Genetic analysis of crosses between hexaploid bread (Triticum aestivum L.) and tetraploid durum wheat (T. turgidum spp durum)

An ability to access and then transfer genes from bread wheat into durum wheat and viceversa is an excellent way to improve the genetic architecture of these two closely related but a different ploidy level wheat species. Bread wheat has number of desirable characters such as partial resistance to crown rot and head blight that can complement durum wheat. Durum wheat has a number of desirable traits such as seed weight, seed colour, and nematode tolerance that can complement bread wheat. Therefore, developing hexaploid/tetraploid crosses can be one of the useful breeding techniques to addresses bread and durum wheat improvement for yield, pest and disease resistance. Before screening for any traits that have been incorporated from bread and durum wheat into hexaploid/tetraploid derived lines, it is necessary to understand how these inter-ploidy crosses are different with regards to inheritance of the nuclear and cytoplasmic genomes. Thus the present study aimed to screen nuclear and cytoplasmic genome inheritance of different hexaploid/tetraploid wheat crosses. To determine the proportion of nuclear genome inheritance from either parent of the hexaploid/tetraploid derived wheat lines, high-density polymorphic DArT markers and cytological genomic and fluorescence in situ hybridisation were employed. To investigate the cytoplasmic mitochondrial inheritance, targeted cytochrome maturation genes ccmfn, ccmfc and nad3 genes of bread and durum wheat were sequenced using Sanger sequencing. Different exaploid/tetraploid crosses were established following different breeding techniques, i.e., reciprocal crosses, crosses involving different hexaploid and tetraploid cultivars, crosses made at different time points; and crosses involving a bread wheat cultivar with an introgressed 2G segment. Retention of D-genome chromosomes, proportion of chromosome A and B genome alleles inherited, and how introgressed 2G segment of bread wheat cultivars inherits when combined with tetraploid durum wheat were discussed in different respective research chapters. This thesis also has an additional chapter summarising the maternal inheritance of cytoplasmic DNA in polyploidy crosses. Overall this study has illustrated how hexaploid/tetraploid wheat crosses can be used in the commercial plant breeding programs for bread and durum wheat improvement

Pentaploid wheat hybrids: applications, characterisation, and challenges

Interspecific hybridisation between hexaploid and tetraploid wheat species leads to the development of F1 pentaploid hybrids with unique chromosomal constitutions. Pentaploid hybrids derived from bread wheat (Triticum aestivum L.) and durum wheat(Triticum turgidum spp. durum Desf.) crosses can improve the genetic background of either parent by transferring traits of interest. The genetic variability derived from bread and durum wheat and transferred into pentaploid hybrids has the potential to improve disease resistance, abiotic tolerance, and grain quality, and to enhance agronomic characters. Nonetheless, pentaploid wheat hybrids have not been fully exploited in breeding programs aimed at improving crops. There are several potential barriers for efficient pentaploid wheat production, such as low pollen compatibility, poor seed set, failed seedling establishment, and frequent sterility in F1 hybrids. However, most of the barriers can be overcome by careful selection of the parental genotypes and by employing the higher ploidy level genotype as the maternal parent. In this review, we summarize the current research on pentaploid wheat hybrids and analyze the advantages and pitfalls of current methods used to assess pentaploid-derived lines. Furthermore, we discuss current and potential applications in commercial breeding programs and future directions for research into pentaploid wheat

A study on conventional IMRT and RapidArc treatment planning techniques for head and neck cancers

AimTo evaluate the performance of volumetric arc modulation with RapidArc against conventional IMRT for head and neck cancers.BackgroundRapidArc is a novel technique that has recently been made available for clinical use. Planning study was done for volumetric arc modulation with RapidArc against conventional IMRT for head and neck cancers.Materials and methodsTen patients with advanced tumors of the nasopharynx, oropharynx, and hypopharynx were selected for the planning comparison study. PTV was delineated for two different dose levels and planning was done by means of simultaneously integrated boost technique. A total dose of 70[[ce:hsp sp="0.25"/]]Gy was delivered to the boost volume (PTV boost) and 57.7[[ce:hsp sp="0.25"/]]Gy to the elective PTV (PTV elective) in 35 equal treatment fractions. PTV boost consisted of the gross tumor volume and lymph nodes containing visible macroscopic tumor or biopsy-proven positive lymph nodes, whereas the PTV elective consisted of elective nodal regions. Planning was done for IMRT using 9 fields and RapidArc with single arc, double arc. Beam was equally placed for IMRT plans. Single arc RapidArc plan utilizes full 360° gantry rotation and double arc consists of 2 co-planar arcs of 360° in clockwise and counter clockwise direction. Collimator was rotated from 35 to 45° to cover the entire tumor, which reduced the tongue and groove effect during gantry rotation. All plans were generated with 6[[ce:hsp sp="0.25"/]]MV X-rays for CLINAC 2100 Linear Accelerator. Calculations were done in the Eclipse treatment planning system (version 8.6) using the AAA algorithm.ResultsDouble arc plans show superior dose homogeneity in PTV compared to a single arc and IMRT 9 field technique. Target coverage was almost similar in all the techniques. The sparing of spinal cord in terms of the maximum dose was better in the double arc technique by 4.5% when compared to the IMRT 9 field and single arc techniques. For healthy tissue, no significant changes were observed between the plans in terms of the mean dose and integral dose. But RapidArc plans showed a reduction in the volume of the healthy tissue irradiated at V15[[ce:hsp sp="0.25"/]]Gy (5.81% for single arc and 4.69% for double arc) and V20[[ce:hsp sp="0.25"/]]Gy (7.55% for single arc and 5.89% for double arc) dose levels when compared to the 9-Field IMRT technique. For brain stem, maximum dose was similar in all the techniques. The average MU (±SD) needed to deliver the dose of 200[[ce:hsp sp="0.25"/]]cGy per fraction was 474[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]80[[ce:hsp sp="0.25"/]]MU and 447[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]45[[ce:hsp sp="0.25"/]]MU for double arc and single arc as against 948[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]162[[ce:hsp sp="0.25"/]]MU for the 9-Field IMRT plan. A considerable reduction in maximum dose to the mandible by 6.05% was observed with double arc plan. Double arc shows a reduction in the parotid mean dose when compared with single arc and IMRT plans.ConclusionRapidArc using double arc provided a significant sparing of OARs and healthy tissue without compromising target coverage compared to IMRT. The main disadvantage with IMRT observed was higher monitor units and longer treatment time

Association between presence of Triticum timopheevii introgression and D-genome retention in hexaploid/tetraploid wheat crosses

The 2G Triticum timopheevii introgression harbours genes for multiple disease resistance and quality traits in bread wheat. In order to transfer this segment from bread wheat into durum, the bread wheat line Sunguard, which carries this introgressed 2G segment was crossed with three tetraploid durum parents. A significant difference was observed in the segregation ratio of the 2G segment in the different crosses at the F2 generation with two of the three populations indicating segregation distortion against the hexaploid 2G segment. In these populations, the presence of the 2G segment was strongly correlated with the presence of D-genome chromosomes. These results were confirmed in the F4 generation of these populations. Six plants were identified in the F4 generation, which had retained the introgressed 2G segment in a homozygous condition and did not have a complete D-genome set. Two of these lines only had two non-homologous D-genome chromosomes in the F5 generation. Thus, the 2G segment and possibly other translocations can be transferred into durum wheat through hexaploid/tetraploid hybridisation

The effects of target motion in kV-CBCT imaging

Background: To study the impact of target motion in kV-CBCT imaging. Material/Methods: To simulate the respiratory movement, dynamic phantom was programmed to move in threedimension with a period of four seconds and of two different amplitudes (PA1 and PA2). The targets of well defined geometries (cylinder, sphere, solid triangle, U-shaped and dumbbell) were made using wax. The static targets were CT imaged (reference image). Using CBCT, the targets in static and dynamic modes were imaged under full-fan beam. The line profiles along cranio-caudal direction, influence of target's initial moving phase and volume estimation using auto-contouring tool were used to analyze the effects of target motion on CBCT imaging. Results: Comparing the line profiles of targets in CBCT with CT, the length of average HU spread was reduced by 42.54±1.85%, except the cylindrical target which is by 19.35% for PA1. The percentage difference in reconstructed volume of static targets imaged using CBCT and CT (HU WW -500 to 0) ranges from -1.32% to -5.94%. The volume losses for targets imaged in dynamic mode PA1 ranges from 14.35% to 30.95% and for PA2 it was 21.29% to 43.80%. The solid triangle and cylindrical targets suffered the maximum and minimum volume losses respectively. Conclusions: Non-gated CBCT imaging of the moving targets encounters significant loss of volumetric information, due to scatter artifacts. These may result in a systematic error in re-contouring when CBCT images are used for the re-planning work

Genome inheritance in populations derived from hexaploid/ tetraploid and tetraploid/hexaploid wheat crosses

Hexaploid/tetraploid and tetraploid/hexaploid wheat hybrids were established using the hexaploid (Triticum aestivum L.) bread wheat LRC2010-150 and the tetraploid durum wheat (T. turgidum spp. durum) WID802. Thirty F2 progeny from each cross were characterised using Diversity Arrays Technology (DArTseq™) markers to determine whether there are differences between the crosses in the proportion of A, B and D genomic material inherited from each parent. Inheritance of the A and B genome from the tetraploid durum parent varied from 32 to 63% among the 60 lines assessed, and results indicated significant differences between the two F2 populations in the mean overall proportion of chromosomes A and B inherited from each parent. Significant differences were also observed between the crosses in the proportion of chromosomal segments on 2B, 3A, 3B and 4A inherited from the tetraploid parent. The F2 populations also showed significant differences in the average retention of D chromosomes per line with the tetraploid/hexaploid cross retaining a mean of 2.83 chromosomes while the reciprocal cross retained a mean of 1.8 chromosomes per line. A strong negative correlation was observed in individual lines from both populations between the proportion of the A and B genome inherited from the tetraploid durum parent and the retention of the D genome. The implication of these results for the design of efficient crossing strategies between hexaploid and tetraploid wheats is discussed

Exit fluence analysis using portal dosimetry in volumetric modulated arc therapy

AimIn measuring exit fluences, there are several sources of deviations which include the changes in the entrance fluence, changes in the detector response and patient orientation or geometry. The purpose of this work is to quantify these sources of errors.BackgroundThe use of the volumetric modulated arc therapy treatment with the help of image guidance in radiotherapy results in high accuracy of delivering complex dose distributions while sparing critical organs. The transit dosimetry has the potential of Verifying dose delivery by the linac, Multileaf collimator positional accuracy and the calculation of dose to a patient or phantom.Materials and methodsThe quantification of errors caused by a machine delivery is done by comparing static and arc picket fence test for 30 days. A RapidArc plan, created for the pelvis site was delivered without and with Rando phantom and exit portal images were acquired. The day to day dose variation were analysed by comparing the daily exit dose images during the course of treatment. The gamma criterion used for analysis is 3% dose difference and 3[[ce:hsp sp="0.25"/]]mm distance to agreement with a threshold of 10% of maximum dose.ResultsThe maximum standard deviation for the static and arc picket fence test fields were 0.19[[ce:hsp sp="0.25"/]]CU and 1.3[[ce:hsp sp="0.25"/]]CU, respectively. The delivery of the RapidArc plans without a phantom shows the maximum standard deviation of 1.85[[ce:hsp sp="0.25"/]]CU and the maximum gamma value of 0.59. The maximum gamma value for the RapidArc plan delivered with the phantom was found to be 1.2. The largest observed fluence deviation during the delivery to patient was 5.7% and the maximum standard deviation was 4.1[[ce:hsp sp="0.25"/]]CU.ConclusionIt is found from this study that the variation due to patient anatomy and interfraction organ motion is significant

Treatment planning and dosimetric comparison study on two different volumetric modulated arc therapy delivery techniques

AimTo compare and evaluate the performance of two different volumetric modulated arc therapy delivery techniques.BackgroundVolumetric modulated arc therapy is a novel technique that has recently been made available for clinical use. Planning and dosimetric comparison study was done for Elekta VMAT and Varian RapidArc for different treatment sites.Materials and methodsTen patients were selected for the planning comparison study. This includes 2 head and neck, 2 oesophagus, 1 bladder, 3 cervix and 2 rectum cases. Total dose of 50[[ce:hsp sp="0.25"/]]Gy was given for all the plans. All plans were done for RapidArc using Eclipse and for Elekta VMAT with Monaco treatment planning system. All plans were generated with 6[[ce:hsp sp="0.25"/]]MV X-rays for both RapidArc and Elekta VMAT. Plans were evaluated based on the ability to meet the dose volume histogram, dose homogeneity index, radiation conformity index, estimated radiation delivery time, integral dose and monitor units needed to deliver the prescribed dose.ResultsRapidArc plans achieved the best conformity (CI95%[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]1.08[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.07) while Elekta VMAT plans were slightly inferior (CI95%[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]1.10[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.05). The in-homogeneity in the PTV was highest with Elekta VMAT with HI equal to 0.12[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.02[[ce:hsp sp="0.25"/]]Gy when compared to RapidArc with 0.08[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.03. Significant changes were observed between the RapidArc and Elekta VMAT plans in terms of the healthy tissue mean dose and integral dose. Elekta VMAT plans show a reduction in the healthy tissue mean dose (6.92[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]2.90)[[ce:hsp sp="0.25"/]]Gy when compared to RapidArc (7.83[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]3.31)[[ce:hsp sp="0.25"/]]Gy. The integral dose is found to be inferior with Elekta VMAT (11.50[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]6.49)[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]104[[ce:hsp sp="0.25"/]]Gy[[ce:hsp sp="0.25"/]]cm3 when compared to RapidArc (13.11[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]7.52)[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]104[[ce:hsp sp="0.25"/]]Gy[[ce:hsp sp="0.25"/]]cm3. Both Varian RapidArc and Elekta VMAT respected the planning objective for all organs at risk. Gamma analysis result for the pre-treatment quality assurance shows good agreement between the planned and delivered fluence for 3[[ce:hsp sp="0.25"/]]mm DTA, 3% DD for all the evaluated points inside the PTV, for both VMAT and RapidArc techniques.ConclusionThe study concludes that a variable gantry speed with variable dose rate is important for efficient arc therapy delivery. RapidArc presents a slight improvement in the OAR sparing with better target coverage when compared to Elekta VMAT. Trivial differences were noted in all the plans for organ at risk but the two techniques provided satisfactory conformal avoidance and conformation