Fungal Biocontrol in Coffee: A Case Study in Agroecology.

In light of mounting concerns over the profound environmental, health, and social costs of conventional agriculture, there is a compelling need to develop alternatives for growing food and fiber. Development of a truly sustainable agriculture will require a forward-looking agenda that embraces the tools of modern science. However, what is needed is not the reductionist science of the Green Revolution, but rather a science that recognizes and embraces the inherent complexity of natural systems, i.e., an agricultural science that benefits from and contributes to the science of ecology. This dissertation details a case study in which this paradigm, agroecology, was applied to the study of a fungal biocontrol agent in a coffee agroecosystem. The fungus Lecanicillium lecanii attacks two potential coffee pests: the green coffee scale (Coccus viridis) and coffee rust (Hemileia vastatrix). Despite the potential importance of this biological control agent, there is still much that is unknown about its basic ecology. The first half of this dissertation represents a step toward addressing this deficiency. Through a combination of field and laboratory studies, it was shown that L. lecanii can persist in the soil; that it can be translocated from the soil via rain splash; and that the ant Azteca instabilis can subsequently spread the fungus between individuals of C. viridis. The potential for L. lecanii to play a key role in generating the spatial structure of the system was demonstrated using a probabilistic cellular automata model. Finally, a previously unreported one-year lag in the suppression of H. vastatrix by L. lecanii was demonstrated using field surveys. The final chapters demonstrate the potential for agroecological research to inspire more general ecology theory, and for ecology theory to inspire models with implications for the management of agroecosystems. These chapters detail an evolutionary model that demonstrates how a low-connectivity host spatial structure could evolve as an anti-pathogen phenotype; the implications of the self-organization of habitat patches on population persistence; and how recent research on the detection of impending regime shifts might enable the detection of an imminent loss of L. lecanii from the coffee system.PHDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/94026/1/dougjack_1.pd

Fungal Biocontrol in Coffee: A Case Study in Agroecology.

In light of mounting concerns over the profound environmental, health, and social costs of conventional agriculture, there is a compelling need to develop alternatives for growing food and fiber. Development of a truly sustainable agriculture will require a forward-looking agenda that embraces the tools of modern science. However, what is needed is not the reductionist science of the Green Revolution, but rather a science that recognizes and embraces the inherent complexity of natural systems, i.e., an agricultural science that benefits from and contributes to the science of ecology. This dissertation details a case study in which this paradigm, agroecology, was applied to the study of a fungal biocontrol agent in a coffee agroecosystem. The fungus Lecanicillium lecanii attacks two potential coffee pests: the green coffee scale (Coccus viridis) and coffee rust (Hemileia vastatrix). Despite the potential importance of this biological control agent, there is still much that is unknown about its basic ecology. The first half of this dissertation represents a step toward addressing this deficiency. Through a combination of field and laboratory studies, it was shown that L. lecanii can persist in the soil; that it can be translocated from the soil via rain splash; and that the ant Azteca instabilis can subsequently spread the fungus between individuals of C. viridis. The potential for L. lecanii to play a key role in generating the spatial structure of the system was demonstrated using a probabilistic cellular automata model. Finally, a previously unreported one-year lag in the suppression of H. vastatrix by L. lecanii was demonstrated using field surveys. The final chapters demonstrate the potential for agroecological research to inspire more general ecology theory, and for ecology theory to inspire models with implications for the management of agroecosystems. These chapters detail an evolutionary model that demonstrates how a low-connectivity host spatial structure could evolve as an anti-pathogen phenotype; the implications of the self-organization of habitat patches on population persistence; and how recent research on the detection of impending regime shifts might enable the detection of an imminent loss of L. lecanii from the coffee system.PHDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/94026/1/dougjack_1.pd

Electromagnetic Momentum in Dispersive Dielectric Media

When the effects of dispersion are included, neither the Abraham nor the Minkowski expression for electromagnetic momentum in a dielectric medium gives the correct recoil momentum for absorbers or emitters of radiation. The total momentum density associated with a field in a dielectric medium has three contributions: (i) the Abraham momentum density of the field, (ii) the momentum density associated with the Abraham force, and (iii) a momentum density arising from the dispersive part of the response of the medium to the field, the latter having a form evidently first derived by D.F. Nelson [Phys. Rev. A 44, 3985 (1991)]. All three contributions are required for momentum conservation in the recoil of an absorber or emitter in a dielectric medium. We consider the momentum exchanged and the force on a polarizable particle (e.g., an atom or a small dielectric sphere) in a host dielectric when a pulse of light is incident upon it, including the dispersion of the dielectric medium as well as a dispersive component in the response of the particle to the field. The force can be greatly increased in slow-light dielectric media.Comment: 9 pages. To be published by Optics Communication

The Nitrate/(Per)Chlorate Relationship on Mars

Nitrate was recently detected in Gale Crater sediments on Mars at abundances up to approximately 600 mg/kg, confirming predictions of its presence at abundances consistent with models based on impact-generated nitrate and other sources of fixed nitrogen. Terrestrial Mars analogs, Mars meteorites, and other solar system materials help establish a context for interpreting in situ nitrate measurements on Mars, particularly in relation to other cooccuring salts. We compare the relative abundance of nitrates to oxychlorine (chlorate and/or perchlorate, hereafter (per)chlorate) salts on Mars and Earth. The nitrate/(per)chlorate ratio on Mars is greater than 1, significantly lower than on Earth (nitrate/(per)chlorate greater than 10(exp.3)), suggesting not only the absence of biological activity but also different (per)chlorate formation mechanisms on Mars than on Earth

Quantum statistical effects in nano-oscillator arrays

We have theoretically predicted the density of states(DOS), the low temperature specific heat, and Brillouin scattering spectra of a large, free standing array of coupled nano-oscillators. We have found significant gaps in the DOS of 2D elastic systems, and predict the average DOS to be nearly independent of frequency over a broad band f < 50GHz. At low temperatures, the measurements probe the quantum statistics obeyed by rigid body modes of the array and, thus, could be used to verify the quantization of the associated energy levels. These states, in turn, involve center-of mass motion of large numbers of atoms, N > 1.e14, and therefore such observations would extend the domain in which quantum mechanics has been experimentally tested. We have found the required measurement capability to carry out this investigation to be within reach of current technology.Comment: 1 tex file, 3 figures, 1 bbl fil

Matrix Black Holes

Four and five dimensional extremal black holes with nonzero entropy have simple presentations in M-theory as gravitational waves bound to configurations of intersecting M-branes. We discuss realizations of these objects in matrix models of M-theory, investigate the properties of zero-brane probes, and propose a measure of their internal density. A scenario for black hole dynamics is presented.Comment: 26 pages, harvmac; a few more references and additional comment

A simple combinatorial treatment of constructions and threshold gaps of ramp schemes

We give easy proofs of some recent results concerning threshold gaps in ramp schemes. We then generalise a construction method for ramp schemes employing error-correcting codes so that it can be applied using nonlinear (as well as linear) codes. Finally, as an immediate consequence of these results, we provide a new explicit bound on the minimum length of a code having a specified distance and dual distance

Over-expression of a putative poplar glycosyltransferase gene, PtGT1, in tobacco increases lignin content and causes early flowering

Family 1 glycosyltransferases catalyse the glycosylation of small molecules and play an important role in maintaining cell homeostasis and regulating plant growth and development. In this study, a putative glycosyltransferase gene of family 1, PtGT1, was cloned from poplar (Populus tomentosa Carr.). Sequence analysis showed that this gene encodes a protein of 481 amino acid residues with a conserved PSPG box at its C-terminal, suggesting that it is active in the glycosylation of plant secondary products. The PtGT1 gene was expressed in poplar stems and leaves, with a particularly high expression level in elongating stems. Transgenic tobacco plants ectopically over-expressing PtGT1 were obtained and phenotypes were analysed. Wiesner and Mäule staining showed that stem xylem of transgenic tobacco plants stained more strongly than controls. Measurement of the Klason lignins showed much higher lignin content in the transgenic lines than in control plants. Furthermore, the ectopic over-expression of PtGT1 in tobacco resulted in an early flowering phenotype. These findings offer a possible starting point towards better understanding of the function of poplar PtGT1, and provide a novel strategy for lignin engineering and flowering control in plants through the genetic manipulation of a poplar glycosyltransferase gene