Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Mal de Río Cuarto (MRC) is a devastating disease that reduces yield, quality and economic value of maize in Argentina. The objective of the present study was to map quantitative trait loci (QTL) for reactions to MRC from recombinant inbred lines (RILs). Reactions to the endemic MRC disease were evaluated in 145 advanced F2:6 lines, derived from a cross between a resistant (BLS14) and a susceptible (Mo17) line, at four environments in the temperate semi-arid crop region of Argentina. The evaluations of disease score (SCO), disease incidence (INC) and disease severity (SEV) were carried out on each individual RIL. Low heritability estimates were found across environments for SCO (0·23), INC (0·27) and SEV (0·22). A genetic map of simple sequence repeat (SSR) markers covering a total genetic distance of 1019 cM was built. QTL for resistance to MRC disease were found on different maize chromosomes. Four significant QTL, each explaining between 0·08 and 0·14 of the total phenotypic variation, were located on chromosomes 1, 4 and 10. Two QTL specific to the INC, and one specific to SEV, may be involved in different mechanisms of resistance to MRC. Although MRC reaction is highly affected by environmental effects, the QTL×environment interaction for INC and SEV was low. Most of the QTL for reaction to MRC detected in the present study were mapped to regions of the maize genome containing genes conferring resistance to various pathogens. The significant QTL across environments are good candidates to select for MRC resistance.

Objectives: To investigate the indications for, and outcome of, cardiac catheterisation in infants weighing less than 2500 g at a single institution over an 8-year period. Patients and Methods: We assessed all infants who were less than 2500 g at the time of cardiac catheterisation at Texas Children's Hospital from January 1993 to January 2001. Comparisons of morbidity and mortality were drawn with an equivalent number of infants of similar age weighing greater than 2500 g seen over the same period of time. Results: We performed interventional procedures in 22, and diagnostic catheterisations in 12 infants weighing less than 2500 g. Interventions included pulmonary valvoplasty in six patients, balloon angioplasty of critical coarctation in one, aortic valvoplasty in two, septostomy in ten, and coil occlusion of an arteriovenous malformation, redirection of a subclavian venous line, and coil occlusion of a patent arterial duct in one patient each. The median age at catheterisation was 5 days for children less than 2500 g, and 10 days for those above 2500 g. The median weights were 2.3 kg and 3.3 kg, and the median gestational ages were 35 weeks and 38 weeks, for the two respective groups. Of those weighing less than 2500 g, two died (6%), with no deaths occurring in those weighing more than 2500 g. In 3 patients weighing less than 2500 g (9%), there was vascular compromise, one child with bilateral femoral venous obstruction requiring fasciotomy compared, to one in the group weighing greater than 2500 g (2%). Conclusion: There is a significantly increased risk of mortality and vascular compromise in infants weighing less than 2500 g. Interventional catheterisation in these infants may be lifesaving, but given the aforementioned risks, diagnostic catheterisation should be deferred if possible in favor of noninvasive modalities.

‘Mal de Río Cuarto’ (MRC) disease, caused by a member of the family Reoviridae belonging to the genus Fijivirus, is considered to be the most damaging viral disease of maize (Zea mays L.) in Argentina. Resistance to MRC disease is a quantitative trait with moderate heritability ranging from 0·44 to 0·56. The objective of this study was to identify simple sequence repeats (SSR) loci linked to quantitative trait loci (QTL) contributing to MRC disease resistance. Two hundred and twenty-seven F3 derived-lines from a cross between a susceptible inbred line, Mo17, and a partially resistant inbred line, BLS14, were evaluated across four Río Cuarto environments. A disease severity index (DSI) based on disease grades was calculated and used to rate F3 derived-lines for their resistance to MRC disease. A subset of parental F2 plants belonging to susceptible and resistant F3 derived-lines from field assessments was assayed for 180 SSR primer pairs to map resistance genes. Fifty-six maize SSR were employed for the testing of linkage among DNA markers and the mapping of QTL through composite interval mapping. Resistance to MRC disease was affected by two QTL on chromosomes 1 and 8 which showed overdominance and dominant gene action, respectively. A simultaneous fit with these QTL in the joint analyses explained 36·2% of the phenotypic variance. In spite of the fact that relative efficiency of marker-assisted selection (MAS) in comparison to phenotypic selection was close to 1, the mapped QTL could improve the efficiency of efforts in breeding for resistance to MRC disease.

No genetic estimates for resistance to Mal de Río Cuarto (MRC) disease in Zea mays (L.) are currently available in the literature. Therefore, the objectives of this investigation were (i) to estimate the variance and heritability of partial resistance to MRC disease and of other agronomic traits from maize families and (ii) to examine associations among MRC disease severity values across different environments and between MRC and other agronomic traits. These estimations, obtained in an endemic area, could contribute to the design of efficient enhancement programmes and evaluation activity for the improvement of MRC resistance. The research was conducted by testing 227 F3 derived-lines from a cross between a susceptible dent line, Mo17, and a partially resistant flint line, BLS14, for MRC disease at two Río Cuarto locations in each of 2 years. The resistance of the lines, measured with a disease severity index (DSI), was normally distributed across environments. Genotypic variances were highly significant on all scoring environments. Estimates of genotype–environment interaction were also significant, suggesting that certain genotypes have little stability over different environments. For disease severity index all estimates demonstrated moderate heritabilities ranging from 0.44 to 0.56 and were similar when based on individual environments or across environment. Confidence interval widths ranged from 34.88 to 50.30% as large as the heritability point estimate. The correlations between environments were small enough to indicate that families did not rank similarly in individual environments for MRC resistance. Disease severity index correlated significantly (P<0.01) with plant height, leaf surface, leaf border, leaf length and tassel type. Heritability estimates for plant height and tassel type were 0.48 and 0.38 respectively and for the various leaf traits heritability values were very low. On the basis of the substantial genotype–environment interaction and the little association between DSI values in the different environments, selection for an increased resistance to MRC disease would require evaluation of germplasm across multiple years and locations. Tassel type would be a useful predictor of DSI and can be used effectively to improve screening procedures.

Repetitious gene cassettes that encode the consensus decapeptide repeat of Mytilus edulis bioadhesive protein were cloned and expressed in Escherichia coli. The bioadhesive precursor (BP, Mx−25,000) was expressed from one 600-bp gene comprised of a 30-bp unit repeat. The repetitious gene appeared stable in a T7-based host/vector system.

Using the T7 expression system for induction, BP was produced at levels approaching 60% of total cell protein. BP was found both in intracellular inclusions and in the soluble fraction. Interestingly, methionine was processed from the N-terminus of the purified protein to give an authentic consensus precursor protein.

A family of totally synthetic genes coding for multiple tandem repeats of the amino acid sequence (Gly-Pro-Pro) has been prepared and inserted into the Clal cloning site of the expression vector pJL6. A representative recombinant plasmid, pACI, with an insert of about 340 bp, was established in an Escherichia coli strain bearing a defective λ prophage, to study expression of the CII-collagen analog fusion protein produced from pACI upon heat induction. The in vivo levels of synthetic gene expression obtained showed that the fusion protein was synthesized in E. coli, but was labile compared to other cellular proteins. This degradation could be significantly reduced by the genetic inhibition of a bacterial protease system.

The nucleation and glide of misfit dislocations in GaAs/Si system is investigated using transmission electron microscopy. GaAs epilayers of different thicknesses were examined by electron microscopy (plan and cross-section) and the elastic strain remaining in the film has been related to the average spacing of the misfit dislocations at the interface. A model is developed based on minimum energy considerations to determine the strain-thickness relationship. The theoretical predictions of strain relaxation are compared with experimental observations using high resolution electron microscopy.

The growth of high-quality single crystal GaAs on Si wafers up to six inches in diameter by organometallic chemical vapor deposition (OMCVD) is reported. These wafers have specular surfaces, excellent thickness uniformity, and are shown to have properties comparable to those of smaller diameter GaAs on Si wafers. The mechanical and electrical properties of the six inch GaAs on Si wafers are shown to be suitable for GaAs device fabrication.

GaAs epitaxial layers grown on Si substrates up to 4 inches in diameter by OMCVD are characterized with respect to the materials parameters important for their application for device and circuit manufacturing. The layers are characterized using commercial flatness and surface quality measurement instrumentation, x-ray diffraction, Schottky diode characteristics, and photoluminescence. The 4-inch diameter GaAs epilayers are a singleoriented phase and are of comparable quality to GaAs epilayers grown on smaller diameter Si substrates.

InxGa11-xAs-GaAsl-yPy strained layer superlattice buffer layers have been used to reduce threading dislocations in GaAs grown on Si substrates. However, for an initially high density of dislocations, the strained layer superlattice is not an effective filtering system. Consequently, the emergence of dislocations from the SLS propagate upwards into the GaAs epilayer. However, by employing thermal annealing or rapid thermal annealing, the number of dislocation impinging on the SLS can be significantly reduced. Indeed, this treatment greatly enhances the efficiency and usefulness of the SLS in reducing the number of threading dislocations.

The electronic properties of tilt boundaries with misorientation angles ranging from 0 to 30° in n-type GaAs bicrystal layers have been investigated. The current-voltage and capacitance-voltage characteristics are consistent with a double-depletion-region model. The height of the grain boundary potential barrier remains constant while the density of grain boundary states varies with misorientation angle. Deep level transient spectroscopy has revealed the presence of two bands of grain boundary states at approximately 0.65 and 0.9 eV below the conduction band. These states are attributed to bond reconstruction at the grain boundary.