EQUIPPING DURUM WHEAT WITH A MAJOR QTL FOR RESISTANCE TO FUSARIUM DISEASES TRANSFERRED FROM THINOPYRUM ELONGATUM AND ITS PYRAMIDING WITH VALUABLE GENES FROM TH. PONTICUM

Favoured by climate changes, Fusarium head blight (FHB), a devastati ng disease of small-grain cereals worldwide, is increasingly spreading also in unusual environments where bread wheat (BW) and durum wheat (DW) are largely culti vated. The scarcity of effi cient resistance sources within adapted germplasm is parti cularly alarming for DW, mainly uti lized for human consumpti on, hence at high risk of kernel contaminati on with health-dangerous mycotoxins. To cope with this scenario, we looked outside the wheat primary genepool and recently transferred an excepti onally eff ecti ve FHB resistance QTL (Fhb-7EL) from the 7EL chromosome arm of the wheatgrass Thinopyrum elongatum onto 7DL of BW recombinant lines. The latt er already possessed valuable genes (Lr19, Yp, yield-related QTL) from a Th. ponti cum 7el1L arm segment, distally inserted onto 7DL. BW lines with the 7el1L+7EL assembly were crossed with previously developed DW-Th. ponti cum recombinants, having small 7el1L distal segments on 7AL arms. As proved by GISH analysis, homologous pairing occurred with high frequency in the shared 7el1L region between the BW and DW recombinant chromosomes. As a result, desirable 7EL+7el1L recombinant types with 2n = 28 were isolated in the BC1 progeny to DW, aided by PCR-based markers. Homozygous recombinant plants selected in the BC2F2 progeny were challenged by Fusarium graminearum spike inoculati on to verify the Fhb-7EL QTL effi cacy into the DW background. Infecti on outcomes confi rmed what previously observed in BW, with around 90% reducti on of disease severity vs. suscepti ble controls, invariably associated with presence of the Fhb-7EL QTL. Moreover, as for the BW types, the same Fhb-7EL was found to provide the novel DW recombinants also with resistance to the crown rot disease, as from seedling infecti on with F. culmorum. Through alien segment pyramiding we succeeded in equipping DW with a very eff ecti ve barrier against diff erent Fusarium diseases and other positi ve att ributes contributi ng to yield security and safety

The effect of a paraffin screen on the neutron dose at the maze door of a 15 MV linear accelerator

Purpose: The purpose of this study was to explore the effects of a paraffin screen located at various positions in the maze on the neutron dose equivalent at the maze door. Methods: The neutron dose equivalent was measured at the maze door of a room containing a 15 MV linear accelerator for x-ray therapy. Measurements were performed for several positions of the paraffin screen covering only 27.5% of the cross-sectional area of the maze. The neutron dose equivalent was also measured at all screen positions. Two simple models of the neutron source were considered in which the first assumed that the source was the cross-sectional area at the inner entrance of the maze, radiating neutrons in an isotropic manner. In the second model the reduction in the neutron dose equivalent at the maze door due to the paraffin screen was considered to be a function of the mean values of the neutron fluence and energy at the screen. Results: The results of this study indicate that the equivalent dose at the maze door was reduced by a factor of 3 through the use of a paraffin screen that was placed inside the maze. It was also determined that the contributions to the dosage from areas that were not covered by the paraffin screen as viewed from the dosimeter, were 2.5 times higher than the contributions from the covered areas. This study also concluded that the contributions of the maze walls, ceiling, and floor to the total neutron dose equivalent were an order of magnitude lower than those from the surface at the far end of the maze. Conclusions: This study demonstrated that a paraffin screen could be used to reduce the neutron dose equivalent at the maze door by a factor of 3. This paper also found that the reduction of the neutron dose equivalent was a linear function of the area covered by the maze screen and that the decrease in the dose at the maze door could be modeled as an exponential function of the product \u3d5\uaf\ub7\u112 at the screen.Peer reviewed: YesNRC publication: Ye

The effect of a paraffin screen on the neutron dose at the maze door of a 15 MV linear accelerator

Purpose: The purpose of this study was to explore the effects of a paraffin screen located at various positions in the maze on the neutron dose equivalent at the maze door. Methods: The neutron dose equivalent was measured at the maze door of a room containing a 15 MV linear accelerator for x-ray therapy. Measurements were performed for several positions of the paraffin screen covering only 27.5% of the cross-sectional area of the maze. The neutron dose equivalent was also measured at all screen positions. Two simple models of the neutron source were considered in which the first assumed that the source was the cross-sectional area at the inner entrance of the maze, radiating neutrons in an isotropic manner. In the second model the reduction in the neutron dose equivalent at the maze door due to the paraffin screen was considered to be a function of the mean values of the neutron fluence and energy at the screen. Results: The results of this study indicate that the equivalent dose at the maze door was reduced by a factor of 3 through the use of a paraffin screen that was placed inside the maze. It was also determined that the contributions to the dosage from areas that were not covered by the paraffin screen as viewed from the dosimeter, were 2.5 times higher than the contributions from the covered areas. This study also concluded that the contributions of the maze walls, ceiling, and floor to the total neutron dose equivalent were an order of magnitude lower than those from the surface at the far end of the maze. Conclusions: This study demonstrated that a paraffin screen could be used to reduce the neutron dose equivalent at the maze door by a factor of 3. This paper also found that the reduction of the neutron dose equivalent was a linear function of the area covered by the maze screen and that the decrease in the dose at the maze door could be modeled as an exponential function of the product \u3d5\uaf\ub7\u112 at the screen.Peer reviewed: YesNRC publication: Ye