The effect of herbicides on the root system of wheat plants

Three commercial herbicides, at the rates normally recommended for selective weed control in cereal crops, deformed the roots of spring wheat plants grown in sand culture. Affected roots produced large numbers of short swollen lateral branches which later grew on to form tassel-like bundles of side roots. Only the mecoprop and MCPA components of the mixtures were responsible for the deformities; ioxynil and dicamba had no effect. Mecoprop applied to the rooting medium severely deformed the roots but foliar application also resulted in some abnormalities. The effects of the herbicides on root and shoot dry weights were not correlated with their deformative effects.     

The effects of alien chromosomes on common wheat resistance to biotrophic fungal pathogens

Effective, perhaps new genes of resistance to brown rust and powdery mildew expressed in common wheat genome in plant ontogenesis were revealed on additive chromosomes of Aegilops searsii, Aegilops longissima, Secale montanum and Elytrigia elongata.     

Effects of alien cytoplasmic variation on carbon assimilation and productivity in wheat

In glasshouse studies of four alloplasmic wheat series, phenotypiccharacters were least affected when the recipient parent cytoplasm wasreplaced by donor cytoplasm of the S or D plasmatype. In the T.aestivum cv. 'Selkirk' series, cytoplasm substitution did notaffect Pmax per unit leaf area, although the flag leafarea (and photosynthetic rate per leaf) of each alloplasmic line wasgreater than that of euplasmic 'Selkirk'. In field trials, all the Dplasmatype alloplasmics tested produced more earsm^-2 than did euplasmic 'Selkirk'. The increasedtiller number and leaf area of alloplasmic lines resulted in greater canopylight interception than euplasmic 'Selkirk' early in the season. Thischaracteristic was associated with reduced weed populations under crops ofalloplasmic 'Selkirk' lines grown under low-, but not high-input, agronomicregimes, with Ae. cylindrica- and Ae.ventricosa-'Selkirk' significantly outyielding alloplasmic'Selkirk' under low-input conditions. The F2 populations from crossesbetween European wheat varieties and 'Selkirk' lines exhibited higherstandard deviations for grain yield for alloplasmic than for euplasmic'Selkirk', suggesting potential for selecting heterotic nuclear-cytoplasmiccombinations with alien cytoplasms.     

The chromosomal organization of simple sequence repeats in wheat and rye genomes

The physical distribution of ten simple-sequence repeated DNA motifs (SSRs) was studied on chromosomes of bread wheat, rye and hexaploid triticale. Oligomers with repeated di-, tri- or tetra-nucleotide motifs were used as probes for fluorescence in situ hybridization to root-tip metaphase and anther pachytene chromosomes. All motifs showed dispersed hybridization signals of varying strengths on all chromosomes. In addition, the motifs (AG)₁₂, (CAT)₅, (AAG)₅, (GCC)₅ and, in particular, (GACA)₄ hybridized strongly to pericentromeric and multiple intercalary sites on the B genome chromosomes and on chromosome 4A of wheat, giving diagnostic patterns that resembled N-banding. In rye, all chromosomes showed strong hybridization of (GACA)₄ at many intercalary sites that did not correspond to any other known banding pattern, but allowed identification of all R genome chromosome arms. Overall, SSR hybridization signals were found in related chromosome positions independently of the motif used and showed remarkably similar distribution patterns in wheat and rye, indicating the special role of SSRs in chromosome organization as a possible ancient genomic component of the tribe Triticeae (Gramineae). Received: 13 February 1998; in revised form: 18 August 1998 / Accepted: 18 August 1998     

Gene-containing regions of wheat and the other grass genomes

Deletion line-based high-density physical maps revealed that the wheat (Triticum aestivum) genome is partitioned into gene-rich and -poor compartments. Available deletion lines have bracketed the gene-containing regions to about 10% of the genome. Emerging sequence data suggest that these may further be partitioned into "mini" gene-rich and gene-poor regions. An average of about 10% of each gene-rich region seem to contain genes. Sequence analyses in various species suggest that uneven distribution of genes may be a characteristic of all grasses and perhaps all higher organisms. Comparison of the physical maps with genetic linkage maps showed that recombination in wheat and barley (Hordeum vulgare) is confined to the gene-containing regions. Number of genes, gene density, and the extent of recombination vary greatly among the gene-rich regions. The gene order, relative region size, and recombination are highly conserved within the tribe Triticeae and moderately conserved within the family. Gene-poor regions are composed of retrotransposon-like non-transcribing repeats and pseudogenes. Direct comparisons of orthologous regions indicated that gene density in wheat is about one-half compared with rice (Oryza sativa). Genome size difference between wheat and rice is, therefore, mainly because of amplification of the gene-poor regions. Presence of species-, genera-, and family-specific repeats reveal a repeated invasion of the genomes by different retrotransposons over time. Preferential transposition to adjacent locations and presence of vital genes flanking a gene-rich region may have restricted retrotransposon amplification to gene-poor regions, resulting into tandem blocks of non-transcribing repeats. Insertional inactivation by adjoining retro-elements and selection seem to have played a major role in stabilizing genomes.     

The effect of wheat cytoplasm on the synthesis of wheat x rye hybrids

Summary Four nuclear genotypes of Triticum aestivum L., each substituted into the cytoplasm of T. timococcum Kostoff, Aegilops ventricosa Tausch and T. timopheevi Zhuk., were crossed with four homozygous Secale cereale L. inbred lines to produce 48 alloplasmic octoploid primary triticales. Crossability, embryo differentiation, amphihaploid plantlet recovery in vitro, and response to colchicine treatment were investigated. It was found that in general the effects of the wheat cytoplasm on the characteristics studied were of equal importance as those of the wheat and the rye nuclear genotypes. Cytoplasm can be regarded as an additional source of variation in the synthesis of primary triticales. Cross-compatibility in wheat x rye hybrids appeared to be determined by specific parental genotypes and their nucleo-cytoplasmic interactions rather than by any general compatibility of particular nuclear genotypes and/or cytoplasms.     

The influence of combinations of alien translocations on in vitro androgenesis in near-isogenic lines of spring bread wheat

The features of in vitro androgenesis were studied in cultured anthers of spring bread wheats L503 and Dobrynya, having 7DS-7DL-7Ae#1L translocation with genes Lr19/Sr25 (Lr19 translocation) from Agropyron elongatum (Host.) P.B. and their near-isogenic lines carrying combinations of Lr19 translocation with translocations: 1BL-1R#1S with genes Pm8/Sr31/Lr26/Yr9 (Lr26 translocation) from Secale cereale L., 4BS-4BL-2R#1L with genes Lr25/Pm7 (Lr25 translocation) from Secale cereale, 3DS-3DL-3Ae#lL with genes Lr24/Sr24 (Lr24 translocation) from Agropyron elongatum and 6BS-6BL-6U#1L with gene Lr9 (Lr9 translocation) from Aegilops umbellulata Zhuk. In comparison with those varieties having received the Lr19 translocation, the following was established: (1) the combination of translocations Lr19 + 26 increased embryo frequency and green plant regeneration; (2) the combination of translocations Lr19 + 9 decreased embryo frequency but increased green plant regeneration; (3) the combination of translocations Lr19 + 24 decreased embryo frequency but increased green and albino plant regeneration; (4) the combination of translocations Lr19 + 25 increased embryo frequency and green plant regeneration but decreased albino plant regeneration. Thus, on near-isogenic lines of spring bread wheat, the influences of genotypes of four alien translocation combinations on in vitro androgenesis were determined.     

Effects of alien cytoplasm substitution on the response of wheat cultivars to Septoria nodorum

The effects of alien cytoplasm substitution on the response of wheat to Septoria nodorum were studied, using alloplasmic series of two cultivars, Chris and Selkirk. In general, cytoplasmic substitution caused unidirectional effects on Septoria-response, alloplasmic lines of both cultivars expressing lower levels of partial resistance (in leaf and head tissue) but higher levels of yield tolerance than the corresponding euplasmic line. The reduced resistance in alloplasmics was closely associated with reduced incubation periods of Septoria infection in both leaf and head tissue. Cytoplasmic substitution resulted in increased yield tolerance to Septoria-infection in both the non-tolerant Selkirk and the relatively tolerant Chris. Unlike their effects on partial resistance, specific cytoplasms exerted similar effects on tolerance in the two parental cultivars, several cytoplasms of the D plasmatype being particularly effective in increasing Septoria-tolevance. The potential for the development of Septoria-toterant cultivars by the incorporation of alien cytoplasms is discussed, in view of the observed neutral effects of D plasmatype cytoplasms on other agronomic traits.     

Identification of an alien chromosome in the common wheat line multi 6R

The chromosome of Agropyron intermedium (Host) Beauv. substituting chromosome 6D has been identified in the karyotype of the Triticum aestivum L. line Multi 6R with the use of C-banding. The alien chromosome, temporarily designated 6Ag1, contains gene(s) of the resistance to the Saratov population of Puccinia recondita Rob. ex. Desm. f. tritici. It has been demonstrated that the resistance gene(s) is(are) highly efficient and that chromosome 6Ag1 is preferably transferred through gametes.     

Genetic analysis of anther culture response in wheat carrying alien translocations

A bread wheat cultivar, Saratovskaya 29, (S29), its nearly isogenic lines carrying alien translocations [Lr9 from Aegilops umbellulata (Eg29) and (Lr19) from Agropyron elongatum (Ps29)] and two F₁ hybrids between three nearly isogenic lines of S29 that differed by the Lr19+Rht1,Pro1+Pro2 and Ppd1+Ppd2 gene complexes, namely the S29 (Lr19+Rht1)/S29 (Ppd1+Ppd2) F₁ and the S29 (Pro1+Pro2)/S29 (Lr19+Rht1) F₁ were studied for their culture response with the following results. (1) Translocations with Lr9 and Lr19 decreased embryo frequency and green plant regeneration. (2) Both F₁ hybrids showed a decrease in embryo frequency. One of the F₁ hybrids, S29 (Lr19+Rht1)/S29 (Ppd1+Ppd2) showed a decrease, with respect to S29 for green plant regeneration; the other F₁ S29 (Pro1+Pro2)/S29 (Lr19+Rht1), equalled S29 for green plant regeneration. (3) The gene complex of the F₁ hybrid S29 (Pro1+Pro2)/S29 (Lr19+Rht1) was better than that of the F₁ hybrid S29 (Lr19+Rht1)/S29 (Ppd1+Ppd2) for embryo induction and green plant regeneration. This effect was possibly induced by interactions between the Pro1+Pro2 and Lr19+Rht1 genes or was the result of direct actions of the Pro1+Pro2 genes.     

The effect of molybdenum on seed dormancy in wheat

Molybdenum deficiency was induced in wheat growing in sand culture under controlled environmental conditions. Half the plants were treated with foliar applications of molybdenum at the six and flag leaf stages. Molybdenum-treated plants produced seed which was significantly more dormant that that harvested from the molybdenum-deficient plants. Molybdenum treatment also resulted in a higher nitrate and protein content of the seed. These findings, seen in the light of the proven success of molybdenum in preventing pre-harvest sprouting in maize, would seem to indicate that molybdenum has the potential to restrict pre-harvest sprouting losses in wheat growing in soils deficient in molybdenum.     

The pretreatment effect on wheat straw saccharification

Enzymatic hydrolysis of cellulose is potentially an attractive method for converting cellulose into glucose which can then be used as a chemical feed or as a growth substrate for a number of microorganisms to produce microbial products. An enzymatic hydrolysis of wheat straw with cellulase preparation “Trichocease” was made. The wheat straw used was pretreated mechanically and with NaOH. A procedure of pretreatment was investigated in 26 variants. The dynamics of enzymatic hydrolysis was studied. An assay of this dynamics based on the amount of reducing sugars formed during the cellulase reaction and depending upon enzyme and substrate concentration and time of action was carried out.     

Yesterday's polyploids and the mystery of diploidization

Thirty years after Susumu Ohno proposed that vertebrate genomes are degenerate polyploids, the extent to which genome duplication contributed to the evolution of the vertebrate genome, if at all, is still uncertain. Sequence-level studies on model organisms whose genomes show clearer evidence of ancient polyploidy are invaluable because they indicate what the evolutionary products of genome duplication can look like. The greatest mystery is the molecular basis of diploidization, the evolutionary process by which a polyploid genome turns into a diploid one.     

The effect of soil strength on the yield of wheat

Although it is well-known that high soil strength is a constraint to root and shoot growth, it is not clear to what extent soil strength is the main physical stress that limits crop growth and yield. This is partly because it is difficult to separate the effects of soil drying and high soil strength, which tend to occur together. The aim of this paper is to test the hypothesis that for two different soil types, yield is closely related to soil strength irrespective of difference in soil water status and soil structure. Winter (Triticum aestivum L., cv. Hereward) and spring wheat (cv. Paragon) were grown in the field on two soils, which had very different physical characteristics. One was loamy sand and the other sandy clay loam; compaction and loosening treatments were applied in a fully factorial design to both. Crop growth and yield, carbon isotope discrimination, soil strength, water status, soil structure and hydraulic properties were measured. The results showed that irrespective of differences in soil type, structure and water status, soil strength gave a good prediction of crop yield. Comparison with previous data led to the conclusion that, irrespective of whether it was due to drying or compaction (poor soil management), soil strength appeared to be an important stress that limits crop productivity.     

Genetic interactions between wheat and rye genomes in triticale

Summary Six primary triticale lines were produced from two advanced breeding lines of Triticum durum and three inbred genotypes of Secale cereale. The wheat and rye parents and the triticale derivatives were crossed in all possible combinations within each species group. Chiasma and univalent frequency of parents and hybrids were determined. The primary triticale lines had more univalents and less chiasmata per pollen mother cell than the corresponding wheat and rye parents together. The parental wheat F₁ exhibited negative heterosis for chiasma frequency whereas all rye hybrids had much higher chiasma frequencies than their inbred parents. Triticale F₁s generally showed lower chiasma frequencies and more univalents than their parents, but the degree of pairing failure was dependent upon which of the parental species within the triticale, wheat or rye, was in the heterozygous state. F₁s with heterozygous wheat genome only showed the least reduction in chiasma number (presumably caused by gene actions within the wheat genome), while F₁s with heterozygous rye genome showed high reduction in chiasma frequency and an increase in pairing failure (induced by negative interactions between the heterozygous rye and the wheat genome in triticale). A high correlation was found between the frequency of undisturbed pollen mother cells and the frequency of aneuploids in the subsequent generation. A higher number of aneuploids occurred in those populations which were heterozygous for the rye genome.