| Genetic improvement of the traits relating to mineral nutrition is one of the effective and practical approaches to enhance nutrient use efficiency in crops. In rice, nitrogen-use-efficiency for grain output (NUEg) is the key index in describing the overall nitrogen efficiency, and many previous studies have demonstrated that NUEg differs genotypically among rice cultivars, which indicates genetic improvement of NUEg is possible. However, studies and reports on the relationship between NUEg and basic traits, including grain yield formation, nitrogen uptake, source-sink relation, root properties, biomass and nitrogen translocation in rice plant, are in scarce yet. In this study, 88 and 122 conventional indica rice cultivars collected both from domestic and abroad were solution-cultured. Leaf-area-index (LAI), morphological and physiological traits in root, dry matter and nitrogen content in different parts of rice plant were measured at heading and mature stages, and grain yield and yield components were also tested. Basic on NUEg, rice cultivars were grouped into six types (A, B, C, D, E, F) using clustering method. The relationship between NUEg and the above traits were then analyzed. The purposes of the study were to investigate the basic characteristics of indica rice cultivars with higher NUEg and to provide fundamental information for genetic improvement of NUEg in rice breeding and proper nitrogen management in rice production. Results were as following:1. NUEg differed greatly among indica rice cultivars used in this study. Based on NUEg, rice cultivars could be grouped into six types (A, B, C, D, E, F). The mean value of NUEg for each type was 20.51, 31.04, 35.64, 39.46, 43.55, 50.92 g·g-1 in 2001 and 24.33, 31.61, 35.83, 39.06, 43.51, 50.00 g·g-1 in 2002, respectively. Xinshiruanzhan, 6078, Zaiyeqing, Zhengzhuai, Guicao 2 and 1826 showed higher NUEg, and NUEg of Aizizhan, Yangdao 3, Yangdao 2, Yangdao 5, Tesanai, Taizhongbendi 1 was medium while that of Cpslo17, Yangdao 6, BlueBelle, Taizhongxian, IR74 and Zaoxiandang was lower.2. There was significant positive correlation between NUEg and grain yield (r=0.5111**, 0.3071**, 0.370** for 2001, 2002 and 2001 plus 2002, respectively), and higher NUEg was characterized with higher grain yield. Multiple regression analysis showed grain yield responded to both NUEg and N uptake (R2=0.957-0.974). Direct path coefficient of N uptake to grain yield was 0.848 in 2001 and 0.964 in 2002, while that of NUEg to grain yield was 0.596 in 2001 and 0.565 in 2002. These results indicated that improvement of N uptake and NUEg could lead to enhancement of grain yield level in indica rice.3. NUEg was negatively correlated with days from sowing to heading (r=-0.3818**, -0.5002** in 2001 and 2002, respectively). Cultivars with shorter growth duration showed higher NUEg. No significant relation between NUEg and plant height was found in this study.4. Indica rice cultivar with higher NUEg were characterized with lager number of panicles per unit area, higher percentage of productive tillers and grain-setting, while NUEg was not apparently linked with spikelets per ear, 1000-grain-weight and maximum tillers. Integration of simple correlation, multiple regression, and path analysis indicated that number of panicles per unit area, percentage of productive tillers and grain-setting could be used as index for higher NUEg selection in indica rice cultivars.5. In source-sink relation, indica rice cultivars with higher NUEg showed lower LAI in heading stage, slower decline rate of LAI during grain-filling period, higher NAR and sink potential. Sink potential per unit of leaf area, dry matter and N uptake was also higher in indica cultivars with higher NUEg. Multiple regression analysis indicated that NUEg was significantly affected by above-mentioned source-sink traits (R2=0.749-0.809). Path analysis showed that NUEg was more affected by sink potential per unit of N uptake at heading stage, sink potential per unit of dry matter and grain yield per unit of sink potential than by LAI at heading stage and LAI decline rate during grain filling period.6. Biomass production had no obvious effect on NUEg, but cultivars with higher NUEg tended to have lower dry matter accumulation at heading stage. Dry matter production after heading and its proportion to total biomass were higher in cultivars with higher NUEg. The ratio of dry matter of root and stem & sheath at heading stage to total biomass did not significantly differ among NUEg types, but cultivars with higher NUEg tended to have lower ratio at mature stage. The ratio of dry matter of leaf at heading and mature stage to total biomass was lower while that of panicle was higher in the cultivars with higher NUEg. Cultivars with higher NUEg had higher harvest index and higher rate of dry matter translocation from leaf, stem &sheath to panicle during grain filling period.7. No significant difference of N content (%) at heading stage was observed among different NUEg types of indica rice. In the cultivars with higher NUEg, however, N content in leaf, stem& sheath and entire rice plant decreased more during grain filling period which lead to lower N content in rice plant at mature stage. Cultivars with higher NUEg were characterized with lower N uptake before heading and at mature stage, lower rate of N distributed in leaf, stem &sheath and higher translocation rate from leaf and stem &sheath to panicle, which contributed to higher N use efficiency in biomass production and harvest index.8. NUEg was negatively correlated with number of adventitious root, dry matter accumulation, total length of adventitious root, total & active absorption area andα-NA oxidation capacity per plant(R2=0.003-0.138). But NUEg did not respond to the root traits calculated on the base of single adventitious root (e.g. length, diameter, dry weight per adventitious root and per unit length of adventitious root) and root activity index on the base of root weight (e.g.α-NA oxidation capacity, total and active absorption area per unit of root dry weight).
|
PDF Full Text Request