228 research outputs found

    The twenty-first century, the century of plant breeding

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    To achieve global food security by 2050 primary production must almost be doubled, at least to 80% by increasing production per unit land. The challenge to plant breeding is tremendous. It is necessary to convince the public of this challenge, who are already dealing with concerns about climate change, a scarcity of good arable land, the demands placed on land with regard to biomass production, scarcity of water and phosphorous as well as increasing consumption of meat. In terms of breeding, concerns are the very small number of major crops and low rates of breeding progress in self-pollinating cereals. Society and politicians can be easily distracted from the dire need to invest in basic breeding research and breeding applications when so many environmental concerns are being emphasized. A holistic approach to these problems is essential. The focus here is on both the obstacles to be overcome and the opportunities to ensure global food security by producing excellent germplasm by 2050. This can be achieved by new technologies and genomics as well as the continuing development of more traditional breeding methodologie

    Genetic diversity of Swiss maize ( Zea mays L. ssp. mays ) assessed with individuals and bulks on agarose gels

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    About 65years ago, more than 150 Swiss maize landraces (Zea mays L. ssp. mays) of the flint type were collected and conserved ex situ. Due to the climatically and culturally diverse environment of the Alps, a considerable genetic diversity of this material was assumed. To prove this, an efficient method was required to carry out genetic profiling of all the accessions in the Swiss Gene Bank. Simple sequence repeat marker (SSR) profiling in combination with the visualization of the polymerase chain reaction (PCR) products on agarose gels was chosen. Here a set of 19 different landrace accessions was analyzed to: (i) investigate their genetic diversity, (ii) investigate and display the population structure and (iii) determine whether DNA bulks rather than single plants can be used for such analyses. Four repeated samples of one accession were found to be much closer to one another than to the rest of accessions. Furthermore, specific alleles were identified for several accessions. The PCR products of the bulked DNA samples represented only a small part of the variation revealed by the analysis of individuals. Loci with four base repeat motifs performed better in the analysis of bulks than loci with other repeat motifs. The correlation between genetic distance matrices, based on the analysis of individuals and bulks, respectively, was significant. Thus, the single plant approach allowed for sufficient differentiation of accessions, and DNA bulks visualized on agarose gels led to correlated genetic distances although a limited number of alleles were detected. Although the limited resolution of agarose gels likely causes some bias, profiling of larger sets with the individual plant approach appears feasible and more informative compared to the bulk analysis we conducte

    Root distribution and morphology of maize seedlings as affected by tillage and fertilizer placement

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    Suboptimal soil conditions are known to result in poor early growth of maize (Zea mays L.) in no-tillage (NT) systems in contrast with conventional tillage (CT) systems. However, most studies have generally focused on maize roots at later growth stages and/or do not give details on root morphology. In a 2-year field study at two locations (silt loam and loam soils) in the Swiss midlands, we investigated the impacts of tillage intensity, NT vs. CT, and NP-fertilizer sidebanding on the morphology, vertical and horizontal distribution, and nutrient uptake of maize roots at the V6 growth stage. The length density (RLD) and the length per diameter-class distribution (LDD) of the roots were determined from soil cores taken to a depth of 0.5 m and at distances of 0.05 and 0.15 m from both sides of the maize row. The temperature of the topsoil was lower, and the bulk density and penetration resistance were greater in the topsoil of NT compared with CT. The growth and the development of the shoot were slower in NT. RLD was greater and the mean root diameter smaller in CT than in NT, while the vertical and horizontal distribution of roots did not differ between CT and NT. RLD increased in the zone enriched by the sidebanded fertilizer, independent of the tillage system, but LDD did not change. The poorer growth of the roots and shoots of maize seedlings was presumably caused by the lower topsoil temperature in NT rather than by mechanical impedance. The placement of a starter fertilizer at planting under NT is emphasize

    Anatomy of Seedling Roots of Tropical Maize (Zea mays L.) Cultivars at Low Water Supply

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    Establishment of maize seedlings can be difficult at low soil moisture content. Anatomy of root metaxylem vessels may influence the capacity for water transport and respective genotypic differences might be useful for selection purposes. To test this, six tropical maize (Zea mays L.) cultivars were grown in large PVC tubes containing a sandy substrate at 5% (M5) and 10% (M10) moisture contents for 2 weeks. The percentage changes in root diameters due to M5 was similar for most cultivars but differed for main root types. Root diameters were not consistently related to metaxylem structure, but in a few cases, thin roots had smaller diameter metaxylem vessels. The M5 treatment reduced the number of late metaxylem vessels of primary roots by about 0 to 20%, while effects on nodal roots were slight. Generally, the ratio of cross-sectional areas between late and early metaxylem vessels increased from primary to seminal and nodal roots. Within the cultivar Tuxpefio this ratio was much reduced by M5. A few cultivars maintained the combined cross-sectional areas of metaxylem vessels at M5 in some main root types, but only one cultivar could achieve this for the total of cross-sectional areas of metaxylem vessels, calculated over all root axes, by increasing the number of seminal and nodal roots. These anatomical traits seemed to be mostly constitutive with limited response to an actual environment, but they could be decisive for the suitability of a cultivar to an environment with frequent water shortages during seedling establishmen

    Mapping of quantitative trait loci associated with chilling tolerance in maize (Zea mays L.) seedlings grown under field conditions

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    The effect of low growth temperature on morpho-physiological traits of maize was investigated by the means of a QTL analysis in a segregating F2:3 population grown under field conditions in Switzerland. Chlorophyll fluorescence parameters, leaf greenness, leaf area, shoot dry weight, and shoot nitrogen content were investigated at the seedling stage for two years. Maize was sown on two dates in each year; thus, plants sown early were exposed to low temperature, whereas those sown later developed under more favourable conditions. The main QTLs involved in the functioning of the photosynthetic apparatus at low temperature were stable across the cold environments and were also identified under controlled conditions with suboptimal temperature in a previous study. Based on the QTL analysis, relationships between chlorophyll fluorescence parameters and leaf greenness were moderate. This indicates that the extent and functioning of the photosynthetic machinery may be under different genetic control. The functioning of the photosynthetic apparatus in plants developed at low temperature in the field did not noticeably affect biomass accumulation; since there were no co-locations between QTLs for leaf area and shoot dry weight, biomass accumulation did not seem to be carbon-limited at the seedling stage under cool conditions in the fiel

    Assimilate transport in maize (Zea mays L.) seedlings at vertical low temperature gradients in the root zone

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    Even moderate chilling temperatures may cause important modifications in assimilate movement in maize seedlings from the shoot to the roots, but there is no information on long-distance transport of assimilates in plants subjected to vertical gradients of moderately low temperatures in the root zone. Seedlings of a chilling-tolerant (KW1074) and a chilling-sensitive inbred line (CM109) of maize were grown in a system that allowed the maintenance of temperature gradients between the topsoil (0-10 cm) and the subsoil (10-50 cm). After pregrowth at 24°C until the thirdleaf stage, plants were subjected to chilling-stress regimes for 6 d (17/17/17 °C, 17/17/12°C, 12/12/12°C, 12/12/17°C, air/topsoil/subsoil). The time taken for the assimilates to enter the phloem from the second leaf increased at low temperatures for both lines, but to a much greater extent in CM109. Although mainly influenced by air and topsoil temperature, low temperature in the subsoil also affected this trait in CM109. The speed of assimilate transport between the second leaf and the mesocotyl in KW1074 was strongly reduced by cool temperatures in the shoot and topsoil as well as by 12°C in the subsoil in CM109, because the latter line had a larger portion of its root system in the subsoil as compared to KW1074. The portion of assimilates allocated to the root decreased at low temperatures in both lines, but to a greater extent in CM 109, and was controlled mostly by the subsoil temperature. After rewarming, values of all measured parameters of assimilate transport returned to near pregrowth levels within a few day

    Rapid attainment of a doubled haploid line from transgenic maize ( Zea mays L.) plants by means of anther culture

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    Summary: We present a strategy for establishing a transgenic doubled haploid maize line from heterozygous transgenic material by means of anther culture. Compared to conventional inbreeding, the in vitro androgenesis technique enables a faster generation of virtually fully homozygous lines. Since the androgenic response is highly genotype-dependent, we crossed transgenic, non-androgenic plants carrying a herbicide resistance marker gene (pat, encoding for phosphinothricin acetyl transferase) with a highly androgenic genotype. The transgenic progenies were used as donor plants for anther culture. One transgenic and three non-transgenic doubled haploid lines have been established within approximately 1 yr. The homozygosity of all four doubled haploid lines was tested by analysis of simple sequence repeat (SSR) markers at 19 different loci. Polymorphisms were found between the lines but not within the lines indicating the homozygous nature of the entire plant genome gained by anther culture. Southern blot analysis revealed that the transgenic donor plants and their doubled haploid progeny exhibited the same integration pattern of the pat gene. No segregation of the herbicide resistance trait has been observed among the progeny of the transgenic doubled haploid lin

    QTL involved in the partial restoration of male fertility of C-type cytoplasmic male sterility in maize

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    Partial restoration of male fertility limits the use of C-type cytoplasmic male sterility (C-CMS) for the production of hybrid seeds in maize. Nevertheless, the genetic basis of the trait is still unknown. Therefore, the aim to this study was to identify genomic regions that govern partial restoration by means of a QTL analysis carried out in an F2 population (n=180). This population was derived from the Corn Belt inbred lines B37C and K55. F2BC1 progenies were phenotyped at three locations in Switzerland. Male fertility was rated according to the quality and number of anthers as well as the anthesis-silking interval. A weak effect of environment on the expression of partial restoration was reflected by high heritabilities of all fertility-related traits. Partial restoration was inherited like an oligogenic trait. Three major QTL regions were found consistently across environments in the chromosomal bins 2.09, 3.06 and 7.03. Therefore, a marker-assisted counter-selection of partial restoration is promising. Minor QTL regions were found on chromosomes 3, 4, 5, 6 and 8. A combination of partial restorer alleles at different QTL can lead to full restoration of fertility. The maternal parent was clearly involved in the partial restoration, because the restorer alleles at QTL in bins 2.09, 6.04 and 7.03 originated from B37. The three major QTL regions collocated with other restorer genes of maize, a phenomenon, which seems to be typical for restorer genes. Therefore, a study of the clusters of restorer genes in maize could lead to a better understanding of their evolution and function. In this respect, the long arm of chromosome 2 is particularly interesting, because it harbors restorer genes for the three major CMS systems (C, T and S) of maiz

    Mapping of QTLs for lateral and axile root growth of tropical maize

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    Maize genotypes may adapt to dry environments by avoiding desiccation by means of a deeper root system or by maintaining growth and water extraction at low water potentials. The aim of this study was to determine the quantitative genetic control of root growth and root morphology in a population of 236 recombinant inbred lines (RILs) from the cross between CML444 (high-yielding)×SC-Malawi (low-yielding), which segregates for the response to drought stress at flowering. The RILs and the parental lines were grown on blotting paper in growth pouches until the two-leaf stage under non-stressed conditions; the parents were additionally exposed to desiccation stress induced by polyethylene glycol with a molecular weight of 8000 Dalton (PEG-8000). The lengths of axile and lateral roots were measured non-destructively at 2, 5, 7 and 9days after germination, by scanning with an A4 scanner followed by digital image analysis. CML444 had a lower rate constant of lateral root elongation (kLat) than SC-Malawi, but the two genotypes did not differ in their response to desiccation. QTLs affecting root vigor, as depicted by increments in kLat, the elongation rate of axile roots (ERAx) and the number of axile roots (NoAx) were identified in bins 2.04 and 2.05. QTLs for NoAx and ERAx collocated with QTLs for yield parameters in bins 1.03-1.04 and 7.03-04. The correspondence of QTLs for axile root traits in bins 1.02-1.03 and 1.08 and QTLs for lateral roots traits in bins 2.04-2.07 in several mapping populations suggests the presence of genes controlling root growth in a wide range of genetic background

    Yield of tropical Asian maize (Zea mays L) at alternating row irrigation and at severe drought

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    Drought is a major reason for inconsistent grain yield of maize in lowland tropical and subtropical areas. In bimodal rainy seasons with unequal amounts of rainfall, the shorter season requires germplasm with sufficient residual yields at various situations of low water availability. Thus farmers will avoid the risk of cultivation failure. The respective adaptation of eight Thai hybrids was tested in two dry seasons from late November 2003 to April 2005. Furrow irrigation of 40 mm was applied at seven days intervals from planting to physiological maturity (control, W1); 50% less water supply than W1 from the sixth week onwards by alternating irrigation of one of two rows (W2); withholding water from 5 weeks after planting to the beginning of anthesis (W3). At W3, three hybrids excelled with yields above 350 g m-2, i.e. residual yields of more than two of them performed very well at W2 too, with more than 650 g m-2, a residual yield of about 80%. This genetic range is encouraging to breed for earlier hybrids that can be cultivated in the minor rainy season with a reduced risk of failure
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