Correlated response to recurrent selection for groat-oil content in oats

Summary One hundred random oat (Avena sativa L.) lines from a base (C₀) and each of three populations (C₁, C₂, and C₃) improved for groat (caryopsis) oil content by phenotypic recurrent selection were evaluated for correlated changes in several unselected agronomic traits. In addition, the parents of the base population and four check varieties were evaluated for the same traits. Phenotypic recurrent selection for high groat-oil content resulted in no significant correlated response in mean expression of any trait. Mean grain yield, biomass, groat yield, and harvest index of the improved populations were equal or superior to the mean of the parents and, with the exception of harvest index, equivalent to the mean of the check varieties. Mean test weight and seed weight of all populations were lower than for parents or check varieties. Selection for high groat-oil content caused a decline in genotypic variance for test weight and groat fraction, but reductions in genotypic variance for heading date and plant height may have resulted from culling for good agronomic type. Broad-sense heritability remained moderate to high for all traits except groat fraction. Phenotypic and genotypic correlation coefficients revealed negative, though mostly nonsignificant, relationships between groat-oil content and several traits, which may reflect a purported bioenergetic limitation to increasing groat-oil content in oats. Oil yield, however, was positively correlated with grain and groat yield, groat fraction, biomass, and harvest index. Results suggest that development of high-oil oat cultivars with current levels of production traits via phenotypic recurrent selection is possible.Journal Paper no. J-13038 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project 2447.     

Responses in Agronomic Traits Associated with Three Recurrent Selection Regimes for Groat-Oil Content in Oat*

Crop strains with high values for the selected trait but unacceptable agronomic characteristics are not useful as varieties. In this study, we determined whether selection for groat-oil content in oat (Avena sativa L.) via three recurrent selection regimes caused associated changes in 10 agronomic traits. Random lines of each cycle of selection of each regime were evaluated in a replicated field experiment at two locations. Biomass, grain yield, groat yield, and test weight decreased in all three regimes. Seed weight and plant height decreased in two regimes, and groat fraction in one. Oil yield increased in two regimes and decreased in the other. Plants headed earlier in one and later in another regime over cycles of selection. No changes in harvest index occurred. Heritabilities and genetic variances were relatively high for all traits in each regime. Factor analysis of the phenotypic correlation matrices indicated that simultaneous increases in grain yield and in groat-oil content are possible, that continuous selection for groat-oil content decreases groat fraction and test weight, and that seed weight is strongly and negatively associated with groat-oil content. A new recurrent selection regime for increasing groat-oil content of oat that may overcome the negative responses of agronomic traits was proposed.     

Changes in fatty acid composition associated with recurrent selection for groat-oil content in oat

Summary Groat oil of oat (Avena sativa L.) is a well-balanced oil with respect to saturated, monounsaturated, and polyunsaturated fatty acids. In this study, we measured the effect of six cycles of recurrent selection for high groat-oil content on the fatty acid composition of the groat oil. From each cycle of selection, 50 oat lines were grown in a replicated field experiment at two sites and were evaluated for groat-oil content and fatty acid composition.Concentrations of palmitate and linolenate decreased moderately over cycles of selection, whereas stearate content increased. A major increase occurred in the content of oleate and a major decrease in linoleate. Most of the modification of fatty acid composition took place within the saturated and unsaturated classes. The ratio of unsaturated to saturated fatty acids increased over cycles of selection. Significant genetic variation was present for each fatty acid, indicating that selection for different desired fatty acid compositions in groat oil of oat should be possible in this population.Abbreviations GO groat-oil content - 16:1 palmitate - 18:0 stearate - 18:1 oleate - 18:2 linoleate - 18:3 linolenate     

Agronomic and Bioenergetic Consequences of Selection for High Groat-Oil Content and High Protein Yield in Oat*

Few studies have examined the effects of selection for high oil or protein content on the chemical composition of cereal seeds. This study was conducted to examine agronomic and bioenergetic consequences that result with changes in the chemical composition of groats of oat (Avena sativa L.). Oat lines with low and high groat-oil content (GO) and with low and high groat-protein content (GP) were chosen from each of five cycles of a recurrent selection program for increasing GO and from each of four cycles of a recurrent selection program for increasing protein yield via elevating GP, respectively. These lines were evaluated at three Iowa locations in 1988. The results indicated that GP was not significantly affected by selection for high GO and that GO significantly increased during selection for high protein yield via elevating GP. Both selection procedures resulted in oat lines with higher groat-energy contents. A bioenergetic cost analysis showed that for GO in the oil population and GP in the protein population to be increased, additional photosynthate needed to be available.     

Genetic interrelations among grain quality indicators and agronomic traits for oat

Summary Test weight, seed weight, and groat percentage are three common measures of grain quality for oat (Avena sativa L.). There is considerable disagreement, however, about the utility of each of these traits as measures of grain quality, so it is important to understand the genetic interrelations among them and between them and other agronomic traits. In this study, 50 random F2-derived F3 lines from each of 13 biparental oat crosses were evaluated. Genotypic variances, heritabilities, and genotypic correlations for test weight (TW), seed weight (SW), groat percentage (GP), grain yield (GY), harvest index (HI), plant height (PH), and date of heading (DH) were used to predict and compare direct and indirect gains from single-trait selection. Direct selection was always the most effective method for improving single traits; average predicted improvement of population means was 4% for TW, 10% for SW, 1% for GP, and 14% for GY when 10% selection intensity was applied. Genotypic correlation coefficients, averaged for all crosses, were 0.04 for TW with SW, 0.37 for TW with GP, -0.09 for SW with GP, and 0.29, 0.36, and 0.30 for GY with TW, SW, and GP, respectively. Thus, direct selection for TW, SW, or GP should not greatly affect the other two grain quality indicators. For the seven traits considered, there seemed to be no large advantage or disadvantage, in terms of correlated responses, associated with selection for any of the grain quality indicators.Contribution as Journal Paper No. J-14650 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2447.     

Estimates of selection parameters associated with harvest index in oat lines derived from a bulk population

Summary Harvest index of grain crops is defined as grain yield divided by total plant yield. We estimated the heritability percentages of harvest index and its components, grain yield and plant weight, the genotypic and phenotypic correlations among these three traits, and the genotypic correlations of harvest index with plant height, 100-seed weight, grain number, and heading date by using a population of 1200 F₉-derived oat lines tested in six environments. Furthermore, we examined the relative selection efficiencies of indirect selection for yield through harvest index and of index selection for yield through yield plus harvest index.Heritability percentages were computed by use of variance-component, standard-unit, and realizedheritability methods. The heritability percentages for harvest index, grain yield, and plant weight were similar, and averaged between 50 and 65 precent across environments. Standard-unit and realized heritability percentages agreed closely and generally were lower than those computed via the variance-component method. Expected heritability percentages for harvest index calculated by using grain and plant yield data agreed almost exactly with actual values. Genotypic correlations were 0.88 between grain yield and plant weight, 0.42 between harvest index and grain yield, and –0.07 between harvest index and plant weight. Genotypic and phenotipic correlations were similar in magnitude. Theoretical and actual genotypic and phenotypic correlations of harvest index with grain yield and plant weight agreed closely. Genotypic correlations, computed via parent-offspring relationships, between harvest index and plant height, 100-seed weight, grain number, and heading date averaged –0.41, 0.43, 0.00, and –0.33 respectively.Indirect selection for grain yield through harvest index was 43 percent as efficient as direct selection, and a selection index that combined harvest index and grain yield was no more efficient than direct selection for yield. Harvest index had little value as a selection criterion for grain yield improvement when unrestricted selection was used. Indirect selection for grain yield through harvest index, however, would be expected to retain lines with a more favorable combination of yield, plant height and heading date than would unrestricted direct selection for yield.Journal Paper No. J-7914 of the Iowa Agriculture and Home Economic Experiment Station, Ames, Iowa 50010, Project No. 1752.     

Recurrent selection for seed quality traits in an opaque-2 maize population

Summary The aim of this research was to evaluate the response to phenotypic recurrent selection for four seed quality traits, i.e. protein content, dye binding capacity, tryptophan content, and specific weight, in a modified opaque-2 population of maize (Zea mays L.). Changes in other agronomic traits were also studied. Four selection cycles, using as selection criterion an index constructed from the four seed quality traits, were completed on an individual plant basis. The material from each cycle and from testerosses of each cycle with a homozygous opaque-2 tester was grown for two consecutive years to evaluate the progress due to selection. The results showed that four cycles of recurrent selection induced sizeable variations among cycles for all selected traits. The rate of progress for the four seed quality traits was nearly linear. Further-more, theldata show that improvement in seed-protein related traits had no negative effects on grain yield and kernel weight, when evaluated as the mean performance of testerosses. There was also no appreciable alteration in the other agronomic traits caused by selection for seed quality traits.     

Recurrent selection for broad adaptation affects stability of oat

A recurrent selection program for adaptation to diverse environments was successful in improving mean oat (Avena sativa L.) grain yield within and across testing environments. The objectives of this research were to determine if this selection program also resulted in changes in other agronomic traits or altered yield stability. Additionally, we investigated how selection modified the response of genotypes to climatic conditions. We evaluated random samples of 100 families from the original population and each of three selection cycle populations in replicated yield trials in Idaho, Iowa, and Norway for two years. Yield stability was assessed via joint regression analysis and superiority analysis. For each cycle, genetic relationships among yields observed indifferent environments were assessed by estimating phenotypic correlations between pairs of target environments. The effect of climate variables on genotype-by-environment interaction (GEI) responses was determined with partial least squares regression. Selection resulted in a small increase in mean heading date, a decrease in mean test weight, and no change in total above-ground biomass or plant height. Genotypic regression coefficients on environmental indices and deviations from regression were larger in the last cycle population, but superiority analysis demonstrated that selection significantly improved the adaptability of the population to the target testing environments. Improved adaptation was also demonstrated by increased phenotypic correlations among the most divergent pairs of environments in the later cycles. Partial least squares regression of GEI effects on climate variables suggested that later cycle families tended to respond more favorably to cooler than average conditions than the original population. Selection resulted in improved yield stability as well as improved mean yield. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic variability and interrelationship of traits in the industrial oil crop Vernonia galamensis

Vernonia galamensis is a wild plant from the family Asteraceae which is endemic to East Africa and has the potential to become a new oil crop for industrial uses. Its seed oil is rich in vernolic acid, a fatty acid of high interest for oleochemical applications. However, a breeding program for Vernonia galamensis cultivars with high seed and oil yields requires knowledge about the genetic variability of traits that influence seed and oil production. This study was undertaken to examine phenotypic and genotypic variability, broad-sense heritability, genetic advance under selection and interrelationships of agronomic and seed quality traits. A total of 122 Vernonia accessions, 115 collected from different regions of Ethiopia and seven introduced, were grown at two locations in Ethiopia (Alemaya and Babile), in 2001/2002 and were analyzed for 20 traits including phenology, yield, yield components, and seed quality with special emphasis on fatty acid composition. The collections exhibited significant variation for all traits except for days to emergence. Genotypes and locations interacted significantly (P 0.01) for all traits. Broad-sense heritability estimates ranged from 11% (for days to emergence) up to 79% (for days to maturity). Expected genetic advance was between 1.3% (for days to emergence) and 44.8% (for seed oil yield). Genetic correlation analysis revealed that seed yield per plant is highly and positively correlated with seed weight and head number; highly significant and negative correlations (r = –0.59, –0.82, –0.85, and –0.89) were found between vernolic acid and palmitic, stearic, oleic, and linoleic acid, respectively. Highly significant positive correlations (r = 0.55, 0.44, and 0.36) were observed between vernolic acid and oil content, meal protein content and seed oil yield, respectively. Path-coefficient analysis indicated seed weight and secondary head number to be the most important components of seed yield per plant. Vernolic acid, oleic acid and linoleic acid had positive direct effects and stearic acid had a negative direct effect on oil content. The direct positive effect of oleic acid on oil content was, however, compensated by the negative indirect effects of stearic and vernolic acid resulting in a negative correlation (r = –0.60) between oleic acid and oil content. These observations will support the selection of accessions with high seed and oil yield, high meal protein contents, and high vernolic acid content.     

籼型黑米稻粒形性状与其中某些矿质元素含量的遗传相关性

采用禾谷类作物种子数量性状遗传模型, 分析籼型黑米稻品种双列杂交F1和F2种子粒形性状与其中矿质元素Fe、 Zn、 Mn和P含量间的多种遗传相关性. 结果表明, 籼型黑米粒重、粒长、粒宽、粒长/粒宽与其中Fe、 Zn、 Mn和P含量除存在明显的表现型相关和基因型相关外, 尚存在较明显的种子直接加性相关、直接显性相关、细胞质相关、     

Correlated Response to Selection for Protein Yield in Oats After Three Cycles of Recurrent Selection

Three oat (Avena saliva L.) populations (i.e., lines of descent), high grain yield (HG), high protein content (HP), and high protein yield per se (HGP), each developed by three cycles of S, recurrent selection, were evaluated for the effect of selection for groat-protein yield upon other agronomic traits. Selections making up the HG line of descent had high protein yield primarily due to high grain yield, and those selected for HP had high protein yield due to both high protein content and high grain yield. Selection in HGP was on the basis of protein yield per se. Selection caused increases in bundle weight, harvest index, vegetative growth rate, and seed number in all lines of descent. Heading date, plant height, and seed weight were unaffected, whereas groat percentage and test weight were decreased in HP and HGP. Heritabilities were high for heading date, plant height, test weight, and seed weight, moderate for harvest index and bundle weight, and low for groat percentage. Genetic variability generally declined from CO to C3 for all traits. Groat-protein yield and amount of protein per groat increased in all lines of descent. In HG, the increase in groat weight was due primarily to increases in the nonprotein fraction, with groat-protein content actually decreasing. In HGP, groat weight increased due to increases in protein and nonprotein fractions, and groat protein content remained constant. In HP, groat weight and amount of nonprotein per groat decreased, thus increasing groat-protein content. Three cycles of recurrent selection resulted in oat lines with groat-protein yields significantly higher than the highest lines from CO. Utilization of index selection may be desirable to obtain populations of greater breeding value.     

Inheritance of groat-oil content and high-oil selection in oats (Avena sativa L.)

Summary The potential for breeding for high groat-oil content in oats was investigated by (a) conducting generation means analyses on data from three matings among adapted Avena sativa L. cultivars, (b) practicing one cycle of phenotypic recurrent selection in a segregating population derived from eight species backcrosses (Avena sativa x (A. sativa x A. sterilis)) among 24 parents, and (c) identifying transgressive segregates from interspecific (A. sativa x A. sterilis) matings.Additive gene action was the most important component in explaining the variation among generation means for groat-oil content. Dominance and epistatic interactions involving dominance were not significant in any mating. Significant residual genetic variation occurred in one mating, even after additive, dominance, and three digenic interactions were fitted. The importance of additive genes action implies that desired allelic combinations for high groat-oil content can be obtained in pure-line cultivars.One cycle of phenotypic recurrent selection using single plants as the selection units resulted in a genetic gain of 1.7 to 2.1% in groat-oil content. Individual plants selected for initiating the second cycle had from 9.5 to 12.6% groat oil.Over all 12 interspecific matings, the F₂ progeny means were similar to the midparent values. Only two were significantly deviant. Transgressive segregates for high and low groat-oil content from these matings provided evidence that A. sterilis possesses alleles for high and low groat-oil content that are different from those in the gene pool of cultivated oats.Journal Paper No. J-11340 of the Iowa Agric. and Home ECon. Exp. Stn., Ames, Iowa 50011. Project 2447. This study was supported in parts by grants from the Iowa Committee for Agricultural Development and the International Harvester Company.     

Response of a new IR50/Moroberekan recombinant inbred population of rice (Oryza sativa L.) from an indica × japonica cross for growth and yield traits under aerobic conditions

Genetic variability, correlation, path coefficient analysis and test of normality was conducted in an F₈ recombinant inbred aerobic rice population developed by single seed descent method to evaluate its potential as a mapping population. Estimates of genotypic variance, phenotypic variance, genotypic coefficient of variance (GCV), phenotypic coefficient of variance (PCV), heritability in the broad sense (H) and expected genetic advance at 5% selection index (GA) for grain yield and other attributing characters were computed. In all the cases, PCV was higher than GCV indicating the influence of environment on the characters. High heritability coupled with high GA was observed for several plant traits; number of tillers, plant height, total number of spikelets panicle⁻¹, biomass plant⁻¹, straw weight, harvest index and grain yield plant⁻¹ and hence offered good scope for selection. Grain yield plant⁻¹ was found to be positively correlated with plant height, number of tillers, panicle length, panicle exsertion, number of panicles plant⁻¹, single panicle weight, test weight, number of fertile spikelets panicle⁻¹, straw weight, biomass plant⁻¹, harvest index and grain breadth both at genotypic and phenotypic levels. Harvest index exerted maximum positive direct effect, followed by biomass plant⁻¹ and straw weight on grain yield plant⁻¹ at phenotypic level. Shapiro-Wilks “W test of normality” indicated that the population was skewed towards female parent IR50 for some traits and for some others towards Moroberekan, the male parent. Most of the characters that showed skewness were platykurtic with a kurtosis value of less than 3.     

Use of index selection in recurrent selection programs in maize

Summary Phenotypic and genotypic correlations were examined for four traits in seven populations of maize (Zea mays L.) undergoing recurrent selection. Correlations among grain yield and percentage of grain moisture, root lodging, and stalk lodging were low (|r|<0.3) except for the correlation between grain yield and stalk lodging, which was high and negative. The phenotypic and genotypic correlations agreed well from cycle to cycle within populations. Variation of correlations among populations was not significantly larger than variation among cycles. Heritabilities of these traits generally were high (h²>0.5). Two indices, one that used heritabilities as index weights and one that used relative economic weights (base index) as index weights, were compared with the Smith-Hazel index (optimim index). Relative efficiencies of the two indices, in terms of predicted gains for the individual traits and the composite trait, compared with the Smith-Hazel index, were high. The use of an index in which heritabilities were used as index weights was recommended because:1) the heritabilities were the same as the optimum weights when the traits were uncorrelated, and for the data examined the correlations were low; and 2) heritabilities were computed in routine data analyses and were available at no additional cost.Joint contribution: USDA-SEA-AR and Journal Paper No. 10152 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project 2194.     

Using unsupervised learning techniques to assess interactions among complex traits in soybeans

Soybean yield components and agronomic traits are connected through physiological pathways that impose tradeoffs through genetic and environmental constraints. Our primary aim is to assess the interdependence of soybean traits by using unsupervised machine learning techniques to divide phenotypic associations into environmental and genetic associations. This study was performed on large scale, jointly analyzing 14 quantitative traits in a large multi-parental population designed for genetic studies. We collected phenotypes from 2012 to 2015 from a soybean nested association panel with 40 families of approximately 140 individuals each. Pearson and Spearman correlations measured phenotypic associations. A multivariate mixed linear model provided genotypic and environmental correlations. To evaluate relationships among traits, the study used principal component and undirected graphical models from phenotypic, genotypic, and environmental correlation matrices. Results indicate that high phenotypic correlation occurs when traits display both genetic and environmental correlations. In genetic terms, length of reproductive period, node number, and canopy coverage play important roles in determining yield potential. Optimal grain yield production occurs when the growing environment favors faster canopy closure and extended reproductive length. Environmental associations found among yield components give insight into the nature of yield component compensation. The use of unsupervised learning methods provides a good framework for investigating interactions among various quantitative traits and defining target traits for breeding.     

Continued response through seven cycles of recurrent selection for grain yield in oat (Avena sativa L.)

Long-term selection experiments provide germplasm to study the effects of selection in a closed population. Recurrent selection to enhance grain yield in oat has been ongoing at the University of Minnesota since 1968. The objectives of this study were: (i) estimate the GCA and SCA effects for three agronomic traits in the seventh cycle of selection, (ii) assess the effect of the current methods of selection on parental contribution and unselected traits, and (iii) determine the direct and indirect responses to seven cycles of recurrent selection for grain yield. Progeny of the Cycle 6 parents and parents for Cycles 0 through 7 were grown in two separate tests. Grain yield, heading date and plant height were evaluated in each test. Grain yield was increased by 21.7% after seven cycles of selection. Evaluation of Cycle 6 progeny showed that GCA effects were significant for all three traits studied, and SCA effects were significant only for grain yield. Four Cycle 6 parents did not have any progeny selected as Cycle 7 parents. Results from this study indicate that long term recurrent selection has continued to increase grain yield. Alternative selection strategies may be necessary to maintain the genetic variability in this population, particularly when improvement of secondary traits is required. This revised version was published online in August 2006 with corrections to the Cover Date.     

甘蓝型油菜DH群体主要品质性状相关性及主成分分析

为了研究甘蓝型油菜品质性状之间的相关性,以期有效的改良油菜的品质性状,将170份DH纯系群体于2009-2012年进行田间试验,检测油菜种子品质性状,对其表型、相关性及主成分进行分析。结果表明：亲本中芥酸含量的变异系数最大(相差15.53%)。油菜DH群体中硫甙含量的变异幅度最大(128.43μmol/g饼粕),饱和脂肪酸的变异幅度最小(1.97%)。DH群体的品质性状表型变异幅度显示出了超亲遗传的现象。除了芥酸,含油量与其他组分呈现出极显著的负相关,特别是与蛋白质含量的负相关系数最大(-0.72)；蛋白质含量与油酸、亚油酸、亚麻酸和硫甙含量均呈极显著的正相关,与含油量和芥酸呈极显著的负相关；除了蛋白质,其他组分含量皆与硫甙含量呈现出极显著或者不显著的负相关。通过主成分分析可将品质性状综合为油酸亚油酸酸因子,蛋白质因子,亚麻酸因子和硫甙因子,累积贡献率达到93.94%,基本反映甘蓝型油菜DH系群体脂肪酸组分信息。     

Harvest index in lentil (Lens culinaris Medik.)

Summary Correlation and path coefficient analyses were conducted to find out the characters associated with grain yield and dry matter production and the ways to improve harvest index in lentil.Correlation studies revealed positive association of harvest index with grain yield but no association with plant dry matter. Grain yield and plant dry matter showed positive correlation with pod number, plant height, and number of primary and secondary branches but negative correlation with 100-seed weight. Generally, the genotypic correlations were in agreement with phenotypic correlations, though the magnitude of the values was higher in the former case. In path analysis, plant height and pod number showed the highest direct effect and, therefore, seem to be the main characters influencing grain yield and plant dry matter. Number of primary and secondary branches, on the other hand, showed negative direct effect on grain yield and plant dry matter. Use of phenotypic or genotypic correlations in path analysis resulted in similar conclusions. It is, therefore, suggested that either phenotypic or genotypic correlations may be used in path analysis with equal efficiency. Based on this study it is suggested to develop tall varieties with good pod bearing but with low number of branches.     

Increasing grain yield of oats by independent culling for harvest index and vegetative growth index or unit straw weight

Summary Most variation in grain yield of oats is due to variation in harvest index and vegetative growth index, but the latter traits are negatively associated. Therefore we used independent culling levels to select oat genotypes with high levels of vigor traits and a desirable level of harvest index in an attempts to maximize grain yield. Harvest index and vegetative growth index or harvest index and unit straw weight were selected at various culling levels. Intensive selection for harvest index resulted in high harvest index but no grain yield improvement, because the selected lines had poor vigor. Intensive selection for vegetative growth index or unit straw weight resulted in high biomass but low harvest index.The most effective combination of culling levels was to select 25% of the original population for harvest index and, subsequently, to select for vegetative growth index or unit straw weight at an 8% intensity in the remnant population.Journal Paper No. J-11272 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project 2447. This work was supported in part by the World Food Institute, Iowa State Univ., in the form of a Senior Fellowship for the senior author.     

Low-nitrogen stress tolerance and nitrogen agronomic efficiency among maize inbreds: comparison of multiple indices and evaluation of genetic variation

Limited information is available on genetic variation in low-nitrogen (low-N) stress tolerance and N-use efficiency (NUE) among maize inbreds. To unveil this information, a panel of 189 diverse maize inbred lines was evaluated under contrasting levels of N availability over 2 years. Low-N agronomic efficiency (LNAE), absolute grain yield (GY) at low-N conditions, and the ratio between GY at low-N and optimum-N conditions were taken into account to represent low-N tolerance. Additionally, N-agronomic efficiency (NAE) along with other agronomic traits was also analyzed. Analysis of variance revealed significant effects of genotype on LNAE, NAE, and GY. The estimated broad-sense heritability was 0.38 for LNAE while it was only 0.11 for NAE, implying that selection based on LNAE should be more effective than NAE. LNAE exhibited highly positive genotypic and phenotypic correlations with GY, ear kernel number (EKN), kernel weight, plant height (PH), and chlorophyll content at low-N conditions, while it was negatively correlated with grain-N content and anthesis-silking interval. Path analysis indicated that the EKN at low-N stress had the highest positive effects on LNAE.