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.     

Genotype by environment effects and selection for drought tolerance in tropical maize. II. Three-mode pattern analysis

A selection program in three tropical maize populations aimed to improve tolerance of mid-season to late season drought environments while maintaining grain yield (GY) potential. The selection process employed other attributes that included maintaining a constant anthesis date (AD) and, under drought, shortening the anthesis-silking interval (ASI) and increasing ear number per plant (EPP). Three-mode (genotypes × environments × attributes) pattern analysis, which consists of clustering and ordination, should be able to collectively interpret these changes from ten evaluation trials. Mixture maximum likelihood clustering identified four groups that indicated the populations' performance had changed with selection. Groups containing the advanced cycles of selection were higher yielding in most environments and had lower ASI and higher EPP, particularly in drought environments. Check entries with no selection for drought tolerance remained grouped with the initial cycles of selection. A 3 × 2 × 3 (genotypes by environments by attributes) principal component model explained 70% of the variation. For the first environmental component, ASI was shown to be highly negatively correlated with both GY and EPP while anthesis date (AD) was virtually uncorrelated with other traits. The second environmental component (explaining 10% of the variation) contrasted droughted and well-watered environments and showed that EPP and GY were better indicators of this contrast (in terms of changes in population performance) than were AD or ASI. Three-mode analysis demonstrated that improvements with selection occurred in both droughted and well-watered environments and clearly summarised the overall success of the breeding program. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Genotypic Variation for Cold Tolerance among Twelve Maize (Zea mays L.) Populations

The objectives of this study were (1) to ascertain the genetic differences for cold-tolerance traits in a series of diallel crosses among 12 maize populations grown in field experiments, and (2) to compare, in controlled environment rooms, the modification of various metabolic parameters of two sets of four F1 variety crosses which, according to the field experiments, differed largely in seedling early vigour (cold-tolerant [Ct] vs cold-sensitive [Cs] Fl sets). Under field conditions, cold-tolerance adaptability, as monitored by shoot dry matter accumulation, appeared genetically controlled; moreover, considerable differences existed among genotypes. Field data suggested that shoot dry weight was a good indicator of plant adaptability to periods of unfavorable cool conditions. The growth-chamber experiments showed that shoot dry weights of the two sets of hybrids (Ct vs Cs), were more uniform at the highest temperature regimes than under suboptimal temperatures. Moreover, the laboratory study indicated that the interval of time of attain a specific stage of development provided a meaningful and useful criterion for differentiating the capacity of maize plants to grow at low temperatures. Although a clear association between a particular metabolite and the capacity of plants to grow at low temperatures was not observed, it was of interest to note that the total N concentration in the shoot was significantly higher in the Ct plants compared to the Cs ones.     

A Dominant Inhibitor Gene Inhibits the Expression of Ht2 against Exserohilum turcicum Race 2 in Corn Inbred Lines Related to B14

The purpose of this study was to elucidate the genetic cause for the lack of express ion of the gene Ht2 against Exserohilum turcicum race 2 on certain genetic backgrounds related to the inbred line B14. Two such inbreds (A635Rp and B59), susceptible to this pathogen were crossed onto the inbred Oh43—-Ht2Ht2. The following generations: F₁, F₂, F₃, F₄, backcrosses to both parents, selfings of the backcrosses, in addition to the parent lines, were evaluated for Ht2 expression in this study. Plants of each generation were inoculated with E. turcicum race 2 and evaluated for the expression of the chlorotic-lesion resistance determined by the gene Ht2. In spite of the reported dominance of Ht2 on some genetic backgrounds, the F₁ generations studied here did not show Ht2 resistant lesions. The data presented herein suggest that B₁₄ and related inbred lines carry a dominant gene(I) that inhibits the expression of the Ht2 gene. Chi-square analyses of the reactions of 108 progeny families studied supported this hypothesis.     

Effects of decreasing soil water content on seminal lateral roots of young maize plants

Soil micropores that contain water at or below field capacity cannot be invaded by seminal or first‐order lateral roots of maize plants because their root diameters are larger than 10 μm. Hence, at soil‐water levels below field capacity plant roots must establish a new pore system by displacement of soil particles in order to access soil water. We investigated how decreasing soil water content (SWC) influences growth and morphology of the root system of young maize plants. Plants were grown in rhizotrons 40 cm wide, 50 cm high, and approximately 0.7 cm thick. Five SWC treatments were established by addition of increasing amounts of water to soil and thorough mixing before filling the rhizotrons. No water was added to treatments 1–4 throughout the experiment. Treatment 5 was watered frequently throughout the experiment to serve as a control. Seminal‐root length and SWC in soil layers 0–10, 10–20, 20–30, 30–40, and 40–50 cm were measured at intervals of 2–3 d on scanner images by image analysis. At 15 d after planting, for treatments 1–4 shoot dry weight and total root length were directly related to the amount of water added to the soil, and for treatments 4 and 5, total root length and shoot dry weights were similar. Length of seminal roots visible at the transparent surface of the rhizotron for all treatments was highest in the uppermost soil layer and decreased with distance from the soil surface. For all layers, seminal‐root elongation rate was at maximum above a SWC of 0.17 cm³ cm^–3, corresponding to a matric potential of –30 kPa. With decreasing SWC, elongation rate decreased, and 20% of maximum seminal root elongation rate was observed below SWC of 0.05 cm³ cm^–3. After destructive harvest for treatment 1–4, number of (root‐) tips per unit length of seminal root was found uninfluenced over the range of initial SWC from 0.10 to 0.26 cm³ cm^–3. However, initial SWC close to the permanent wilting point strongly increased number of tips. Average root length of first‐order lateral (FOL) roots increased as initial SWC increased, and the highest length was found for the frequently watered treatment 5. The results of the study suggest that the ability to produce new FOL roots across a wide range of SWC may give maize an adaptive advantage, because FOL root growth can rapidly adapt to changing soil moisture conditions.     

运用光谱技术改进Beer-Lambert定律的定量化及其应用研究

 运用简便、快捷的无损测试提供的归一化植被指数（normalized difference vegetation index, NDVI）方法，对Beer-Lambert定律进行定量化改进，构建了以NDVI为自变量的LAI预测模型，并采用不同年份、不同株型的玉米数据对其改进结果进行检验。结果表明，当生长55 d时，叶向值（LOV）显著不同的3种株型的NDVI、LAI和消光系数K的差异均最大；披散型（LOV≤30°）NDVI饱和点的出现较中间型和紧凑型为早；利用NDVI改进Beer-Lambert定律的定量预测模型能够敏感反映植株冠层结构参数的动态变化，且最适用于紧凑型品种。随着玉米育种目标更偏向培育偏紧凑型品种，其改进结果在育种栽培实际中更有利用价值。     

不同核背景的玉米CMS系内源激素关系研究

采用两套同核异质系 ,研究了不同核背景和不同孢质内源激素含量与玉米CMS的关系。结果表明 ,不同核背景以及不同孢质的CMS之间内源激素含量有差异 ;较高的ABA和较低GA、IAA含量、特别是较低的GA3 /ABA、IAA/ABA浓度可能是花粉发生败育的一个重要原因 ;不育系中较高的GA3 和IAA含量可能导致育性不稳定