Pleiotropic effects on the ml-o mildew resistance gene in barley in different genetical backgrounds

Summary The effects on quantitative characters of the ml-o5 allele has been investigated by means of doubled haploid lines produced by the Hordeum bulbosum method. In one series of experiments the genetic background in each cross was found significantly to modify the negative pleiotropic effects. Doubled haploids were also produced from a F1 cross and tested in the field during two years, one with strong and one with weak mildew infections. In the first year only an insignificant reduction in grain yield was detected in the mlo lines, in the second it was significantly reduced with 5.9%. Thousand grain weights were, however, higher in the resistant lines. In both series of experiments the possibility to extract very high yielding mlo genotypes was demonstrated. The nature of the genetic background effect is discussed.     

The evaluation of superior Hordeum bulbosum L. genotypes for use in a doubled haploid barley breeding programme

Summary Eight Hordeum bulbosum selections were produced from a cross between Cb 2920/4 and Cb 2929/1, two genotypes widely used in doubled haploid breeding programmes. The selections were hybridized with barley to evaluate their ability to produce high proportions of well-differentiated haploid embryos compared with Cb 2929/1 as control. We report here an initial small-scale investigation followed by a larger-scale test in two different environments to assess seed setting, haploid embryo differentiation rates and VB hybrid formation. These VB embryos contain both parental sets of chromosomes and occur more frequently in the glasshouse during the winter. Two of the eight selections were identified as combining the desirable characteristics of both parents, namely high seed setting on cv. Vada which is partially incompatible with H. bulbosum, large numbers of well-differentiated haploid embryos and a low incidence of VB hybrids. The selections are available for release to interested research workers and plant breedersAbbreviations DH doubled haploid - VB a hybrid from H. vulgare x H. bulbosum which contains both parental sets of chromosomes     

The use of reversed-phase high performance liquid chromatography as an aid to the identification of European barley cultivars

Summary A reversed-phase high performance liquid chromatography (RP-HPLC) system was used to separate the storage proteins (hordeins) extracted from European barley cultivars. From a total of 38 barleys tested, 26 types of hordein patterns could be distinguished after RP-HPLC. This appears to be a marked improvement in resolution over that achieved in a similar survey of European barley cultivars using SDS polyacrylamide electrophoresis (32 hordein patterns resolved by SDS PAGE from a total of 160 spring and winter barleys tested).Different hordein patterns were resolved by RP-HPLC within each of two groups of barley previously classified by SDS PAGE as indistinguishable within groups (three distinct patterns identified in a total of five cultivars tested from group 1A and five patterns observed among eight cultivars from group 3B). Thus RP-HPLC achieves a higher resolution than undirectional electrophoresis and promises to be a valuable aid in the identification of European barley cultivars.     

Field assessment of partial resistance to powdery mildew in spring barley

Summary Partial resistance to powdery mildew in spring barley was evaluated in three plot types: large isolation plots, in 1.4 m² plots in chessboard design with guard plots of spring wheat and in single rows. Percentage leaf area covered by powdery mildew was scored four to six times during the season and partial resistance was characterized by the area under the disease progress curve. Varietal differences were revealed in al three plot designs, differences between the most resistant and susceptible genotypes being of a factor five. Differences between varieties decreased with decreasing plot size. The relationship between single scores of amount of powdery mildew on the upper four leaves and the area under the disease progress curve was high in all plot designs during the first two to three weeks after heading, allowing selection for the trait by one or two scorings. Differential ranking of varieties between different plot designs was observed, and is assumed to be due to increasing plot interference with reduced plot size and reduced distance between plots. A reliable selection for partial resistance could be made in large isolation plots and in 1.4 m² plots, but hardly in single rows.     

Chlorophyll fluorescence transient as a genetic marker of productivity in barley

Summary The photosynthetic characteristics of the penultimate leaf in barley genotypes (reciprocal F1 combinations and varieties) were studied at the flowering stage in order to analyze the relationship between these traits and the biological yield and the economic yield. The biological yield was correlated with the leaf area whereas the economic yield was more dependent on the green area duration of the leaf or the combination of the two factors, leaf area and green area duration. The net photosynthesis per unit leaf area, determined at anthesis, was not a factor of productivity. On the other hand, the chlorophyll fluorescence (P), which was negatively correlated with the leaf area (+0.5) and with the combination of leaf area and green area duration (+0.5), was found to be a good marker of the economic yield. In view of its high heritability, it may provide an effective selection criterion.     

The importance of abortive stoma penetration in the partial resistance and nonhost reaction of adult barley and wheat plants to leaf rust fungi

Summary Early stages of the infection process of Puccinia hordei isolate 1.2.1 and of a P. recondita f.sp. tritici isolate were studied on adult plants of four barley lines and one wheat line. Two of the barley lines are extremely susceptible to P. hordei, the other two have a very high level of partial resistance.A histological study based on a trypan blue staining indicated that stoma penetration by P. hordei isolate 1.2.1 was equally successful on the susceptible as on the partially resistant adult barley plants. Abortion of substomatal vesicles was rare in all lines. These results do not support a hypothesis that mechanisms of partial resistance in adult plants differ from those in seedlings by a substantial abortive stoma penetration.Also in the nonhost combinations wheat-P. hordei and barley-P. recondita f.sp. tritici inhibition of stoma penetration and of substomatal vesicle development appears to play a biologically insignificant role in adult plants.The proportion of stoma penetration on the leaf sheaths of two of the barley lines was as high as on the leaf blades of the flag leaf and the leaf below the flag leaf. There was no evidence for stomatal exclusion as a crucial factor in the relatively low infectibility of leaf sheaths to leaf-blade specialized rust species.     

Yield potential and drought tolerance of segregating populations of barley in contrasting environments

Summary Using the traditional approach (selection for grain yield) it has been found that F₃ families derived from F₂'s selected under unfavourable conditions were more vigorous in the early stages of growth, taller, earlier in heading and with larger yields than F₃ families derived from F₂'s selected under favourable conditions. A high and negative correlation coefficient was found between the drought susceptibility index and grain yield at the driest site, whereas at the wettest site the correlation coefficients were lower and in some cases positive, indicating the existence of traits which are desirable under drought and undesirable under favourable conditions, or vice versa.Expected responses to selection for grain yield using different selection criteria indicated that selection under stress conditions is expected to be more efficient than selection under favourable conditions when dry areas is the target environment.Expected responses to selection for grain yield using different selection criteria indicated that selection under stress conditions is expected to be more efficient than selection under favourable conditions when dry areas is the target environment.Part of this work was supported by Opec Fund for International Development.     

Screening for resistance against Rhopalosiphum padi (L.). 2. Hordeum species and interspecific hybrids

Summary Twenty-seven accessions of Hordeum species and interspecific hybrids were screened in a growth chamber for resistance against the aphid Rhopalosiphum padi. Resistance measurement was based on the aphids' population growth during a 16-day period. The mean number of nymphs produced per female was only about 14% of that on the control cv. Tellus. H. bogdani was the most resistant accession. As a group, interspecific F₁-hybrids with common barley (H. vulgare × H. sp.) held an intermediate position. Differences in resistance between hybrids as well as between species (H. jubatum and H. lechleri) were observed. The most resistant species were all diploids. No effects of the host plant on formation of alatae or on the within-plant distribution of aphids were found.     

An Evaluation of Hordeum vulgare L. ×Psathyrostachys fragilis (Boiss.) Nevski Crosses for Doubled Haploid Barley Production

Investigations were carried out to assess the suitability of the intergeneric cross Hordeum vulgare×Psathyrostachys fragilis for haploid barley production. H. vulgare cvs. ‘Emir’ and ‘Vada’ were each pollinated with P. fragilis P.I. 343192 and plants regenerated from embryos cultured on a modified B5 medium. Seed sets on ‘Vada’ were significantly lower than on ‘Emir’, and all the planes from ‘Vada’×P. fragile remained hybrid. Several of these flowered but there was little pairing between the parental chromosomes. Most of the plants from ‘Emir’×P. fragilis died, as seedlings but 3 plants developed into haploid barley. Because of the practical limitations of pollen availability from P. fragilis and the inconsistencies in haploid plant formation, it is unlikely that the cross will prove as valuable as that between H. vulgare×H. bulbosum for a doubled haploid barley programme.     

The effect of anther orientation on microspore-derived plant production in barley (Hordeum vulgare L.)

Summary The effect of anther orientation on culture response has been examined in a range of barley cultivars of agronomic importance. Anther orientation did not significantly affect the percentage of anthers responding. However, orientation of the anthers in the up position with one lobe in contact with the medium significantly increased the number of green plants produced when compared to anthers cultured in the flat position. Green plantlet production was observed directly from embryoids i.e. without an intermediate callus phase. Cytological examination of the regenerants indicated that the majority of the plantlets possessed the normal barley karyotype. The implications of these results for Barley breeding are discussed.