Synchronization of flowering in maize (Zea mays L.) by the genetic system pg11 pg12

Summary The mutant genotype pg11pg11 pg12pg12-epistasis of double recessive factors-determines greater precocity of flowering. The possibility of using this mutant in the production of hybrid seed as a mean of synchronizing flowering in parent strains of different earliness is studied. The differences between mutant and green control genotypes in the characters of days to pollen shedding, pollen production, and height of plants are evaluated. Four mutant lines are considered together with their respective green near-isolines in two distinct localities and across four successive plantings.The mutant near-isolines presented lower values than those of the green near-isolines for all the characters. The maximum reductions in days to flowring were obtained in early plantings and late maturity strains. The reduction in pollen production was about 50%. The reduced height of the mutants is explained, at least in part, by the correlation of this factor with days to flowering. The mutants did not prove to be more sensitive to the environment than their green near-isolines. Seed production was not studied since the mutant is very deficient for this character and it could therefore only be utilized as the male parent. We concluded that the mutant, could be used to synchronize flowering in the industrial production of hybrid seed.     

Techniques for the vegetative propagation of maize (Zea mays L.)

Summary Techniques for the vegetative progapation of maize are described. The techniques were successful for a long-season, day length-sensitive variety of maize.     

Breeding for provitamin A biofortification of maize (Zea mays L.)

Vitamin A deficiency is widely prevailing in children and women of developing countries. Deficiency of vitamin A causes night blindness, growth retardation, xerophthalmia and increases the susceptibility against epidemic diseases. Among different interventions of overcoming malnutrition, biofortification is the most acceptable and preferred intervention among researchers, growers and consumers. Maize is grown and consumed in those regions where vitamin A deficiency is most prevalent; thus, targeting this crop for provitamin A biofortification is the most appropriate solution. Different breeding strategies including diversity analysis, introduction and stability analysis of exotic germplasm, hybridization, heterosis breeding, mutagenesis and marker‐assisted selection are practised for exploring maize germplasm and development of provitamin A‐enriched cultivars. Genome‐wide association selection and development of transgenic maize genotypes are also being practised, whereas RNA interference and genome editing tools could also be used as potential strategies for provitamin A biofortification of maize genotypes. The use of these breeding strategies for provitamin A biofortification of maize is comprehensively reviewed to provide a working outline for maize breeders.     

Genetic dissection of haploid male fertility in maize (Zea mays L.)

Haploid genome doubling is a key limiting step of haploid breeding in maize. Spontaneous restoration of haploid male fertility (HMF) provides a more promising method than the artificial doubling process. To reveal the genetic basis of HMF, haploids were obtained from the offspring of 285 F_2:3 families, derived from the cross Zheng58 × K22. The F_2:3 families were used as the female donor and Yu high inducer No. 1 (YHI‐1) as the male inducer line. The rates of HMF from each family line were evaluated at two field sites over two planting seasons. HMF displayed incomplete dominance. Transgressive segregation of haploids from F_2:3 families was observed relative to haploids derived from the two parents of the mapping population. A total of nine quantitative trait loci (QTL) were detected, which were distributed on chromosomes 1, 3, 4, 7 and 8. Three major QTL, qHMF3b, qHMF7a and qHMF7b were detected in both locations, respectively. These QTL could be useful to predict the ability of spontaneous haploid genome doubling, and to accelerate the haploid breeding process by introgression or aggregation of those QTL.     

Zinc biofortification of maize (Zea mays L.): Status and challenges

Zn deficiency is one of the leading health problems in children and women of developing countries. Different interventions could be used to overcome malnutrition, but biofortification is most impactful, convenient, sustainable and acceptable intervention. Maize is one of the major crops grown and consumed in the regions with prevalent Zn malnutrition; therefore, this is suitable target for Zn biofortification. Zn biofortification of maize could be achieved through agronomic and genetic approaches. Discussion of agronomic approaches with genetic approaches is prerequisite because soils in developing countries are deficit of Zn and availability of Zn in soils is mandatory for estimating the genetic responses of maize genotypes through genetic approaches. Seed priming, foliar and soil applications are agronomic tools for biofortification, but solo and combined applications of these treatments have different effects on Zn enrichment. Genetic approaches include the increase of Zn bioavailability or increase of kernel Zn concentration. Zn bioavailability could be increased by reducing the anti‐nutritional factors or by increasing the bioavailability enhancers. Kernel Zn concentration could be improved through hybridization and selections, whereas genetically engineered attempts for improving Zn uptake from soil, loading in xylem, remobilization in grains and sequestration in endosperm can further improve the kernel Zn concentration. Key challenges associated with dissemination of Zn biofortified maize are also under discussion in this draft. Current review emphasized all of above‐mentioned contents to provide roadmap for the development of Zn biofortified maize genotypes to curb the global Zn malnutrition.     

Heterosis in relation to genetic divergence in maize (Zea mays L.)

Summary The magnitude of heterosis was examined in relation to genetic divergence among 10 parents in a 10 × 10 diallel cross of maize. The 10 parents (varieties) were selected on the basis of multivariate analysis of quantitative characters using Mahalanobis' D²-statistic from a lot of 64 varieties of maize belonging to different geograshical regions of the world. The magnitude of heterosis for grain yield and its components was found to be higher with moderate (intermediate) parential diversity than with extreme ones. The results indicated that not only the genetic diversity but the high per se performance with respect to specific characters of interest should be taken into consideration also while selecting parents for hybridization.     

The early stress response of maize (Zea mays L.) to chloride salinity

Chloride is a micronutrient required for photosynthesis but when applied in the concentration of a macronutrient, it may also promote growth by regulating turgor. However, if chloride accumulates excessively, it can induce toxicity. The aim of this study was to identify physiological dysfunctions in maize (Zea mays L.) that arise in response to excessive chloride ion accumulation. For this, a novel water sensor was employed for the first time allowing the in vivo measurement of water content in the plant by using two near IR‐wavelengths with different absorption of water. This enabled to analyse whether water imbalances occurred. Chloride was given together with calcium as companying counter cation. Results show that most of the tested maize genotypes were able to maintain growth, photosynthesis and normal water content when stressed with concentrations as high as 757.1 mg chloride/kg soil dry matter. Leaf blades accumulated only 8.5 mg chloride/g dry matter, with the most genotypes not even showing salt stress necrosis at the leaves. A comparison between more tolerant and more sensitive genotypes revealed that restriction of chloride root‐to‐shoot translocation is a trait of chloride tolerance.     

Mapping QTLs in breeding for drought tolerance in maize (Zea mays L.)

Summary Grain yield in the maize (Zea mays L) plant is sensitive to drought in the period three weeks either side of flowering. Maize is well-adapted to the use of restriction fragment length polymorphisms (RFLPs) to identify a tight linkage between gene(s) controlling the quantitative trait and a molecular marker. We have determined the chromosomal locations of quantitative trait loci (QTLs) affecting grain yield under drought, anthesis-silking interval, and number of ears per plant. The F₃ families derived from the cross SD34(tolerant) × SD35 (intolerant) were evaluated for these traits in a two replicated experiment. RFLP analysis of the maize genome included non-radioactive DNA-DNA hybridization detection using chemiluminescence. To identify QTLs underlying tolerance to drought, the mean phenotypic performances of F₃ families were compared based on genotypic classification at each of 70 RFLP marker loci. The genetic linkage map assembled from these markers was in good agreement with previously published maps. The phenotypic correlations between yield and other traits were highly significant. In the combined analyses, genomic regions significantly affecting tolerance to drought were found on chromosomes 1,3,5,6, and 8. For yield, a total of 50% of the phenotypic variance could be explained by five putative QTLs. Different types of gene action were found for the putative QTLs for the three traits.     

Temperature adaptation of tropical highland maize (Zea mays L.) during early growth and in controlled conditions

For economic and ecological reasons, the chilling tolerance of maize must be further improved. This seems to be possible by the introgression of tropical highland germplasm if chilling and heat tolerance can be combined to obtain a high yield consistency. Two adapted and two semi-exotic highland varieties were grown at 16, 25 and 30°C until the third and sixth leaf stage. Thereafter, some plants were transplanted and grown at 24°C in the glasshouse until anthesis. Exotic germplasm improved the leaf appearance and shoot growth during the early heterotrophic phase at all temperatures, with a marked advantage at low temperature. This superiority was almost completely lost during the succeeding autotrophic growth phase with some residual effects at low temperature and a marked relative retardation in leaf appearance and growth at high temperature. Relative growth rates (RGR) of exotic germplasm were not superior at low temperature or inferior at high temperature. At low temperature, their comparatively reduced leaf area ratio (LAR) was still compensated by a high net assimilation rate (NAR). Their expression of the latter trait was comparatively decreased at a high temperature, which explained the low RGR. Early growth at low and medium temperatures had similar effects on final leaf number for all varieties; a high temperature increased the final leaf number up to 20%, especially in exotic germplasm. In conclusion, the good early vigor of Mexican highland germplasm seems to be mainly restricted to the heterotrophic phase; a relation to adaptative mechanisms, such as a low LAR, must be overcome for an efficient utilization in conventional breeding programs.     

转基因玉米NK603基体标准物质研制

转基因安全管理和标识制度的实施需要标准化的检测方法和转基因检测标准物质,转基因标准物质是获得准确、可靠、可比检测结果的保证。目前,转基因玉米NK603已在我国批准进口用作加工原料,其安全监管亟须制备标准物质。本研究将筛选后的转基因玉米NK603杂合种子和对应的非转基因受体种子,按转基因质量分数为60.0mg g^-1、100.0 mg g^-1、1000 mg g^-1 (理论值)的比例配置了3个梯度浓度水平的转基因基体标准物质。利用二重微滴数字聚合酶链式反应(droplet digital polymerase chain reaction, ddPCR)对研制的标准物质进行均匀性与稳定性检测。结果表明:研制的标准物质均匀性良好,可在60℃下运输14 d,稳定性不低于6个月。同时,由8家实验室采用二重ddPCR方法联合测定标准物质NK603转化体与内标基因的拷贝数比值,其标准值及不确定度为:(2.75±0.26)%、(4.68±0.39)%、(51.8±3.7)%。本批标物使用时最小取样量100 mg。可用于转基因食品和饲料...     

Identification of maize (Zea mays L.) cultivars by the surface relief of the kernel pericarp

Summary The relief of the outer surface of the kernel pericarp of 17 cultivars was examined to determine if relief characteristics could be used to describe and distinguish cultivars. Distinct differences in pattern, cell relief height and cell width were found among the cultivars. Over all cultivars, the means ranged from 1.00 to 2.98 m for cell relief height and from 15.3 to 27.6 m for cell width. Comparisons of single cross hybrids having all possible combinations of C103 and Oh43 as the female parent and Ag13 and R177 as the male parent indicated that the differences involving only one parent could be readily detected. The results indicated that relief patterns are quite cultivar-specific and could be used to describe and distinguish cultivars.Journal Series No. 5381, Florida Agricultural Experiment Station.     

Breeding for yield, in mixtures of common beans (Phaseolus vulgaris L.) and maize (Zea mays L.)

Summary Despite the growing industrialization, technification and transformation that is happening in the agriculture around the world, and despite that agricultural research has always concentrated its effort on sole crops, multiple cropping systems have historically been important for common bean production in tropical countries. The reasons for this fact, are economical and social, as well as biological. Bean breeders have always been questioned on their work, because the development of new varieties is usually done in sole crop, but the varieties are grown in either systems. This paper addresses a set of questions that are usually presented to the breeders, in light of the evidence obtained from many trials conducted in Brazil and in the U.S.A.: Will the genotypes bred for sole crop conditions, perform well when grown in intercrop; How different should a genotype be, for cultivation in intercropping compared to genotypes developed for sole crop conditions; Is there a need for special breeding programs for intercropping and How could a breeding program focus the question of multiple (associated) cropping?     

Genetic variation for resistance to low-temperature photoinhibition of photosynthesis in maize (Zea mays L.)

Summary In the partially allogamous faba bean, yield and yield stability can be improved significantly by heterozygosity and heterogeneity. The commercial production of hybrid varieties for the full exploitation of heterosis is still unfeasible. Hence, the breeding of synthetic varieties has repeatedly been recommended. The present study aimed at investigating whether and to what extent effects due to heterozygosity and heterogeneity occur in such varieties, particularly in relation to Syn-generation. A sample of 36 inbred lines (Vicia faba L. minor) was used to generate several entries of different population structure, e.g. blends of inbred lines (=Syn-0), experimental synthetics of generations Syn-1 to Syn-4 and polycross progenies. In 1986 to 1991 these entries were evaluated together with their parental lines grown in pure stands in six series of multi-locational field trials in West Germany. The yield of the synthetics increased with successive Syn-generations and asymptotically approached its maximum by as early as generations Syn-2 or Syn-3. The yield increase was mainly caused by heterozygosity. In two synthetics the yield increase corresponded to about one-half to two-thirds of the mid-parent heterosis. Effects due to heterogeneity were small and mostly non-significant. In one out of three expriments significant effects due to seed source were observed which, however, did not alter the yield increase with successive Syn-generations. Hence, Syn-generations Syn-2 or Syn-3 may be sold to the farmer.     

Development and mapping of gene-tagged SNP markers in laccases of maize (Zea mays L.)

Laccases, EC 1.10.3.2 or p -diphenol : dioxygen oxidoreductases, have been proposed to be involved in the oxidative polymerization of monolignols into lignins in plants. While 17 laccases have been identified in Arabidopsis , only five ( ZmLac1–5 ) have so far been identified in maize. By a bioinformatic approach, 14 putative laccases were identified in maize. One putative laccase was identical to ZmLac1 , while five were highly homologous to either ZmLac4 or ZmLac5 . Sequence alignment of allelic sequences enabled the development of TaqMan single nucleotide polymorphism (SNP) markers for nine putative laccases. Four of these gene-tagged SNP markers were validated in a doubled-haploid mapping population of 140 individuals, mapping these loci to chromosomes 1, 2, 3 and 7, respectively.     

Effects of selection for color intensity on antioxidant capacity in maize (Zea mays L.)

Maize kernels with diverse colors have pigments and other substances with antioxidant capacity that can be highly beneficial for human health. Our objectives were to analyze antioxidant capacity of the different maize kernel colors, to investigate if selection for color intensity increases antioxidant capacity and to check the effect of bakery processing on antioxidant capacity. Pigment content was directly related to antioxidant capacity in maize kernels and also to the hydrophilic fraction, while the lipophilic fraction was not related to antioxidant capacity. Visual selection for kernel color increased anthocyanin content from 0.55 to 1.13 μmol/g of fresh weight in one unique cycle of selection. The traditional method for making maize bread out of whole maize flour has not significant effects on pigment content or antioxidant capacity. Therefore, maize bread made out of black or purple maize provides significant amounts of antioxidant substances potentially beneficial for human health.     

玉米（Zea mays L.）×大刍草（Zea diploperennis L.）远缘杂交选育玉米自交系的研究

为了丰富玉米遗传变异,从1990年起,我们进行了玉米(Zea mays L.)和多年生二倍体大刍草(Zea diploperennis L.)远缘杂交的研究。经过5年8个世代的杂交、回交和自交选择,目前已获得抗逆性、抗病虫能力较强,农艺性状优良的玉米自交系14个。在测配1000个杂交组合中,所选系表现出较高的一般配合力和特殊配合力。实践证明,这是一条导入外缘种质、拓宽玉米遗传基础,进一步提高杂交种增产潜力的途径之一。