In an attempt to provide low-cost, low-input alternatives for regenerating pine-hardwood mixtures, this study examined several mechanisms that influence the growth of pine-hardwood stands. The Regeneration Alternatives Study is an ongoing experiment that was designed to gain biological and economical information concerning the growth and yield of loblolly pine and mixed hardwood species. Low-cost herbicide applications (stump treatment, basal stem spray, release, and soil spot release) were used to control competing vegetation during the study. The four even-aged regeneration treatments applied to loblolly pine and mixed hardwood stands of this study had a significant effect on their growth. Loblolly pine growth increased and mixed hardwood growth decreased as the intensity of herbicide treatment increased for all age classes. In general, loblolly pine was more productive with more intense treatment applications on poorer sites following a growing season harvest. Hardwood species were more productive with less intense treatment applications on higher-quality sites following a dormant season harvest for all age classes. Loblolly pine planting following clearfelling, coupled with a herbicide stump and release treatment (treatment 4), resulted in the highest yields of loblolly pine, the greatest economic returns, and the greatest level of site utilization. However, treatment 4 also resulted in the lowest yield of mixed hardwoods and the lowest level of species richness. Loblolly pine planting following clearfelling, with (treatment 3) and without (treatment 2) a hardwood stump treatment application, resulted in a more even distribution of pines and hardwoods, depending on the treatment. Treatment 3 favored loblolly pine growth, especially following a growing season harvest on poor sites. Treatment 2 favored mixed hardwood growth, especially following a dormant season harvest on good sites. There were no differences between methods of release (basal spray or soil spot herbicide application). Economically, treatments 2 and 3 did not realize a profit on returns. Pine yields, dbh, and basal area were all significantly greater following a summer season harvest as opposed to pine growth following a winter harvest with the same chemical treatments. The pine growth data indicated that less intense chemical treatments following a summer harvest can achieve the same or greater growth results than more intense chemical treatments following a winter harvest. The results of this study indicate a significant biological and economic tradeoff, depending on the level of hardwood control applied and the time of harvesting. / Master of Science

Italian ryegrass (Lolium perenne) is one of the most troublesome weeds of rice in Mississippi. Its resistance to multiple modes of action has made it more difficult to control in recent years. The most effective and economical management strategy to control Italian ryegrass is fall-applied residual herbicides; however, the most effective products are not labeled for use in the fall prior to rice seeding. Therefore, research was conducted in Stoneville, MS, to evaluate the effect of fall-applied residual herbicides on rice growth and development. Acetochlor should not be applied in fall targeting Italian ryegrass in fields where rice is scheduled for seeding the following spring. Clomazone remains the only viable treatment as a fall-applied residual herbicide in rice areas.

Herbicide safeners (protectants, antidotes) are used to protect crop plants from herbicide injury. Currently our understanding of the mechanisms involved in the protection of plants by safeners is not well defined; therefore, investigations were conducted to elucidate the mechanism(s) of action of the oxime ether safeners. Molecular comparisons of selected herbicide-safener combinations using computer-aided molecular modeling revealed that the chemical structures of safeners and herbicides are very similar at the molecular level; and, indicate that these compounds could bind at the same active site of the target protein or they may serve as inducers of metabolic enzymes which detoxify herbicides. Metolachlor at 10 μM and seed-applied CGA-133205 had no effect on germination while treatment with seed-applied oxabetrinil significantly reduced germination of grain sorghum. Results from experiments on ¹⁴C-acetate incorporation into lipids indicate that metolachlor and the oxime ether safeners influence lipid metabolism causing a redistribution of carbon in the lipid fractions of germinating sorghum roots. Results from studies with acetyl-CoA carboxylase indicate that this enzyme is not a target site for either metolachlor or the oxime ether safeners. Metolachlor and the oxime ether safeners enhanced glutathione levels in grain sorghum seedlings at 12 to 48 hr after imbibition was initiated with oxabetrinil being more stimulatory than metolachlor or CGA-133205. Glutathione reductase activity was also stimulated in safener-treated grain sorghum seedlings. Both safeners slightly enhanced nonenzymatic and enzymatic conjugation of metolachlor with reduced glutathione. Oxabetrinil conjugated enzymatically or nonenzymatically with reduced glutathione at a slow rate, but CGA-133205 did not. These data suggest that during the early stages of seed germination and seedling development of grain sorghum, safeners can enhance the detoxication of metolachlor by enhancing glutathione levels and enzymatic and nonenzymatic conjugation of metolachlor with glutathione. It appears that oxabetrinil and CGA-133205 are conferring protection to grain sorghum by increasing the rate of metolachlor metabolism. / Ph. D.

La synthèse enzymatique de terpénoides chez les mammifères provient de la voie mevalonique. Récemment une voie différente a été découverte et s'est révélée être prépondérante pour de nombreux organismes comme les plantes et bactéries. L'identification d'un inhibiteur de cette cascade enzymatique permettrait le développement d'une nouvelle famille d'herbicide. Les caractéristiques de la 1-déoxy-D-xylulose 5-phosphate réductoisomérase (DXR) font de cette enzyme très spécifique une cible pour la synthèse de nouveaux composés. La Fosmidomycine ainsi que son analogue acétylé le plus proche, FR-900098 restent des références pour l'inhibition de la DXR. Dans ce contexte, l'ensemble des molécules décrites dans la littérature en tant qu'inhibiteurs a été classé en fonction des modifications apportées sur le substrat naturel ou la Fosmidomycine. A partir de l'ensemble de ces informations, cinq familles ont été synthétisées pour trouver un nouveau motif complexant. Pour deux d'entre elles, le squelette de base contient un acide phosphonique et un acide phosphinique sur lequel a été introduit la diversité moléculaire grâce aux réactions de Pudovik et de couplage pallado-catalysé. Les autres motifs complexant originaux sont constitués d'une fonction carbonyle et d'un hétérocycle en α ou β. Après optimisation de la synthèse des précurseurs, la diversité a été introduite à l'aide, par exemple, d'une réaction de trois composantes permettant la préparation d'hétérocycle. Enfin, deux modifications ont été faites sur le bras espaceur : l'introduction d'atomes de fluor pour modifier les propriétés physicochimiques ou d'un atome d'azote, point d'attache de nouveaux groupements. / The non-mevalonate pathway is widely found in higher plants and in many eubacteria, including pathogenic ones, but not in mammals. Identifying a non-mevalonate pathway inhibitor would greatly contribute to the search for new herbicides. The unique properties of 1-Deoxy-D-xylulose 5-phosphate reductoisomerase make it remarkable and rational target for drug design. The phosphonohydroxamic acid Fosmidomycin, which acts through inhibition of DXR, is a natural compound produced in the fermentation of Streptomyces and still remains, with its N-acetyl homologue FR900098, one of the most active compounds. First of all, the enzyme and all the potential inhibitors tested in literature were classified in order to understand the global quest for therapeutically useful compounds. In this context, we designed and synthesized five different families of Fosmidomycin analogues containing a new chelating unit. Two targets molecules families bearing a phosphinophonic acid as common core were imagined. Divergent approach allowed the introduction of the chemical diversity thank to powerful pallado-catalyzed coupling reaction. The other families containing carbonyl group and heterocycle in α‐ and β‐position were regarded as highly potent complexing units. Chemical diversity was introduced mainly at the end of the synthesis. For one of them convergent ring formation using three-components reaction was developed. Finally two modifications of the Fosmidomycin linker were performed by the introduction of fluorine atoms on the parent structure as well as the replacement of a carbon by a nitrogen atom in order to create a new point of modifications.

Sorghum (Sorghum bicolor) is an important cereal crop in sub-Saharan Africa. The parasitic weed Striga hermonthica is a major biotic constraint to sorghum production. A novel technology where planting seeds are coated with herbicide to kill Striga that attach to the roots of the host has been shown to be effective in protecting the cereal crop from Striga damage. However, the host plant must have herbicide tolerance. This technology has not been tested in sorghum because there are no herbicide tolerant sorghum varieties available in Kenya and is, therefore, unavailable for subsistence farmers. One of the ways in which genetic variation can be enhanced and herbicide resistance developed is through chemical mutagenesis with ethyl methane sulfonate (EMS). The objectives of this project, therefore, were to: 1) identify sorghum production constraints through farmer PRA in order to determine breeding priorities.in two Striga endemic districts in western Kenya; 2) develop an EMS mutagenesis protocol for sorghum and to enhance the genetic variability of the crop using chemical mutagenesis; 3) evaluate EMS-derived sorghum mutants for improved agronomic performance; 4) develop acetolactate synthase (ALS) herbicide resistance in sorghum and to characterize the mode of inheritance of the trait; 5) determine the effect of herbicide coating of seed of herbicide tolerant sorghum on Striga infestation. In order to determine breeding priorities and constraints in sorghum production and the likelihood of adoption of herbicide seed coating technology, a survey involving 213 farmers was conducted in two Striga endemic rural districts of Nyanza province in Kenya. Results indicated that local landraces like Ochuti, and Nyakabala were grown by more farmers (> 60%) than the improved varieties like Seredo and Serena (48%). Popularity of the landraces was linked to Striga tolerance, resistance to drought, bird damage and storage pests, yield stability and high satiety value. Major constraints to sorghum production were drought, Striga weed, storage pests, bird damage and poverty among the rural farmers. Important characteristics farmers wanted in new varieties were Striga and drought resistance, earliness, resistance to bird and weevil damage and good taste. Striga infestations in sorghum fields were > 70%. Cultural Striga control options were considered inadequate while inorganic fertilization and chemical control were considered effective but unaffordable. Farmers’ willingness to pay a premium of over 30% for a Striga solution gave indication that herbicide seed coating if effective could be adopted by farmers. As a prerequisite to development of herbicide resistance, a comparative study was carried out to determine optimum conditions for mutagenesis and to induce genetic variation in the sorghum. Two sorghum varieties were mutagenized using varying concentrations (0.1 to 1.5% v/v) of EMS and two exposure times (6h and 12h). In laboratory and greenhouse experiments, severe reduction of sorghum root and shoot lengths indicated effective mutagenesis. The LD50 based on shoot length reduction was 0.35% and 0.4% EMS for 6h for Seredo and Kari/mtama-1, respectively. The highest mutation frequency based on chlorophyll abnormalities was 56% for 0.3% EMS for 6h. In the M2 generation, phenotypic variances for panicle characteristics were increased on treatment with EMS. However, significant effects of exposure time and variety indicated the necessity of genotype optimization for some traits. In order to determine the significance of mutation breeding in sorghum, 78 mutant lines derived from EMS mutagenesis, their wild type progenitor (Seredo) and two local checks (Kari/mtama-1 and Serena) were evaluated for agronomic performance in two locations in Kenya. There were significant (P = 0.05) effects among entries for grain yield, 1000-seed weight and visual scores for height uniformity, head exertion, head architecture and overall desirability. The highest yielding entry-mutant line “SB2M13” had a yield of 160% and 152% relative to the wild type (Seredo) and the best check Kari/mtama-1, respectively. Mutant line “tag27” had the highest 1000-seed weight which was 133% relative to the wild type. Seven mutant lines were rated superior to the wild type for panicle characteristics, head exertion and overall desirability. However, the majority of mutants were inferior to the wild type for most characteristics. Superior mutant lines may be developed into direct mutant varieties after multi-location trials or used as breeding material for sorghum improvement. In order to develop acetolactate synthase (ALS) herbicide resistance in sorghum, over 50,000 seeds of Seredo were mutagenized with 0.3% EMS. Over four million M2 plants were screened using 20g ha-1 of the ALS herbicide, sulfosulfuron. Five mutants (hb46 hb12, hb462, hb56 and hb8) survived the herbicide treatment and were confirmed to be tolerant. Mutant lines displayed differential herbicide tolerance, and the general order of tolerance after spray or seed coat application was hb46 > hb12 > hb462 ~ hb56 > hb8. The LD50 values for herbicide application as a spray, or seed coat, showed mutant lines to be up to 20 and 170 fold, respectively, more resistant than the wild type. Chi square analysis of data from herbicide screening of F2 generation of mutant X wild type crosses indicated no difference from the Mendelian segregation of 1:2:1 indicating the herbicide tolerance was inherited as a single semi-dominant gene. Mutant X mutant crosses did not show allelism indicating that the tolerance in all five mutants could be a result of the same gene mutation. To determine effect of herbicide seed coating on Striga infestation, the five herbicide tolerant mutant lines, hb46, hb12, hb462, hb56 and hb8 and the wild type progenitor Seredo were coated with varying concentrations (0.5-1.5% g ha-1) of sulfosulfuron and planted in a Striga endemic field. There were significant (P=0.05) effects of herbicide concentration on Striga density, Striga flowering and seed set, and sorghum plant stand and biomass. All treatments with herbicide coated on sorghum seeds had lower Striga emergence. Coating sorghum seed with 1g ha-1 sulfosulfuron reduced Striga infestation, Striga flowering and Striga seed set by 47%, 52% and 77%, respectively, and was considered the most effective rate as it did not result in sorghum biomass reduction. Mutants displayed differential herbicide tolerance and Striga resistance. Combining seed coating with high herbicide tolerance and inherent Striga resistance would be most effective for Striga control. Overall, the study showed that EMS mutagenesis is effective in inducing variation in sorghum for several traits including herbicide resistance. The mutants developed in this study will be important for sorghum breeding and for protection of sorghum against the Striga weed. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009.

No description available.

Doctor of Philosophy / Department of Agronomy / Johanna A. Dille / Challenges in weed management include occurrence of multiple weed species in the field, variable emergence among weed species, different spatial distribution and weed densities, which leads to the persistence of weed patches. The overall objective of this research was to understand the interaction of weed emergence, weed density, herbicide choice, and herbicide rate in soybean. Specific objectives were 1) to characterize the seedbank and emergence patterns of shattercane (Sorghum bicolor L.), prickly sida (Sida spinosa L.), and ivyleaf morningglory (Ipomoea hederacea Jacq.) including initial, peak, end, and duration of emergence in response to crop and herbicide treatments in soybean, and 2) to evaluate large crabgrass (Digitaria sanguinalis L.), shattercane, Palmer amaranth (Amaranthus palmeri S.), and velvetleaf (Abutilon theophrasti Medik.) mortality and dry weight reduction in response to herbicide rates across varying weed densities as well as to determine the influence of velvetleaf growth stage and density on herbicide efficacy. In the emergence study of 2006 to 2008, four treatments were nocrop, no-residual herbicide, half-rate of residual herbicide and full-rate of residual herbicide. Reduction in weed emergence was observed over the years in the same species patch. Species emerged in mid-May in both years, coinciding with soybean planting. Extended emergence was observed for shattercane when moisture was low and temperature high, while for prickly sida and ivyleaf morningglory, extended emergence was observed when moisture was high and temperature low. Applying residual herbicide decreased weed emergence. Herbicide choice was the whole plot, herbicide rates were subplots and weed densities were sub-subplots in field experiments conducted in 2006 and 2007. Shattercane was more susceptible to both glyphosate and clethodim than large crabgrass. Increasing large crabgrass density reduced percent mortality with clethodim, while with glyphosate, density did not affect both species mortality. Shattercane dry weight was reduced to 0 g per plot with 0.1X labeled rate of clethodim or glyphosate while 0.5X of the labeled rate reduced dry weight of large crabgrass to 0 g per plot. For broadleaf weeds, higher percent mortality was observed with glyphosate than with lactofen at high densities. Palmer amaranth was more susceptible than velvetleaf. Velvetleaf response was density dependent, such that increasing density did not increase dry weight. Velvetleaf growth stage was of importance, as stage affected herbicide efficacy, with higher mortality achieved at the two-leaf stage than the four- and six-leaf stages. For glyphosate, 0.125X of labeled rate on velvetleaf density of 5 seedlings per pot achieved more than 90% mortality when applied at the two-leaf stage, but dropped to 60 and 50% mortality when applied at the four- and six-leaf stage, respectively. The trend was the same for velvetleaf at a density of 30 seedlings per pot, which had 80, 60, and 55% mortality for the two-, four-, and six-leaf stages, respectively. Weed managers and farmers have the opportunity to better select herbicide choice and rate based on weed species, weed emergence patterns, and weed density.

Thesis (MSc (Conservation Ecology and Entomology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Much of South African lowland fynbos vegetation has been transformed by agriculture and invasive alien grass species. The artificial reduction of plant available N and P levels in soils, through the addition of carbon and calcium respectively, may provide a means of retarding the growth of alien grasses stimulated by soil nutrient enrichment. Furthermore, the competitive advantage of native lowland fynbos species adapted to nutrient impoverished soils may be increased by these additions. The above premise was tested in both field- and greenhouse-based trials by applying systemic and contact herbicides to reduce the large alien invasive grass biomass. This was followed by the addition of C as sucrose and Ca as gypsum to reduce plant available N and P respectively in the soils. The effects of these combined herbicide and soil nutrient amendment treatments on plant physiology and growth were examined in both resident alien and indigenous species and in several herbaceous and woody native species introduced as seeds and seedlings. Also, soils sampled from the different treatments in both trials were chemically analyzed. There was a total absence of seedling recruitment from seeds of all 9 indigenous species sown into soils in the field-based trial while introduced juveniles of another 9 indigenous species displayed a high mortality during the dry summer season. These detrimental effects were less severe in the greenhouse-based trial which received more regular watering and where successful seedling recruitment from seeds sown occurred in four indigenous species. Sucrose additions, both exclusively and in combination with gypsum, caused significant reductions in foliar chlorophyll, photosystem II (PSII) function and above-ground biomass of most resident and introduced alien and indigenous species. These reductions were less prominent where herbicides were applied, a possible consequence of N and P supplementation of soils by the decomposing plant biomass. This was supported by the elevated soil K, Na and N concentrations measured in soils where contact and systemic herbicides were applied. However, no significant changes in soil N or P were apparent following sucrose and gypsum additions respectively, the latter attributed to the acidic soils which precluded the formation of insoluble P complexes. A second study tested the hypothesis that exogenous sucrose addition to soils inhibits plant growth by stimulating soil microbial biomass which accumulates soil nitrogen rendering it unavailable to plants. Two native, early seral species (Dimorphotheca pluvialus (L.) Moench and Ursinia anthemoides (L) Poir. subsp anthemoides) were cultured in heat sterilized (2200C for 72 hours) and non-sterilized soils in a greenhouse under four different levels of sucrose (0, 100, 200 and 300 g m-2) supplied monthly over a four-month active growing period. Foliar chlorophyll iii contents, photosystem II (PSII) efficiencies, shoot and root lengths and dry mass, inflorescence numbers and N and P contents were measured in the plants, and N and P contents and bacterial cell and coliform numbers analyzed in the soils. Both D. pluvialis and U. anthemoides displayed significant reductions in PSII efficiency, chlorophyll content, accumulation of biomass and N and P in response increased levels of sucrose, which initially seemingly supported the hypothesis as these reductions were of substantially greater magnitude in plants cultivated in non-sterilized than sterilized soils. Despite this, there was no evidence of any significant increases in bacterial and coliform cell numbers in response to increased levels of sucrose supplied or any significant reductions in soil N and P contents following sucrose additions in both sterile and non-sterilized soils. Greater numbers of bacteria and coliforms were measured in sterilized than non-sterilized soils which corresponded with reduced soil N contents but these were not reflected in like changes in plant PSII efficiency and growth and total amounts of N taken up by plants which displayed massive increases in sterilized soils. The findings did not support the hypothesis and pointed to an abiotic mechanism of sucrose inhibition of plant photosynthesis and growth. The study concludes that the suitability of adding sucrose and gypsum to degraded renosterveld ecosystem soils to promote the competitiveness of native taxa against alien grasses is dubious. Other restoration alternatives such as natural re-colonization, transfer of soils containing viable seeds from pristine communities and top soil removal should be considered. / AFRIKAANSE OPSOMMING: Baie van Suid Afrika se laagland fynbos plantegroei is verander deur landbou en uitheemse indringer grasspesies. Die kunsmatige reduksie van plantbeskikbare N en P vlakke in die grond deur die toevoeging van koolstof en kalsium onderskeidelik, kan ’n metode wees om die groei van indringer grasse te vertraag, wat gestimuleer word deur grondvoedingstofverryking. Die kompeterende voordeel van die inheemse laagland fynbosspesies wat aangepas is tot voedingstofarme grond kan verhoog word deur die toevoegings. Bogenoemde postulaat is in beide die veld- en die glashuis-gebaseerde eksperimente getoets deur die aanwending van sistemiese en kontak onkruiddoder om die groot indringer grasbiomassa te verminder gevolg deur die byvoeging van C as sukrose en Ca as gips om die plantbeskibare N en P onderskeidelik te verminder in die grond. Die effekte van die gekombineerde onkruiddoder en grondvoedingstof verbeteringsbehandelings op die fisiologie en groei van die plante is ondersoek in beide inheemse- en residente indringerspesies asook in verskeie kruidagtige- en houtagtige inheemse spesies wat aangeplant was as sade en saailinge. Grondmonsters van die verskillende behandelings in beide studies was versamel en was chemies geanaliseer. Daar was ’n definitiewe afwesigheid van nuwe saailinge van sade van al nege indringerspesies wat gesaai was in grond in die veldgebaseerde studie, en saailinge van nog nege inheemse spesies het ’n hoë mortaliteit getoon gedurende die droë somerseisoen. Hierdie skadelike effekte was minder ernstig in die glashuisgebaseerde studie wat meer benat was, en waar nuwe saailinge suksesvol geproduseer was deur sade in vier inheemse spesies. Sukrose byvoegings, beide uitgesluit en in kombinasie met gips, het ’n afname in blaarchlorofil, fotosisteem II en bogrondse biomassa van die meeste van die residente en aangeplante indringer- en inheemse spesies getoon. Hierdie afnames was minder prominent waar onkruiddoder aangewend was, ’n moontlke oorsaak van N en P aanvulling van grond deur die verrottende plantbiomassa. Dit word ondersteun deur verghoogde grond K, Na en N konsentrasies, gemeet in grond waar kontak en sistemiese onkruiddoder toegevoeg was. Geen noemenswaardige veranderinge in grond N of P was sigbaar na byvoeging van sukrose en gips onderskeidelik nie. Laasgenoemde het bygedra tot suuragtige grond wat die formasie van onoplosbare P komplekse verkom het. ‘n Tweede studie het die hipotese getoets waar eksogene sukrose byvoeging tot grond plantegroei inhibeer deur die grond mikrobe biomassa te stimuleer wat akkumuleer wat in grond stikstof en dit nie beskikbaar maak vir plante nie.Twee inheemse vroeë intermediêre stadium spesies (Dimorphotheca pluvialus (L.) Moench en Ursinia anthemoides (L) Poir. subsp v anthemoides) was gekweek in hitte gesteriliseerde grond (2200 C vir 72 uur) en in nie-gesteriliseerde grond in ’n glashuis onder vier verskillende vlakke van van sukrose (0, 100, 200 en 300 g m-2) bygevoeg maandeliks oor ‘n 4 maande aktiewe groei periode. Blaarchlorofilinhoud, fotosisteem II (FS II) doeltreffendheid, groeipunt en wortel lengte en droë massa, blomgetalle en N en P inhoud was gemeet in die plante sowel as N en P inhoud en bakteriële sel en kolivorm getalle was geanaliseer in die grond. Beide D. pluvialis en U . anthemoides het ’n afname getoon in FS II doeltreffendheid, chlorofilinhoud, biomassa akkumulasie, N en P response op verhoogde vlakke van sukrose, wat aanvanklik aangetoon het dat dit die hipotese ondersteun want hierdie afnames wat heelwat groter in plante wat gekweek was in ongesteriliseerde grond as in gesteriliseerde grond. Daar was geen toename in baketriële en kolivorm sel getalle in rssponse tot verhoogde vlakke van sukrose byvoegings of enige noemenswaardige in grond N en P inhoud na byvoeging van sukrose in beide steriele en nie-steriele grond nie. Groot getalle bakterieë en kolivorme was gemeet in gesteriliseerde grond as in ongesteriliseerde grond. Dit korrespondeer met verminderde grond N inhoud maar dit was nie gereflekteer in veranderinge in plant FS II doeltreffendheid, groei en die totale hoeveelhede N wat opgeneem was deur plante wat ’n massiewe toename getoon het ongesteriliseerde grond nie. Hierdie bevindings het nie die hipotese ondersteun nie en het gewys na ’n abiotiese meganisme van sukrose inhibisie van plant fotosintese en groei. Die studie lei dus af dat die geskiktheid om sukrose en gips by te voeg tot gedegradeerde renosterveld ekosisteemgrond om kompetisie tussen inheemse plante en indringer grasse te promoveer, twyfelagtig is. Ander restorasie alternatiewe soos natuurlike herkolonisasie, oordrag van grond wat lewensvatbare sade bevat van onbeskadigde gemeenskappe en bogrond verwydering word oorweeg.

Weed infestation is one of the yield limiting factors in crop production. Weeds have negative effect on crop growth and productivity due to competition, allelopathy or hosting other harmful organisms. For large-scale wheat production, the use of wide spectrum pre-emergence or post-emergence herbicides remains the most valuable weed control tool. In South Africa, annual grass weeds are a major wheat production constraint, which is usually managed through application of pre-emergence herbicides. Due to limited water availability and low soil moisture content, these herbicides can often become ineffective and result into high weed infestations, which then have to be managed by manual cultivation or post-emergence herbicidal applications. However, there are no effective selective post-emergence herbicides available to control grass weeds in wheat. There is also limited option to use broad-spectrum post-emergent herbicides because they non-selectively kill the crop and weeds. Consequently, the use of herbicide resistant crops is a viable weed management system in wheat production. Breeding herbicide resistant crop varieties would allow farmers to safely use post-emergence herbicides without damaging the crop. Subsequently yield and quality losses will be reduced significantly. Thus, the development of herbicide resistant crop varieties through mutation breeding is a novel approach for effective weed management under both small-scale and commercial farmers. Mutagenesis has been recognized as one of the most efficient method to induce genetic variation in plants. Through induced mutations, development of new variants is possible that could be manipulated in plant breeding programs. Mutation leads to alteration of various traits in crop plants including plant height, improved nutritional quality, shorter growing period, increased tolerance or resistance to abiotic and biotic stresses. Ethylmethanesulphonate (EMS) is one of the most widely used chemical mutagens to induce mutagenesis in crop plants. The objectives of this study were to: 1) determine the optimum EMS concentration, treatment temperature and duration that would provide desired germination percentage and vigorous and healthy seedlings for effective mutagenesis in wheat, 2) investigate variations in agro-morphological traits in two selected wheat varieties (SST56 and SST875) after EMS mutagenesis and 3) select herbicide resistant wheat germplasm after inducing genetic variation using EMS using two selected wheat varieties (SST56 and SST875). The objectives were achieved through three independent studies as outlined below: In the first study seeds of four selected wheat varieties (B936, B966, SST387 and SST875) were treated in two replicates with three EMS concentrations (0.3, 0.5, and 0.7%), three temperature regimes (30, 32.5 and 35 °C) at four time durations (0.5, 1, 1.5 and 2 hrs). Results showed highly significant interactions (P<0.01) among varieties, EMS concentrations, temperature and exposure time on seedling emergence, germination and seedling height. Seeds treated with the highest EMS dose (0.7%), temperature (35ºC) and long exposure time (2 hr) showed delayed emergence by 18 days. At 30ºC, 0.5hr and 0.3% EMS varieties B936, B966 and SST875 had early emergence (6 days). B936 and SST387 had 50% while B966 and SST875 had 53% and 57% germination, respectively. These results were observed at EMS level of 0.7%, 300C and 1.5 hr exposure time in B936 and EMS at 0.5%, 350C and 1.5 hr in B966. SST387 and SST875 required EMS dose at 0.5%, 32.50C and 2 hr treatment time. Other low or high treatment combinations were invariably ineffective comparedto untreated control. During the second study two selected varieties (SST56 and SST875) were subjected to EMS mutagenesis using 0.5% v/v EMS at 32.5oC for 1 hr. Field trials were carried out at Ukulinga research farm of the University of KwaZulu-Natal in the randomized complete block design with two replicates. Data on nine important agro-morphological traits were collected and analyzed using the analysis of variance (ANOVA), correlation and principal component analysis (PCA) procedures. Significant variations were found among the agro-morphological traits between M1 individuals compared to untreated checks. The mutagenesis significantly reduced seed germination in the field at 40% in both varieties. The treatment significantly delayed days to heading by 8 days and shortened days to maturity by 13 days in both varieties. EMS treatment also significantly reduced plant height at 18 cm in SST56 and 21 cm in SST875 and spike length reduced by ~2.5 cm in both varieties. Plant height had positive and significant correlation with number of tillers, number of seeds per spike, flag leaf length and 100 seed weight. However, it had negative correlation with the number of days to maturity. The PCA revealed that three principal components (PC1, PC2 and PC3) accounted to 57% of the total variations among the agro-morphological traits in both varieties. PC1 alone contributed to 27.7% of the variation which was well-correlated with plant height (0.767), tiller number (0.812), number of seeds per spike (0.599) and seed yield (0.720). PC2 explained 15.6% of the variation and well-correlated with germination percentage (0.784), spike length (0.554) and flag leaf length (0.772). PC3 accounted to 12.4% of the variation and had negative correlation with days to maturity (-0.730). In the last study, seeds of two selected wheat varieties (SST56 and SST875) were treated with EMS at 0.5% concentration for 2 hr at 32.5ºC. Treated seeds and comparative controls were planted at the experimental farm of the University of KwaZulu-Natal using the randomized complete block design. Four weeks after planting M1 plants and untreated standard checks were sprayed with two herbicides, i.e. metsulfuron-methyl and bromoxynil at three different doses viz. 2x, 4x and 8x above the recommended rate of 4 g ha-1 and 2 kg ha-1, respectively. Two weeks after the treatment herbicide resistance were assessed. Results showed significant difference among varieties, tested herbicides and doses used. The EMS treated wheat lines showed variable degree of herbicide resistance compared to untreated controls. Overall, the study established the requirement of variety specific EMS dose and treatment temperature and duration that could be used for inducing large-scale mutation to select targeted mutant individuals in wheat. Further, the study found that EMS has the potential to increase agro-morphological variations in wheat to select useful and novel mutants with desired phenotypic traits and herbicide resistance which will be subjected for further selections to identify stable and herbicide resistance lines. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Master of Science / Department of Horticulture, Forestry, and Recreation Resources / Steven Keeley / Common dandelion (Taraxacum officinale Weber) is an important perennial weed in turfgrass. Fall is considered the optimal time for postemergence herbicidal control of dandelions; however, applications in spring, when volatility damage to surrounding plants is an additional concern, are often needed. Therefore, we conducted research to determine the volatility of common broadleaf herbicides, and their efficacy when applied at spring and fall application timings. Volatility was determined by applying herbicides to turfgrass and using potted tomatoes as indicator plants. Tomatoes exposed to turfgrass treated with Trimec Classic, Confront, Surge, Escalade 2, and Imprelis exhibited little or no volatility damage, while exposure to Speedzone, 4 Speed XT, and Cool Power caused significant damage. In general, herbicides causing little or no damage were amine formulations. Two field studies determined the effect of spring and fall application timing on dandelion control with several herbicides. Herbicide applications in the spring coincided with dandelion anthesis stages: pre-bloom, peak bloom, and post-bloom. Results were dependent on dandelion pressure in the studies. In 2010, with lower pressure, there were no differences among herbicides at any spring timing when dandelion control was evaluated after one year; all herbicides gave ≥ 80% control. In 2011, with higher dandelion pressure, Imprelis SL and 4 Speed XT provided ≥ 96% dandelion control at the spring pre- and post-bloom timings, which was better than Surge, Escalade 2, Cool Power, and Confront. The best choices for spring efficacy combined with minimal to no volatility were Escalade 2 and Trimec Classic. Finally, because interest in organic dandelion control is increasing, we compared several organic weed control tactics with a conventional herbicide. In a two-year field study, the conventional herbicide gave much better control (> 96%) than any organic method. Horticultural vinegar corn gluten meal, and fertilizer-only gave < 25% control, while hand-weeding gave 58 to 71% control. While hand-weeding was the best of the organic tactics, the time required was considered prohibitive for turfgrass managers, unless initial weed levels were very low.