Tolerance to Low Phosphorus and Its Agronomic and Physiological Characteristics of Rice Cultivars
[Objective]The purpose was to elucidate the evaluation index of tolerance to low phosphorus (LP) and agronomic and physiological characteristics of rice cultivars with strong resistance to LP. [Method]Eleven typical japonica rice cultivars applied in Jiangsu Province during the last 70 years were used and two levels of phosphorus concentrations, low phosphorus level (1/20 of the phosphorus concentration in the standard nutrient solution formulation, LP) and the normal phosphorus concentration (International Rice Research Institute standard nutrient solution formulation, control), were designed. [Result]LP tolerance index (grain yield of LP treatment × LP tolerance coefficient/average grain yield of LP treatment for all tested cultivars) and dry matter index (dry matter of LP treatment/dry matter of control) were significantly or extremely significantly and positively correlated with the LP tolerance coefficient (grain yield of LP treatment/ grain yield of control) and grain yield under the LP treatment. Therefore,the LP tolerance index and dry matter index were chosen as indexes to evaluate the tolerance to LP for rice cultivars. The tested cultivars were classified into three categories based on the two indexes: strong tolerance to LP (both LP tolerance index and dry matter index >1), medium resistance to LP (both LP tolerance index and dry matter index > 0.6 and either LP tolerance index or dry matter index < 1) and weak tolerance to LP (both LP tolerance index and dry matter index≤0.6). Compared with those with weak tolerance to LP, the cultivars with strong tolerance to LP exhibited higher root dry weight, stronger root activity, more tiller number at the early tillering stage, larger total leaf area index (LAI), high-efficiency LAI, effective LAI and sink capacity, more accumulation of sugars in the stem and sheath at heading time and greater dry matter production capacity from heading to maturity. The LP treatment increased internal phosphorus use efficiency (grain yield/phosphorus uptake of plants) and the phosphorus harvest index (phosphorus in the grain/the total absorbed phosphorus in plants) in comparison with the control. Moreover, the cultivars with strong tolerance to LP showed much higher internal phosphorus use efficiency.[Conclusion]The LP tolerance index and dry matter index can be used as indexes to evaluate the tolerance to LP for a rice cultivar. Under the LP treatment, higher root dry weight, more tiller number at the early tillering stage, larger sink capacity and greater dry matter production capacity during gain-filling period are the main agronomic and physiological characteristics of rice cultivars with strong tolerance to LP and high phosphorus use efficiency.
grain yieldtolerance to low phosphorusevaluation indexagronomic and physiological trait
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