Gated detection of the output of a fiber-optic-coupled radiation dosimeter effectively eliminated the direct contribution of Cerenkov radiation to the signal. The radiation source was an external beam radiotherapy machine that provided pulses of 6-MeV x rays. Gated detection was used to discriminate the signal collected during the radiation pulses, including Cerenkov interference, from the signal collected between the radiation pulses due only to phosphorescence from the Cu(1+)-doped glass detector. Gated detection of the long-lived phosphorescence of the Cu(1+)-doped glass provided real-time dose measurements that were linear with the absorbed dose and that were accurate for all field sizes studied.

Xanthomonas vasicola pv. vasculorum is an emerging bacterial plant pathogen that causes bacterial leaf streak on corn. First described in South Africa in 1949, reports of this pathogen have greatly increased in the past years in South America and in the United States. The rapid spread of this disease in North and South America may be due to more favorable environmental conditions, susceptible hosts and/or genomic changes that favored the spread. To understand whether genetic mechanisms exist behind the recent spread of X. vasicola pv. vasculorum, we used comparative genomics to identify gene acquisitions in X. vasicola pv. vasculorum genomes from the United States and Argentina. We sequenced 41 genomes of X. vasicola pv. vasculorum and the related sorghum-infecting X. vasicola pv. holcicola and performed comparative analyses against all available X. vasicola genomes. Time-measured phylogenetic analyses showed that X. vasicola pv. vasculorum strains from the United States and Argentina are closely related and arose from two introductions to North and South America. Gene content comparisons identified clusters of genes enriched in corn X. vasicola pv. vasculorum that showed evidence of horizontal transfer including one cluster corresponding to a prophage found in all X. vasicola pv. vasculorum strains from the United States and Argentina as well as in X. vasicola pv. holcicola strains. In this work, we explore the genomes of an emerging phytopathogen population as a first step toward identifying genetic changes associated with the emergence. The acquisitions identified may contain virulence determinants or other factors associated with the spread of X. vasicola pv. vasculorum in North and South America and will be the subject of future work.

An optical fibre point dosemeter based on the gated detection of the luminescence from a Cu(1+)-doped fused quartz detector effectively eliminated errors due to Cerenkov radiation and native fibre fluorescence. The gated optical fibre dosemeter overcomes serious problems faced by scintillation and optically stimulated luminescence approaches to optical fibre point dosimetry. The dosemeter was tested using an external beam radiotherapy machine that provided pulses of 6 MV X rays. Gated detection was used to discriminate the signal collected during the radiation pulses, which included contributions from Cerenkov radiation and native fibre fluorescence, from the signal collected between the radiation pulses, which contained only the long-lived luminescence from the Cu(1+)-doped fused quartz detector. Gated detection of the luminescence provided accurate, real-time dose measurements that were linear with absorbed dose, independent of dose rate and that were accurate for all field sizes studied.

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19Xanthomonas vasicola pv. vasculorum (Xvv) is an emerging bacterial plant pathogen that 20 causes bacterial leaf streak on corn. First described in South Africa in 1949, reports of this 21 bacteria have greatly increased in the past years in South America and in the U.S., where it is 22 now present in most of the corn producing states. Phenotypic characterization showed that 23 the emerging U.S. and South American Xvv populations may have increased virulence in corn 24 compared to older strains. To understand the genetic mechanisms behind the increased 25 virulence in this group, we used comparative genomics to identify gene acquisitions in Xvv 26 genomes from the U.S. and Argentina. We sequenced 41 genomes of Xvv and the related 27 sorghum-infecting X. vasicola pv. holcicola (Xvh). A comparison of all available X. vasicola 28 genomes showed the phylogenetic relationships in the group and identified clusters of genes 29 associated with the emerging Xvv populations. The newly acquired gene clusters showed 30 evidence of horizontal transfer to Xvv and included candidate virulence factors. One cluster, in 31 particular, corresponded to a prophage transferred from Xvh to all Xvv from Argentina and the 32 U.S. The prophage contains putative secreted proteins, which represent candidates for 33 virulence determinants in these populations and await further molecular characterization. 34