Evaluation of whitefly-mediated inoculation techniques to screen Lycopersicon esculentum and wild relatives for resistance to Tomato yellow leaf curl virus

For two consecutive years nine hybrids and three varieties of tomato, four Lycopersicon peruvianum and four Lycopersicon chilense accessions were screened for Tomato yellow leaf curl virus (TYLCV) resistance. Three inoculation techniques using Bemisia tabaci, the vector of TYLCV, were compared: (1) artificial mass inoculation-simultaneous infection of cultivated and wild material in greenhouses; (2) artificial cage inoculation-individual infection in insect-proof cages; (3) natural field infection. Artificial inoculations led to higher levels of infection, but different patterns of response to each inoculation technique were found depending on the resistance level. Tomato varieties showed an important fruit set reduction after both artificial and natural inoculations. In contrast, field infection was milder in tomato hybrids, in which yield was barely affected. These hybrids showed a wide range of reactions with the two artificial inoculation techniques, but infection was always more severe after mass inoculation. Extreme severity of mass infection made it difficult to differentiate among variable degrees of resistance that were more reliably detected with cage inoculation. The hybrids F3524, F3522, Fiona, and Tyking showed the highest level of resistance. F3524 and F3522 had an acceptable yield in field and cage assays, but their resistance collapsed under massive conditions of infection. Tyking and Fiona exhibited the best response in all conditions, although their yield was moderately reduced in mass assays. Mass inoculation was not adequate for the screening of wild Lycopersicon. Some susceptible plants escaped infection, probably as a consequence of non-preference mechanisms and loss of vector infectivity. Individual inoculation in cages prevented the risk of non-infection, ensuring 100% disease incidence. This technique allowed the selection of highly resistant wild sources. L. chilense LA 1969 and LA 1963 had the highest level of resistance with the three inoculation techniques. L. peruvianum PI-126944 and L. chilense LA 1932, which were only tested in mass and field conditions, also exhibited a promising response. The results proved that the inoculation technique influences the response of tomato and wild Lycopersicon spp to TYLCV. It is concluded that artificial cage inoculation, although more time-consuming, is the most efficient, adequate, and reliable technique to screen both cultivated and wild Lycopersicon species for resistance to TYLCV. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrate reductase and nitrite reductase as targets to study gene silencing phenomena in transgenic plants

Nitrate assimilation is a fundamental function in any plant including those that can fix atmospheric nitrogen in symbiosis with soil bacteria. In recent years, attempts have been made to understand the biological significance of the complex regulation of this pathway using genetic engineering techniques. Transgenic plants that either over- or under-express genes of the nitrate assimilation pathway were created in order to determine whether such directed changes affect the regulation of the metabolism. Apart from interesting physiological results, unexpected gene silencing phenomena have been observed resulting from the introduction of five different transgenes derived from either the tobacco Nia or Nii genes encoding nitrate reductase and nitrite reductase, respectively. In this review, each of these five silencing phenomena is described, with the emphasis on the advantages provided by the use of both Nia and Nii genes to analyze the molecular and genetic basis of gene silencing in transgenic plants.     

A proposal for aluminum tolerance selection in white oat under hydroponic conditions

White oat genotypes were subjected to Al stress in hydroponic conditions in order to verify the viability of methods based on minimum nutrient solution (MNS) in comparison to complete nutrient solution (CNS), commonly used in the characterization and selection for Al tolerance in this species. The experimental design was completely randomized blocks with three replicates composed of 10 seedlings each. Six white oat genotypes subjected to different Al levels in minimum (0, 3, 6, and 9 mg L⁻¹) and complete (0, 10, 20, and 30 mg L⁻¹) solutions were evaluated. In this evaluation, the MNS was efficient in identifying aluminum-tolerant, white oat genotypes under hydroponics. The root growth resumption showed to be the most effective trait in the aluminum-tolerant plant selection. At concentrations equal to or higher than 3 mg Al L⁻¹ in minimum and 10 mg Al L⁻¹ in complete solution, severe damage caused by the toxic element on root development was verified. The white oat cultivars UFRGS 14, ALBASUL, and BARBARASUL showed aluminum tolerance in the tested conditions.     

Inheritance of trichome density in Ethiopian mustard leaves

A pubescent mutant of Ethiopian mustard (Brassica carinata A. Braun), N2-9531, was developed from the glabrous line C-101. The objective of this research was to study the inheritance of trichome density in this mutant. Plants of N2-9531 and C-101 were reciprocally crossed and F₁, F₂, and BC₁F₁ generations were analysed for trichome density. The average trichome density differed in the reciprocal F₁ and F₂ generations, indicating partial cytoplasmic effects. The trichome density of F₁ plants was lower than the midparent value, revealing a partial dominance of absence over high trichome density. Segregation in the F₂ and BC₁F₁ generations approximated 1:4:6:4:1 and 1:2:1 ratios, respectively indicating that two independent loci (H ₁ and H ₂) acting in an additive manner contributed equally to the expression of trichome density. The proposed genotypes were h ₁ h ₁ h ₂ h ₂ for N2-9531 and H ₁ H ₁ H ₂ H ₂ for C-101. The simple inheritance of this trait should facilitate the transfer of leaf pubescence to other Ethiopian mustard lines. This revised version was published online in July 2006 with corrections to the Cover Date.     

Exploring the recent upsurge in productivity disparities among European regions

This paper analyses thse evolution of productivity disparities across 156 European regions in the period 2000–2015. Using regional data, a battery of inequality indexes enables us to assess the extent of regional disparities. After confirming that labour productivity is the main component of income disparities, a dynamic shift-share analysis is carried out at a 10-industry level of disaggregation. The study evaluates the relative role of the three components underlying the disparities in regional productivity: changes in the industry mix, and within- and between-industry productivity gaps. The main results can be summarised as follows. First, regional disparities are on the rise again in the EU. Second, most regions are now closer to the average, while a small group of the richest regions are moving further away. Third, the main drivers of productivity disparities are within-industry differences in labour productivity with regard to the richest regions and, less importantly, the specialisation of the richest regions in more progressive industries. Finally, the net effect of structural change is still making a positive contribution to convergence with the leading regions.     

Increasing biodiversity of irrigated rice in Africa by interspecific crossing of Oryza glaberrima (Steud.) × O. sativa indica (L.)

The African rice Oryza glaberrima, traditionally cultivated since more than 3.500 years, is of poor agronomic performance but resistant/tolerant to various stresses and diseases. The introduction of these characters into O. sativa cultivars is difficult since crossing barriers cause spikelet sterility in F1. Backcrossing can restore fertility and recently facilitated the development of fertile O. glaberrima × O. sativa ssp. japonica hybrid progenies for rain fed systems. With the objective to gain access to African rice germplasm for improvement of irrigated rice, crosses were performed with eighteen O. glaberrima and twenty O. sativa ssp. indica accessions. In total about one hundred F1-hybrid grains were obtained. The F1 plants were all completely sterile and backcrossing (BC) to O. sativa was performed in order to restore spikelet fertility. Monitoring of Tog5681 × IR64 hybrid progenies under field conditions revealed a broad genetic diversity within the BC₁ and BC₂ populations. Some BC₁ and BC₂ progeny plants outperformed the O. sativa parent, indicating that the heterozygocity level and complementary gene action after two backcrosses are still sufficient to positively influence plant vigor. Spikelet fertility of progenies was highly variable, but almost complete fertility was already observed within the BC₁F₂ population. High spikelet fertility was preserved in one out of two analyzed BC₁F₃ families and inmost of the BC₂F₃ families. The ability to restore spikelet fertility within few generations and the potential of the genetic diversity present in interspecific progenies facilitates the development of plant types specifically designed for the African irrigated and lowland environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of resistance to systemic symptom expression of Melon necrotic spot virus (MNSV) in Cucumis melo L. `Doublon'

In melon (Cucumis melo L.) a resistance mechanism to Melon necrotic spot virus (MNSV) controlled by a single recessive gene called nsv has been reported. We found that following mechanical inoculation of the virus C. melo cv. ‘Doublon’ shows only local reaction, but it does not develop any systemic symptom and the virus only can be recovered from the local lesions. This reaction could be considered as a new source of resistance to MNSV. In this work,the genetic control of this behaviour in the progenies from the cross ‘Doublon’ × ‘ANC-42’ (a susceptible line) is studied. We report two complete dominant genes, which we propose to call Melon necrotic resistance 1 (Mnr1) andMelon necrotic resistance 2 (Mnr2), controlling this character. The genetic linkage between one of these genes and nsv in the populations derived from the cross between ‘Doublon’ and ‘PMR-5’ (a resistant line) is also reported. The map distance between these two loci was estimated to be 19 cm. This revised version was published online in July 2006 with corrections to the Cover Date.     

An Integrative Approach to Value‐Added Planning: From Community Needs to Local Authority Revenue

The concept of value‐added planning (as part of the Valuing Attractive Landscapes in the Urban Economy, INTERREG IVB North West Europe Project) is introduced in this paper to facilitate integrative planning, focusing on the benefits that use and non‐use green spaces can provide to an urban area. The aim is to stress the need to plan for, and protect, green spaces in urban areas by determining the economic values connected to the green spaces and relate that values to community benefit and local authority revenue. The paper identifies tools that can be used to determine the economic value of green spaces based on the environmental, social, and economic benefits. The first section (value) refers to the social value of green spaces as determined from the public perspective and introduces the workbench method as a tool to assist with participatory planning and capturing of the social benefits of green spaces. The second section (added) refers to the environmental benefits of green spaces and, by means of the Green Credit Tool, introduces ways to ensure the protection of the green resources in an area. The final section (planning) refers to the economic benefit of green space, bringing use values and non‐use values of green spaces together. The paper concludes with an integrative framework for value‐added planning, incorporating all the tools presented in the paper, capturing the social, environmental, and economic benefits of green spaces and relating it to community benefit and local authority revenue.     

Genomic prediction of the general combining ability of maize lines (Zea mays L.) and the performance of their single crosses

The objective of this study was to assess the effectiveness of genomic selection (GS) on predicting the general combining ability (GCA) of maize lines and the performance of their single crosses. Eight maize lines developed from the different self‐pollination generations of Chalqueño race, along with their 24 single crosses, were evaluated in the field during the years of 2011, 2012 and 2013. Genomic prediction results using genotyping‐by‐sequencing‐based single nucleotide polymorphisms showed that the GCA classification of the parental lines estimated from the SNP information was consistent with the phenotypic classification of the lines evaluated from the field trial data. The prediction accuracy values estimated from the cross‐validation method ranged from 0.49 to 0.61 in the different prediction models. Yield performance of the unevaluated single crosses was predicted based on their SNP information. The total genetic variance of the yield of the single crosses was most explained by the GCA effects. Compared with phenotyping method, GS is a more effective and efficient approach to predict the GCA of maize lines and their hybrid performance.     

Wheat pollen dispersal under semiarid field conditions: potential outcrossing with Triticum aestivum and Triticum turgidum

Isolation distance is the main barrier to crop-to-crop gene-flow. A 3-year study assessed the maximum potential outcrossing under field conditions between two wheat cultivars (Triticum aestivum L.) and between wheat and durum wheat (Triticum turgidum L. var. durum). Outcrossing was measured by seed set on emasculated recipient plants placed at four sides with different distances from a 3 m × 3 m T. aestivum (cultivar Chinese Spring) pollen source. Frequencies of seed set at 0 m distance were 45% (37–56%) for T. aestivum cultivars and 18% (5–30%) with T. turgidum. These values agree with hybridization in non-limiting pollen conditions measured by manual crosses in greenhouse. The number of pollen grains and the outcrossing frequencies decreased at increasing distances influenced by the prevailing wind direction. Under semiarid conditions of this assay, viable pollen was found 14 m from the pollen source, with a maximum distance of 8 m at which cross-pollination decreases below 1%. Ambient conditions affect pollen viability, hybridization and pollen dispersal. Data presented in this paper emphasize the major role played by environmental conditions in outcrossing. Data obtained in one area may therefore not coincide with the prevailing situation in different locations and climates.