Genetic variation among European maize inbreds for resistance to the European corn borer and relation to agronomic traits

The univoltine European corn borer (ECB) has become a major limiting factor for maize (Zea mays L.) production in central Europe. The objective of this study was to survey the genetic variation for ECB resistance in European elite maize germplasm. Eighteen flint and 23 dent inbreds were screened under artificial ECB infestation at two locations in 1993 and 1994. Resistance was assessed by damage rating of broken plants, measurement of tunnel length in dissected stalks, and yield reduction in infested plots relative to insecticide-protected control plots. Flint lines showed significantly greater means for damage rating than dent lines with grain yield reduction of 35% and 24%, respectively. Significant genotypic variances among lines and high heritabilities were found for agronomic traits and damage rating. Heritabilities were intermediate for tunnel length and relative grain yield. Significant associations of days to silking, ear dry matter content, and dry matter yield of the whole plant with damage rating and tunnel length suggested a better resistance in late-maturing, high-yielding inbreds. Genotypic correlations of relative grain yield with tunnel length and damage rating ranged between ?0.46 and ?0.72. Partial correlations, eliminating the effect of flowering time, confirmed these associations. Damage rating of stalks is the most suitable trait for evaluation of ECB damage owing to its high heritability and easy recording. Tunnel length below the primary ear is a useful trait for assessing antibiosis because it is not correlated with days to silking. Inbreds with extreme resistance and susceptibility were identified which can be used as parents for establishing breeding and QTL mapping populations.     

Recurrent selection for maysin, a compound in maize silks, antibiotic to earworm

A thorough knowledge of the inheritance of maysin, a flavone glycoside with antibiosis to corn earworm, Helicoverpa zea Boddie, in the silks of maize will assist breeders in choosing the most efficient method of incorporating this trait into elite inbreds. Two breeding populations, one having exotic origin (EPM), the other from southern inbred lines (SIM) were subjected to six cycles of recurrent selection for increased silk maysin. Ten per cent of the individuals evaluated in populations were selected for recombination as S₁ progenies in each cycle. Progress was evaluated as C0 to C6 population cycles in a randomized complete‐block experiment with five replications in 1997 and 1998. Maysin fresh weights in silks of the C0 populations were 0.54% for EPM and 0.36% for SIM. Responses of 0.19% per cycle in EPM and 0.22% per cycle in SIM resulted in an EPM (C6) population with 1.76% maysin and an SIM (C6) population with 1.69% maysin. Silk maysin concentrations above 0.2% begin to substantially reduce larval growth and prevent completion of the life cycle when husk coverage is sufficient to force the insect to feed on silks while entering the ear. Chlorogenic acid and two analogues of maysin, apimaysin and 3′‐methoxymaysin, were found in such minor quantities in silks that they could not be credited with any impact on antibiotic activity against the insect. Selection has effectively increased silk maysin concentration in both EPM and SIM. Trait responses for maysin are highly heritable and will allow the plant breeder to introgress resistance to the corn earworm into elite material easily.     

Graphical Genotype of Maize Inbred B86 Revealed by RFLPs

The objective of this study was to investigate the origin of chromosome segments of maize (Zea mays L.) inbred B86 from its parental inbreds B52 and Oh43 using RFLPS. B86 was selected to combine resistance to the first and second brood of the European corn borer with the favorable agronomic performance of Oh43. RFLP analyses of the three inbreds were performed with three restriction enzymes (EcoRI, EcoRV, HindIII) and 178 DNA probes covering all ten maize chromosomes. For two DNA probes in combination with one enzyme, B86 showed a new RFLP pattern not present in the two parents. Based on results from 119 polymorphic DNA probes, the proportion of the B86 genome contributed by B52 (51.3 %) and Oh43 (48.7 %) was almost equal.     

Congruence of conventional and molecular studies to locate genes that control flavone synthesis in maize silks

The presence of maysin, a flavone glycoside, and its analogues in the silks of corn is an important defence against invasion of the ear by corn earworm in the southeastern USA. Three dent maize inbreds with high silk‐maysin concentrations were evaluated for chromosomal location of major genes controlling synthesis of three antibiotic chemicals by crossing them to a series of waxy‐marked chromosome 9 reciprocal translocations. The data indicated that genes for maysin and its analogues are probably present on the short arms of chromosomes 1 and 10, and long arms of chromosomes 5 and 8 for inbred line GT114, the short arms of chromosome 1 and 6, and the long arms of chromosome 5 and 8 for inbred line GE37, and the short arms of chromosomes 1 and 10, and the long arm of chromosome 4 for inbred line SC102. These results are in general agreement with other translocation studies on corn earworm injury to sweet corn inbreds and gene and restriction fragment length polymorphism marker studies to locate quantitative trait loci (QTL) for maysin synthesis, with the exception that QTL on chromosome 9 have been found to be strongly associated with flavone synthesis. The most significant concordance between conventional and molecular techniques for locating chromosome regions influencing synthesis of antibiotic chemicals from silks of high silk antibiosis sources is found for the short arm of chromosome 1. This region is the most likely one on which to place emphasis during the initial stages of transferring high‐maysin silks to elite inbred lines. A chromosome 1 marker plus at least one more from any chosen high‐maysin inbred source should be sufficient to transfer high maysin silks to other lines. Other markers may be needed for transfer of specific traits when recovering recurrent parent genome types in a backcrossing procedure.     

Mass selection for kernel depth in early maize

Summary Effectiveness of mass selection for kernel depth in an early maize (Zea mays L.) synthetic, i.e. NDSAB, was evaluated in eight North Dakato environments. Four cycles of selection for deeper kernels were evaluated for grain yield and associated traits by using corresponding randomly selected subpopulations of NDSAB to adjust out inbreeding effects on selected subpopulations. General combining ability (GCA) effects of selected subpopulations also were evaluated for these traits.Subpopulations selected from one to four cycles for deep kernels were reciprocally crossed to corresponding randomly selected subpopulations in a factorial mating design. Subpopulations, selfed subpopulations, and subpopulation crosses were evaluated for yield and associated traits. Subpopulations selected for deep kernels generally had deeper kernels, higher yields, heavier kernels, more kernel rows per ear, and lower test weights than corresponding randomly selected subpopulations. Differences in GCA effects among selected and unselected subpopulations generally corresponded to differences between selected and unselected parental subpopulations. Inbreeding effects from selfing were observed for all traits, but no average heterosis was detected when subpopulation crosses were compared to parental subpopulations. Reciprocal differences were observed for all traits except kernel depth, but these differences were inconsistent relative to whether deep kerneled females made superior hybrids to unselected females.Results supported the use of mass selection for kernel depth as a means of grain yield improvement in the short term for NDSAB. However, negative associations of kernel depth with test weight may restrict long term use of this procedure.Journal Article No. 1505 of the North Dakota Agric. Exp. Stn., Fargo     

Epistasis in Maize (Zea mays L.) III. Comparison of Single and Three-Way Crosses for Forage Traits

The importance of epistasis for forage performance and quality traits was studied in early maturing European maize (Zea mays L.) breeding materials. Sixty-six three-way crosses (3W), 33 of the flint x (dent · dent) and 33 of the dem × (flint · flint) type, were compared with the mean of their respective non-parental single crosses () using data obtained in six environments. For each of the 11 traits examined, at least 6 out of the 66 three-way crosses displayed significant (P < 0.05) epistatic deviations, calculated as – 3W. Averaged over crosses and environments, epistatic deviations were highly significant (P < 0,31] for 8 trails, but of minor importance except for grain yield. In general, the variance of epistatie deviations was appreciably smaller than the variance of genotype × environment interactions. Highly significant correlations occurred among epistatie deviations for silking date, dry matter content of ear, and dry matter yield of grain and stover. The reliability of predicting the performance of three-way crosses from 2W as opposed to assessing them directly was investigated as a function of the number of test environments. Disturbing e fleets of epistasis on prediction only became important under intense testing (> 3 or 4 environments), With fewer test environments, both procedures were almost equivalent, due to a smaller influence of genotype × environment interaction on the values, Epistasis is concluded to be of minor importance with regard to the optimum type of hybrid for forage use.     

Evaluation of Near Infra-red Reflectance Spectroscopy for Predicting Grain and Stover Quality Traits in Maize

The prediction of grain and stover quality parameters in maize {Zea mays L.) by near infra-red reflectance spectroscopy (NIRS) was studied. A total of 110 grain and 135 stover samples originating from different genotypes and environments were assayed. Calibration equations for content of crude protein (CP), crude fat (CF), starch (ST), and water soluble carbohydrates (WSC) in grain were obtained by multiple linear regression of known manual values on NIRS data from the odd numbered samples. Calibrations for CP, acid detergent fibre (ADF), in vitro digestible organic matter according to the Tilley & Terry (IVDOM-T & T) and the gas production (IVDOM-Gp) method, respectively, and metabolizable energy (ME) in stover were developed analogously. Equations were validated with the evennumbered .samples and for ME additionally with the 1584 stover samples from an experiment with 66 F₁ hybrids tested in six environments. The coefficients of multiple determination (R²) of the prediction equations ranged from 0.80 for IVDOM-Gp and ME in stover to 0.94 for CP in grain. Standard errors of calibration (SEC) and prediction (SEP) were in most cases not higher than commonly reported for conventional manual assays. With regard to the correct ranking of hybrids, prediction equations for ME applied well to stover samples from other environments with one exception. We concluded that NIRS can evaluate the quality traits investigated to a similar degree to that of conventional methods of analysis. Since NIRS is simple and safe to operate and allows rapid screening of several quality traits simultaneously, it should be particularly attractive for breeding purposes.     

Wheat embryogenesis and haploid production in wheat × maize hybrids

Summary Embryogenesis was analyzed in wheat × maize hybrids using paraffin sectioning. Embryogenesis in wheat × maize hybrids is different from that in self-pollinated wheat plants. Development of the embryo is not accompanied by the formation of an endosperm. The endosperm nuclei remain free in the cytoplasm, fail to advance into the cellular stage, and degenerate at a later time. The antipodal cells quickly degenerate in the fertilized ovaries of wheat × maize hybrids similar to self-pollinated ovaries. The antipodal cells remain normal in unpollinated ovaries. The pre-embryo will abort if it is allowed to develop on the plant, because of a nutritional shortage in the absence of an endosperm. Therefore, embryo rescue is necessary for haploid production from a wheat × maize hybrids. Haploid polyembryos were obtained from spikelet culture of wheat × maize hybrids. The formation of polyembryos is due to the cleavage of the pre-embryo and the effect of 2,4-D. The frequency of haploid embryo production and plant regeneration is affected significantly by maize genotypes, but not by wheat genotypes. The concentration of 2,4-D affects only the size of the embryo.     

从天冬-玉米的示范种植探讨"粮-药间套"增益模式

采用天冬单作、玉米单作和天冬-玉米套作3种种植模式,考查了整个生产过程中其主要生产资料和劳动力的投入以及产值等关键指标.对不同种植模式的经济效益对比分析结果表明,天冬-玉米套作比天冬单作增收21.8%,比玉米单作增收564.9%.天冬单作虽比玉米单作增收446.0%,但天冬种植三年后才能收获药材,没有短期收益.因此,3种模式中天冬-玉米套作的效果最佳.这一研究结果为种植业提供了一条"粮-药间套"的有效增益模式.     

Modified full-sib selection and best linear unbiased prediction of progeny performance in a European F2 maize population

Four cycles of modified recurrent full‐sib (FS) selection were conducted in an intermated F₂ population of European flint maize. The objectives of our study were to monitor trends across selection cycles in the estimates of population mean, inbreeding coefficients and variance components, and to investigate the usefulness of best linear unbiased prediction (BLUP) of progeny performance under the recurrent FS selection scheme applied. We used a selection rate of 25% for a selection index, based on grain yield and dry matter content. A pseudo‐factorial mating scheme was used for recombination. In this scheme, the selected FS families were divided into an upper‐ranking group of parents mated to the lower‐ranking group. Variance components were estimated with restricted maximum likelihood (REML). Average grain yield increased 1.2 t/ha per cycle, average grain moisture decreased 20.1 g/kg per cycle, and the selection index relative to the F₂ check entries decreased 0.3% per cycle. For a more precise calculation of selection response, the four cycles should be tested together in multi‐environmental trials. We observed a significant decrease in additive variance in the selection index, suggesting smaller future selection response. Predictions of FS family performance in Cn + 1 based on mean performance of parental FS families in Cn were of equal precision as those based on the mean additive genetic BLUP of their parents, and corresponding correlations were of moderate size for grain moisture and selection index.