Tolerance To Low Phosphorus And Its Agronomic And Physiological Characteristics Of Rice Cultivars

Phosphorus is one of the three essential nutrient elements for plant growth,and it is also a non-renewable resource.Rice is one of the major food crops in China and its requiring phosphorus is very large.Therefore,it is very important to breed and select rice cultivars with high phosphorus use efficiency,which will reduce the application of phosphate fertilizer,improve the yield of rice and increase phosphorus use efficiency.However,the indicator used for screening a phosphorus-efficient rice cultivar is not available,and its agronomic and physiological characteristics are not clear.To deal with these problems,this study used 11 typical japonica rice cultivars applied in production in Jiangsu Province during the last 70 years and designed 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).The evaluation index of rice tolerance to low phosphorus(LP),agronomic and physiological characteristics of the tolerance to LP for a cultivar,and the effect of LP treatment on rice quality were investigated.The main results are as follows.1.Low phosphorus(LP)treatment reduced grain yield of each test cultivar,and the reduction in grain yield was mainly due to the decrease in panicle number and spikelet number per panicle.But the reduction in grain yield varied with cultivars.Several indexes for evaluating the tolerance to LP were used.They were the LP tolerance coefficient(grain yield of LP treatment/grain yield of control),LP tolerance index(grain yield of LP treatment × LP tolerance coefficient/average grain yield of LP treatment for all tested cultivars),dry matter index(dry matter of LP treatment/dry matter of control),plant height index(plant height of LP treatment/plant height of control),stress sensitivity index[(1-LP tolerance coefficient)/(1-average grain yield of LP treatment for all tested cultivars/average grain yield of control for all tested cultivars)],and comprehensive resistance to LP index[relative plant height × relative grain yield per plant/relative days from sowing to heading × 110(relative value = the trait LP treatment/the same trait of control)].The results showed that LP tolerance index was significantly or very significantly and positively correlated with the LP tolerance coefficient,dry matter index and grain yield under LP treatment,and correlation coefficients(r)were:0.70*,0.80**and 0.94**respectively.The dry matter index was significantly and positively correlated with the grain yield of LP treatment(r=0.78**).Therefore,the LP tolerance index and dry matter index were used as indexes to evaluate the tolerance to LP for a rice cultivar.The tested cultivars were classified into three groups according to the two indexes:(1)both LP tolerance index and dry matter index ? 1,cultivars were strong resistance to LP,(2)both LP tolerance index and dry matter index>0.6,and either LP tolerance index or dry matter index<1,cultivars were medium resistance to LP,and(3)both LP tolerance index and dry matter index ? 0.6,cultivars were weak resistance to LP or sensitive to LP.According to the above classification,the cultivars Yongyou 2640,Guihuaqiu,and Yanjing 2 were strong tolerant to LP;Liming,Lianjing 7,and Zhendao 88 were weak tolerant to LP;and Jinnanfeng,Guihuahuang,Sidao 8,Huaidao 5,and Xudao 2 were medium tolerant to LP.2.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.These characteristics could be used as important agronomic and physiological traits of tolerance to LP for rice cultivars.3.Compared with the normal phosphorus concentration(control),the LP treatment reduced the milled rice percentage,the whole milled rice percentage and the amylose content of most test cultivars,and increased the breakdown value and reduced setback value of starch rapid viscosity analyzer(RVA).The percentage of chalkiness,chalky area and chalkiness were significantly decreased,indicating that LP treatment could reduce the processing quality,but improve the taste and appearance quality of rice.The effect of LP on grain quality was not clossly associated with the tolerance to LP for a cultivar.4.Compared with the control,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),reduced N uptake,and increased the absorption of potassium in rice roots.Under the LP treatment,the internal phosphorus use efficiency was higher for the cultivars with strong tolerance to LP than those with weak tolerance to LP.