Genome-wide association analyses reveal complex genetic architecture underlying natural variation for flowering time in canola.

Optimum flowering time is the key to maximize canola production in order to meet global demand of vegetable oil, biodiesel and canola-meal. We reveal extensive variation in flowering time across diverse genotypes of canola under field, glasshouse and controlled environmental conditions. We conduct a genome-wide association study and identify 69 single nucleotide polymorphism (SNP) markers associated with flowering time, which are repeatedly detected across experiments. Several associated SNPs occur in clusters across the canola genome; seven of them were detected within 20 Kb regions of a priori candidate genes; FLOWERING LOCUS T, FRUITFUL, FLOWERING LOCUS C, CONSTANS, FRIGIDA, PHYTOCHROME B and an additional five SNPs were localized within 14 Kb of a previously identified quantitative trait loci for flowering time. Expression analyses showed that among FLC paralogs, BnFLC.A2 accounts for ~23% of natural variation in diverse accessions. Genome-wide association analysis for FLC expression levels mapped not only BnFLC.C2 but also other loci that contribute to variation in FLC expression. In addition to revealing the complex genetic architecture of flowering time variation, we demonstrate that the identified SNPs can be modelled to predict flowering time in diverse canola germplasm accurately and hence are suitable for genomic selection of adaptative traits in canola improvement programmes.

Localisation of quantitative trait loci for quality attributes in a doubled haploid population of wheat (Triticum aestivum L.).

Selection of wheat germplasm for a range of quality traits has been a challenging exercise because of the cost of testing, the variation within testing data, and a poor understanding of the underlying genetics. The objective of this study was to identify quantitative trait loci (QTLs) underlying quality traits in wheat. A doubled haploid population comprising 190 lines from Chara/WW2449 was grown in two different environments and evaluated for various quality traits. A molecular map comprising 362 markers based upon simple sequence repeat, sequence tagged microsatellite, glutenin, and DArT loci was constructed and subsequently exploited to identify QTLs using a whole-genome approach. Fifteen QTLs that were consistent in the two different environments were identified for thousand kernel mass, grain protein content, milling yield, flour protein content, flour colour, flour water absorption, dough development time, dough strength (extensograph height and resistance at 5 cm), and dough extensibility (extensograph length) using the whole genome average interval mapping approach. The amount of genetic variation explained by individual QTLs ranged from 3% to 49%. A number of QTLs associated with dough strength, dough extensibility, dough development time, and flour water absorption were located close to the glutenin Glu-B1 locus on chromosome 1B. Identification of the chromosomal location and effect of the QTLs influencing wheat quality may hasten the development of superior wheats for target markets via marker-assisted selection.

Identification of AFLP and microsatellite markers linked with an aluminium tolerance gene in barley ( Hordeum vulgare L.).

Barley is the most sensitive among the cereals to aluminium (Al) stress and breeding for more tolerant cultivars is a priority. To enhance selection efficiency for Al tolerance in barley, PCR-based AFLP and microsatellite markers linked to a locus conferring tolerance to aluminium were identified. The study used F(2) progeny derived from a single cross between Yambla (moderately tolerant of Al) and WB229 (tolerant of Al) and developed hydroponic pulse-recovery screening methods to assess tolerance of phenotypes based on root growth. The segregation ratios of tolerant and sensitive genotypes and F(3) progeny testing suggest that a single major gene controlled Al tolerance ( Alt). In order to determine the chromosomal location of the Alt gene, we used the AFLP technique coupled with bulk segregant analysis. We evaluated tolerant and sensitive bulks using 30 combinations of EcoRI/ MseI primers, and 12 of these permitted differentiation of the sensitive and tolerant bulks. More than 1,000 amplified fragments were obtained, and 98 polymorphic bands were scored. AFLP analysis of wheat-barley chromosome addition lines indicated that the Alt gene was located on barley chromosome 4H. Four chromosome 4H-specific microsatellite markers (Bmac310, Bmag353, HVM68 and HVMCABG) were tightly linked to Alt. The large allelic variation detected with microsatellite marker Bmag353 allowed us to implement this marker for routine marker-assisted selection for Al tolerance, and 396 plants could be screened on a single gel.

Clinical characteristics of respiratory syncytial virus infection in hospitalized healthy infants and young children in Qatar.

To evaluate seasonal trends, clinical profile, and outcome of disease in previously healthy infants and young children hospitalized for respiratory syncytial virus (RSV) infection at Hamad Medical Corporation in the state of Qatar, we reviewed the records of 257 children admitted between 1 January 1996 and 31 December 1998. RSV epidemics occurred yearly during the winter months with peak hospitalizations occuring between November and February. Of the 257 admissions, 160 (62.3 per cent) were male and 97 (37.7 per cent) female. The mean age of all children was 5.7 months (range, 10 days to 32 months). The most common admitting diagnoses were bronchiolitis (59.9 per cent), pneumonia (17.5 per cent), bronchiolitis with pneumonia (8.9 per cent), possible sepsis (7.8 per cent), asthma (4.7 per cent) and apnea (1.2 per cent). A family history of asthma was quite common (63.8 per cent), although no statistical significant difference was noted in complication or length of stay. Treatment was supportive, the majority of the patients received oxygen therapy in 77.8 per cent of cases, bronchodilators in 85.4 per cent, and antibiotics therapy in 49.4 per cent. The median duration of hospital stay was 6 days (range, 1 to 29 days). Of the 14 (5.4 per cent) patients requiring intensive care, four (1.6 per cent) needed mechanical ventilation. No deaths were reported, but subjects aged < or = 12 months had a significantly higher oxygen requirement, intensive care unit admission, bronchodilators and antibiotics therapy than those > 12 months old. Within 1-2 years after admission with RSV infection, 63 of the 257 patients attended for recurrent episodes of wheezy chest. These results indicate that, during the season of infection, RSV is an important pathogen in infants and young children in the state of Qatar, highlighting the need for development of effective vaccines to ameliorate the impact of annual RSV epidemics in infants and young children.