Germplasm Screening And Genes (QTLs) Identification Of Nitrogen Use Efficiency In Rice

Two hundred and fifty-six different genotypes of rice were screened, evaluated and identified by low nitrogen stress treatment at seedling and whole growth stage. Some high nitrogen use-efficiency rice genotypes were selected. At the same time, a screening and identifying method was established. A set of reciprocal introgressive line populations was used to study phenotypic index, physiological index and yield characteristic of rice under normal and low-N conditions. Molecular markers were applied in QTL analysis of low-N stress. Results were as followed:1. Screening and identifying of high nitrogen use-efficiency rice at seedling stageA pot experiment was conducted using 224 different genotype rice under different N levels at seedling stage. The results show that there existed significant difference among rice genotype under low-N stress. The relative plant height (RPL) ranged from 69.31% to 132.77%, relative tilling number (RTN) was from 72.14 %to 178.46% and relative shoot dry weight (RSDW) is from 62.05 to 350.00. All these three indices might response to the sensitivity of rice to low-N stress.The orders of SD and CV were both RSDW>RTN>RPH. Therefore the shoot dry weight(SDW) might be a more sensitive index compare to tilling number and plant height.According to the order of RSDW, RTN and RPH, the rice genotypes could be classified into three catalogs, high nitrogen use efficiency (NUE), low-N sensitivity(LNS) and midst. Among the 224 genotypes, 16 ones showed HNUE and 24 ones possessed LNS. Those 40 genotypes were considered as extreme materials. Which should be valuable in high nitrogen use-efficiency breeding.The most sensitive time of difference rice to low-N stress appeared at 35 days after sowing, which was observed from the study of 40 extreme rice under two N levels, suggesting that the properly time of high nitrogen use-efficiency rice screening was 30-40 days after sowing.2. Evaluation of the screening method of high nitrogen use-efficiency rice during the whole growth peroidThirty-two different genotypes of rice were selected condition to evaluate the high nitrogen use-efficiency during the whole growth period in fields. The plant height(PH), tilling number per plant(TN), chlorophyll content of flag leaf(CC), panicle length(PL),spikelet number per panicle(SN), seed setting rate(SS), 100-grain weight(100G), shoot dry weight(SDW) and grain weight(GW) were conducted under normal and low-N levels at maturity stage.The CV order of the tolerance index was GW(26.8%) > SDW(19.6%) > SN(18.3%)>TN(17.3%) > CC(12.7%) > SS(10.5%) > PL(5.4%) > 100G(4.8%) > PH(4.7%).Variance analysis showed that among the above 9 traits, except the PL was not significant difference between two N applied levels, the difference of other eight traits were significant(P<0.01).The relative correlation analysis indicated that these 9 traits were significant correlated each other under two N applied levels, including a positive correlation between SDW and GW 0.696 and 0.769, respectively.These evidences indicated that the grain weight, shoot dry weight and tilling number per plant could be selected as the screening indices to evaluate the rice high nitrogen use-efficiency. Because of the tilling number is easier to operate, it was choosed as screening index at large-scale and primary screening of rice high nitrogen use-efficiency at seedling stage. In addition the shoot dry weight and chlorophyll content of flag leaf would be selected as screening index. 3. QTL analysis of rice high nitrogen use-efficiencyQTL for eight important traits including plant height at early stage(PHE), plant height at late stage(PHL), tilling number at early stage(TNE), tilling number at late stage(TNL), chlorophyll content of flag leaf(CC), photosynthetic rate (PR), shoot dry weight(SDW) and grain weight per plant(GW) were investigated using reciprical introgressive line populations from an cross of "TeqingxLemont" under normal and low-N levels.Two parents , "Teqing: and "Lemont", had obviously different sensitivity to low-N stress Teqing was more sensitive compared to Lemont. Among the investigated 8 phenotypic values, plant height was nonsignificant different between two parents. The tolerance index of low-N stress of Teqing ranged from 62.15% to 89.51% and that of Lemont was 72.59% to 95.20% for other traits.A total of 58 QTL was distributed on 11 rice chromosomes, Covering 40 regions except the Chr.8 in Teqing population, including 26 and 32 QTL at low-N and normal levels, respectively. Most of them were located on chromosome 2,3 and 12.Forty-one QTL in 29 regions on all rice chromosomes were detected in Lemont population. 16 and 25 QTL were observed under low-N and normal levels, respectively.There were 13 and 8 chromosomal regions were found in Teqing and Lemont on which controlled more than two traits or were detected under two N applied levels, suggesting existing of some pleiotropil.