Breeding oat for resistance to the crown rust pathogen Puccinia coronata f. sp. avenae: achievements and prospects

Crown rust, caused by Puccinia coronata f. sp. avenae (Pca), is a significant impediment to global oat production. Some 98 alleles at 92 loci conferring resistance to Pca in Avena have been designated; however, allelic relationships and chromosomal locations of many of these are unknown. Long-term monitoring of Pca in Australia, North America and elsewhere has shown that it is highly variable even in the absence of sexual recombination, likely due to large pathogen populations that cycle between wild oat communities and oat crops. Efforts to develop cultivars with genetic resistance to Pca began in the 1950s. Based almost solely on all all-stage resistance, this has had temporary benefits but very limited success. The inability to eradicate wild oats, and their common occurrence in many oat growing regions, means that future strategies to control Pca must be based on the assumption of a large and variable prevailing pathogen population with high evolutionary potential, even if cultivars with durable resistance are deployed and grown widely. The presence of minor gene, additive APR to Pca in hexaploid oat germplasm opens the possibility of pyramiding several such genes to give high levels of resistance. The recent availability of reference genomes for diploid and hexaploid oat will undoubtedly accelerate efforts to discover, characterise and develop high throughput diagnostic markers to introgress and pyramid resistance to Pca in high yielding adapted oat germplasm.

Androgenic response to preculture stress in microspore cultures of barley

Various stresses such as starvation and cold or heat shocks have been identified as triggers in the induction of the microspore embryogenesis. This study attempts to quantify the effects of different pretreatment conditions for successful microspore culture of malting barley (cv. Scarlett). While the sporophytic microspore development could be induced from treated and nontreated microspores, abiotic stress was essential for embryo formation and plant regeneration. The type of stress treatment applied affected the numbers and the ratios of albino and green plants regenerated, as well as their fertility. The highest number of green plants was obtained after the treatment of anthers in 0.3 M mannitol at 32 degrees C for 24 h before microspore culture.

Direct embryogenesis and green plant regeneration from isolated microspores of hexaploid triticale (x Triticosecale Wittmack) cv. Bogo

The use of doubled haploids improves the efficiency of cultivar development in many crops and can be helpful in genetic and molecular studies. The major problem with this approach is the low efficiency of green plant regeneration. We describe here an efficient method for inducing embryos and regenerating green plants directly from isolated microspores of hexaploid triticale (x Triticosecale Wittmack) cv. Bogo. The absence of growth regulators in the induction medium was the most effective condition for the formation of embryo-like structures. The highest induction rates were observed at microspore densities of 1.5x10(5) microspores and 2x10(5) microspores per milliliter. Such cultures produced an average of 54.9 green plants per single donor spike. The frequency of albino plants ranged from 9.3% to 22.9%. Among the green progeny tested, 30.8% were spontaneously doubled haploids.

Nonsymbiotic haemoglobins in plants

General aspects regarding the presence of nonsymbiotic haemoglobin in plants are presented with the emphasis on those related to its function. As it becomes apparent that the nonsymbiotic haemoglobins are widespread across the plant kingdom and that they represent a more primitive and evolutionary older form of the plant globin genes, the question of their function becomes more attractive. While the physiological functions of the symbiotic haemoglobins in plants are well understood, almost nothing is known about their nonsymbiotic predecessors. Therefore, the known and hypothetical functions of haemoglobins in various systems are described along with information concerning properties and the regulation of expression of the nonsymbiotic haemoglobins. Interestingly, a number of nonsymbiotic haemoglobins have been shown to be hypoxia-inducible. The spatial and temporal pattern of this induction in barley may suggest that it is an integral part of the plants response to limiting oxygen stress.

Nonsymbiotic haemoglobins in plants

General aspects regarding the presence of nonsymbiotic haemoglobin in plants are presented with the emphasis on those related to its function. As it becomes apparent that the nonsymbiotic haemoglobins are widespread across the plant kingdom and that they represent a more primitive and evolutionary older form of the plant globin genes, the question of their function becomes more attractive. While the physiological functions of the symbiotic haemoglobins in plants are well understood, almost nothing is known about their nonsymbiotic predecessors. Therefore, the known and hypothetical functions of haemoglobins in various systems are described along with information concerning properties and the regulation of expression of the nonsymbiotic haemoglobins. Interestingly, a number of nonsymbiotic haemoglobins have been shown to be hypoxia-inducible. The spatial and temporal pattern of this induction in barley may suggest that it is an integral part of the plants response to limiting oxygen stress.

Reduction of trachoma in a sub-Saharan village in absence of a disease control programme

BACKGROUND

Trachoma is a leading cause of blindness in the developing world and is most prevalent among people who live in poor rural communities in arid locations.

METHODS

We analysed the results of surveys of trachoma prevalence in Marakissa, a rural village in The Gambia. These surveys were undertaken in 1959, by the Medical Research Council, and in 1987 and 1996 by the Gambian National Eye Care Programme.

FINDINGS

During this 37-year period, the prevalence of active inflammatory trachoma among children aged 0-9 years fell from 65.7 cases per 100 children in 1959 to 2.4 cases per 100 children in 1996. The prevalence also fell dramatically among people of 10-19 years (52.5 to 1.4 per 100) and among people of 20 years and older (36.7 to 0 cases per 100).

INTERPRETATION

The dramatic fall in disease occurrence was paralleled by improvements in sanitation, water supply, education, and access to health care in the village. Of particular importance is that the decline in trachoma occurred without any trachoma-specific intervention.

Susceptibility of methicillin-resistant Staphylococcus aureus clinical isolates to various antimicrobial agents

Resistance patterns against 23 antimicrobial agents were examined for 42 strains of methicillin-resistant Staphylococcus aureus (MRSA). Thirty-four strains were isolated at Hiroshima University Hospital during 1984-1990 and 8 strains were collected in Tokushima city in 1986. Overall resistance to the antimicrobial agents in clinical use is summarized as follows: methicillin 100%, flomoxef 93% (beta-lactams); kanamycin 98%, tobramycin 88%, amikacin 83%, isepamicin 81%, gentamicin 60%, dibekacin 64%, arbekacin 0% (aminocyclitol aminoglycosides); ofloxacin 31%, TA-167 33% (fluoroquinolones); erythromycin 100%, clarithromycin 100%, josamycin 71% (macrolides); vancomycin 0% (glycopeptide); tetracycline 43%, minocycline 31% (tetracyclines); fosfomycin 93%. The MRSA strains remained susceptible to the non-clinical peptide group of antibiotics except for mikamycin B: mikamycin A 2%, mikamycin B 69%, nosiheptide 0%, bottromycin A2 0%, bottromycin D-1 0%, bottromycin D-2 0%. Since April 1990, the MRSA strains isolated at Hiroshima University Hospital showed a tendency to acquire resistance to tetracyclines and fluoroquinolones and to lose mikamycin B-resistance. As of August 1990, none of the MRSA strains isolated at Hiroshima University Hospital was resistant to vancomycin and arbekacin.

Infrared spectroscopy of plant cell cultures : noninvasive measurement of viability

Infrared spectroscopy was used to examine suspension-cultured pear (Pyrus communis L.) and Spartina pectinata cells. Noninvasive measurements were made using internal reflectance sampling. Spectra of actively growing cells exhibited a pronounced absorbance at 2343 reciprocal centimeters. The absorbance peak was identified and verified as CO(2) dissolved in water. This peak was absent in nonviable cells. Peak height was directly proportional to percent viability in artificial mixtures of viable and nonviable cells, indicating that the level of intracellular CO(2) production could be used as a viability determinant for plant cells. Suspension-cultured cells were slowly cooled to subzero temperatures and analyzed for viability using infrared spectroscopy and tetrazolium staining. Both methods showed similar trends in viability assessment. Infrared spectroscopy could provide a more detailed understanding of cell viability and allow measurement on a noninvasive basis.

National survey of blindness and low vision in The Gambia: results

A population based survey of blindness and eye disease has been conducted throughout the whole country of The Gambia, and 8174 people were examined. The prevalence of blindness (best acuity less than 3/60) was 0.7% and low vision (6/24-3/60) 1.4%. The causes of blindness were cataract (55%), non-trachomatous corneal opacity/phthisis (20%), and trachoma (17%). An estimated 5500 people in The Gambia require cataract surgery, 4600 eyelid surgery for entropion, and 4600 people spectacles to correct a refractive error which causes a visual acuity of less than 6/18. More than half the current burden of blindness in The Gambia is potentially remediable through the provision of cataract surgery and aphakic spectacles.

The anesthetic nitrous oxide affects dioxygen utilization by bovine heart and bean seed mitochondrial particles

Nitrous oxide affects dioxygen utilization by both bean seed and bovine heart submitochondrial particles when either succinate or reduced cytochrome c are used as substrates. Bovine heart particles exhibit reversible, dose-dependent partial inhibition of respiratory activity when exposed to N2O. Bean seed particle respiration is stimulated by low levels of N2O, but higher concentrations are inhibitory. These findings can be explained in terms of one locus of anesthetic action: cytochrome c oxidase, the terminal component of the mitochondrial respiratory chain. Alterations in respiration rates are expected to make important contributions to anesthesia in animals and to control of germination in plants.

Serotypes of trachoma agent isolated in the Gambia: with an observation on the relation between serotype and morphology

Of 60 TRIC agents isolated from Gambian children with trachoma, 25 were serotype 1 and the remainder type 2. There was a pronounced difference in the proportions of these types in the two villages studied. In the village with a predominance of type 2 strains, TRIC agents remained confined to 2 adjacent compounds over a 14 month observation period. All 19 type 1 strains examined were characterized by the appearance in yolk sac smears of compact aggregates of elementary bodies; such aggregates were seen in only 2 of 35 type 2 strains, and may reflect a chemical difference in the surface of the elementary bodies or in a substance elaborated during their replication.

The serum and conjunctival antibody response to trachoma in Gambian children

Ninety-nine young Gambian children were studied for 61 weeks. About half of them had trachoma at the outset, and 80% of the remainder acquired the disease while under observation. IgG trachoma antibody in the serum and IgG and IgA antibodies in the conjunctival secretions (CS) were titrated by an indirect immunofluorescence method. In serum samples obtained in capillary tubes the mean titre was slightly higher than in samples collected on filter paper. Serum antibody at titres >/= 1/10 was invariably associated with a clinical diagnosis of trachoma; it increased both in frequency and titre as the disease progressed, and was present in about half of those with Tr II. In CS, IgG antibody was present less often and at lower titres than in serum, and IgA antibody was detected even less frequently. There was some evidence of correlation between the titres of IgG and IgA antibodies in CS, but none for a relationship between the titres of the antibodies in serum and those in CS. Antibodies were almost never present in the absence of conjunctival follicles, but their titres were unrelated to the degree of follicular hyperplasia; there was no obvious relationship between the serological findings and corneal lesions. In children diagnosed clinically as trachoma, serum antibody was present in almost all those with conjunctival inclusions, and in a proportion of inclusion-negative subjects; the mean titre was much higher in the inclusion-positive group.These findings do not settle whether CS antibodies are made locally, or are derived partly or wholly from the blood. They suggest that the indirect immunofluorescence test may be a useful diagnostic aid in trachoma, particularly in view of the rarity of false positive reactions; but there is at present little to choose between it and complement-fixation tests in terms of sensitivity.

A comparison of the iodine and fluorescent antibody methods for staining trachoma inclusions in the conjunctiva

In terms of the rate of positive diagnoses the indirect fluorescent antibody (FA) test was rather more effective than iodine for demonstrating trachoma (TRIC) inclusions in conjunctival scrapings, but the degree of advantage was not statistically significant. In duplicate scrapings stained at random by one or the other method, FA staining yielded the higher inclusion count significantly more often than did iodine. Some inclusions that failed to stain with FA were found on subsequent staining with Giemsa. A method is described for improving the post-FA Giemsa staining of conjunctival smears stored at subzero temperatures. Given adequate facilities, the FA stain is preferable to iodine for demonstrating TRIC inclusions in the conjunctiva; but the iodine method, properly used, holds advantages for field use.

Trachoma vaccine field trials in The Gambia

The ability of two live trachoma vaccines to protect against naturally acquired infection was tested in young Gambian children. With a mineral oil adjuvant vaccine prepared from a Gambian strain of trachoma (MRC–187) a barely significant measure of protection was demonstrable 6 months after the first dose, but not at 1 year, despite a reinforcing dose given 6 months after the first. In a later trial an aqueous vaccine prepared from the ‘fast-killing’ variants of strains ‘SA–2’ and ‘ASGH’ failed to induce immunity. Two years after vaccination, the proportion of vaccinated children progressing to cicatricial trachoma was less than in the controls, and the average severity of the disease in terms of clinical score was greater; vaccine-induced hypersensitivity may have contributed to this result.

Irrespective of whether they had received trachoma vaccine, children with completely normal eyes at the outset were less likely to acquire trachoma than those with slight conjunctival folliculosis or papillary hyperplasia. In children acquiring trachoma, there was a highly significant positive correlation between severity of the disease and the presence of conjunctival inclusions. The pattern of trachoma differed significantly in the two villages used in both trials; the prev alence, severity and proportion of inclusion-positive subjects were all higher in the village with the greater population density.

An efficient follow-up organization, use of a slit-lamp for clinical observations, and a scoring system for recording physical signs are all desirable for trachoma vaccine field trials.

We are highly indebted to Dr G. Turner (Lister Institute, Elstree, Herts) for his assistance in making the vaccine used for Trial II; to Dr N. M. Lam (Pfizer Ltd.) and Dr C. H. Smith (Evans Medical Ltd.) for making the Trial III vaccine; to Dr I. A. Sutherland (M.R.C. Statistical Unit) for his advice and help with the statistical aspects; to the Pennsylvania Refinery Co. Inc. for a generous gift of Drakeol 6 VR; and to Mr M. Race for his invaluable technical assistance in The Gambia. We are also grateful to the Director and staff of the M.R.C. Laboratories, The Gambia, for various facilities; and to The Gambian Government for per mission to undertake these trials.