deficiency of 0.5mg/L with hydroponic culture. The results indicated a significant genotypic variation of low phosphorus tolerance in the tested 16 germplasms, showing that Xianyou63, IR74, Xianyorl61 and so on, were tolerant to low P deficiency and Namcheung, IR71379-2B-10-2-3--1, IR72413-3R-26-2, etc, were sensitive genotypes.The three rice genotypes with different P-efficiency (IR74: the higher P-efficiency type; IR71331-2B-2-1: the middle type of P-efficiency; IR71379-2B-10-2-3-1: the lower P-efficiency type) were selected from 16 rice cultivars. The difference in morphological and physiological characters of three rice varieties under P-deficiency stress and P-adequate conditions were studied by using solution culture.The results showed that the higher P-efficiency type IR74 and the middle type of P-efficiency, IR71331-2B-2-1, had higher P uptake efficiency, which were significantly higher than that of IR71379-2B-10-2-3-1. The middle type JR71331-2B-2-1, performed its lowest P use efficiency compared to the two other cultivars, and IR74 showed its highest P use efficiency. The result of study on the ability of transporting P from root to shoot indicated that transportation efficiency of IR74 was also highest, the reverse was true in the case of IR71331-2B-2-1. Further studies showed that IR74 maintained higher root fresh/dry weight and ratio of root to shoot, bigger root volume under the deficient P stress or adequate P condition, and it had the larger increasing amount of APase activity in rice concerned exposed to low P stress. Therefore, it suggested that the higher P uptake efficiency of IR74 was caused by the strong root growth and high APase activity. The results also indicated that root efficiency ratio (equal to shoot P uptake/root dry weight) of the middle type of P-efficiency ,IR71331-2B-2-l ,was significantly higher than that of the other genotypes under low P stress. The results obtained from the study on uptake area and kinetics of H2PO4"uptake by root of rice plant concerned indicated that IR71331-2B-2-1 had a marked advantage in active uptake area, specific surface area, Imax and Km compared to IR74 and IR71379-2B-10-2-3-1 under stress condition. This implied that the high P-absorption efficiency of IR71331-2B-2-1 resulted from higher root activity and stronger affinity to P. As for as IR713 79-2B-10-2-3-1 was concerned, all corresponding performances were always poor.Finally, the differences in morphological and physio-biochemical characters of rice varieties with different P efficiency were further discussed in this paper. It could beconcluded that rice genotypes tolerant to low P stress resulted from the co-ordination of P absorptive efficiency, internal utilization efficiency and its translocation efficiency; additionally, relative tiller dry weigh, relative biomass and APase activity et al were also important morphological and physio-biochemical indices in screening and identification of high P-efficiency rice germplasms for exploring and utilizing the unavailable phosphorus in soil. |
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