Donor Blocks Research Articles

Dihydro‐1H‐Pyrazoles as Donor Blocks in Donor–Acceptor Chromophores for Electro‐Optics: A DFT Study of Hyperpolaizability and Electronic Excitations

ABSTRACTA diverse set of promising donors for donor–acceptor chromophores based on dihydro‐1H‐pyrazole (pyrazoline) for use in electro‐optics was investigated using DFT at M06‐2X/aug‐cc‐pVDZ level of theory. These calculations showed that it is possible to achieve a molecular hyperpolarizability of up to 1700*10−30 esu (up to three times higher compared to conventional diethylaniline donors) for a simple tricyanofuran‐based acceptor by carefully tuning the donor structure. It was shown that the molecular hyperpolarizability is mainly affected by the substituents in the aryl rings in positions 3 and 1 of the pyrazoline cycle, while the substituents of the aryl ring in position 5 and the pyrazoline ring itself can be varied without significant effects on the hyperpolarizability. For one of the compounds, a detailed study of the lowest energy electronic excitation was performed using the TD‐DFT, confirming the role of the pyrazoline ring as a secondary donor.

New synthesis of oligosaccharides modelling the M epitope of the Brucella O-polysaccharide.

Brucellosis is a dangerous zoonotic disease caused by bacteria of the genus Brucella. Diagnosis of brucellosis is based on the detection in animal and human sera of antibodies to the O-polysaccharide of Brucella lipopolysaccharide. The currently employed serodiagnosis of brucellosis relies on the use of the Brucella O-polysaccharide as a diagnostic antigen. However, the existence of bacterial species, which also express O-polysaccharides structurally similar to that of Brucella, may decrease the specificity of the brucellosis detection due to false-positive test results. It has been shown that the efficiency of the test can be significantly improved by using synthetic oligosaccharides that correspond to the so-called M epitope of the Brucella O-antigen. This epitope is characterized by an α-(1→3)-linkage between d-perosamine units and is unique to Brucella. Here we report on an efficient approach to the synthesis of oligosaccharides that model the M epitope of the Brucella O-polysaccharide. The approach is based on the use of the α-(1→3)-linked disaccharide thioglycoside as the key donor block. Its application allowed the straightforward assembly of a set of four protected oligosaccharides, which includes a disaccharide, two trisaccharides, and a tetrasaccharide, in five glycosylation steps. The synthesized oligosaccharides are planned to be used in the development of diagnostic tools for identifying brucellosis in humans and domestic animals, as well as a potential vaccine against it.

High‐Performance Terpolymers with Well‐Defined Structures Facilitate PCE Over 19% for Polymer Solar Cells

AbstractTernary copolymerization is a cost‐effective and time‐saving approach to improve device performance and batch stability of polymer donors. However, the structure of the ternary polymer donor obtained by the traditional one‐pot polymerization is vague due to the different monomer reaction order, which has a great influence on the absorption, crystallization, molecular stacking, and device performance. Therefore, it is necessary to obtain terpolymers with definite structures, and systematically study the differences in device properties of polymers with different sequence structures. Herein, three terpolymers D1, D2, and D3 are developed. Random copolymer D3 is obtained via the traditional one‐pot method while alternating copolymer donor D1 and block copolymer D2 are synthesized by stepwise polymerization. Because the block copolymer D2 possess periodic sequence distribution and retains the excellent properties of the two polymer matrix very well, the D2‐based device shows enhanced tightened π‐face‐on molecular stacking, distinguished efficient exciton dissociation, and decreased energy loss. As a result, the D2:L8‐BO‐based polymer solar cells achieve one of a record power conversion efficiency of 19.03%. The work demonstrates changing the sequence structure of the polymers to synthesize well‐defined structures polymer donors not only maintains the features of polymer matrix, but also combines the advantages of ternary copolymerization.

Navigating Tissue Microarray Construction: A Guide for Avoiding Pitfalls and Mastering Key Technical Aspects

Introduction: Tissue Microarray (TMA) is a novel technique that is now integral in pre-clinical and translational research. In resourcelimited settings, automated microarrayers and molds are out of reach, and manual TMA construction may be done instead. Aim: To explore the pitfalls encountered while constructing manual TMAs and to troubleshoot these problems using the available resources. Materials and Methods: A cross-sectional study was done between September 2019 and March 2021 in the Department of Pathology at a tertiary healthcare center in New Delhi using 60 mastectomy specimens. Five manual TMAs were constructed using simple, cheap, and readily available resources. Problems encountered during the construction were identified and documented. Solutions attempted to troubleshoot the common problems were documented, and their outcomes were evaluated. Results: Difficulty in core extraction, cracking of TMAs during core insertion, loss of cores, misalignment of cores, bulging of blocks, difficulty in sectioning due to non-uniform cores, and loss of cores during sectioning were major problems identified. Simple measures such as prior warming of both donor and recipient blocks, use of punch biopsy needles with a plunger, maintaining a margin around the cores, using wax cores to align cores, and adequate cooling prior to sectioning helped in overcoming these problems. Other solutions that were attempted but did not yield satisfying results included the use of agarose in paraffin blocks and the use of liquid wax to seal cracks and gaps. Conclusion: Manual TMA is not only feasible, it is easy to construct once the technique is learned and the problems that commonly arise in its construction are tackled. The modifications suggested in the present study can aid in constructing these microarrays faster and avoid both wastage of time and resources. TMAs can thus be used as an alternative to traditional paraffinbased techniques for research applications in resource-limited centers with high patient loads.

18.6% Efficiency All-Polymer Solar Cells Enabled by a Wide Bandgap Polymer Donor Based on Benzo[1,2-d:4,5-d']bisthiazole.

The limited selection of wide bandgap polymer donors for all-polymer solar cells (all-PSCs) is a bottleneck problem restricting their further development and remains poorly studied. Herein, a new wide bandgap polymer, namely PBBTz-Cl, is designed and synthesized by bridging the benzobisthiazole acceptor block and chlorinated benzodithiophene donor block with thiophene units for application as an electron donor in all-PSCs. PBBTz-Cl not only possesses wide bandgap and deep energy levels but also displays strong absorption, high-planar structure, and good crystallinity, making it a promising candidate for application as a polymer donor in organic solar cells. When paired with the narrow bandgap polymer acceptor PY-IT, a fibril-like morphology forms, which facilitates exciton dissociation and charge transport, contributing to a power conversion efficiency (PCE) of 17.15% of the corresponding all-PSCs. Moreover, when introducing another crystalline polymer acceptor BTP-2T2F into the PBBTz-Cl:PY-IT host blend, the absorption ditch in the range of 600-750nm is filled, and the blend morphology is further optimized with the trap density reducing. As a result, the ternary blend all-PSCs achieve a significantly improved PCE of 18.60%, which is among the highest values for all-PSCs to date.

Blue/green-to-transmissive electrochromic-supercapacitor bifunctional polymer films via electropolymerization containing 3,4-propylenedioxythiophene derivatives as novel donor units

Developing novel donor-acceptor conjugated polymers is essential to obtain desirable electrochromic properties. Herein, naphthobisthiadiazole, 2,1,3-benzothiadiazole and 2,3-dimethylquinoxaline as electron-deficient units, along with ProDOT-Me2 as an electron-rich block, to create novel donor-acceptor (D-A) type electrochromic polymers (pQWL, pBt and pDBt) for the investigation. The electrochemical/spectroelectrochemistry/colorimetry properties-structure of the ProDOT-Me2-based D-A polymers were systematically investigated. Benefiting from ProDOT-Me2 as an available donor block and matching electron-accepting units for the construction of D-A structures, pQWL and pDBt exhibited blue/green-to-transmissive with excellent electrochromic properties. The pQWL and pDBt exhibited remarkable bifunctional characteristics with reversible colors-to-high transmissive states, shorter switching times, long-term stability, good color memory, excellent coloration efficiency, low color chromaticity in the oxidation state, and large area-specific capacitance. These findings highlight the significant potential of ProDOT-Me2-based D-A polymers as versatile building units for polymer electrochromic-supercapacitor bifunctional materials.

A DMBA-induced ovarian cancer model: Could it be clinically useful to test OncoTherad and erythropoietin as anticancer approaches?

e17589 Background: The term ovarian carcinoma (OC) refers to a heterogeneous collection of five distinct diseases known as histotypes. While histotype-specific treatment is still a clinical challenge, well-characterized models are required for testing new therapies. OncoTherad is a nanoimmunotherapy developed by University of Campinas/Brazil, which exhibits antitumor properties. Erythropoietin (EPO) has cytoprotective effects including in the ovaries. We assessed whether a chemically-induced animal OC model was representative of human disease by evaluating which histotype it best represents. We evaluated both mutational and immunohistochemical (IHC) biomarkers routinely used for human OC and used the observed features to provide context in the evaluation of OncoTherad and EPO effects. Methods: Thirty-five Fischer rats were distributed into 5 groups: Control (Sham surgery); Cancer (7,12-dimethylbenzoanthracene – DMBA injection in the ovarian bursa, 1.25 mg/kg); OncoTherad (20mg/kg IP); EPO (8.4 µg/kg IP); and OncoTherad+EPO (same doses). Ovary specimens were formalin-fixed into paraffin-embedded donor blocks. After DNA extraction and tissue microarray construction, we assessed typical gene mutations directly by Sanger sequencing (Pik3ca, Ctnnb1, and Kras) or indirectly using IHC surrogates (Arid1a and p53). Finally, we examined biomarkers typical of different OC histotypes (Wt1, Pr, Hnf1β) as well as lymphocyte density (CD3) by IHC. Results: The results were consistent across the cancer-induced animals. The majority of abnormal epithelial cells were Wt1+, Pr-, and Hnf1b-. Therefore, our rat model of DMBA-induced ovarian cancer was most likely serous type ovarian carcinoma, in agreement with the histopathological analysis. The ovarian lesions were molecularly similar to low-grade serous ovarian carcinoma as abnormal pattern of p53 staining was rarely observed. Loss of immunoreactivity for Arid1a protein was seen in some abnormal epithelium. However, the interpretability of mutation surrogates in rat tissues may not always be consistent with IHC analysis systems applied for human tissues. Furthermore, DNA sequencing did not reveal driver mutations in any of the sampled specimens. The treatments, especially OncoTherad+EPO, increased the number of CD3 positive immune cells. After EPO treatment, the tumor and abnormal areas showed a higher number of CD3+ lymphocytes than the normal regions; following a previous work, this could be due to substantial presence of Foxp3 positive cells. Conclusions: The features analyzed favored a low-grade serous carcinoma model in which treatments with OncoTherad and EPO showed immunomodulatory properties related to the reduction of ovarian lesions seen in previous work. The overall data highlight the importance of further characterizations of animal models to provide a complete and specific panel for testing new drugs.

Constructing high-density tissue microarrays with a novel method and a self-made tissue-arraying instrument.

Tissue microarrays (TMAs), also called tissue chips, contain hundreds to thousands of tissue cores obtained from different tissue donor blocks. By using TMA technology, a molecular marker, such as protein, RNA or DNA, can be simultaneously examined in hundreds of different specimens under the same experimental conditions. A growing number of previous studies have introduced different methods for constructing TMAs. Many authors tried to use various methods to implant more tissue cores in a single recipient block, and most of these methods involved reducing the diameter of the tissue cores and/or the spacing between adjacent tissue cores. However, when creating TMAs, it is difficult to reduce the distance between tissue cores to zero except with extremely expensive automatic TMA arrayers. Here, we introduce a novel method to construct a high-density TMA that does not have spacing between the tissue cores. We also introduce a method for preparing a self-made tissue-arraying instrument. With this method and the tissue-arraying instrument, we successfully created a TMA containing 126 tissue cores that were 2mm in diameter. H&E staining and immunohistochemical staining were performed on the sections cut from the TMA without any tissue spot loss. This method is easy to operate, and the materials for creating the tissue-arraying instrument are inexpensive and can be purchased anywhere. Therefore, this method can be applied in all laboratories.

Enhanced Efficiency and Stability of Novel Pseudo-ternary Polymer Solar Cells Enabled by a Conjugated Donor Block Copolymer.

The recent breakthrough in power conversion efficiencies (PCEs) of polymer solar cells (PSCs) that contain an active layer of a ternary system has achieved values of 18-19%; this has sparked interest for further research. However, this system has difficulties in optimizing the composition and controlling the interaction between the three active materials. In this study, we investigated the use of a donor1 (D1)-donor2 (D2) conjugated block copolymer (CBP), PM6-b-TT, to replace the physical blend of two donors. PM6-b-TT, which exhibits an extended absorption range, was synthesized by covalently bonding PM6, a medium-band gap polymer, with PBDT-TT, a wide-band gap polymer. The blend films containing PM6-b-TT and Y6-BO acceptor, demonstrated excellent crystallinity and a film morphology favorable for PSCs. The corresponding pseudo-ternary PSC exhibited significantly higher PCE and thermal stability than the PM6:PBDT-TT-based ternary device. This study unambiguously demonstrates that the novel D1-D2 CBP strategy, combined with the conventional binary and ternary system advantages, is a promising material production strategy that can boost the performance of future PSCs.

Design of donor-acceptor small molecules based on diazaisoindigo unit: Synthesis, theoretical calculations and photophysical studies

Two donor-acceptor-donor (D–A–D) and two donor-acceptor (D-A) small molecular systems involving alkyl bithiophene and thiophene derivatives as donor blocks and 5,5′- and 5-linked 7,7′-diazaisoindigo (DAIID) as acceptor blocks have been synthesized and investigated with theoretical calculations and photophysical studies. The incorporation of the thiophene groups led to significant changes in the UV–vis absorption spectra and electronic structure of the diazaisoindigo. Bithiophene and thiophene derivatives did not show fluorescence, in contrast to their dibrominated and brominated precursors. This fact was attributed to both a decrease of the radiative rate constant and an increase of the non-radiative deactivation associated to the incorporation of the thiophenyl groups. Additionally, picosecond transient absorption experiments revealed short time decays for the thiophenyl derivatives indicating a faster non-radiative deactivation associated to a rotation of the central double bond of 7,7′-diazaisoindigo in the excited state.

Efficient and Nonhalogenated Solvent-Processed Organic Solar Cells Enabled by Conjugated Donor–Acceptor Block Copolymers Containing the Same Benzodithiophene Unit

Organic solar cells (OSCs) based on conjugated block copolymers (CBCs) have gained considerable attention owing to their simple one-pot solution process. However, their power conversion efficiencies (PCEs) require significant improvement. Furthermore, the majority of efficient CBC-based OSCs are processed using environmentally toxic halogenated solvents. Herein, we develop a new CBC (PBDB-T-b-PY5BDT) and demonstrate efficient and stable OSCs achieved by a halogen-free solution process. We design a (D1-A1)-b-(D1-A2)-type CBC (PBDB-T-b-PY5BDT) that shares the same benzodithiophene (BDT) units in donor and acceptor blocks. This alleviates unfavorable molecular interactions between the blocks at their interfaces. The PBDB-T-b-PY5BDT-based devices exhibit a high PCE (10.55%), and they show good mechanical, thermal, and storage stabilities. Importantly, we discuss the potential of our OSCs by preparing two different control systems: one based on a binary polymer blend (PBDB-T:PY5BDT) and another based on a conjugated random copolymer (CRC, PBDB-T-r-PY5BDT). We demonstrate that the photovoltaic performance, device stability, and mechanical robustness of the CBC-based OSCs exceed those of the binary all-polymer solar cells and CRC-based OSCs.

Exploring the Optoelectronic Properties of D-A and A-D-A 2,2'-bi[3,2-b]thienothiophene Derivatives.

The synthesis of some novel donor-acceptor and acceptor-donor-acceptor systems containing a 2,2'-bi[3,2-b]thienothiophene donor block and various electron-accepting units is described alongside their photophysical properties studied using electrochemistry, optical spectroscopy and theoretical calculations. The obtained results show that the energy levels can be modulated by changing the strength of the acceptor unit. Among the three investigated end-groups, 1,1-dicyanomethylene-3-indanone exhibited the largest bathochromic shift and the lowest band gap suggesting the strongest electron-withdrawing character. Moreover, the emissive properties of the investigated systems vary greatly with the nature of the terminal group and are generally lower compared to their precursor aldehyde derivatives.

Luminescent push-pull triphenylamine-based molecules end-capped with various electron-withdrawing groups: Synthesis and properties

Organic luminescent materials are widely used in various electronic and optoelectronic devices upon growing demands of science and technology. Enhancement of spectral-luminescence characteristics for such materials and in depth understanding of “structure-property” relationships remain challenging tasks. Herein, we report on synthesis and comprehensive investigation of the series of novel luminescent push-pull molecules with triphenylamine unit as an electron donor block and thiophene as a π-spacer, which end-capped with various types of electron-withdrawing groups (EWGs), which are commonly used for the molecular design of various functional materials in organic electronics. The results allowed us to evaluate the impact of EWG type used on the target materials characteristics. Phenyl-substituted EWGs were found to be more suitable for the design of highly thermally and electrochemically stable materials with relatively high melting temperatures and melting enthalpies. Depending on the EWG nature luminescence maxima of the luminophores demonstrated significant variability, e.g. from 509 nm to 750 nm, while the photoluminescence quantum yield (PLQY) values laid in the range of 1–89%. All luminophores showed good compatibility with a polystyrene (PS) matrix, in which PLQYs were generally higher (up to 25-fold enhancement) compared to the corresponding solutions or polycrystalline films. The changes of spectral characteristics observed for these luminophores were well described using basic relations of the semi-empirical theory of solvatochromism. Based on lifetime of excited states measurements, it was shown that the excited state non-radiative deactivation constants values the major contributors to PLQY values in THF solutions, while increase of the PLQY values in PS films can be associated with decrease of the probability of non-radiative deactivation of the excited states.

Enhanced blue thermally activated delayed fluorescence with rigid adamantane as non-conjugated linker for space-confined donor-acceptor charge transfer: a theoretical study

A lack of control over the relative orientation of donor and acceptor moieties in solid films is the main reason for poor electroluminescence efficiency found in most D-σ-A patterns. In this study, adamantane was introduced as the linker for the construction of a D-σ-A system since its rigid but non-conjugated nature. For a systematic study, the same donor (9,9-dimethyl-10-phenyl-9,10-dihydroacridine, DMTPA) and acceptor (2,4,6-triphenyl-1,3,5-triazine, TPZ) block were attached at different sites of the adamantine molecule, forming three kinds of configuration including face-to-face (FF), head-to-tail (HT), and chair (CH) style. DFT/TD-DFT simulation was carried out to investigate the electronic structures, optical characteristics, and charge transfer (ICT) properties of these three designed molecules. Attributed to a non-conjugated adamantane linker, the conjugation between donor and acceptor was disrupted for either of these molecules, resulting in high triplet energy of 2.79, 2.99, and 3.10 eV, respectively. Among them, the face-to-face style molecule presents the smallest ΔEST and greatest charge transfer excitation from donor to acceptor, suggesting an excellent potential for thermal activated delayed fluorescence (TADF). Face-to-face type molecule is a good option for a high-performance blue organic light-emitting diode (OLED) host material based on these results. Our investigation may open a door for designing new host molecule with other donor and acceptor groups to further enhance the efficiency and longevity of OLEDs.

Management of Donor and Acceptor Building Blocks in Dopant-Free Polymer Hole Transport Materials for High-Performance Perovskite Solar Cells.

The dominant hole transport material (HTM) in state-of-the-art perovskite solar cells (PSCs) is Spiro-OMeTAD, which needs to be doped using hydrophilic dopants to improve its hole mobility and conductivity, resulting in inferior device stability. Here, we propose an effective molecular design strategy to construct dopant-free polymer HTMs by selecting four structurally related polymers and investigating their structure-property relationship. It is found that the donor and acceptor units with longitudinal conjugate extension, such as BDT-T and BDD, could not only enhance the planarity of the conjugated polymer backbone and tune the energy levels but also promote the face-on orientation, resulting in superior charge extraction and transport. The optimized device utilizing dopant-free polymer HTM shows a high open-circuit voltage of 1.19 V and a champion efficiency of 24.04 % with greatly improved operational stability, making it among the best performance PSCs based on dopant-free HTMs.

Management of Donor and Acceptor Building Blocks in Dopant‐Free Polymer Hole Transport Materials for High‐Performance Perovskite Solar Cells

AbstractThe dominant hole transport material (HTM) in state‐of‐the‐art perovskite solar cells (PSCs) is Spiro‐OMeTAD, which needs to be doped using hydrophilic dopants to improve its hole mobility and conductivity, resulting in inferior device stability. Here, we propose an effective molecular design strategy to construct dopant‐free polymer HTMs by selecting four structurally related polymers and investigating their structure–property relationship. It is found that the donor and acceptor units with longitudinal conjugate extension, such as BDT‐T and BDD, could not only enhance the planarity of the conjugated polymer backbone and tune the energy levels but also promote the face‐on orientation, resulting in superior charge extraction and transport. The optimized device utilizing dopant‐free polymer HTM shows a high open‐circuit voltage of 1.19 V and a champion efficiency of 24.04 % with greatly improved operational stability, making it among the best performance PSCs based on dopant‐free HTMs.

Binary Blend All-Polymer Solar Cells with a Record Efficiency of 17.41% Enabled by Programmed Fluorination Both on Donor and Acceptor Blocks.

Despite remarkable breakthrough made by virtue of “polymerized small‐molecule acceptor (PSMA)” strategy recently, the limited selection pool of high‐performance polymer acceptors and long‐standing challenge in morphology control impede their further developments. Herein, three PSMAs of PYDT‐2F, PYDT‐3F, and PYDT‐4F are developed by introducing different fluorine atoms on the end groups and/or bithiophene spacers to fine‐tune their optoelectronic properties for high‐performance PSMAs. The PSMAs exhibit narrow bandgap and energy levels that match well with PM6 donor. The fluorination promotes the crystallization of the polymer chain for enhanced electron mobility, which is further improved by following n‐doping with benzyl viologen additive. Moreover, the miscibility is also improved by introducing more fluorine atoms, which promotes the intermixing with PM6 donor. Among them, PYDT‐3F exhibits well‐balanced high crystallinity and miscibility with PM6 donor; thus, the layer‐by‐layer processed PM6/PYDT‐3F film obtains an optimal nanofibril morphology with submicron length and ≈23 nm width of fibrils, facilitating the charge separation and transport. The resulting PM6/PYDT‐3F devices realizes a record high power conversion efficiency (PCE) of 17.41% and fill factor of 77.01%, higher than the PM6/PYDT‐2F (PCE = 16.25%) and PM6/PYDT‐4F (PCE = 16.77%) devices.

Manual Construction of a Tissue Microarray using the Tape Method and a Handheld Microarrayer

The tissue microarray (TMA) is an important research tool in which many formalin fixed paraffin embedded (FFPE) samples can be represented in a single paraffin block. This is achieved by using tissue cores extracted from the region of interest of different donor FFPE blocks and arranging them into a single TMA paraffin block. Once constructed, sections from the completed TMA can be used to perform immunohistochemistry, chromogenic, fluorescence in situ hybridization (FISH) and RNA ISH studies to assess protein expression as well as genomic and transcriptional alterations in many samples simultaneously, thus minimizing tissue usage and reducing reagent costs. There are several different TMA construction techniques. One of the most common construction methods is the recipient method, which works best with cores of the same length for which a minimum length of 4 mm is recommended. Unfortunately, tissue blocks can be heavily resected during the diagnostic process, frequently resulting in "non-ideal" donor block thicknesses of less than 4 mm. The current article and video focus on the double-sided adhesive tape method; an alternative manual, low cost, easy to use, and rapid method to construct low density (<50 cores) TMAs that is highly compatible with these non-ideal donor blocks. This protocol provides a step-by-step guide on how to construct a TMA using this method, with a focus on the critical importance of pathological review and post construction validation.

Manual Construction of a Tissue Microarray using the Tape Method and a Handheld Microarrayer.

The tissue microarray (TMA) is an important research tool in which many formalin fixed paraffin embedded (FFPE) samples can be represented in a single paraffin block. This is achieved by using tissue cores extracted from the region of interest of different donor FFPE blocks and arranging them into a single TMA paraffin block. Once constructed, sections from the completed TMA can be used to perform immunohistochemistry, chromogenic, fluorescence in situ hybridization (FISH) and RNA ISH studies to assess protein expression as well as genomic and transcriptional alterations in many samples simultaneously, thus minimizing tissue usage and reducing reagent costs. There are several different TMA construction techniques. One of the most common construction methods is the recipient method, which works best with cores of the same length for which a minimum length of 4 mm is recommended. Unfortunately, tissue blocks can be heavily resected during the diagnostic process, frequently resulting in "non-ideal" donor block thicknesses of less than 4 mm. The current article and video focus on the double-sided adhesive tape method; an alternative manual, low cost, easy to use, and rapid method to construct low density (<50 cores) TMAs that is highly compatible with these non-ideal donor blocks. This protocol provides a step-by-step guide on how to construct a TMA using this method, with a focus on the critical importance of pathological review and post construction validation.

Pollen-mediated transfer of herbicide resistance between johnsongrass (Sorghum halepense) biotypes

Johnsongrass (Sorghum halepense) is a troublesome weed in row crop production in the United States. Herbicide resistance is a growing concern in this species, with resistance to ACCase-, ALS-, and EPSPS-inhibitors already reported. Pollen-mediated gene flow (PMGF) is capable of spreading herbicide resistance, but the extent of PMGF has not yet been studied in johnsongrass. Field experiments were conducted in a Nelder-wheel design to quantify the distance and frequency of PMGF from ALS-inhibitor-resistant (AR) to -susceptible (AS) johnsongrass across three environments (summer 2018, fall 2018, and fall 2019). The AR biotype (pollen donor) was established at the center of the wheel (5-m diameter), and a naturally occurring johnsongrass (AS) infestation was utilized as the pollen recipient, in eight directions and at nine distances (5, 10, 15, 20, 25, 35, 40, 45, and 50 m) within each direction. Seeds collected from the AS plants in each distance and direction were screened for survival to the ALS-inhibitor herbicide nicosulfuron (Accent Q) at 95 g ai ha−1 under greenhouse conditions. The survivors (i.e. hybrids) were further confirmed based on the presence of the Trp574Leu mutation. At the closest distance of 5 m, PMGF was 9.6–16.2% across the directions and environments, which progressively declined to 0.8–1.2% at 50 m. The exponential decay model predicted 50% reduction in PMGF at 2.2 m and 90% reduction at 5.8 m from the pollen donor block. Results demonstrate that herbicide resistance can spread between adjacent field populations of johnsongrass through PMGF, which necessitates sound monitoring and management.