Development of SCAR markers linked to a scald resistance gene derived from wild barley

The F₂ progeny of a third backcross(BC₃) line, BC line 240, derived from a Turkish accession of wild barley (Hordeum vulgare ssp. spontaneum),segregated for resistance to scald (Rhynchosporium secalis) in a manner indicating the presence of a single dominant resistance gene. Two SCAR marker slinked to this resistance were developed from AFLP markers. Screens of disomic and ditelosomic wheat-barley addition lines with the SCAR markers demonstrated that the scald resistance gene is located in the centromeric region of barley chromosome 3H,a region previously reported to contain a major scald resistance locus, Rrs1. Markers that flank the Rrs1 locus were used to screen the wild barley-derivedBC₃F₂ population. These markers also flank the wild barley-derived scald resistance, indicating that it maps to the same locus as Rrs1; it may beallelic, or a separate gene within a complex locus. However, BC line 240 does not respond to treatment with the Rhynchosporium secalis avirulence factorNIP1 in the same way as the Rrs1-carrying cultivar Atlas46. This suggests that the scald resistance gene derived from wild barley confers a different specificity of response to theRrs1 allele in Atlas46.In order to increase the durability of scald resistance in the field, we suggest that at least two scald resistances should be combined into barley cultivars before release. The scald resistance gene described here will be of value in the Australian environment, and the several markers linked to it will facilitate pyramiding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation for dry matter and nitrogen accumulation and translocation in two-rowed spring barley: I. Dry matter translocation

A 4-year field study was carried out to determine dry matter and nitrogen accumulation until anthesis and at grain filling period and dry matter translocation and utilization in grain filling of barley. Twenty two-rowed spring barley (Hordeum vulgare ssp. distichum L.) cultivars originated from different countries (Yugoslavia, Germany, Australia, the Czeck Republic, Netherlands, France and USA) were grown during 1995–1998 on a non-calcareous chernozem soil near Novi Sad (45° 20′N, 15° 51′E, 86 m asl). Dry matter and nitrogen accumulation depended on the cultivar and year. In a year with favorable weather conditions, 58% of dry matter was accumulated during pre-anthesis, while in a year with less favorable weather the amount was 48%. In the favorable year 91% and in unfavorable year 65% of nitrogen was accumulated until anthesis. The results indicated that the greater amount of dry matter and nitrogen accumulated before anthesis. Dry matter translocation efficiency depended on the cultivar and ranged from 3 to 16.4%, while the contribution of pre-anthesis assimilates to kernel varied from 4 to 24.2%. Cultivars that have been developed for the growing conditions of the area where the experimental site was located, i.e. adapted ones, did not use pre-anthesis dry matter for grain filling. High positive correlations (P<0.01) were found between biomass at anthesis and biological yield, dry matter translocation efficiency, contribution of translocated dry matter to grain yield, and total plant nitrogen at maturity. Accumulated nitrogen at anthesis was positively correlated (P<0.01) with growing degree–days until anthesis, dry matter at anthesis and dry matter translocation parameters. Heritability for the investigated characters was rather high, over 0.60.     

Mutation genetics of salt tolerance in barley: An assessment of Golden Promise and other semi-dwarf mutants

A review of research at the Scottish Crop Research Institute (SCRI) on the effects of semi-dwarfing genes on salt tolerance in barley is given. Work began in1993 with the fortuitous and unexpected result that the cultivar ‘Golden Promise’ showed considerable tolerance to salt. Golden Promise is a gamma-ray induced semi-dwarf mutant of the cultivar ‘Maythorpe’. The parent and mutant cultivars are presumed to be isogenic, but show significant differences in their responses to salt stress. The positive and pleiotropic effects of the mutant gene, commonly known as GPert were found to be effective in a number of genetic backgrounds. Earlier, in 1991 Frackowiak showed that the GPert mutation was allelic to the ari-e mutants in barley. The ari-emutants were salt tested and found to show the same positive responses to salt stress as Golden Promise. This supported the allelism tests, and consequently the GPert symbol was changed to ari-e.GP. The semi-dwarf mutant sdw1 (also known as denso) and the erectoides semi-dwarf mutant,ert-k ³² were also tested for their effects on tolerance to salt, but did not show any positive effects. Salt tolerance was therefore not a general phenomenon of semi-dwarf stature but specific to mutations at the Ari-e locus in these lines. Genetic markers (RAPDs, AFLPs and SSRs) have been used for fingerprinting, genetic mapping, and QTL analysis. The markers have helped 1) confirm the isogenic relationship between Maythorpe and Golden Promise, 2)clarify the confusion over the pedigree of Golden Promise, and 3) genetically map the ari-e.GPlocus and examine its pleiotropic effects. This revised version was published online in August 2006 with corrections to the Cover Date.     

Search for partial resistance against Puccinia hordei in barley landraces from the Fertile Crescent

A collection of 111 barley landraces from the Fertile Crescent was screened for resistance to barley leaf rust in the field and under controlled conditions. Large variation was observed for disease severity under field conditions. Accessions with high resistance because of hypersensitivity were identified. Also segregation was observed in some accessions, with individual plants showing hypersensitive reactions (IT ≤ 6). Partial resistance due to a reduction of infection in spite of a compatible infection was commonly found (19%). Resistance of 12 accessions selected for their low disease severity and high IT, was shown to be due to a prolonged latency period and increased percentage of early aborted colonies not associated with host cell necrosis. A high correlation was observed between the microscopic and macroscopic components of partial resistance.     

Abscisic acid, gibberellin and cell viability in cereal aleurone

The aleurone layer of cereals is a secretory tissue whose activity is regulated by abscisic acid (ABA) and gibberellins (GAs). Whereas GA triggers enzyme synthesis and secretion and initiates a program that culminates in cell death, ABA prevents enzyme production and cell death. Reactive oxygen species (ROS) are key players in regulating cell viability and GA sensitizes the aleurone cell to ROS. Sensitivity of GA-treated cells results in part from a reduction in steady-state amounts of mRNAs encoding enzymes that scavenge ROS. mRNAs encoding catalase, superoxide dismutase and ascorbate peroxidase are almost undetectable in aleurone layers 24 h after incubation in GA. For layers incubated in ABA, however, the amounts of these mRNAs increase. Western blotting and enzyme activity assays confirm that GA but not ABA reduced the amount and activity of ROS scavenging enzymes (Fath et al., 2001b). Substantial amounts of ROS are produced by enzymes engaged in lipid metabolism, and by the electron transport chain in the mitochondria. Aleurone layers contain abundant stores of triglycerides and ROS are produced as these lipids are rapidly converted to sugars. We hypothesize that the ROS produced in GA-treated aleurone cells bring about cell death by disrupting the plasma membrane. Aleurone cells incubated in ABA, on the other hand, are better able to maintain redox balance. ABA does not initiate rapid triglyceride metabolism, and the activities of ROS-scavenging enzymes remain high in ABA-treated cells. We conclude that GA initiates a metabolic cascade in aleurone cells that results in death from ROS. ABA maintains viability by keeping ROS under control. This revised version was published online in August 2006 with corrections to the Cover Date.     

The grain yield of uniculm barley (Hordeum vulgare L.) in two contrasting environments

Summary Four six-rowed uniculm lines of spring barley were grown in two yield trials at different sowing densities. One trial was grown on light sandy soil in 1990. The second trial was grown on clay soil in 1991 and included the two-rowed, tillering cultivar Golf. In the trial on sandy soil, the grain yield of the uniculm lines approached that of Golf grown in an adjacent trial, but in 1991 when the growing conditions were more favourable, Golf yielded significantly more than the uniculm lines. Uniculm lines apparently perform relatively better under marginal growing conditions than in high yielding environments.The uniculm lines do not conform to the ideotype proposed for wheat by Donald (1968) but the results show that a drastic change in plant type need not to imply a large drop in grain yield.     

Genetical Studies on the Mode of Inheritance and Localization of the amo1 (High Amylose) Gene in Barley

In the high amylose starch mutant ‘Glacier AC38’, a single recessive gene designated amo1 is responsible for an amylose content of up to 45%. A rapid technique was established in order to evaluate the amylose/amylopectin ratio in half kernels. To localize this gene, crosses with multiple marker lines and trisormes were conducted. In addition, RFLP markers were used to determine their mapping distance to amo1. Two markers are located 2 cM and 7 cM, respectively, from amo1 on chromosome 5S (1HS). The relationship between the wx and amo1 genes was also examined and the role of the amo1 gene in starch synthesis is discussed.     

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.     

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.