No abstract

The beet-cyst nematode (Heterodera schachtii\ud Schmidt) is one of the major pests of sugar beet. The identification\ud of molecular markers associated with nematode tolerance\ud would be helpful for developing tolerant varieties. The\ud aim of this study was to identify single nucleotide polymorphism\ud (SNP) markers linked to nematode tolerance from the\ud Beta vulgaris ssp. maritima source WB242. A WB242-\ud derived F2 population was phenotyped for host-plant nematode\ud reaction revealing a 3:1 segregation ratio of the tolerant and\ud susceptible phenotypes and suggesting the action of a gene\ud designated as HsBvm-1. Bulked segregant analysis (BSA)\ud was used. The most tolerant and susceptible individuals were\ud pooled and subjected to restriction site associated DNA sequencing\ud (RAD-Seq) analysis, which identified 7,241 SNPs.\ud A subset of 384 candidate SNPs segregating between bulks\ud were genotyped on the 20 most-tolerant and most-susceptible\ud individuals, identifying a single marker (SNP192) showing\ud complete association with nematode tolerance. Segregation of\ud SNP192 confirmed the inheritance of tolerance by a single\ud gene. This association was further validated on a set of 26\ud commercial tolerant and susceptible varieties, showing the\ud presence of the SNP192 WB242-type allele only in the tolerant\ud varieties. We identified and mapped on chromosome 5 the first\ud nematode tolerance gene (HsBvm-1) from Beta vulgaris ssp.\ud maritima and released information on SNP192, a linked marker\ud valuable for high-throughput, marker-assisted breeding of nematode\ud tolerance in sugar beet

Beta vulgaris genetic resources are essential for broadening genetic base of sugar beet and developing cultivars adapted to adverse environmental conditions. Wild beets (sea beets, B. vulgaris spp. maritima and their naturalized introgressions with cultivated beets known as ruderal beets) harbor substantial genetic diversity that could be useful for beet improvement. Here, we compared molecular and morpho-physiological traits of wild beets collected on the Adriatic coast of Italy with sugar beet using eight primer-pairs amplifying 194 polymorphic fragments and four root traits (glucose and fructose content in the root tip, root elongation rate, number of the of root tips, total root length and its distribution among diameters ranges). Genetic diversity was higher in the sea beet accession, which may be due to the highly variable selection pressures that occur in heterogeneous ecological niches, compared with the ruderal and cultivated beets. Sea and sugar beet accessions showed contrasting root patterns in response to sulfate deprivation: sugar beet showed an increase of reducing sugars in the root tips and higher root elongation rate, and the sea beet accession showed an increase in root tip number, total root length and fine root length (average diameter\0.5 mm). The ruderal beet showed intermediary responses to sea and sugar beet accessions. AFLP and morpho-physiological cluster analyzes showed sea, ruderal and cultivated beets to be genetically distinct groups. The results of this study indicate variability in response to sulfate deprivation is present in undomesticated beets that could be deployed for sugar beet improvement

BackgroundGenomic information can be used to predict not only continuous but also categorical (e.g. binomial) traits. Several traits of interest in human medicine and agriculture present a discrete distribution of phenotypes (e.g. disease status). Root vigor in sugar beet (B. vulgaris) is an example of binomial trait of agronomic importance. In this paper, a panel of 192 SNPs (single nucleotide polymorphisms) was used to genotype 124 sugar beet individual plants from 18 lines, and to classify them as showing “high” or “low” root vigor.ResultsA threshold model was used to fit the relationship between binomial root vigor and SNP genotypes, through the matrix of genomic relationships between individuals in a genomic BLUP (G-BLUP) approach. From a 5-fold cross-validation scheme, 500 testing subsets were generated. The estimated average cross-validation error rate was 0.000731 (0.073%). Only 9 out of 12326 test observations (500 replicates for an average test set size of 24.65) were misclassified.ConclusionsThe estimated prediction accuracy was quite high. Such accurate predictions may be related to the high estimated heritability for root vigor (0.783) and to the few genes with large effect underlying the trait. Despite the sparse SNP panel, there was sufficient within-scaffold LD where SNPs with large effect on root vigor were located to allow for genome-enabled predictions to work.

The efficiency of sulfate uptake was evaluated in excised roots of 22 maize genotypes, 12 inbreds and 10 hybrids, in order to study the relationship between the kinetic characteristics of the uptake and the grain productivity. During root elongation, the uptake capacity showed a pulse which appeared when the root reached V3 to V2 of its final length. The size of the accumulated pool of sulfate was significantly correlated with the productivity. The kinetic parameters of the uptake, Vmax and Km, followed the same trend, showing pulses, whoxe maximum had the same position for Vmax and Km in each genotype. The variability with the genotype of the size and duration of the Vmax pulse was not strictly connected with that of Km. The main correlation between Vmax and Km patterns was the following; inbreds were generally characterized by low Vmax and low Km; hybrids by high Vmax and high Km. As a consequence, in most cases, the benefit of the heterotic stimulation of Vmax was contrasted by the loss of affinity of the transport system or the nutrients.