Genetic diversity of Pakistan wheat germplasm as revealed by RAPD markers

Wheat breeding in Pakistan started in 1930s before partition in the United India and so far has released more than 68 cultivars, but no systematic analyses of the genetic diversity of Pakistan wheat have been made. Twenty Pakistan wheat cultivars released from 1933 to 2002 were examined for genetic diversity and relationships using random amplified polymorphic DNA (RAPD) markers. Forty-two RAPD primers were applied and 184 polymorphic bands were generated for each cultivar. Most of the cultivars were genetically interrelated, although six of them displayed some genetic distinctness. The RAPD variation observed among these cultivars was low. Only 40.7% of the total scorable bands were polymorphic, and 26.1% of the polymorphic bands were observed most frequently (f = 0.95) among the 20 cultivars. The proportions of polymorphic bands for each cultivar ranged from 0.67 in ‘Yecora’ to 0.84 in ‘C-250’ with an average of 0.76. About 1.4% of the RAPD variation might have been fixed over the 69 years of wheat breeding, but such fixation was not statistically significant. These results are significant for future improvement and conservation of Pakistan wheat.     

Analysis of Genetic Variability in a Sample of the Durum Wheat (Triticum durum Desf.) Spanish Collection Based on Gliadin Markers

In this work gliadin proteins were used to analyse the genetic variability in a sample of the durum wheat Spanish collection conserved at the CRF-INIA. In total 38 different alleles were identified at the loci Gli-A1, Gli-A3, Gli-B5, Gli-B1, Gli-A2 and Gli-B2. All the gliadin loci were polymorphic, possessed large genetic diversity and small and large differentiation within and between varieties, respectively. The Gli-A2 and Gli-B2 loci were the most polymorphic, the most fixed within varieties and the most useful to distinguish among varieties. Alternatively, Gli-B1 locus presented the least genetic variability out of the four main loci Gli-A1, Gli-B1, Gli-A2 and Gli-B2. The Gli-B1 alleles coding for the gliadin γ-45, associated with good quality, had an accumulated frequency of 69.7%, showing that the Spanish germplasm could be a good source for breeding quality. The Spanish landraces studied showed new gliadin alleles not catalogued so far. These new alleles might be associated with specific Spanish environment factors. The large number of new alleles identified also indicates that durum wheat Spanish germplasm is rather unique.     

A reliable method for the selection of axenic seedlings

Summary Sterile seedlings are required for the investigation of interactions between microorganisms and plants. The present study was designed to develop a simple and reliable method for the selection of sterile seedlings by the use of liquid nutrient media, avoiding some of the disadvantages of solid media. The method of germinating surface-sterilized seedlings on solid water agar or nutrient media was compared with our method for sterility control in nutrient broth. Sterile plant selection in liquid media was the most sensitive method for detecting bacterial and fungal contaminants. Sterile plants grow with the same vigour as unsterilized plants and can be used for sterile plant experiments.     

Improvement of somatic embryogenesis and plant regeneration from durum wheat (Triticum turgidum var. durum Desf.) scutellum and inflorescence cultures

Scutellum and inflorescence explants of four genotypes of durum wheat(Triticum turgidum var. durum Desf.) were used to define culture conditions to obtain high frequencies of embryogenesis and plant regeneration in vitro. Under all conditions tested, scutellum cultures gave higher frequencies of embryogenesis and plant regeneration than inflorescence cultures. Two different auxins, 2,4-D(2,4-dichlorophenoxyacetic acid) and picloram(4-amino-3,5,6-trichloropicolinic acid), were compared for their effect on scutellum and inflorescence explant response in vitro. Picloram was found to significantly increase the frequency of plant regeneration from both explants. When cultures were grown on regeneration medium containing zeatin for two three-week passages, the frequency of plant regeneration increased by between 20–30% compared with cultures exposed to hormones for a single three-week passage. Finally, the addition of 1 mg/l 6-BAP (6-benzyl aminopurine) to the plantlet growth medium was found to enhance tiller production in regenerants. The optimized culture conditions were applicable to the four genotypes tested and frequencies of plant regeneration varied between 97% to 100% for scutellum cultures (2 mg/l picloram in induction medium) and between45% and 80% for inflorescence cultures (4 mg/l picloram in induction medium). The number of plants regenerated per explant was improved over previous procedures, with means of 34 plants per scutellum, and 16 plants per inflorescence explant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationship between electrophoretic pattern of storage proteins and gluten strength in durum wheat landraces from Turkey

A collection of 180 Triticum durum lines from Turkey and 22 Italian cultivars were investigated by electrophoretic techniques and evaluated for grain parameters such as protein content and sodium dodecyl sulphate (SDS)-sedimentation test. A total of 14 different patterns were observed for high-molecular-weight (HMW) glutenin subunits resulting from the combination of three alleles from the A genome and seven from the B genome. Three new allelic variants, one at Glu-A1 and two at Glu-B1, were found. Five different alleles were detected at the Glu-B1 locus. Genotypes with the same allelic variant at Gli-B1 showed inconsistency of composition in B group of low-molecular-weight (LMW) glutenin subunits. A total of 11 different B-subunit patterns were identified in the material analysed. A substantial proportion (78%) of the variation in gluten properties could be explained in terms of protein composition, with the LMW glutenin subunits making the largest contribution (54%). Results indicate that, in addition to Glu-B3 encoded proteins, variation at other loci coding for some intermediate and fastest B subunits might also influence rheological properties.     

Coleoptile tiller development is associated with fast early vigour in wheat

Summary Faster canopy development in temperate cereals can result in more efficient utilization of wate, light and nutrients if these are in limited supply. It can also result in more competitive plants and less use of herbicides. The possible importance of the coleoptile tiller for increasing early vigour in wheat (Triticum aestivum L.) was determined for twelve F4 lines in two experiments. Each F4 line was chosen for variation in the presence and absence of a coleoptile tiller in plants in the previous generation; each F4 line was traced to a single F2 plant from a multiple convergent cross of sixteen parents. Eight plants of each of the F4 lines were grown in a single row in both experiments. Just after the coleoptile tiller appeared, plants within each line were classified into one of two groups; one group contained plants with large coleoptile tillers whereas the other group had either small coleoptile tillers or none at all. Leaf expansion rates were determined non-destructively at regular intervals, and plants were harvested to determine leaf and tiller characteristics when there were about five mainstem leaves. There was substantial variation in the leaf area of the coleoptile tiller both between groups and among lines. In both experiments plants with a large coleoptile tiller had 24–30% more leaf area and dry weight than plants selected with a small or absent coleoptile tiller up to the final harvest. Leaf expansion rates (increase in leaf area per day) were 25 to 35% greater in the large coleoptile tiller selections from the time tillers first appeared to the time of harvest, whereas the relative leaf expansion rate (increase in leaf area per unit of leaf area present per day) of the large selections was significantly greater than the small selections only at the time of appearance of the coleoptile tiller and just after. There was no evidence that the early appearance of a coleoptile tiller was associated with the largest seedlings or that it inhibited the growth of later tillers. It is concluded that selection for the appearance of a large coleoptile tiller should improve the early vigour of temperate cereals.Abbreviations DAS days after sowing - LA leaf area - LAR leaf area ratio - LER leaf expansion rate - RLER relative leaf expansion rate - SLA specific leaf area - VPD vapor pressure deficit - +COL large coleoptile tiller group - –COL small or absent coleoptile tiller group     

Optimization of culture conditions for improved plant regeneration efficiency from wheat microspore culture

The production of haploid plants through microspore culture is a very important tool for plant breeding. However, progress in microspore culture for many species has been hampered by a number of factors that have resulted in low recovery of regenerated green plants. In this study, a series of experiments were conducted to increase the regeneration of haploid green plants from isolated wheat microspores. The use of different basal media and variations in media components resulted in the increased recovery (approximately double) of regenerated haploid wheat plants. Our findings demonstrate that CHB medium, in combination with 2,4-d, was a better medium for embryoids induction and plant regeneration than medium MC17 with either 2,4-d or PAA growth hormones. Wheat microspores cultured without ovary co-cultivation did not respond. Furthermore, high efficiency of microspore derived embryoids (up to 296 MDEs per 100 anthers) and green plant regeneration (up to 71 green plants per 100 anthers) were achieved by the use of gelrite instead of agarose as a gelling agent, and by the addition of media additives such as spent medium or MET.     

Genetic analysis of bread-making quality in wheat and spelt

Bread‐making quality in wheat and spelt reflects the combination of several, mostly quantitatively inherited parameters. The aim was to find molecular markers linked to quantitative trait loci (QTL) for quality parameters. Zeleny sedimentation values (Zel), protein (Prot), kernel hardness (KH) and 1000‐kernel weight (TKW) of 226 F₅ recombinant inbred lines (RILs) from a cross between wheat and spelt were assessed in different environments. The dough properties of 204 RILs were assessed with an alveograph. Based on a genetic map of 187 loci, nine QTL were found for Zel and Prot, explaining 47% and 51% of the phenotypic variance, respectively. Fifty‐four per cent of the variance was explained by 10 QTL for KH and eight for TKW. For the alveograph parameters 10 QTL were found for baking strength, nine for tenacity, seven for configuration ratio, and four for elasticity index and extensibility. The phenotypic variance explained ranged from 25% to 48%. The population mean of the dough parameters was shifted towards the spelt parent. It is concluded that non‐additive effects are crucial in the expression of high bread‐making quality of wheat. The consequences for wheat and spelt breeding programmes are discussed.     

Rapid introduction of disease resistance from rye into common wheat by anther culture of a 6x triticale × nulli-tetrasomic wheat

Powdery mildew (caused by Erysiphe graminis) and yellow rust (caused by Puccinia striiformis) are the two most serious wheat diseases found in China. Rye chromosomes, carrying genes for resistance to these diseases, were introduced into common wheat in two generations using chromosome engineering and anther culture. The F₁ hybrids from a cross involving a hexaploid triticale (×Triticosecale Wittmack) בChinese Spring’ nulli‐tetrasomic N6DT6A wheat aneuploid line were anther cultured and doubled‐haploid plants were regenerated. Using genomic in situ hybridization, C‐banding and biochemical marker analyses, one of the anther‐cultured lines (ZH‐1)studied in detail, proved to be a doubled‐haploid with one rye chromosome pair added (1R) and a homozygous 6R/6D substitution (2n= 44). The line was tested for expression of disease resistance and found to be highly resistant to powdery mildew and moderately resistant to yellow rust.     

Genetic analysis of resistance to leaf-rust (Puccinia recondita f. sp. tritici) pathotypes in the durum wheats 'PBW 34' and 'DWL 5023'

Genetic analysis of leaf-rust resistance was conducted on two durum wheats. Triticum durum cvs. ‘PBW 34’ and ‘DWL 5023’ were crossed with the leaf-rust-susceptible durum wheat ‘Malvi Local’. The F₁, F₂ and F₃ generations were tested against leaf-rust pathotypes 1, 77A and 108. In ‘PBW 34’, a single dominant gene was effective against each of the pathotypes 1 and 108, whereas two independently inherited dominant genes were effective against pathotype 77A. In ‘DWL 5023’, two independently inherited dominant genes were operative against pathotypes 1 and 77A, whereas a single dominant gene was identified as being operative against pathotype 108. Allelic tests on F₂ generation and joint segregation analysis on F₃ generation seedlings, suggested that two different genes in each cultivar are effective against these three leaf-rust pathotypes. Cultivar ‘PBW 34’ has Lrd1 and Lrd2 genes whereas Lrd1 and Lrd3 genes are present in ‘DWL 5023’.