Thesis (Ph. D.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references.

Thesis (Ph.D.(Plant Pathology))--University of Pretoria, 2005. / Abstract in English. Includes bibliographical references.

Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

Please read the abstract in the 00front part of this document. / Dissertation (MSc Agric (Weed Science))--University of Pretoria, 2001. / Plant Production and Soil Science / Unrestricted

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No description available.

Anaerobic soil disinfestation (ASD) is a promising alternative to chemical fumigation to control soil-borne plant pathogens and weeds. This research focused on evaluating several locally available carbon sources for ASD on weed control, evaluating the performance of brewers' spent grain (a promising carbon source) under field conditions, and evaluating whether yeast addition enhanced the effectiveness of ASD treatments. A series of greenhouse trials were conducted at the Southern Piedmont AREC (Agricultural Research and Extension Center). The greenhouse trials were conducted in PVC tubes, 20 cm tall and 15 cm in diameter. The first set of trials evaluated ASD conducted over 21-day periods of ASD using locally available carbon sources. The carbon sources included brewer`s spent grain, buckwheat (Fagopyrum esculentum), cowpea (Vigna unguiculata), paper mulch, peanut (Arachis hypogaea) shells, rice bran, sorghum-sudangrass (Sorghum drummondii), and waste coffee grounds applied at 4 mg of C/g of soil. The targeted weed species included common chickweed (Stellaria media (L.) Vill.), redroot pigweed (Amaranthus retroflexus L.), white clover (Trifolium repens L.), and yellow nutsedge (Cyperus esculentus L.). All ASD treatments significantly reduced weed viability compared to the non-treated control. The yeast amendments enhanced weed control over ASD without yeast. The second set of greenhouse trials was focused on ASD using brewer`s spent grain, and on evaluating ASD at the half and one-third carbon dose rates. The target pests were the same weed species in the first set of trials, and Pythium irregulare was added as an additional target pest. This set of trials indicated yeast enhanced addition the effect of BSG in ASD on both weeds and P. irregulare, indicating the potential to reduce carbon input necessary for effective ASD. A follow-up, two seasons, open-field trial conducted over two growing seasons at the Hampton Roads AREC focused on understanding the effects of ASD on weed density and strawberry fruit yield and fruit quality in annual hill strawberry production. The treatments included ASD at standard or half carbon dose rates, with or without yeast. Fumigation (80% chloropicrin + 20% 1,3-dichloropropene) and non-treated plots were used as control groups. Weed suppression with ASD was consistent for most of the broadleaf weed species, and total weed counts were significantly reduced compared to non-treated controls. Yield from ASD with yeast was higher than ASD without yeast and non-treated control in one growing season, while the increase in yield did not occur in another growing season. Yeast may have potentially enhanced the yield effects of ASD but lacked consistency. Yeast may have the potential to enhance ASD effectiveness. / Doctor of Philosophy / Strawberry is a high-value crop known for its brightly colored, sweet tasting, juicy and fleshy fruit that possesses a unique aroma. The southern region is the second large region of strawberry production in the United States. Strawberry is susceptible to soil-borne pests, including weeds and diseases. Preplant control of soil-borne diseases and weeds is important for strawberry production. Early season weeds can compete with newly transplanted strawberry plugs for nutrients, light, and other resources. However, currently, the limited options of pre-plant chemical fumigants and herbicides available in strawberry plasticulture make weed control a challenge in strawberry production. Anaerobic soil disinfestation (ASD) may be an effective alternative to preplant chemical fumigation. Anaerobic soil disinfestation involves three steps- applying carbon sources to the soil, covering the bed with black tarp, and watering the soil to maintain certain soil moisture to field capacity generally for 21 days. However, there are only a few studies on weed control using ASD in the southern region; locally available carbon sources also need to be evaluated. Thus, this study focused on evaluating several locally available carbon sources (cover crops, brewer`s spent grain, used coffee ground, paper mulch, peanut shell) for ASD to control troublesome weeds (common chickweed, redroot pigweed, white clover, yellow nutsedge). This study also explored a new method that involves mixing distiller's yeast with solid carbon sources in order to enhance the ASD weed control effect. Additionally, this study evaluated the effect of ASD using reduced carbon inputs, potentially reducing the total cost of ASD by reducing the carbon input. A series of greenhouse studies were conducted at the Southern Piedmont Agricultural Research and Extension Center (AREC), Blackstone, VA, with a follow-up field study done at the Hampton Roads AREC. The greenhouse trials evaluated carbon sources including brewer`s spent grain, buckwheat, cowpea, paper mulch, peanut shells, rice bran, sorghum-sudangrass, and waste coffee grounds. These greenhouse experiments were conducted in containers made from PVC tubes, and strawberry plants were not involved. The main objective of the greenhouse trial was to test the suppression of four troublesome weeds, including common chickweed, redroot pigweed, yellow nutsedge, and white clover. The most effective treatments in the greenhouse studies were further investigated in the field trial. The brewer`s spent grain was again used in the field trial, and treatments included ASD using a full or half dose of brewer's spent grain, with or without yeast. We evaluated the effects of these treatments on weed control, plant crop growth, and crop yields. Fruit quality factors, including fruit firmness, sweetness, and size, were also evaluated. In summary, all of the carbon sources evaluated provide similar weed control. Adding yeast showed potential to enhance the effect of ASD using brewer`s spent grain. Adding yeast also increased the effectiveness of the half-rate of the carbon source, showing the potential for effective pre-plant pest control for strawberry using ASD treatments with significantly reduced C dose rates.

Cucumber (Cucumis sativus L.), pumpkin (Cucurbita maxima Duch. ex Lam.), and summer squash (Cucurbita pepo L.) are economically important crops in Virginia. Only a few herbicides are registered for weed control in these crops. Halosulfuron is a sulfonylurea herbicide which controls several broadleaf weeds and yellow nutsedge (Cyperus esculentus L.). Cucurbit crops have some tolerance to this herbicide. The efficacy of halosulfuron for control of several weed species and tolerance of four vine crops to halosulfuron were investigated in field and greenhouse studies in 1999, 2000, and 2001. In the field, halosulfuron was applied to cucumber, pumpkin, zucchini squash, and yellow summer squash at 4, 9, 18, and 27 g ai/ha preemergence (PRE) and postemergence (POST) in combination with clomazone at 174 g ai/ha plus ethalfluralin applied PRE at 630 g/ha. Crop injury, weed control, and crop yield was collected from the field studies. Weed control by halosulfuron was dependent upon application method. Halosulfuron applied preemergence controlled only common ragweed (Ambrosia artemisiifolia L.) and smooth pigweed (Amaranthus hybridus L.). Postemergence halosulfuron controlled common ragweed, smooth pigweed, morningglory species (Ipomoea spp.), yellow nutsedge, and rice flatsedge (Cyperus iria L.). All four crops treated with halosulfuron produced yields equal to or higher than the crops receiving clomazone and ethalfluralin alone or the hand-weeded check. In the greenhouse, tolerance of cultivars of each crop to halosulfuron was investigated with the same rates applied in the field. Cultivars responded similar to postemergence halosulfuron applications with respect to fresh and dry weights in all four crops. The response of several populations of acetolactate synthase inhibiting (ALS) resistant smooth pigweed to postemergence halosulfuron was also investigated. Halosulfuron activity against ALS-inhibitor resistant smooth pigweed was population dependent. In the greenhouse, postemergence halosulfuron at the same rates used in the field studies controlled yellow nutsedge. / Master of Science

Cyperus rotundus L. CYPRO (purple nutsedge) and Cyperus esculentus L. CYPES (yellow nutsedge) are problematic weeds on every continent. At present there is no comprehensive means of controling these weeds.. The primary means of control is herbicides, although the weeds are becoming more resistant. Bioherbicide control of purple and yellow nutsedge is an important avenue of research, with much of the focus being to increase the virulence of current fungal pathogens of C. rotundus and C. esculentus. The primary aim of this study was to increase the virulence of a fungal pathogen of C. rotundus and C. esculentus, with the objective of creating a viable bioherbicide. A possible means of increasing the virulence of a pathogen would be to increase the amount of amino acid produced by the fungus. This was proposed as a means of increasing the virulence of Dactylaria higginsii (Luttrell) M. B. Ellis. Overproduction of amino acids such as valine and leucine result in the feedback-inhibition of acetolactate synthase (ALS), an enzyme which is a target for many herbicides currently on the market. By applying various amino acids to tubers of purple nutsedge and comparing the results with a reputable herbicide, glyphosate, it was possible to determine the success of the amino acid applications. Only glutamine treatment at 600 mg.r1 resulted in significantly less (P<O.OOI) germination compared with the water control, while the glyphosate application resulted in no germination. Four treatments were significantly different (P<O.OOI) from the water control in terms of shoot length, but no pattern or conclusion could be drawn from the results. Injecting amino acids and glyphosate into the leaves of the plants gave similar results to those obtained with the tubers, with no visible damage on those plants injected with the amino acids and complete plant death of those injected with glyphosate. Amino acids had little effect on the growth of the C. rotundus plant or tuber. It was later determined by a colleague (Mchunu1 , unpublished) working on the same project, that D. higginsii does not infect the local ecotypes of C. rotundus in Pietermaritzburg, South Africa. A second fungus, Cercospora caricis Oud., was isolated from C. rotundus growing in the region, and confirmed as a Cercospora species by conidial identification. Like many Cercospora species, C. caricis produces a phytotoxin, cercosporin. An increase in production of cercosporin would theoretically lead to an increase in virulence of C. caricis. Mutation of hyphae by i J Makhosi Mchunu: Address: National department ofAgriculture; Private Bag 3917; Port Elizabeth; 6056 Email: Makhosimc@NDA.agric.za ultraviolet-C light was perfected on C. penzigii Sacc., where 5 min exposure to DV-C light resulted in approximately 99% cell death. Surviving colonies were analysed by spectrophoresis, and the surviving mutant gave an absorbance value of approximately 5% more than the median. Samples were analysed by high-performance liquid chromatography (HPLC) to determine the presence of cercosporin. No definitive result was obtained. Exposure of C. caricis to DV-C for 5 min. resulted in approximately 65% hyphal cell death, with 20 min. resulting in approximately 95% death. A spontaneous mutant was observed in a colony that had been exposed to DV-C. This mutant showed sectored growth with red and grey growth patterns. The red section of the mutant was subcultured and analysed by spectrophoresis and HPLC. The red C. caricis gave an absorbance reading of approximately 140 on HPLC compared with about 22 from the grey colony. HPLC analysis of the wild-type C. caricis did not produce a peak corresponding to that of the cercosporin standard, although no conclusion could be obtained on the presence or absence ofthe toxin. The virulence of the mutant C. caricis could not be determined as inoculation experiments were unsuccessful, and had to be discontinued due to time constraints. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

We evaluated the genetic diversity of Penstemon's Centromeric Histone 3 (CENH3), which localizes to chromosome centromeres in eukaryotes. From RNA extractions of 56 species, we successfully amplified two CENH3s (termed CENH3a and CENH3b), which share approximately 69% sequence homology across the length of the gene and about 85% across the histone fold domain (HFD). CENH3a is generally 72 bp longer than CENH3b and contains seven exons while CENH3b is made of five. Unlike studies of CENH3 in other plants, Penstemon's CENH3 N-tail was found to be highly conserved, indicative that the genus has undergone a short evolutionary history. Surprisingly, of the 99 CENH3 sequences obtained during this study, 32 appeared to be mis-spliced and contained premature stop codons. Of those aberrant transcripts, 84.4% originated from CENH3b genomic DNA. Most mis-spliced transcripts resulted from the retention of all or part of an intron. In some cases, all or portions of an exon were missing, including one that was missing the L1 motif. Second, we systematically cataloged interspecific breeding data in Penstemon, on which we then conducted a network analysis. The resulting network provides breeders with a better visualization of successful parental combinations and also identifies gaps in interspecific breeding. This method allowed for the identification of species with a high degree of interspecific compatibility, which we compared to the CENH3 sequencing data. Finally, we studied the performance of soil streaming in high tunnel production of tomatoes (Solanum lycopersicum L.). Our experiments revealed that soil steaming and mulch reduced weed coverage of Palmer amaranth (Amaranthus palmeri S. Watson), large crabgrass (Digitaria sanguinalis L.), and yellow nutsedge (Cyperus esculentus L.). Steam and mulch increased the tomato plant size, fruit size, fruit number, and fruit yield. Additionally, soil steaming reduced tomato southern blight, caused by Sclerotium rolfsii, by 5.8-fold. These findings provide promising results for high tunnel tomato producers, particularly those involved in organic production where pesticide and fumigation use is limited.