Typescript (photocopy). / Digitized by Kansas Correctional Industries

Pyroxasulfone is a VLCFA inhibitor labeled to control grasses and small-seeded broadleaf weeds. Little information is available regarding this herbicide being applied postemergence. Two field experiments were conducted to evaluate the efficacy of pyroxasulfone used postemergence. Pyroxasulfone applied to 2-leaf wheat controlled up to 83% of the green foxtail but had little to no effect on broadleaves. An additional field study was conducted to determine if pyroxasulfone could give supplemental green foxtail control when tank-mixed with ALS inhibitors. Few tank-mix combinations increased control, and the tank-mixes that did had inadequate control, <70%. Greenhouse experiments were also conducted. The first concluded that a wide range of grass species are susceptible to pyroxasulfone applied postemergence. The second demonstrated weed control with pyroxasulfone is almost exclusively due to root uptake. Contradicting levels of control between field and greenhouse experiments suggests more information is needed before pyroxasulfone can be utilized as a postemergence herbicide. / North Dakota State University. Department of Plant Sciences

Jointed goatgrass (Aegilops cylindrica Host; 2n=4x=28; CCDD) is an agriculturally important species both as a weed and as a genetic resource for wheat (Triticum aestivum L.; 2n=6x=42; AABBDD) improvement. In order to better understand the evolution of this species, the diversity of Ae. cylindrica was evaluated along with its progenitors, Ae. markgrafii (Greuter) Hammer (2n=2x=14; CC) and Ae. tauschii Coss. (2n=2x=14; DD), using chloroplast and nuclear microsatellite markers. Ae. cylindrica had lower levels of plastome and nuclear diversity than its progenitors. The plastome diversity of Ae. cylindrica was lower than its nuclear diversity. Ae. cylindrica was found to have either C-or D-type plastomes, derived from Ae. markgrafii or Ae. tauschii, respectively, where the C-type plastome was found to occur at a lower frequency than the D-type plastome. The nuclear genomes of Ae. cylindrica accessions with C-or D-type plastome were found to be very closely related, suggesting a monotypic origin. Furthermore, analyses suggests that Ae. tauschii ssp. tauschii contributed its D genome and D-type plastome to Ae. cylindrica. Ae. cylindrica accessions collected near Van Lake in southeastern Turkey, an area where Ae. tauschii ssp. tauschii and Ae. markgrafii overlap, showed high allelic diversity and may represent the site where Ae. cylindrica formed. Population structure analyses suggested a lack of regional genetic structure in Ae. cylindrica and evidence of migration of Ae. cylindrica among various regions. Finally, Ae. cylindrica accessions in the USA were found to be closely related to accessions from at least three regions of its native range central Anatolia, central East Turkey and western Armenia, and Caucasia. Wheat and jointed goatgrass are closely related and both have the D-genome. These two species can hybridize and produce backcross derivatives under natural conditions, a situation that may allow gene flow between these two species. In order to better understand mating patterns between these two species, a total of 413 first-generation backcross (BC₁) seeds obtained from 127 wheat-jointed goatgrass F₁ hybrids, produced under natural conditions, were evaluated for their parentage using chloroplast and nuclear microsatellite markers. Of the 127 F₁ hybrids evaluated, 109 had jointed goatgrass as the female parent, while the remaining 18 F₁ plants had wheat as the female parent. Of the 413 BC₁ plants analyzed, 358 had wheat and 24 had jointed goatgrass as the recurrent male parent. The male parentage of 31 BC₁ plants could not be determined. Although the majority of hybrids were pollinated by wheat, backcrossing of hybrids to jointed goatgrass would enable gene flow from wheat to jointed goatgrass. Though the observed frequency of jointed goatgrass-backcrossed hybrids (F₁ X jointed goatgrass) was low under field conditions, their absolute number is dependent on frequency of hybrids, which in turn, depends on the density of jointed goatgrass in wheat fields. Therefore, the recommendations to control jointed goatgrass in wheat fields and adjacent areas and to plant jointed goatgrass free wheat seed should be followed in order to avoid gene flow from wheat to jointed goatgrass. / Graduation date: 2006

Call number: LD2668 .T4 1985 L435 / Master of Science

Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Ripgut brome (Bromus diandrus Roth.) is a weed that causes great problems in the most wheat and grain producing areas and also in livestock practices. Until recently (1995) there were no registered chemicals for the management of ripgut brome in wheat, in South Africa. After the registration of sulfosulfuron and iodosulfuron + mesosulfuron for the management of ripgut brome in wheat, these two herbicides were widely used and in the case of wheat monocultures, it was used repeatedly. During the last few years, reports of ripgut brome that were suspected to be resistant to these chemicals, increased. With the development of herbicide resistance it is of great importance to investigate methods to confirm resistance and also to control it. The goal of this study was firstly, to confirm resistance in ripgut brome and secondly to compare growth and development of resistant ripgut brome popualtions to that of susceptible ripgut brome populations. The dormancy of Bromus seed was also investigated as were effective methods to break seed dormancy. Lastly, quicker methods to confirm resistance were investigated. A short summary of the experiments follows. In the first experiment the degree of resistance of three different ripgut brome populations were determined, by using the pot spray method. One population each of B. pectinatus and B. rigidus were also included in the study. The seed of the Bromus populations were germinated after which it was planted in plastic pots and were placed in the glasshouse until the three to four leaf stage. Subsequently the plants were treated with the following four herbicides: sulfosulfuron, iodosulfuron + mesosulfuron, imazamox and haloxyfop-R methyl ester, at seven concentrations namely, the recommended dosage, one quarter, one half, twice, four times and eight times the recommended dosage. After six weeks the percentage survival and the dry mass of the plants were determined. Results showed that the three ripgut brome populations had different degrees of resistance to sulfosulfuron and iodosulfuron + mesosulfuron, varying from no resistance to moderate resistance to strong resistance. There was no resistance to imazamox and haloxyfop-R methyl ester. The B. rigidus population exhibited strong resistance or tolerance (natural resistance) to the two sulfonylureum herbicides. In the second experiment the seed of the same Bromus populations were germinated and planted in plastic pots that were filled with three litres of river sand to determine the growth, development and seed production of the plants. The number of leaves for each plant as well as the plant height were measured weekly, until the plants became reproductive. The two resistant populations grew much faster than the susceptible population and they also produced taller plants. The susceptible population produced more leaves, but seed production was delayed considerably. This probably relates more to the plant’s adaptation to their enviroment, than to adaptation due to resistance. The susceptible population was collected from a natural environment, while the others were collected from wheat fields. In the third experiment the seed dormancy of the Bromus populations was investigated. The effect of different treatments on the dormancy of the seed was also investigated. The treatments that were applied were gibberrellic acid, fumigation with ammonia gas and an ammonia treatment combined with a cold treatment. Seed dormancy in all populations was short-lived and the cold treatment was an effective way of stimulating fresh seed to germinate. The last experiment was performed to develop a quicker method for the evaluation of resistance in Bromus spp. In this experiment the petridish method was investigated. Only sulfosulfuron and iodosulfuron + mesosulfuron were used, because resistance to them was proven earlier. Different concentrations of the herbicides were applied to the dishes with the seed and were exposed to a cold treatment before being placed in a germination chamber. The seed in al the treatments germinated and it was decided to let the seed grow for two weeks in the petri dishes to observe whether the herbicides may have a detrimental effect on the growth of the small seedlings. After two weeks there were no differences between treatments and the experiment was terminated. The study showed that resistance is present in some of the Bromus populations and that there are biological differences between populations with different degrees of resistance. However, the fact that the susceptible population comes from a completely different environment than the other populations, complicate matters and further studies are required to obtain a clearer picture. / AFRIKAANSE OPSOMMING: Predikantsluis (Bromus diandrus Roth.) is ‘n onkruid wat in die meeste koringen garsproduserende gebiede, asook in sommige vee praktyke, probleme veroorsaak. Tot redelik onlangs (ongeveer 1995) was daar in Suid-Afrika geen middels geregistreer wat predikantsluis in koring kon beheer nie. Nadat sulfosulfuron en iodosulfuron + mesosulfuron vir predikantsluisbeheer in koring geregistreer is, is die twee middels op groot skaal, en in die geval van koring monokultuurstelsels, aanhoudend toegedien. Gedurende die afgelope paar jaar is berigte ontvang dat beheer van predikantsluis met die middels nie meer so doeltreffend is nie, moontlik as gevolg van onkruiddoderweerstand wat ontwikkel het. Met die ontstaan van onkruiddoderweerstand is dit belangrik om praktyke en maniere te vind om weerstand vinniger te bevestig en doeltreffend te bestuur. Die doel van hierdie studie was eerstens om weerstand in predikantsluis te bevestig en tweedens om die groei en ontwikkeling van plante afkomstig van vermoedelike weerstandbiedende predikantsluis populasies te vergelyk met plante uit ‘n vatbare populasie. Die saadproduksie en dormansie van die saad is ook ondersoek asook effektiewe metodes om dormansie te breek. Laastens is ondersoek ingestel na ‘n vinniger manier (petribakkie metode) om weerstand te bevestig. Hieronder volg ‘n oorsig oor die vier eksperimente wat uitgevoer is. In die eerste proef is die mate van weerstand van drie verskillende predikantsluis populasies bepaal, deur van die gewone potspuit metode gebruik te maak. Daar is ook een populasie elk van Bromus pectinatus en vermoedelik Bromus rigidus ingesluit in die studie. Die sade van die verskillende populasies is toegelaat om te ontkiem en daarna is dit in plastiese potjies geplant en in ‘n glashuis geplaas totdat die drie tot vier blaarstadium bereik is. Die plante is daarna gespuit met die volgende vier middels: haloksifop-R-metielester (Gallant Super), imasamoks (Cysure), iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor), teen sewe konsentrasies elk, nl. teen die aanbevole dosis, asook teen een kwart van, een helfte van, twee keer, vier keer en agt keer die aanbevole dosis. Na ses weke is die persentasie oorlewendes en die droëmassa van die plante bepaal. Resultate het getoon dat die drie predikantsluis populasies verskillende grade van weerstand teen die twee sulfonielureums (sulfosulfuron en iodosulfuron + mesosulfuron) toon, dit wil sê van geen tot matig tot sterk weerstandbiedend. Daar is egter geen weerstand teen haloksifop-R-metielester (Gallant Super) en imasamoks (Cysure) waargeneem nie. Die B. rigidus populasie het sterk weerstand of toleransie (natuurlike weerstand) teen die sulfonielureum middels getoon. In die tweede proef is saad van dieselfde Bromus populasies ontkiem en oorgeplant in plastiese potte gevul met 3 liter riviersand om die groei en ontwikkeling en saadproduksie van die plante te evalueer. Die aantal blare per plant en hoogte van die plante is weekliks bepaal totdat die plante reproduktief geraak het. Hierna is die metings gestaak om te voorkom dat die saadproduksie van die plante benadeel word. Die resultate het getoon dat die twee weerstandbiedende predikantsluis populasies vinniger groei as die vatbare populasie en ook langer plante vorm, terwyl die vatbare populasie vinniger en meer blare vorm, maar langer neem om saad te vorm. Hierdie waarnemings hou egter waarskynlik meer verband met die oorsprong van die populasies as met die graad van weerstandbiedendheid. Die vatbare populasie is versamel in natuurlike veld vêr van enige landerye terwyl die ander populasies almal uit graanlande afkomstig is. In die derde proef is saaddormansie van die Bromus populasies ondersoek. Daar is ook ondersoek ingestel na verskillende behandelings om dormansie te breek. Die behandelings wat toegepas is, is ‘n gibberelienesuur behandeling teen verskillende konsentrasies, beroking met ammoniak vir verskillende tye en ‘n ammoniak behandeling tesame met ‘n koue behandeling. Die resultate het getoon dat saaddormansie van die Bromus populasies van korte duur is, maar dat kouebehandeling effektief is om ontkieming van vars saad te stimuleer. Die vierde proef is uitgevoer om vas te stel of daar vinniger evaluasiemetodes is vir die evaluasie van weerstand in Bromus spp., deur van die petribakkie metode gebruik te maak. In hierdie proef is slegs die middels iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor) gebruik, omdat daar ‘n mate van weerstand teen hulle waargeneem is in die eerste proef. Die middels is teen verskillende konsentrasies in petribakkies gevoeg, tesame met die sade en toe blootgestel aan ‘n kouebehandeling voordat dit in ‘n ontkiemingskabinet geplaas is vir ontkieming. Die sade in al die behandelings het ontkiem en daar is besluit om die saailinge uit die ontkiemingskabinet te haal en vir twee weke te laat groei sodat daar bepaal kon word of die middels ‘n effek op die groei van die plantjies het. Na twee weke kon geen verskil in die groei van die plantjies waargeneem word nie en die proef is beëindig. Die studie het getoon dat daar wel weerstand in sommige van die Bromus populasies voorkom, en dat biologiese verskille voorkom tussen predikantsluis populasies met verskillende grade van weerstand. Die feit dat die vatbare populasie uit ‘n heeltemaal verskillende omgewing kom as die ander populasies, maak definitiewe afleidings moeilik. Daar sal opvolgstudies uitgevoer moet word om van die onduidelikhede op te klaar.

"July 2002" Bibliography: leaves 40-46.

No description available.

A field experiment was conducted in 1998 to determine the efficacy of Puma and Hoelon for littleseed canarygrass control in durum wheat. The herbicide treatments consisted of three rates of Puma, 0.83, 1.24, and 1.66 oz a.i./A, and one rate of Hoelon, 6.8 oz a.i./A, that were applied at two application timings. The early-postemergence (EPOST) applications when canarygrass had 2.2 leaves per plant did not result in commercially acceptable control due to water stress. Increasing rates of Puma applied mid-postemergence (MPOST) when canarygrass had 5 leaves per plant provided increasing canarygrass control (70 to 90 %) with the two higher rates of Puma providing commercially acceptable control. The two highest rates of Puma also resulted in better weed control than the commercial standard, Hoelon, which did not provide commercially acceptable weed control. No herbicide injury symptoms were observed on the wheat at any of the evaluation dates. Grain yield also increased as the rate of Puma applied MPOST increased and yields overall reflected the degree of weed control observed earlier in the season. These data indicate that the combination of Puma applications that killed or stunted emerged canarygrass combined with later season crop competition that suppressed stunted and later emerging canarygrass plants was sufficient to protect grain yields. The highest yielding Puma treatment was equivalent to 4150 lb/A compared to the Hoelon and control treatments which yielded the equivalent of 2753 and 1946 lb/A, respectively.

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.

The two herbicides currently registered for the control of canarygrass in Arizona work by inhibiting lipid biosynthesis. The levels of control with these herbicides have been variable, ranging from 60 to 90 percent. Crop safety has been good. Two newer herbicides utilizing a different mode of action have provided more consistent and higher levels of weed control but with increased crop injury. These are numbered compounds (MKH6561 and F130060) and they are ALS inhibitors.