The Effects of Residue Amounts and Variety Selection on the Development of Wheat Fungal Pathogens in South Dakota

Roughly 50% of South Dakota cropland is under the practice of no-till, with large increases in acres of no-till in the last 20 or so years. No-till is beneficial for Great Plains states, such as South Dakota, as soil residues are withheld. Residues are shown to increase soil health through retention of moisture and increase of microorganisms, but residues can serve as a source of inoculum for fungal pathogens that can overwinter on them. As wheat is one of the most important food crops in the world, it is important to protect this vital crop from diseases. Diseases of wheat can reduce yields by a minimum of 20 percent on a global basis. Some of the most common wheat pathogens that affect plants are fungal pathogens, including leaf rusts, stripe rust, stem rusts, Stagonospora nodorum blotch, Septoria tritici blotch, and tan spot. These diseases were evaluated in seven different varieties (‘Draper’, ‘Ideal’, ‘Redfield’, ‘Thompson’, ‘Expedition’. ‘Wesley’, and ‘Oahe’) and four different residue amounts (20%, 40%, 60%, and 80% ground cover) to determine the importance of choosing a disease resistant variety and the effect of residue amounts on pathogen development and yield. The varieties were chosen due to their differences in tolerance and susceptibility to the pathogens, and the residue amounts were chosen to encompass a wide range of tillage/non-tillage systems. Results from this study indicate that there are multiple different spot pathogens present in South Dakota with the variety ‘Draper’ having significantly higher disease amounts in 2021. In 2022, the most disease amounts were seen on ‘Expedition’ which was susceptible/unrated for all leaf spot pathogens. ‘Expedition’ also had the greatest amount of stripe rust in 2021. The residue amounts were also shown to have a significant effect on disease development. The higher residue levels (60% and 80%) were often significantly higher in disease than the lower levels (20% and 40%). This study was done to establish a baseline for the types of diseases present in South Dakota wheat and to understand the effects that residues have on wheat production and disease development

Applicability of resonant two photon ionization in supersonic beams to halogenated aromatic hydrocarbons

This work investigates problems encountered in the application of one color resonant two‐photon ionization as an ionization source in supersonic beam mass spectroscopy. Of particular interest is the fact that photons of one color may not provide sufficient energy to cause ionization even when the laser source is tuned to an excited vibronic molecular state. We have therefore correlated trends in ionization potential with molecular structure for simple systems, specifically, halogenated aniline, phenol and toluene derivatives and mono‐ and di‐distributed benzenes. In the case of para‐substituted compounds where there is little substituent group interacting ionization occurs efficiently at the S0 → S1 origin, provided ultrafast processes are not active as in the case of iodo substituted benzenes. Many ortho compounds, however, are found not to ionize efficiently. This is probably due to a combination of coulombic and steric interactions which result in an increase in ionization potential. These types of effects have been qualitatively related to the electron releasing and withdrawing properties of the substitutent groups thereby allowing reasonable predictions to be made regarding those types of subsdtituted benzenes which can be probed with R2PI.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87501/2/620_1.pd

Free-jet spectra and structure of o-, m- and p-dihydroxybenzenes

Analysis of the free-jet spectra of hydroquinone (para), catechol (ortho) and resorcinol (meta) shows the presence of multiple origins in each molecular spectrum which are interpreted as belonging to separate structural isomers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25500/1/0000041.pd

Excited state spectroscopy of para di-substituted benzenes in a supersonic beam using resonant two photon ionization

Excited state vibronic spectra of p-aminophenol, p-cresol, p-fluoroaniline, p-fluorophenol, hydroquinone and p-toluidine have been obtained using resonant two photon ionization supersonic beam mass spectrometry. Despite marked similarities in the spectra, notable differences exist and different para polyatomic substituents in the same molecule show vibronic evidence of their real molecular symmetry of C2[nu]. Expansion of the ring is also noted upon excitation in all cases. Further, it is now evident that the assignment of some vibronic bands historically interpreted as sequence structure must be reconsidered since molecules like hydroquinone are mixtures of cis and trans and others have a vibronic structure arising from the polyatomic nature of the substituents (c[function of (italic small f)]. CH3).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26444/1/0000532.pd

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of p-chlorofluorobenzene

The S1 ← S0 (A ~ 1B2 ← X~ 1A1) electronic transition of para-chlorofluorobenzene has been investigated using resonance-enhanced multiphoton ionization (REMPI) spectroscopy. Assignment of the vibrational structure has been achieved by comparison with corresponding spectra of related molecules, via quantum chemical calculations, and via shifts in bands between the spectra of the 35Cl and 37Cl isotopologues. In addition, we have also partially reassigned a previously-published spectrum of para-dichlorobenzene

Multi-photon and electron impact ionisation studies of reactivity in adenine–water clusters

Multi-photon ionisation (MPI) and electron impact ionisation (EII) mass spectrometry experiments have been carried out to probe unimolecular and intermolecular reactivities in hydrated adenine clusters. The effects of clustering with water on fragment ion production from adenine have been studied for the first time. While the observation of NH4+ fragments indicated the dissociation of protonated adenine, the dominant hydration effects were enhanced C4H4N4+ production and the suppression of dissociative ionisation pathways with high activation energies. These observations can be attributed to energy removal from the excited adenine radical cation via cluster dissociation. Comparisons of MPI and EII measurements provided the first experimental evidence supporting hypoxanthine formation in adenine–water clusters via theoretically predicted barrierless deamination reactions in closed shell complexes

The Applicability Of Resonant Two-photon Ionization And Pulsed Laser Desorption In Supersonic Beam Mass Spectrometry.

This work investigates the applicability of one color resonant two photon ionization (R2PI) in supersonic beam mass spectrometry. Of particular interest is the fact that photons of one color may not provide sufficient energy to cause ionization even when a laser source is tuned to an excited vibronic molecular state. We have therefore correlated trends in ionization potential with molecular structure for simple systems, specifically, halogenated aniline, phenol and toluene derivatives, mono- and di-substituted benzenes and several azabenzene compounds. Para substituted benzenes were found to ionize efficiently in the absence of ultrafast relaxation processes such as are found in iodo derivatives. However, many of the ortho compounds do not ionize efficiently, presumably due to a combination of dipolar and steric effects which result in an increase in the ionization potential and smaller Franck Condon factors for absorption. These type of effects have been qualitatively related to the electron releasing and withdrawing properties of the substituent groups. The azabenzenes studied were ionized via n (--->) (pi)* transitions and were found to have smaller cross sections. Resonant three photon ionization with possible autoionization from a Rydberg state is believed to occur in these molecules. An extension of this research has involved the use of low power laser desorption for volatilizing nonvolatile and/or thermally labile biological molecules into a supersonic jet expansion with subsequent ionization in a time of flight mass spectrometer using R2PI. The separation of the desorption and ionization steps as compared to direct laser desorption methods allows for the possibility of selective ionization of the neutral fraction desorbed from the surface. The neutral plume is entrained in a supersonic expansion in these experiments thus increasing the degree of selectivity obtained in the ionization process. This technique was used to detect several classes of labile biomolecules including catecholamines, indoleamines, drugs, purine and pyrimidine bases and small peptides. In each case R2PI provides soft ionization with production of only the molecular ion or minor fragmentation. In addition, by increasing the laser energy fragmentation patterns characteristic of the structure of the molecule are obtained.Ph.D.Physical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127985/2/8702843.pd

APPLICABILITY OF RESONANT TWO PHOTON IONIZATION IN SUPERSONIC BEAMS TO HALOGENATED AROMATIC HYDROCARBONS

Author Institution: Department of Chemistry, University of Michigan; Department of Chemistry, University of MichiganThis work investigates problems encountered in the application of one color resonant two-photoionization as an ionization source in supersonic beam mass spectroscopy. Of particular interest is the fact that photons of one color may not provide sufficient energy to cause ionization even when the laser source is tuned to an excited vibronic molecular state. We have therefore correlated trends in ionization potential with molecular structure for simple systems, specifically, halogenated aniline, phenol and toluene derivatives and mono- and disubstituted benzenes. In the case of para-substituted compounds where there is little substituent group interaction ionization occurs efficiently at the $S_{q} \to S_{1}$ origin, provided ultrafast processes are not active as in the case of iodo substituted benzenes. Many ortho compounds, however, are found not to ionize efficiently. This is probably due to a combination of coulombic and steric interactions which result in an increase in ionization potential. These types of effects have been qualitatively related to the electron releasing and with-drawing properties of the substituent groups thereby allowing reasonable predictions to be made regarding those types of substituted benzenes which can be probed with R2PI."