GENOTYPIC DIFFERENCES IN ROOT MORPHOLOGY AND PHOSPHORUS UPTAKE KINETICS IN BRASSICA NAPUS UNDER LOW PHOSPHORUS SUPPLY

Application of phosphorus (P) fertilizer is important in crop production because of the low bioavailability of phosphorus to plants in both acidic and calcareous soils. Although rapeseed (Brassica napus) is generally sensitive to P deficiency, different cultivars differ widely in this respect. Differences in P uptake and utilization between two rapeseed cultivars, one P-efficient ('97081') and one P-inefficient ('97009'), were evaluated in solution culture by studying the changes in root morphology and parameters of P uptake kinetics in response to low-P stress. The P-efficient cultivar had lower Km and Cmin values and higher Vmax and developed longer and denser lateral root hair with greater number of root tips and branches under low-P stress, which resulted in a better developed root system and more efficient uptake of P. That, in turn, led to higher concentration and accumulation of P in the plants, culminating in higher biomass production. However, P utilization efficiency (biomass production per unit P accumulated in plant) of the P-efficient '97081' was lower than that of '97009' when P was deficient. These results suggest that P efficiency in rapeseed is due to a better developed root system as well as efficient uptake of P.