Evaluation of five strategies for obtaining a core subset from a large genetic resource collection of durum wheat

The use of plant genetic resources contained in a large collection may be enhanced by specifying subsamples, called core samples. Five strategies for selecting a core sample from a collection of 3000 durum wheat accessions were applied and evaluated using four qualitative and eight quantitative spike characters. Each of the following strategies generated about 500 accessions for the core sample: random, random-systematic according to chronology of entry of the accessions into the collection, stratified by countryof-origin, stratified by log frequency by country-of-origin, and stratified by canonical variables. The first three strategies produced samples representative of the whole collection, but the remaining two produced the desired effect of increasing frequencies from less-represented countries-of-origin for several characters. The stratified canonical sample increased phenotypic variances. The quality of core samples is dependent upon good passport and evaluation data to partition the collection. The multivariate approach is extremely useful, but requires considerable data from the whole collection. Ecogeographic origin may be used in the absence of evaluation data on several characters to select useful core samples.     

Microsatellite analysis reveals a progressive widening of the genetic basis in the elite durum wheat germplasm

It has been argued that the level of genetic diversity in the modern durum wheat (Triticum turgidum L. var. durum) elite germplasm may have declined due to the high selection pressure applied in breeding programs. In this study, 58 accessions covering a wide spectrum of genetic diversity of the cultivated durum wheat gene pool were characterized with 70 microsatellite loci (or simple sequence repeats, SSRs). On average, SSRs detected 5.6 different allelic variants per locus, with a mean diversity index (DI) equal to 0.56, thus revealing a diversity content comparable to those previously observed with SSRs in other small-grain cereal gene pools. The mean genetic similarity value was equal to 0.44. A highly diagnostic SSR set has been identified. A high variation in allele size was detected among SSR loci, suggesting a different suitability of these loci for estimating genetic diversity. The B genome was characterized by an overall polymorphism significantly higher than that of the A genome. Genetic diversity is organised in well-distinct sub-groups identified by the corresponding foundation-genotypes. A large portion (92.7%) of the molecular variation detected within the group of 45 modern cvs was accounted for by SSR alleles tracing back to ten foundation-genotypes; among those, the most recent CIMMYT-derived founders were genetically distant from the old Mediterranean ones. On the other hand, rare alleles were abundant, suggesting that a large number of genetic introgressions contributed to the foundation of the well-diversified germplasm herein considered. The profiles of recently released varieties indicate that the level of genetic diversity present in the modern durum wheat germplasm has actually increased over time.Communicated by F. Salamini     

Population structure and long-range linkage disequilibrium in a durum wheat elite collection

A collection of 134 durum wheat accessions, mainly including cultivars (cvs.) representative of the major gene pools, was assembled and characterized with 70 SSRs for genetic diversity and level of long-range linkage disequilibrium (LD). Results of both a distance-based and a model-based (Bayesian) cluster analysis evidenced the presence of a structured diversity. In the model-based analysis, six to eight main distinct subpopulations were identified based on the molecular data. Only a relatively small portion (20%) of the molecular variation was accounted for by the geographical origin of the accessions. Major differences were detected between the North American and the Mediterranean cvs., while a considerable overlap characterized the cvs. from CIMMYT-ICARDA and Italy. The North American cvs. showed the highest within group mean genetic similarity (GS_m = 0.68). French cvs. revealed sizeable similarities with both the North American as well as the Italian and CIMMYT-ICARDA pools. Considering the germplasm as a whole, high levels of LD were found both at locus pairs with an intrachromosomal distance <50 cM as well as at those with distances more than 50 cM and independent (86, 52 and 54% of SSR pairs at p < 0.01, respectively). After re-evaluating LD within each of the three main subgroups identified through the analysis of the germplasm structure, the LD level remained high for tightly to moderately linked locus pairs (<20 cM apart), but was greatly reduced in the loosely linked (more than 50 cM apart) and independent locus pairs. The implications of these findings as to the possibility of using association mapping for gene/QTL discovery in durum wheat are discussed.     

Cadmium uptake and bioaccumulation in selected cultivars of durum wheat and flax as affected by soil type

Accumulation of cadmium (Cd) in crop plants is of great concern due to the potential for food chain contamination through the soil-root interface. Although Cd uptake varies considerably with plant species, the processes which determine the accumulation of Cd in plant tissues are affected by soil factors. The influence of soil type on Cd uptake by durum wheat (Triticum turgidum var. durum L.) and flax (Linum usitatissimum L.) was studied in a pot experiment under environmentally controlled growth chamber conditions. Four cultivars/lines of durum wheat (Kyle, Sceptre, DT 627, and DT 637) and three cultivars/lines of flax (Flanders, AC Emerson, and YSED 2) were grown in two Saskatchewan soils: an Orthic Gray Luvisol (low background Cd concentration; total/ABDTPA extractable Cd: 0.12/0.03 mg kg^-1, respectively) and a Dark Brown Chernozem (relatively high background Cd concentration; total/ABDTPA Cd: 0.34/0.17 mg kg^-1 respectively). Plant roots, stems, newly developed heads, and grain/seeds were analyzed for Cd concentration at three stages of plant growth: two and seven weeks after germination, and at plant maturity. The results showed that Cd bioaccumulation and distribution within the plants were strongly affected by both soil type and plant cultivar/line. The Cd concentration in roots leaves and stems varied at different stages of plant growth. However, all cultivars of both plant species grown in the Chernozemic soil accumulated more Cd in grain/seeds than plants grown in the Orthic Gray Luvisol soil. The different Cd accumulation pattern also corresponded to the levels of ABDTPA extractable and metal-organic complex bound soil Cd found in both soils. Large differences were found in grain Cd among the durum wheat cultivars grown in the same soil type, suggesting the importance of rhizosphere processes in Cd bioaccumulation and/or Cd transport processes within the plant. Distribution of Cd in parts of mature plants showed that durum grain contained up to 21 and 36% of the total amount of Cd taken up by the plants for the Orthic Gray Luvisol and Chernozemic soils, respectively. These results indicate the importance of studying Cd speciation, bioaccumulation and cycling in the environment for the management of agricultural soils and crops.     

Precise mapping of a locus affecting grain protein content in durum wheat

Grain protein content (GPC) is an important factor in pasta and breadmaking quality, and in human nutrition. It is also an important trait for wheat growers because premium prices are frequently paid for wheat with high GPC. A promising source for alleles to increase GPC was detected on chromosome 6B of Triticum turgidum var. dicoccoides accession FA-15-3 (DIC). Two previous quantitative trait locus (QTL) studies found that the positive effect of DIC-6B was associated to a single locus located between the centromere and the Nor-B2 locus on the short arm of chromosome 6B. Microsatellite markers Xgwm508 and Xgwm193 flanking the QTL region were used in this study to develop 20 new homozygous recombinant substitution lines (RSLs) with crossovers between these markers. These 20 RSLs, plus nine RSLs developed in previous studies were characterized with four new RFLP markers located within this chromosome segment. Grain protein content was determined in three field experiments organized as randomized complete block designs with ten replications each. The QTL peaks for protein content were located in the central region of a 2.7-cM interval between RFLP markers Xcdo365 and Xucw67 in the three experiments. Statistical analyses showed that almost all lines could be classified unequivocally within low- and high- protein groups, facilitating the mapping of this trait as a single Mendelian locus designated Gpc-6B1. The Gpc-6B1 locus was mapped 1.5-cM proximal to Xcdo365 and 1.2-cM distal to Xucw67. These new markers can be used to reduce the size of the DIC chromosome segment selected in marker-assisted selection programs. Markers Nor-B2 and Xucw66 flanking the previous two markers can be used to select against the DIC segment and reduce the linkage drag during the transfer of Gpc-6B1 into commercial bread and pasta wheat varieties. The precise mapping of the high GPC gene, the high frequency of recombinants recovered in the targeted region, and the recent development of a tetraploid BAC library including the Gpc-6B1 DIC allele are the first steps towards the map-based cloning of this gene.Communicated by J. Dvorak     

Response of durum wheat cultivars to immature embryo culture,callus induction and in vitro salt stress

Response of twenty eight cultivars of durum wheat (Triticum turgidum var. durum) to immature embryo culture, callus production and in vitro salt tolerance was evaluated. For assessment of cultivars to salt tolerance, growing morphogenic calli were exposed to different concentrations of NaCl (0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 and 2.1% w/v) added to the culture medium during two subsequent subcultures (4 weeks each). Comparison of cultivars for callus induction from immature embryo was based on callus induction frequency and fresh weight growth of callus (FWG). While, for salt tolerance, the relative fresh weight growth (RFWG) and necrosis percent of callus were used. There were significant differences among cultivars for potential of regeneration from immature embryo, and ‘Shahivandi’ a native durum wheat cultivar originating from western Iran was superior among the cultivars tested. The FWG distinguished cultivars more than callus induction frequency did for callus induction evaluation. Hence, a range of FWG from 1.23 to 14.65 g was observed in ‘Mexical-75’ and ‘Omrabi-5’ cultivars, respectively. Growing calli derived from cultivars ‘PI 40100’ and ‘Dipper-6’ showed superiority for tolerating salinity under in vitro conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Production of doubled haploids in durum wheat (Triticum turgidum L.) through isolated microspore culture

The objective of this work was to produce doubled haploid plants from durum wheat through the induction of androgenesis. A microspore culture technique was developed and used to produce fertile doubled haploid plants of agronomic interest. Five cultivars, one selected line, plus a collection of 20 F₁ crosses between different genotypes of high breeding value were used. Studies on several factors such as pre-treatments and media components were carried out in order to develop a protocol to regenerate green haploid plantlets. Anthers were pre-treated in 0.7 M mannitol. Microspores, from anther maceration, were plated on a C₁₇ induction culture medium with ovary co-culture. The optimum regeneration medium J25–8 was used. From 35 microspore isolations, 407 green plantlets were obtained. With this technique mature embryos were obtained. Green plants were regenerated from all genotypes used and approximately 67% of them were spontaneously doubled haploids. Some haploids and a very few polyploids plants were obtained. From the 407 plants, 275 were completely fertile and gave enough seeds to be assayed in the field. This protocol could be used complementary to or instead of the intergeneric crossing with maize as an economically feasible method to obtain doubled haploids from most durum wheat genotypes.     

The effect of metal diffusion and supply limitations on conditional stability constants determined for durum wheat roots

Conditional stability constants (log K), and binding site densities (Γ_max) for dissolved metals and biota are important input parameters for the Biotic Ligand Model. However, determination of these binding parameters is likely to be influenced by solution kinetics because roots have a large metal-binding capacity and can accumulate metals rapidly. The aim of this study was to determine if the rate of free metal ion diffusion to the root surface, and amount of metal in the bulk solution, is sufficient to accommodate the maximum root–metal accumulation capacity. The extent to which these kinetic limitations affect the magnitude of log K and Γ_max values was also assessed. Seven day old hydroponically grown durum wheat (Triticum turgidum L. var durum, cv ‘Arcola’) were exposed to solutions with p{Cu²⁺}s ranging from 10.54 to 2.26 (~20 °C, pH = 6.0, ionic strength = 0.03 M). Exposure solutions were prepared with and without the metal buffer nitrilotriacetic acid (NTA) so that the total amount of metal in the exposure solution, and net flux of metal to the root, could be varied. The results demonstrate that NTA enhances Cu accumulation at exposure p{Cu²⁺}s between 10 and 6. Comparison of the diffusive flux to the root with the metal flux into the root, for (−NTA) and (+NTA) Cu exposures, showed that the flux of the un-buffered free metal ion to the root was not large enough to accommodate the maximum Cu binding capacity between 10 and 6 p{Cu²⁺} in solution. The total amount of Cu in solution may have limited uptake for exposure p{Cu²⁺}s of 10.01 and 9.01, but the background concentrations of Cu in the control plants prevented definitive conclusions from being made within this exposure range. Similar results were found for Mn and Ni. For Cd, which had lower background concentrations in the roots, the amount of metal in solution did not limit uptake until a p{Cd²⁺} of 10.01. Limiting the supply of Cu²⁺ to the root (i.e. low {Cu²⁺}s with no NTA) caused only a moderate bias in Γ_max values, but suppressed the log K value by 3.44 log units. The log K values for Cd, Mn and Ni, in the absence of NTA, were more similar than expected, which suggests that the kinetics of free ion re-supply to the root surface limited metal uptake, as it did for Cu. Section Editor: T. B. Kinraide     

Allozyme and morphological variability,outcrossing rate and core collection formation in lentil germplasm

Summary A survey of qualitative genetic variation at 3 morphological trait loci, 17 isozyme loci and a putative isozyme locus (amylase) was made for 105 lentil (Lens culinaris Medikus) germplasm accessions from Chile, Greece and Turkey. New alleles were found for Lap-1, Me-2, Pgm-c, Pgm-p and 6-Pgd-c. The average proportion of polymorphic loci per population was 0.19, with a range of 0 to 0.42 over populations. Germplasm from Chile was equally variable to that from Greece and Turkey on the basis of individual loci and in a multilocus sense, despite its post-Columbus introduction to the New World. Evidence was found from associations between allelic states at different loci of a complex multilocus structure of lentil populations. A single multilocus genotype represented 10.2% of all plants sampled. The rate of outcrossing varied from 2.2% and 2.9% in Turkish and Greek landraces to 6.6% among Chilean populations. Using the survey data, a random sampling strategy for core collection formation was compared with two stratified sampling methods. The advantage of stratified sampling over random sampling was only significant at P=0.28.     

Screening methods for salinity tolerance: a case study with tetraploid wheat

Fast and effective glasshouse screening techniques that could identify genetic variation in salinity tolerance were tested. The objective was to produce screening techniques for selecting salt-tolerant progeny in breeding programs in which genes for salinity tolerance have been introduced by either conventional breeding or genetic engineering. A set of previously unexplored tetraploid wheat genotypes, from five subspecies of Triticum turgidum, were used in a case study for developing and validating glasshouse screening techniques for selecting for physiologically based traits that confer salinity tolerance. Salinity tolerance was defined as genotypic differences in biomass production in saline versus non-saline conditions over prolonged periods, of 3–4 weeks. Short-term experiments (1 week) measuring either biomass or leaf elongation rates revealed large decreases in growth rate due to the osmotic effect of the salt, but little genotypic differences, although there were genotypic differences in long-term experiments. Specific traits were assessed. Na⁺ exclusion correlated well with salinity tolerance in the durum subspecies, and K⁺/Na⁺ discrimination correlated to a lesser degree. Both traits were environmentally robust, being independent of root temperature and factors that might influence transpiration rates such as light level. In the other four T. turgidum subspecies there was no correlation between salinity tolerance and Na⁺ accumulation or K⁺/Na⁺ discrimination, so other traits were examined. The trait of tolerance of high internal Na⁺ was assessed indirectly, by measuring chlorophyll retention. Five landraces were selected as maintaining green healthy leaves despite high levels of Na⁺ accumulation. Factors affecting field performance of genotypes selected by trait-based techniques are discussed.     

Accumulation of cadmium in near-isogenic lines of durum wheat (Triticum turgidum L. var durum): the role of transpiration

Concentrations of cadmium in the grain of durum wheat (Triticum turgidum L. var durum) are often above the internationally acceptable limit of 0.2 mg kg⁻¹. Cultivars that vary in concentrations of cadmium in the grain have been identified but the physiology behind differential accumulation has not been determined. Three pairs of near-isogenic lines (isolines) of durum wheat that vary in aboveground cadmium accumulation (8982-TL ‘high’ and ‘low’, W9260-BC ‘high’ and ‘low’, and W9261-BG ‘high’ and ‘low’) were used to test the hypothesis that the greater amounts of cadmium in shoots of the ‘high’ isolines are correlated with greater volumes of water transpired. In general, cadmium content was positively correlated with transpiration only in the ‘low’ isolines. Although shoots of the ‘high’ isolines of W9260-BC and W9261-BG contained higher concentrations of cadmium than did their corresponding ‘low’ isolines, they did not transpire larger volumes of water. In addition, isolines of 8982-TL transpired less water than did the other pairs of isolines yet both ‘high’ and ‘low’ isolines of 8982-TL contained higher amounts of cadmium than did the other pairs. The difference between ‘high’ and ‘low’ isolines appears to be related to the relative contribution of transpiration to cadmium translocation to the shoot. Increased transpiration was associated with increased cadmium content in the ‘low’ isolines but in the ‘high’ isolines increased cadmium in the shoot occurred independently of the volume of water transpired.     

Efficient and rapid <Emphasis Type="Italic">Agrobacterium-</Emphasis>mediated genetic transformation of durum wheat (<Emphasis Type="Italic">Triticum turgidum L. var. durum)</Emphasis> using additional virulence genes

Genetic transformation of wheat, using biolistics or Agrobacterium, underpins a range of specific research methods for identifying genes and studying their function in planta. Transgenic approaches to study and modify traits in durum wheat have lagged behind those for bread wheat. Here we report the use of Agrobacterium strain AGL1, with additional vir genes housed in a helper plasmid, to transform and regenerate the durum wheat variety Ofanto. The use of the basic pSoup helper plasmid with no additional vir genes failed to generate transformants, whereas the presence of either virG⁵⁴² or the 15 kb Komari fragment containing virB, virC and virG⁵⁴² produced transformation efficiencies of between 0.6 and 9.7%. Of the 42 transgenic plants made, all but one (which set very few seeds) appeared morphologically normal and produced between 100 and 300 viable seeds. The transgene copy number and the segregation ratios were found to be very similar to those previously reported for bread wheat. We believe that this is the first report describing successful genetic transformation of tetraploid durum wheat (Triticum turgidum L. var. durum) mediated by Agrobacterium tumefaciens using immature embryos as the explant.     

Methods of developing a core collection of annual Medicago species

A core collection is a subset of a large germplasm collection that contains accessions chosen to represent the genetic variability of the germplasm collection. The purpose of the core collection is to improve management and use of a germplasm collection. Core collections are usually assembled by grouping accessions and selecting from within these groups. The objective of this study was to compare 11 methods of assembling a core collection of the U.S. National collection of annual Medicago species. These methods differed in their use of passport and evaluation data as well as their selection strategy. Another objective was to compare core collections with sample sizes of 5%, 10% and 17% of the germplasm collection. Core collections assembled with evaluation data and cluster analysis better represented the germplasm collection than core collections assembled based solely on passport data and random selection of accessions, The Relative Diversity and the logarithm methods generated better core collections than the proportional method. The 5% and 10% sample size core collection were judged insufficient to represent the germplasm collection.     

Cytogenetic identification of Aegilops squarrosa chromosome additions in durum wheat

Summary A set of four normal chromosomes (1D, 2D, 3D, and 6D), and three translocation chromosomes (4DS·5DS, 5DL·7DS, and 7DL·4DL) involving all 14 chromosome arms of the D-genome were obtained as monosomic additions from Aegilops squarrosa (genome D, n=7) in Triticum durum Desf. cv PBW114 (genome AB, n=14). The cyclical translocation occurred during the synthesis of the amphiploid probably as a result of misdivision and reunion of the univalents during meiosis of the F₁ hybrid T. durum x A. Squarrosa. The amphiploid was backcrossed twice with the durum parent to obtain monosomic addition lines. The monosomic addition chromosomes were identified by C-banding and associated phenotypic traits. All monosomic addition lines were fertile. The development of disomic and ditelosomic addition lines is underway, which will be useful for cytogenetic analysis of individual D-genome chromosomes in the background of T. Durum.Contribution No. 90-117-J from the Wheat Genetics Resource Center and Kansas Agricultural Experiment Station, Kansas State University, Manhattan     

Copper uptake and phytotoxicity as assessed in situ for durum wheat (Triticum turgidum durum L.) cultivated in Cu-contaminated, former vineyard soils

This work assessed in situ, copper (Cu) uptake and phytotoxicity for durum wheat (Triticum turgidum durum L.) cropped in a range of Cu-contaminated, former vineyard soils (pH 4.2–7.8 and total Cu concentration 32–1,030 mg Cu kg⁻¹) and identified the underlying soil chemical properties and related root-induced chemical changes in the rhizosphere. Copper concentrations in plants were significantly and positively correlated to soil Cu concentration (total and EDTA). In addition, Cu concentration in roots which was positively correlated to soil pH tended to be larger in calcareous soils than in non-calcareous soils. Symptoms of Cu phytotoxicity (interveinal chlorosis) were observed in some calcareous soils. Iron (Fe)–Cu antagonism was found in calcareous soils. Rhizosphere alkalisation in the most acidic soils was related to decreased CaCl₂-extractable Cu. Conversely, water-extractable Cu increased in the rhizosphere of both non-calcareous and calcareous soils. This work suggests that plant Cu uptake and risks of Cu phytotoxicity in situ might be greater in calcareous soils due to interaction with Fe nutrition. Larger water extractability of Cu in the rhizosphere might relate to greater Cu uptake in plants exhibiting Cu phytotoxic symptoms.     

The addition of Dasypyrum villosum (L.) Candargy chromosomes to durum wheat (Triticum durum Desf.)

Summary Six monosomic addition lines were produced in which different Dasypyrum villosum (L.) Candargy chromosomes were added to the chromosome complement of Triticum durum Desf. cv. Creso. Each added alien chromosome was found to have a specific effect on plant morphology and fertility. Transmission rate varied widely (from 7.5 to 27.7%) among the six univalent chromosomes. Different monotelosomic addition plants derived by a relatively high frequency of chromosome misdivision were isolated. The addition lines should be useful for studying Dasypyrum chromosome homoeology and the introduction of alien variation into durum and common wheats.Research supported by a grant from the Italian Research Council for Finalized Project IPRA. Sub-project Plant Breeding, Paper No. 1095     

Empirical models to approximate calcium and magnesium ameliorative effects and genetic differences in aluminium tolerance in wheat

The activities of inorganic, monomeric aluminium (Al) species in the root environment are important in the toxicity of Al to plant roots, which may be ameliorated by increased activities of basic cations. Additionally, it has been suggested that electro-chemical processes in walls of root cells play a role in Al tolerance. Empirical models were proposed to accomodate genetic and calcium (Ca) and magnesium (Mg) ameliorative effects on Al toxicity. The models were tested using data from a solution culture study (with ionic strength 1.6 to 8.6 mM) in which wheat (Triticum aestivum L.) cvv. Warigal (Al-sensitive) and Waalt (Al-tolerant) were grown for 28 d at 0, 10 and 20 M Al, in factorial combination with 200, 400, 800 and 1600 M Ca and 100, 200, 400 and 800 M Mg. There was a poor relationship between relative total dry mass (TDM) (calculated as a percentage of the average TDM of each cultivar in the absence of added Al) and the activity of Al³⁺ or the sum of the activities of the monomeric Al species in solution. A model based on the ratios of activities of cations in solution, taking valency into consideration, was more successful, accounting for ca 85% of the observed variation in relative TDM. There were no systematic variations between observed values and those estimated by the model.     

Identification,characterization, and comparison of RNA-degrading enzymes of wheat and barley

RNA-degrading enzymes play an important role in regulating gene expression, and sequence analyses have revealed significant homology among several plant RNA-degrading enzymes. In this study we surveyed crude extracts of the above-ground part of the common wheat (Triticum aestivum L.) and the cultivated barley (Hordeum vulgare L.) for major RNA-degrading enzymes using a substrate-based SDS-PAGE assay. Fifteen wheat and fourteen barley RNA-degrading enzymes, with apparent molecular masses ranging from 16.3 to 40.1 kD, were identified. These RNA-degrading enzymes were characterized by their response to pH changes and addition of EDTA and ZnCl₂ to the preincubation or incubation buffers. The 33.2- to 40.1-kD wheat and barley, 31.7-kD wheat, and 32.0-kD barley enzyme activities were inhibited by both zinc and EDTA and were relatively tolerant to alkaline environment. The 22.7- to 28.2-kD enzymes were inhibited by zinc but stimulated by EDTA. The 18.8-kD enzyme exists in both wheat and barley. It was active in an acid environment, was inhibited by zinc, but was not affected by EDTA. Two enzyme activities (31.0 and 32.0 kD) are unique to the common wheat. Contribution from Agriculture Research Division, University of Nebraska, Journal Series No. 9895.     

The inheritance of tetraploid wheat seed peroxidases

Summary Embryo and endosperm peroxidases from dry mature seeds of three subspecies of tetraploid wheat (Triticum turgidum L.) were subjected to genetic analysis. The inheritance of eight isozymes (embryo isozymes a₂, d₁, d₂, e and f; and endosperm isozymes b, d and 4) were studied in F₂'s obtained from different wheat accessions. Simple monogenic inheritance producing three banded: one null segregation and two epistatic segregations (97 and 151) were found. In the case of isozymes b, d and 4, monogenic or epistatic segregation depended on the F₂ analyzed. Segregation data indicated that at least 9 different loci would determine the peroxidase isozymes of tetraploid wheat seed, all the loci studied containing null alleles. Furthermore, several loci determining embryo peroxidases were noticed to be mutually linked. All these data are discussed in context of the inheritance of seed peroxidases in hexaploid wheat and rye.