Evaluation Of Yield And Nitrogen Use Efficiency Of Candidate Green Super Rice Varieties

Improving rice yield is of great significance for ensuring national food security.Variety improvement has significantly increased the yield potential of rice,but it has also led to a significant increase in nitrogen fertilizer input,which restricts the sustainable production of rice.Academician Zhang Qifa proposed the breeding concept of Green Super Rice（GSR）in 2005.GSR varieties can still achieve high yields despite significant reductions in fertilizer,pesticide,and water inputs,and have high economic and ecological benefits.To continue the evaluation and identification of GSR varieties,this experiment compared the yield,nitrogen use efficiency（NUE）,and phosphorus use efficiency（PUE）of 30 candidate GSR varieties in Wuxue City,Hubei Province in 2022.The nitrogen and phosphorus fertilizer inputs in the experiment were 100 kg N ha^-1and40 kg P ha^-1,respectively.The conventional rice variety Huanghuazhan and hybrid rice varieties Yangliangyou 6 and Fengliangyou 4 were used as controls.The objectives of this experiment were 1)to initially screen rice varieties that meet the GSR evaluation criteria;2)to explain the main agronomic characteristics of high-yielding and high-efficiency rice varieties;and 3)to analyze the relationship between high-yield and high-efficiency related traits in rice The main results of the experiment were as follows:（1）2022 was a rare year with high temperatures,with 49 days of high temperature（daily maximum temperature>35°C）,mainly at Panicle initiation stage to Heading stage.Under these conditions,the average yield of all rice varieties in this study reached 8.56 t ha^-1,with 11 rice varieties yielding more than 9 t ha^-1.Among conventional rice varieties,Huanghuasimiao and Shuanghuangzhan increased their yields by 7.5%and 24.9%respectively compared to Huanghuazhan;Among the hybrid rice varieties,a total of nine varieties increased their yields by more than 5%compared to Yanglangyou 6.Only Hualiangyou 21 Xinzhan and E liangyoumeixiangxinzhan had yield increases of more than 5%compared to Fengliangyou 4.Among the yield components,yield was significantly and positively correlated with grain filling,which may be related to differences in heat tolerance among varieties.From the perspective of dry matter production and distribution,yield was significantly and positively correlated with Pre-anthesis dry matter translocation（DMT）,Post-anthesis dry matter accumulation（DMA）and Harvest index（HI）.The contribution of DMT and DMA to yield was 27.3%and72.7%,respectively.The average value of HI was 43.6%.（2）Correlation analysis revealed that yield was significantly and positively correlated with Total nitrogen uptake（TN）,Partial factor productivity of applied N（PFP_N）,Nitrogen use efficiency for grain production（NUEg）and Nitrogen harvest index（NHI）,but significantly and negatively correlated with Nitrogen use efficiency for biomass production（NUEb）.Yield was significantly and positively correlated with Partial factor productivity of applied P（PFP_P）,Phosphorus use efficiency for grain production（PUEg）and Phosphorus harvest index（PHI）.In addition,there was a significant positive correlation between TN and all indicators of PUE（except PUEb）,indicating that nitrogen has a facilitating effect on phosphorus uptake in rice.（3）The rice yield and NUE indicators were clustered and all varieties were classified into four categories:high-yielding and high-efficiency,high-yielding and low-efficiency,low-yielding and high-efficiency and low-yielding and low-efficiency.The high-yielding and high-efficiency type of rice contained 12 varieties,which also had higher PUE,grain weight,dry matter accumulation and translocation capacity,leaf SPAD values and moderate LAI,which ensured higher grain filling and HI.（4）The PFP_Nand PFP_Pof the high-yielding varieties were compared with the control varieties according to GSR evaluation criteria,and four hybrid rice varieties were screened to meet the GSR category I criteria:Yiliangyou 311,Fuliangyou 2877,E Liangyou 263 and Longliangyou 8612,and one conventional rice variety was screened to meet the GSR category II criteria:Shuanghuangzhan.In summary,some candidate GSR varieties can still show high yield under the influence of low nitrogen inputs and high temperature weather.The high yield of rice is closely related to grain filling,harvest index,dry matter accumulation and translocation capacity,and NUE and PUE.Twelve high-yielding and high-efficiency varieties were selected by cluster analysis of yield and NUE indicators,in addition to having both high PUE,higher grain weight and leaf SPAD values.In addition,this study found that 5candidate varieties met the green super rice identification criteria,which can be further validated for future research.