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Use of uprooted invasive buffelgrass (Pennisetum ciliare) parent plants as thatch to reduce progeny seedling emergenceJernigan, Marcus Brendon January 2013 (has links)
Buffelgrass (Pennisetum ciliare) is a perennial bunchgrass native to Africa that has invaded ecologically intact areas of the Sonoran Desert in southern Arizona. It threatens many native plant species by means of competitive exclusion as well as increased fire frequency and intensity. Since the 1990s, efforts have been underway in southern Arizona to control buffelgrass using manual removal. A problem with this method is that the resulting bare, disturbed soil provides a favorable environment for buffelgrass seed germination. This study examined whether thatch composed of uprooted buffelgrass parent plants spread over disturbed areas reduces the density of progeny seedlings. A secondary goal was to determine whether light attenuation and/or autoallelopathy were major factors involved in the effect of thatch on buffelgrass seedling density. The effect of light attenuation on seedling density was tested in containers in the field and in the greenhouse. The propensity of thatch to produce autoallelopathic chemicals was tested in the greenhouse. Field plots with thatch had 1.9 buffelgrass seedlings/m² which was significantly fewer (p= 0.03) than the 2.9 seedlings/ m² in plots without thatch. These results suggest that the placement of thatch over areas disturbed during manual treatment of dense stands of buffelgrass will increase the efficiency of follow-up control of buffelgrass progeny seedlings in these areas. Results of the field container study suggest that light attenuation does not play a significant role (p= 0.39) in the reduction of seedling density by thatch, whereas those of the greenhouse shade treatment study indicated that light attenuation is a significant factor (p= 0.004). However, because percent germination was very low in the field container study, those results may be of little value compared to the greenhouse shade treatment study results which indicate that light attenuation is a mechanism by which thatch reduces buffelgrass seedling emergence. Chemicals leached from decomposed buffelgrass thatch did not have a significant effect (p= 0.09) on buffelgrass seedling density. Only the combination of thatch and leached chemicals significantly reduced (p= 0.014) seedling density. Thatch may also increase the activity of other factors that could reduce seedling density such as pathogens, and predators of seeds and seedlings.
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Alignment between genetic and physical map, and pheromone functions in Gibberella zeaeLee, Jungkwan January 1900 (has links)
Doctor of Philosophy / Department of Plant Pathology / Robert L. Bowden / John F. Leslie / Gibberella zeae is an ascomycete filamentous fungus and the major cause of Fusarium head
blight, also called scab, in small grains. This dissertation contains three related studies of G.
zeae. In the first, the genetic map was aligned with the first assembly of the genomic sequence
released by The Broad Institute (Cambridge, MA). Approximately 99% of the sequence was
anchored to the genetic map, indicating the high quality of the sequence assembly and validity of
the genetic map. The alignments grouped the linkage groups and supercontigs into four sets,
which is consistent with the hypothesis that there are four chromosomes in this fungus. In the
second, the sex pheromone precursor genes (ppg1 and ppg2) and the pheromone receptor genes
(pre1 and pre2) were identified and characterized. Deletion of ppg1 or pre2 ([Delta]ppg1 or [Delta]pre2
strains) reduced the number of perithecia produced by self-fertilization, but did not completely
block perithecial formation. The proportion of crosses resulting from outcrossing increased
when the [Delta]ppg1 strains were used as the female in crosses with male strains containing an intact
ppg1 gene. [Delta]ppg2 and [Delta]pre1 mutants had no discernable effect on morphological phenotype or
self-fertilization. Thus, one of the pheromone/receptor pairs (ppg1/pre2) found in many
Ascomycetes has a role in, but is not essential for, selfing or outcrossing in G. zeae, whereas the
other pheromone/receptor pair (ppg2/pre1) no longer has a detectable function in sexual
reproduction. In the third study, spore germination of G. zeae was tested in the presence of α-
factor-like pheromone peptides of G. zeae or N. crassa. The pheromone peptide of N. crassa
more efficiently inhibited spore germination than did the peptide from G. zeae. Arginine and
lysine residues were the most important determinants in blocking spore germination. In
conclusion, this research has validated the genetic map and the genomic assembly of G. zeae,
characterized sex pheromone functions and characterized pheromone peptide ability to inhibit
spore germination. The pheromone peptides of G. zeae and N. crassa may be useful as control
agents for G. zeae and pheromone peptide efficacy might be further enhanced by judicious
substitutions for some of the amino acids.
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