In this study, eight transformed Solanum tuberosum L. plants, affected in their nitrate assimilatory pathway by the introduction of a tobacco nitrate reductase gene (Nia2), were cultivated in ...glasshouse conditions at INRA Ploudaniel (West Brittany, France). Two irrigation regimes were compared and plants were sampled at four stages of vegetation. Yield, tuber dry matter content, total nitrogen content, nitrate content in the whole plant, and nitrate reductase activities were studied. High frequency irrigation with nutritive solutions negatively affects both yield and dry matter content in tubers. Moreover, the introduction of the tobacco Nia2 gene in the potato genome does not seem to affect the agronomical parameters of the initial genotype apart from the nitrate content of tubers. Five transgenic genotypes out of eight, in fact, showed a drastic decrease (of around 98%) in their tuber nitrate content. This nitrate decrease in the tubers was also correlated with the presence of the mRNA transgene, whereas the potato nitrate reductase transcript does not seem to be expressed in wild‐type tubers. Regarding these genotypes, developmental stage and nutritive solution supply were found to have no effect on tuber nitrate content. In fact, tubers derived from these clones exhibited low nitrate content throughout the vegetation period, while nitrate accumulation in wild‐type tubers is progressive and increases sharply with high nutritive solution supply.
This study presents the development of a core collection capturing the genetic diversity of a collection of 350 tetraploid cultivated potato varieties (
Solanum tuberosum
L.). The core collection was ...established by using simple sequence repeats (SSR) data and the M strategy, which aims at maximizing the allelic diversity. A 48-core collection was defined which captured 99.5% of the SSR alleles used to establish it, and 96.9% of the SSR alleles which belonged to an independent set of markers. The defined core collection was further validated by analysing 35 agro-morphological traits. The class coverage value and the estimates of the Shannon-Weaver diversity index indicated a good representation of the phenotypic diversity in the core collection. Furthermore, the core set included accessions having the most desirable status for several agronomic traits. A linkage disequilibrium (LD) analysis, using data obtained with the SolCAP SNP array on the defined core collection, was performed. The population structure analysis showed that the core collection did not present a clear genetic structure. The linkage disequilibrium analysis carried out between markers located on the same pseudomolecule within 10,000 bp concluded that 41.3% of these pairs of SNP markers have a significant LD. We conclude that this core collection, representative of the genetic diversity of cultivated potato varieties, is a relevant tool for a first screening for genetic variation regarding novel traits of interest.
To find out new resistance sources to late blight in the wild germplasm for potato breeding, we examined the polygenic resistance of Solanum sparsipilum and S. spegazzinii by a quantitative trait ...locus (QTL) analysis. We performed stem and foliage tests under controlled conditions in two diploid mapping progenies. Four traits were selected for QTL detection. A total of 30 QTLs were mapped, with a large-effect QTL region on chromosome X detected in both potato relatives. The mapping of literature-derived markers highlighted colinearities with published late blight QTLs or R-genes. Results showed (a) the resistance potential of S. sparsipilum and S. spegazzinii for late blight control, and (b) the efficacy of the stem test as a complement to the foliage test to break down the complex late blight resistance into elementary components. The relationships of late blight resistance QTLs with R-genes and maturity QTLs are discussed.
Twenty transformed Solanum tuberosum plants issued from five different varieties and carrying a chimeric tobacco nitrate reductase gene (a truncated tobacco Nia2 coding sequence fused to the CaMV 35S ...promoter) were cultivated in field conditions at INRA Ploudaniel in 1999 and 2000. In 60% of the transgenic plants, the presence of the tobacco Nia2 transcript was detected by RT-PCR. These clones exhibited a drastic decrease in the nitrate content in tubers. Indeed the nitrate content decreased by about 95% in the tubers of transformed plants compared to nontransformed potato plants from the same variety. This decrease was correlated with a modified regulation of NR expression as revealed by a higher chlorate sensitivity of these transgenic lines. Two methods of nitrate content determination in tubers were also compared and were found to give similar results.
To decrease the environmental impact of treatments against late blight caused by
Phytophthora infestans
on potato, plant genetic resistance is a keystone in developing new culture strategies. ...Nonspecific resistance to late blight is a complex trait which is difficult to evaluate, while selection is both difficult and time consuming. However, we consider it is important to select for this type of resistance as it is a promising way to achieve durable resistance. In this study, parameters derived from disease progress curves (DPCs) were used to characterise the types of resistance among individuals of three tetraploid full-sib families named G1, B2, and K2. These families were composed of 280 (G1), 280 (B2), and 150 (K2) genotypes. Our aim was to avoid visual inspection of 5,710 DPCs and to identify genotypes exhibiting stable resistance. We used three parameters: the slope of the DPC, the date of appearance of the first symptoms in the tested genotypes compared with a susceptible standard, and the relative area under the disease progress curve (rAUDPC). Using an appropriate threshold for each parameter, we demonstrated that it is possible to classify the response of each genotype in one of the following categories: susceptible, non-specific resistance, specific resistance, non-specific resistance plus specific resistance (or specific resistance not overcome). Data were obtained each year from 2005 to 2007 under conditions of natural infection. According to the parameters analysed, non-specific resistance and specific resistance segregated in the families. The year effect was more than double the family effect for rAUDPC. Empirical adjustment of threshold values in a subsample of the tested genotypes led to an increase in the effectiveness of our classification method. Calculated classification enabled detection of stable genotypes in each family. The impact of the year effect differed with the family. In the G1 family, the distribution of genotypes in each category was relatively stable over the 3 years, whereas in K2, the proportion of genotypes demonstrating specific resistance alone increased, particularly in 2007. In the B2 family, the proportion of genotypes in the non-specific resistance category decreased from 40% to 15% from 2005 to 2006, and then remained stable in 2007. The heritabilities of the parameters ranged from 61% to 96% depending on the family and on the parameter concerned.
We investigated the physiological consequences for nitrogen metabolism and growth of the deregulated expression of an N-terminal-deleted tobacco nitrate reductase in two lines of potato (Solanum ...tuberosum L. cv Safrane). The transgenic plants showed a higher biomass accumulation, especially in tubers, but a constant nitrogen content per plant. This implies that the transformed lines had a reduced nitrogen concentration per unit of dry weight. A severe reduction in nitrate concentrations was also observed in all organs, but was more apparent in tubers where nitrate was almost undetectable in the transgenic lines. In leaves and roots, but not tubers, this nitrate decrease was accompanied by a statistically significant increase in the level of malate, which acts as a counter-anion for nitrate reduction. Apart from glutamine in tubers, no major changes in amino acid concentration were seen in leaves, roots or tubers. We conclude that enhancement of nitrate reduction rate leads to higher biomass production, probably by allowing a better allocation of N-resources to photosynthesis and C-metabolism.
In this study, eight transformed Solanum tuberosum L. plants, affected in their nitrate assimilatory pathway by the introduction of a tobacco nitrate reductase gene (Nia2), were cultivated in ...glasshouse conditions at INRA Ploudaniel (West Brittany, France). Two irrigation regimes were compared and plants were sampled at four stages of vegetation. Yield, tuber dry matter content, total nitrogen content, nitrate content in the whole plant, and nitrate reductase activities were studied. High frequency irrigation with nutritive solutions negatively affects both yield and dry matter content in tubers. Moreover, the introduction of the tobacco Nia2 gene in the potato genome does not seem to affect the agronomical parameters of the initial genotype apart from the nitrate content of tubers. Five transgenic genotypes out of eight, in fact, showed a drastic decrease (of around 98%) in their tuber nitrate content. This nitrate decrease in the tubers was also correlated with the presence of the mRNA transgene, whereas the potato nitrate reductase transcript does not seem to be expressed in wild-type tubers. Regarding these genotypes, developmental stage and nutritive solution supply were found to have no effect on tuber nitrate content. In fact, tubers derived from these clones exhibited low nitrate content throughout the vegetation period, while nitrate accumulation in wild-type tubers is progressive and increases sharply with high nutritive solution supply.
We have demonstrated the fabrication of a monolithic, 5-meter diameter, aluminum reflector with 17.4 \(\mu\)m RMS surface error. The reflector was designed to avoid the problem of pickup due to ...scattering from panel gaps in a large, millimeter-wavelength telescope that will be used for measurements on the cosmic microwave background.
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