Residual allergenicity of amino acid-based and extensively hydrolysed cow’s milk formulas

Background. Criteria for labelling infant feeds as suitable for the dietary management of cow’s milk protein allergy (CMPA) rely on proving the hypoallergenicity of such feeds or clinical studies showing that the feeds are tolerated by 90% of children with proven CMPA. South African (SA) labelling legislation does not indicate what testing is necessary to prove hypoallergenicity.Objectives. To evaluate all extensively hydrolysed cow’s milk formulas and amino acid-based formulas available in SA for residual allergen content, protein size and amino-acid content.Results. All amino-acid and extensively hydrolysed formulas were found to be similar in composition, with no residual cow’s milk allergens detectable by enzyme-linked immunosorbent assay. Furthermore, proteins were absent and only small molecules in the size range of amino acids and possibly of very small oligopeptides were detected.Conclusions. These findings indicate that the formulas are extremely likely to be compliant with the definition of hypoallergenicity as tolerance in 90% of proven sufferers from cow’s milk allergy. The formulas may therefore be labelled as suitable for the dietary management of infants with CMPA

Identification of Thinopyrum distichum chromosomes responsible for its salt tolerance

A Thinopyrum distichuml 4× rye (Secale cereale) hybrid with genomes J1dJ2dRR was pollinated with diploid rye and mostly yielded F1 offspring with 21 chromosomes (two complete rye genomes and seven Thinopyrum chromosomes). Apparently, the closely related homoeologous chromosomes of the J1d and J2d genomes regularly formed bivalents during megasporogenesis, and egg cells mostly received a random, yet balanced set of seven Thinopyrum chromosomes. F1 plants were tested for salt tolerance and a set of fifteen highly salt-tolerant F1 plants were selected and maintained as clones for several years. These were C-banded and the Thinopyrum chromosomes contained in each were determined. By comparing segregation patterns it was now possible to group the Thinopyrum chromosomes into seven homoeologous pairs. For each of four homoeologous pairs, one of its members occurred at a higher than expected frequency, implying that these chromosomes are expressed under salt stress conditions. The results could be confirmed by backcrossing two of the most tolerant F1 plants to diploid rye. While the critical chromosomes can be identified through C-banding, an attempt was made to also find a RFLP marker for each. RFLP probes, diagnostic for the group 2, 3, 4 and 5 homoeologues of wheat, detected polymorphisms on the respective critical Thinopyrum chromosomes. However, the preliminary allocation of the critical chromosomes to homoeology groups needs to be confirmed using more and varied markers.Articl

SCAR markers that specifically tag chromosomes 2D of wheat and 2J 1d of Thinopyrum distichum

A SCAR marker for Thinopyrum distichum chromosome 2J1d (involved in salt tolerance) also amplified a slightly larger fragment in chromosome 2D of common wheat and substituted hexaploid triticale. The Thinopyrum and wheat derived fragments were isolated and used to develop two new and highly specific markers for 2J1dL and 2DL, respectively. The chromosome 2J1dL marker is useful in attempts to introgress salt tolerance into cultivated wheat and triticale whereas the 2DL marker can be used for rapid identification of hexaploid triticales with the 2D(2R) chromosome substitution.Articl

Identification of leaf rust resistance genes in Triticum species for transfer to common wheat

A total of 877 Triticum accessions (27 species) were screened for resistance to leaf rust (Puccinia recondita f. sp. tritici) using mixed inoculum of pathotypes UVPrt2, UVPrt3, UVPrtS, UVPrt9 and UVPrt13. Of these, 206 accessions were resistant/moderately resistant to all races. An attempt was made to cross each resistant accession with common wheat and to determine if resistance is expressed sufficiently in the presence of wheat genomes. Seventy nine accessions have not yet been crossed successfully, while the remaining 127 (representing 19 species) were crossed with common wheat. A number of transfer attempts failed in the F1 as a result of suppression of resistance (44 accessions) or formation of embryoless or non-viable seeds/seedlings (13 accessions). The resistance of 70 hybrids is fully expressed and these are now in various stages of back-crossing to wheat. The resistance was confirmed by retesting the species sources of the 70 successful combinations with the individual leaf rust pathotypes.Articl

A genetic study of the gametocidal effect of the Lr19 translocation of common wheat

The Lr19 translocation is preferentially transmitted to the progeny of a heterozygote due to the actions of at least two genes, Sd1 and Sd2 (new designation). However, only Sd2 occurs in the recombinant, Lr19-149, and often causes self-elimination of the recombined translocated segment in heterozygotes. The degree of segregation distortion is determined by the interaction of the Sd genes with polygenes (responder genes) on various wheat chromosomes. In this study suspected responder alleles derived from 'Inia 66' or 'Indis' (chromosomes 2A, 2B, 3B, 5B, 5D and 6D) appeared mostly to be partially dominant to overdominant over the 'Chinese Spring' derived alleles. A specific allele may not necessarily have the same effect (suppression or enhancement) in different genetic backgrounds. Responder genes may not fully compensate for the absence of a homologue in a hemizygote which may then produce effects quite different from those of the homo- and heterozygotes.Articl

Modification of the Aegilops neglecta - Common wheat Lr62/Yr42 translocation through allosyndetic pairing induction

The Lr62/Yr42 translocation comprises mostly allen chromatin and retains only the very distal end of wheat chromosome arm 6AL, including the telomere. The large amount of foreign chromatin prohibits commercial use of the resistance and an attempt was therefore made to exchange some of the introgressed chromatin for wheat chromatin. Plants heterozygous for the translocation, but lacking the Ph1 locus were testcrossed with Chinese Spring nullisomic 6A tetrasomic 6B or nullisomic 6A tetrasomic 6D plants. Resistant (Lr62) testcross F1 progeny were evaluated for the presence of three marker loci and the data used to do a three-point genetic mapping analysis. Forty one recombinants were identified and characterised with further markers. The data revealed that Lr62/Yr42 occurs towards the distal end of 6AS and that the 6AS telomeres of the wheat and translocation chromosomes were homoeologous. While the wheat (Chinese Spring ph1b mutant) and translocated chromosomes 6A shared sufficient homoeology to allow for regular allosyndetic recombination, there were also major structural differences between them, including a duplication (marked by Xgwm334) and translocation (marked by XsopwT). The duplicated region occurred on chromosome 6A of the CS ph1b mutant and probably resulted from its inherent genomic instability. The structural differences caused irregular meiotic pairing and complex segregation data that were difficult to interpret. It was, however, possible to explain the majority of recombination products in keeping with the expected low frequency of allosyndetic recombination, and to identify the most promising recombinants. These retained both Lr62 and Yr42 within a comparatively small region of foreign DNA at the 6AS telomere.Articl

Development of SCAR markers for a Thinopyrum distichum chromosome that appears to be involved in salt tolerance

Sixty-seven F1 plants from the backcross: Thinopyrum distichuml tetraploid 'Henoch' rye// diploid 'Henoch' rye were cloned, tested for salt tolerance (2-4 replications per genotype) and ranked. Sixty RAPD primers were tested on the parental lines. Nine of these produced Thinopyrum specific fragments and were applied to the whole population. Correlations between salt tolerance and presence of the Thinopyrum specific bands were mostly significant but small, as would be expected with a trait involving genes on several chromosomes. The nine markers were then also tested on a group of 15 B1F1 plants from the same cross in which C-banding has identified the Thinopyrum chromosomes. It appeared that OPK6 (± 1060 bp) and OPK17 (± 652 bp) polymorphisms co-segregated with a chromosome putatively identified as belonging to homoeologous group 2 and implied in salt tolerance in a different study. The diagnostic RAPD bands were cloned and sequenced and specific SCAR primers were designed. These amplified DNA sequences specific for chromosome IIJ1d that will be very useful in future introgression attempts.Articl

Transfer of rust resistance genes from Triticum species to common wheat

A programme aiming to transfer leaf rust resistance genes identified in a collection of wild Triticum species was initiated in 1993. In 2000, 25 promising backcross populations were available, 19 of which bred true for resistance. Seedlings of the above lines were tested with nine leaf rust, four stem rust and two stripe rust pathotypes endemic to South Africa. A subset of five lines in which resistance (derived from T. dicoccoides, T. sharonense, T. speltoides and T. peregrinum) appeared to be integrated on wheat chromosomes and six addition lines with added chromosomes from T. kotschyi, T. peregrinum, T. umbellulatum, T. macrochaetum and T. neglectum appeared to have wide spectrum resistances, and were retained. In several instances promising stem rust and/or stripe rust resistance genes were co-transferred with leaf rust resistance. The stripe rust resistance was also effective to four Australian pathotypes and appeared to be novel. Temporary gene designations were assigned to the resistance genes in four euploid derivatives.Articl

Transfer of rust resistance genes from Triticum species to common wheat

A programme aiming to transfer leaf rust resistance genes identified in a collection of wild Triticum species was initiated in 1993. In 2000, 25 promising backcross populations were available, 19 of which bred true for resistance. Seedlings of the above lines were tested with nine leaf rust, four stem rust and two stripe rust pathotypes endemic to South Africa. A subset of five lines in which resistance (derived from T. dicoccoides, T. sharonense, T. speltoides and T. peregrinum) appeared to be integrated on wheat chromosomes and six addition lines with added chromosomes from T. kotschyi, T. peregrinum, T. umbellulatum, T. macrochaetum and T. neglectum appeared to have wide spectrum resistances, and were retained. In several instances promising stem rust and/or stripe rust resistance genes were co-transferred with leaf rust resistance. The stripe rust resistance was also effective to four Australian pathotypes and appeared to be novel. Temporary gene designations were assigned to the resistance genes in four euploid derivatives.Articl