Saturday, 15 July 2006

Evaluation of Differential Phosphorus Uptake and Utilization Efficiency of Brasscia Cultivars to Applied Phosphorus.

Akhtar M. Shahbaz1, Adachi Tadashi1, Oki Yoko1, Khan M.H. Rashid1, Murata Yoshiyuki2, and Kurimoto Hiroyuki1. (1) Dept of Environmental Management and Engineering, Graduate School of Environmental Science, Okayama Univ, 3-1-1 Tsushima-naka, Okayama, 700-0084, Japan, (2) Dept of Biological Resources Chemistry, Graduate School of Natural Science and Technology, Okayama Univ, 1-1, naka 3-chome,Tsushima, Okayama, Japan

Phosphorus (P) plays a pivotal structural and regulatory role at the nexus of photosynthesis and carbon metabolism but it's availability for plant uptake and utilization is impaired in highly weathered or alkaline calcareous soils. To evaluate the growth performance in P-deficient conditions and response to added P, six Brassica cultivars were grown in pots for 49 days after sowing, using a soil deficient in NaHCO3-extractable P (3.97 mg kg-1) with (+P = 60 mg P kg-1 soil) or without P addition (0P). P-deficiency markedly reduced biomass accumulation, P-concentration and content in roots and aboveground plant parts. However, root: shoot ratio remained unaffected implying that relative partitioning of biomass into roots and shoots had little role to play in Shoot Dry Matter (SDM) production by Brassica cultivars. Shoot and root dry matter yield as well as total biomass accumulation correlated significantly (p < 0.01) with total P uptake and P-utilization efficiency (PUE). Under condition of P-deficiency, the cultivars that produced higher root biomass were able to accumulate higher total plant P content (r = 0.941**), which in turn was related positively to production of SDM and total biomass (r > 0.893*) and negatively to P-stress factor (r = -0.907*). Wide differences of growth observed in this experiment, and better performance of cultivars such as ‘Brown Raya', ‘Con-1' and ‘Rain Bow' under P-deficiency stress encourage screening of more germplasm, especially in the field, to identify P-efficient Brassica cultivars. Better P-acquisition and efficient P-utilization by the efficient cultivars collectively formed the basis of higher SDM production under P-deficiency stress environment.

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