Changes in morphological and physiological traits associated with recurrent selection for grain yield in maize

Summary Experiments were conducted during the growing seasons of 1975 and 1976 to determine changes in morphological and physiological traits associated with recurrent selection for grain yield in maize (Zea mays L.). Four variety hybrids, BSSS(R)CO x BSCB1(R)CO, BSSS(R)C7 x BSCB1(R)C7 [from a reciprocal recurrent selection program involving Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic #1 (BSCB1)], BS12CO x B14A, and BS12C6 x B14A [from a half-sib selection program involving the open-pollinated variety Alph (BS12) and the inbred tester B14A] were grown at 59 300 and 98 800 plants/ha near Ames, Iowa We obtained data on CO₂-exchange rate (an estimate of photosynthetic rate), grain yield, grain-yield components, flowering dates, maturity traits, light interception and use, shelling percentage, harvest index, and various other plant traits.CO₂-exchange rate did not change appreciably with recurrent selection for yield. Grain yield per hectare and per plant were larger for the improved than unimproved hybrids. Grain-yield components did not change significantly with recurrent selection. Kernel weight of BSSS(R)C7 x BSCB1 (R)C7, however, was larger than that of BSSS(R)C0 x BSCB1(R)C0. Pollen-shed-to-silking interval was shorter for the improved than the unimproved hybrids, and grain-filling duration was longer in C7 x C7 than in C₀ x C₀ of the reciprocal recurrent selection program. Furthermore, improved hybrids were characterized by smaller tassels and more upright canopies. Usually, plant traits and leaf-area-related traits were similar for all hybiids.Although dry-matter productivity was similar for all hybrids, those that were improved by recurrent selection produced more grain per unit leaf area and per unit light interception. Also, BS12C6 x B14A was characterized by a higher harvest index than BS12CO x B14A.We concluded that the source (i.e., photosynthetic capacity) was not limiting grain yield in BSSS(R) x BSCB1(R) and BS12. Increased grain yields that resulted from recurrent selection were consequences of longer grain-filling duration for BSSS(R) x BSCB1(R) and increased translocation of photosynthate from source to sink for both BSSS(R) x BSCB1(R) and BS12.Journal Paper J-8953 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project No. 2152.     

Breeding potential of U.S. maize germplasm for utilization in Chinese temperate conditions

U.S. maize germplasm has been considered as a new alternative source of favorable alleles to broaden the narrowing genetic base of temperate germplasm. However, direct utilization of diverse U.S. germplasm in target mega-environments could be hampered by limited adaptation-related information on parental performance or heterotic response in crosses with local germplasm. The objective of this study was to measure the performance of U.S. maize populations for broadening the Chinese germplasm base. Fifteen diverse U.S. populations were testcrossed to three local tester lines, representing Chinese heterotic groups A, B, and D, to evaluate parental adaptation and combining abilities for days to silking (DS), ear height (EH), and grain yield (GY) in target and intermediate mega-environments in northern China. There was genetic variability among U.S. maize populations for additive and non-additive effects for DS and GY, and predominant additive genetic effects for EH. All 15 U.S. populations, except for BS27 and BS31 due to slightly high EH, could be directly used in target mega-environments similar to the U.S. Corn Belt. U.S. populations BS11(HI)C7, BS13(S)C7, BS17(CB)C4, BS31, BSCB1(R)C12, and BSBB(SRCB)C4 had better effects for increasing GY. Favorable effects for DS were also observed in BS11(HI)C5 and BS31, for DS and EH in BS13(S)C7 and BSCB1(R)C12, and for EH in BSBB(SRCB)C4. The best strategies for utilizing these germplasms may be to introgress BS13(S)C7 and BS17(CB)C4 into group A, BS11(HI)C5 into group B, and BSCB1(R)C12 and BSBB(SRCB)C4 into group D to increase genetic variation within Chinese heterotic pools.     

玉米“黄金”群体产量等性状轮回选择改良效果评价研究

利用群体改良方法,充分挖掘地方优异种质的遗传潜力是玉米种质改良与创新的一个重要途径。本研究以黄金群5个轮次改良群体为材料,通过1年2点产量比较试验,分析了混合选择和相互半姊妹轮回选择方法对黄金群产量及穗部性状的改良效果。结果表明,两种选择方法对群体产量改良是有效的,随着改良轮次的增加,黄金群的单株产量逐轮提高,平均每轮提高3.78%,其中,混合选择改良的3轮群体平均每轮提高4.27%,相互半姊妹轮回选择的改良群体提高2.07%;虽然群体产量的变异系数从15.43%下降到12.80%,但群体内仍有较丰富的变异。通过改良群体穗部性状比较发现,穗长和行粒数改良效果显著,分别提高14.71%和17.62%,说明它们的提高是群体单株产量提高的主要因素。     

MS1与MS1-HS两种选择方法的比较研究Ⅱ.遗传方差、配合力及杂种优势

对ZZ4完成了4轮MS1-HS和MS1选择.结果表明,经4轮选择的群体,两种方法均有效地保留了各主要性状的遗传方差.MS1-HS选择的群体遗传方差下降速率更慢,C4群体的单株籽粒产量的遗传方差仅减少3.7%.穗长、穗粗、粒行数、行粒数、出籽率、百粒重的遗传方差的变化与单株籽粒产量一致,MS1C4的遗传方差减少了8%～15%,MS1-HSC4的遗传方差仅减少了4%～15%.株高、穗位高、抽丝期、植株保绿度、抗倒性等相关选择性状的遗传方差的变化与产量性状基本一致.MS1-HS法对改良玉米群体籽粒产量与测验种间的特殊配合力十分有效,呈逐轮上升的趋势;改良群体与测验种综系140间的杂交后代产量平均每轮提高6%,杂种优势平均每轮提高6.9%.两种方法在改良群体产量性状一般配合力方面,均得到了良好的效果.同时,穗部性状及株高、穗位、抽丝期、散粉期、抗性等田间农艺性状的一般配合力也获得了同步改良.通过ZZ4改良群体与6个测验种间杂交组合产量及杂种优势的比较研究,得出ZZ4与黄早四类种质为杂种优势模式对.     

Mass selection for improved cold and density tolerance of two maize populations

Summary Data of planting and plant density are two cultural practices influencing grain yield of maize (Zea mays L.). Our study was designed to evaluate the usefulness of a mass selection scheme to improve cold and density tolerance of the BS2 and BS3 maize populations. Populations were planted at an early planting date and a high plant density, and three cycles of mass selection for well-filled ears on erect plants were conducted at earch of three Corn Belt locations (i.e., Waseca, MN; Ames, IA; Portageville, MO).Results showed that selection improved cold tolerance traits of BS3, but not of BS2. Mass selection did not increase density tolerance of either population at any location. Selection did not improve response to planting dates, although the early planting date did improve agronomic performance and grain yield of all entries. We concluded that mass selection at high plant densities and early planting dates at diverse geographical locations did not produce cycles adapted to specific environmental conditions.     

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.     

Phenotypic recurrent selection in common bean (Phaseolus vulgaris L.) based on performance of S2 progenies

Summary The effect of a recurrent selection procedure for improving seed yield per plant was evaluated in common bean. Progress was registered after three cycles of recurrent selection with S2 progeny evaluation performed on the grain yield/plant. Gain from selection was estimated by field testing 45 random S2 lines from each of the C0, C1 and C2 populations. Response to selection for seed yield/plant was 6 g from C0 to C1 and 4.4 g from C1 to C2. The seed yield improvement was due principally to an increase in pods/plant; little contribution was provided by the 1000-seed weight and seeds/pod traits. Broad-sense heritability and genotypic variance for grain yield remained high in all cycles which suggests further gain from additional selection cycles. Grain yield/plant is significantly correlated to pods/plant and seeds/pod traits in all cycles, indicating that plants with favourable combinations of these traits could be identified. The proposed recurrent selection procedure appears to be effective in improving the population and extracting superior genotypes for varietal development.     

Combining ability,maternal, and reciprocal effects of elite early-maturing maize population hybrids

Choosing germplasm based on elite and diverse genetic sources is essential for the genetic improvement of maize (Zea mays L.) hybrids. The objectives of this research were to evaluate the agronomic and economic potential of maize population and single-cross hybrids and whether significant maternal (ME) and reciprocal effects (RE) reside in elite population hybrids for seed production purposes. Seven elite maize populations currently under recurrent selection at North Dakota State University (NDSU) [NDSCD(M-S)C11, NDSAB(MER-FS)C14, BS21(R)C7, BS22(R)C7, LEAMING(S)C4, CGL(S₁-S₂)C5 and CGSS(S₁-S₂)C5] were crossed in a diallel mating design to form 42 population hybrids, including their reciprocals. The 42 population hybrids with eight single-cross hybrids were evaluated at six U.S. North Central locations in 2005. Data collected across locations indicated that differences across genotypes were significant (P ≤ 0.05) for all traits observed, except for grain yield ear components. General combining ability (GCA) effects were on average larger than specific combining ability (SCA) effects. ME and RE were not significant for all traits, except for ear height. The large grain yield differences between macro-environments were reflected in the ranking of genotypes, with BS21(R)C7 × BS22(R)C7 being the top performer in eastern environments and CGSS(S1-S2)C5 × NDSAB(MER-FS)C14 being the top one across western environments where drought is the major limitation. The increased ethanol production and demand from maize make test weight (and grain quality), earliness, lodging resistance, and drought tolerance as important as grain yield for maintaining a sustainable maize-ethanol relationship. Part of the thesis submitted by McDonald B. Jumbo in partial fulfillment of the requirements for a MS degree at North Dakota State University.     

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.     

MS1与MS1-HS两种选择方法在玉米群体ZZ4中的改良效果比较Ⅰ.主要农艺性状的变化

对中综4号（ZZ4）完成了4轮改良S1-半同胞联合家系选择（简称MS1-HS）和4轮改良S1后代选择（简称MS1）。结果表明：以籽粒产量为主要目标的MS1-HS选择，每轮群体自身产量获得3.6%的遗传增益，群体S1后代籽粒产量可获得6.6%的增益；MS1选择每轮群体则可获得4.0%的遗传增益，群体S1后代籽粒产量可获得7.3%的增益。单穗籽粒产量     

Potential of wild germplasm for increasing yield of grain sorghum

Summary Sorghum [Sorghum bicolor (L.) Moench] backcross populations containing 3 to 50% wild germplasm were evaluated in south central India for grain yield and nine related traits. No individual BC₀F₂- to BC₂F₂-derived lines were high transgressive segregates for grain yield. Only 1.5% of all BC₃F₂- or BC₄F₂-derived lines were transgressive segragates, with 26% higher mean grain yield than their respective recurrent parents. The ten highest-yielding BC₂F₂- to BC₄F₂-derived lines per mating having parent CK60B yielded an average of 14% more than CK60B, which was, at the 5% level, a statistically significant difference. However, the increased yield was associated with increased plant height. The highest-yilding lines from RS/R/A2725 x virgatum and RS/R/A2725 x verticilliflorum were an average of 13.5% higher-yielding than RS/R/A2725 (a significant difference) and were equal in plant height. Selection increased BC₂ mean grain yields by 6 to 27%. Population mean yield, mean yield of selected lines, and frequency of high-yielding lines were highest in the BC₄.Journal paper no. 380, ICRISAT, Patancheru, India; Journal paper no. J-11114, Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, USA.     

两种轮回选择方法对玉米群体主要性状的改良效果

研究了控制双亲混合选择和半同胞-S2:3(HS-S2:3)轮回选择对2个玉米基础群体P_4C_0和P_5C_0主要性状的改良效果.结果表明,对于基础群体P_4C_0,其改良群体P_4HSC_1、P_4MSC_1和P_4MSC_2的单株产量分别比P_4C_0提高21.64%,10.29%和8.70%,达显著或极显著水平;对于基础群体P_5C_0,其改良群体P_5HSC_1的单株产量比P_5C_0降低7.53%,达显著水平;改良群体P_5MSC_1和P_5MSC_2平均单株产量变化与P_5C_0相比,分别降低和提高了2.67%和3.65%,均未达到显著水平.控制双亲混合选择改良群体,其产量的显著改进伴随着株高和穗位高的显著增加;HS-S2:3轮回选择改良群体,不同基础群体,其产量和株高、穗位高的改良效果不同.两种选择方法改良群体,多数性状的表型变异系数随着选择的进行有所下降,但也有部分性状变异系数变化较小或有所增大,群体内仍保持了较丰富的遗传变异,且以控制双亲混合选择保持群体遗传多样性的效果更好.     

Reciprocal recurrent selection for multitrait indices in maize

Summary Reciprocal recurrent selection was carried out with two populations of maize (Zea mays L.) having good combining ability. We selected for higher grain yield, early maturity, shorter plant height and lodging resistance. Two cycles were completed in two years (four seasons), by resorting to late planting of S1 lines for recombination in the main season in which top-cross families were assessed. Top-crosses and selfings were made in the off-season. The original and improved versions of the populations and their crosses were evaluated in multilocation trials. The superiority of the population hybrid was 10.3% for grain yield, 5.5% for plant height and 1.8 days to silk. The improved hybrid had delayed leaf senescence and better resistance to lodging and post-flowering stalk rots. Among the yield components, only ear girth showed improvement. Syn 2 of the improved population cross showed a yield reduction of 6.2% in comparison to Syn 1. Intrapopulation gains were not significant except for lodging resistance in one population.     

Responses to selection and changes in combining ability after three cycles of a modified reciprocal recurrent selection in maize

This research reports responses to selection and changes in general (GCA) and specific (SCA) combining abilities after three cycles of a modified reciprocal recurrent selection procedure (MRRS) in EPB-4 and EPB-5 maize populations. In the MRRS procedure a cycle can be completed in 1 or 2 years depending on the availability of winter breeding nurseries. The original and the three selection cycles of the two populations per se (eight entries) and the partial diallel developed from the crosses between them (16 entries) were evaluated in six environments. Realized response to selection on the population cross was 7.25% cycle⁻¹ for grain yield, −13.63% cycle⁻¹ for plant lodging, and 11.93% cyle⁻¹ for prolificacy, whereas plant and ear heights remained unchanged. GCA estimates increased with selection cycles for both populations for grain yield and prolificacy, and decreased for plant lodging, indicating that the frequency of favorable alleles with additive effects for these traits increased with the MRRS cycles in both populations. SCA estimates increased for grain yield and prolificacy indicating that the frequency of favorable complementary alleles at loci with non-additive effects in the reciprocal populations increased with the MRRS cycles. For grain yield, SCA effects increased more than GCA effects with selection cycles, indicating that MRRS exploited more the non-additive effects than the additive effects for the improvement of this trait. The overall results showed that the MRRS procedure was highly effective in improving the population cross, exploiting both GCA and SCA effects.     

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.     

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.     

Why SR52 is such a great maize hybrid? II. Heritability,correlation and path-coefficient analyses

Although exceptional heterosis for yield in the world’s first commercial single cross maize (Zea mays L.) hybrid SR52 has been confirmed, the role of secondary traits hasn’t been established. Objectives of this study were to establish relationship between grain yield and secondary traits, while assessing heritability and genotypic variation in SR52’s segregating populations. Knowledge on associations between yield and secondary traits would be crucial in extracting productive inbred lines from the population. Traits were subjected to correlation and path-coefficient analyses. Path analysis model accounted for over 70% of variation (R²) in all populations. Consistently high positive correlations with grain yield were observed for ear length and number of kernel rows on ear. Ear girth (0.19), and number of kernels per row (0.48) showed high direct effects on yield in the F₂ population and the trend was consistent in the backcrosses. Positive indirect effects of most traits on grain yield were negligible with the exception of kernel per row via total number of kernels on ear, which was above 0.40 in the F₂ and BCP1. Ear length can be exploited for indirect selection for yield in SR52’s segregating generations. 100-kernel weight and number of kernel rows on ear can, to a lesser extent, be targeted in selecting for grain yield. High to medium phenotypic variability in segregating generations of SR52 for traits such as ear length, number kernel rows on ear and grain yield should give impetus to selection of productive inbred lines from SR52 hybrid because of presence of diversity in the gene pool.     

An evaluation for genetic variation within maize inbred lines maintained by sib-mating and self-pollination

Summary Maintaining maize (Zea mays L.) inbred lines without genetic change is an important concern of maize breeders and seed producers. Long-time inbred lines, however, have been shown to be genetically unstable, and with selection pressure acting on the resulting genetic variation, these lines have evolved into different strains. The objective of this study was to compare maintenance of line integrity under reproduction by sib-mating and self-pollination in ear-to-row progenies. Ten lines, varying from 5 to 35 generations of previous ear-to-row selfing, were maintained for 11 successive generations under each method of reproduction. Alternate generations were compared by using a randomized complete-block design with each family of lines as a separate experiment. Data were collected for 10 plant and yield traits: pollen shed and silk emergence dates, plant and ear heights, tassel branch number, kernel row number, ear length and diameter, grain yield, and 300-kernel weight. Summarizing for F-tests over all traits and experiments, 30% were significant among sib-mated generations and 56% among selfed generations. Also, overall generation means of the two methods were different for 51% of the comparisons, and the selfed lines were less vigorous for 79% of the significant comparisons. It was concluded that sib-mating lessens the effect of genetic instability and that a reproduction system of sib-mating with intermittent generations of selfing may be more beneficial than continuous ear-to-row selfing for certain lines.Joint contribution: USDA-ARS, and Journal Paper No. J-11880 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project No. 2194.     

Yield response to honeycomb selection in maize

Summary This research evaluated the response to three cycles of mass honeycomb selection based on the grain yields of widely-spaced plants from the F₂ generation of a maize (Zea mays L.) single cross hybrid. Frequency distributions of individual plant yields in the selection plots showed strong positive skewness. A significant linear yield increase of 11.23% per cycle compared to the check was obtained. Correlated responses were the significant reduction in days to mid-silking, increases in ear and plant heights and in prolificacy. The selected population was similar to the original hybrid in days to mid-silking, ear and plant heights, but had significantly more ears per plant. It is concluded that mass honeycomb selection at wide spacings was effective in improving grain yield and prolificacy but may produce correlated responses in some other agronomic traits similar to those obtained with other selection schemes.     

玉米人工合成群体配合力效应及遗传潜势研究

选用6个自交系为测验种, 采用NCII遗传交配设计, 对以我国西南地区优良玉米地方种质巫溪14, 兰花早和北美, 热、 亚热带种质为主体的人工合成群体LBM、 WBM、 LLS、 WLS和两个美国优良群体BSSSR、 BS16等6个群体的配合力效应及遗传潜势进行了系统评估。 两年两地(武汉、 安阳)的研究结果表明： LBM、 WBM、 WLS群体的单株