Botany & Plant Ecology

Michigan Academician, Fall 2012 | Go to article overview

Botany & Plant Ecology


Investigating the Environmental and Physiological Causes of Abiotic Leaf Scorch in Quercus rubra. Philip S. Kurzeja, Department of Plant Biology, Michigan State University

Leaf scorch is a common symptom of declining trees in the urban landscape, including Northern red oaks, Quercus rubra. We are investigating the physiological factors that may cause leaf scorch. Established trees with a known history of leaf scorch are systematically evaluated at eight sites, each exhibiting scorched and non-scorched oaks of the same age, planting history, and soil structure. Depth of root flare, girdling root severity, soil compaction (resistance and bulk density), and soil profile are measured to document site problems in the replicated plots. Photosynthetic efficiency, leaf xylem pressure, leaf water conductance, leaf transpiration and plant tissue nutrition are measured to examine differences in physiological performance between scorched and non-scorched oaks on the same site and among sites. Scorched trees exhibited greater planting depth than non-scorched trees, and lower levels of manganese, photosynthesis efficiency, xylem pressure, conductance, and transpiration.

Ray Tissue Response to Urban Wind Environment. David Rayman and Frank Telewski, Plant Biology Department, Michigan State University

Exposure to wind is a mechanical stress that has been known to alter tree development at the tissue level. Cross sections were obtained from Gledistia tricanthos and Tilia americana that experienced mechanical wind stress primarily from just two directions, which resulted in elliptical stems. The purpose of this study is to determine if axes that experience different wind stress due to wind vectors altered by buildings result in developmental changes that affect ray structure. Tree cores from the long and short axes were obtained of different growth rings then cross sectioned by microtome. Tangential sections were then stained and ray length, width and area were measured using image analysis software. Preliminary results indicate that in Tilia rays on the axis that experienced the most mechanical wind stress were shorter and thicker. Shorter and thicker ray cells may provide trees with increased resistance to mechanical bending and thicker ray cells may provide trees with increased resistance to mechanical bending and thus protect against stem damage.

Variant Nuclear Size and Condition Occur in Progeny of Phytophthora infestans, as Determined by Flow Cytometry Analysis. Prissana Wiriyajitsonboom, Department of Plant Pathology, Michigan State University

Phytophthora infestans is a fungus-like Oomycete which causes the disease on potato known as late blight or potato blight. Mating type A1 isolates caused the Irish potato famine in 1845 and subsequent disease, until relatively recently. Late blight is again causing serious epidemics worldwide since the second mating type (A2) migrated from Mexico to other areas of the world in the 1980s. Mating of A1 and A2 types would be expected to lead to new races and virulence phenotypes in progeny. However, populations in the northern temperate zone have continued to reproduce only asexually. Our use of laser flow cytometry has for the first time yielded convincing evidence that different isolates from Michigan usually contain nuclei of different sizes, different DNA content in picograms/nucleus. Additionally, flow cytometry has revealed that some isolates contain two to three nuclear populations of different sized nuclei in a single thallus. Our research has focused on documenting the nuclear condition of diverse parents and then examining the nuclear size and nuclear condition of rare viable progeny. Crosses between a parent containing two nuclear populations and a parent containing one population were generated in the laboratory for three different pairs of parents. The crosses yielded progeny of unique nuclear size and condition. The studies have contributed to understanding sexual reproduction in nature and problems during meiotic conjugation and division which may be involved in the persistence of the clonally reproducing population in Michigan. …

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