Master of Science / Department of Agronomy / Kassim Al-Khatib / Kochia (Kochia scoparia (L.) Schrad) is a troublesome weed throughout the western United States and Great Plains. It is an aggressive warm season annual dicot plant that exhibits protogynous flowering and facultative open pollination. The aggressive growth habit and prolific seed production enable kochia to spread and compete well for light, moisture, and nutrients. Kochia is ranked as one of the most problematic weeds in cultivated fields including corn, sorghum, wheat, soybean, and sugarbeet. Kochia has been found to lower yields as well as hinder mechanical harvest. Glyphosate is a nonselective herbicide that is widely used in controlling kochia in no-till cropping systems. With rapid adoption of no-till systems where glyphosate is used for weed burndown treatment before planting and extensive use of glyphosate resistant crops, it is common that glyphosate is frequently applied on the same field during the growing season. In 2007, poor control of kochia was observed in three fields in Western Kansas. Greenhouse experiments were conducted with 10 kochia populations to determine the efficacy of glyphosate on kochia when applied at 10 different rates and at 3 plant heights. Herbicide rates included 0, 0.0625, 0.125, 0.25, 0.50, 1, 1.5, 2, 4 and 6 times a typical use rate of 870 g ae/ha. Resistance to glyphosate was identified in three kochia populations. The glyphosate resistant populations from Ingalls, Norton, and Moscow Kansas were 4.6, 3.3, and 2.8 times more resistant to glyphosate than a susceptible population, respectively, based on the rate required for 50% control. Glyphosate injury symptoms included stunting, and chlorosis, followed by some necrotic tissue but resistant plants generally recovered from injury, or were slow to show symptoms. In general, the level of resistance is greater in more developed plants compared to younger plants. Experiments also were conducted on the different kochia biotypes to evaluate glyphosate absorption and translocation, and any differences in mineral content of the plants that might be detrimental to glyphosate activity. Differences in glyphosate absorption and translocation and kochia mineral content were not sufficient to explain the resistance to glyphosate.

Call number: LD2668 .T4 1978 G34 / Master of Science

Master of Science / Department of Agronomy / Mithila Jugulam / Extensive, often exclusive, use of glyphosate in crop production has resulted in evolved glyphosate resistance in several weed species globally. Kochia is a competitive summer annual weed, well adapted to the North American Great Plains and has recently evolved resistance to glyphosate by gene amplification of 5-enolpyruvyl shikimate 3-phosphate synthase (EPSPS), the target-site of glyphosate. The overall objective of this research was to investigate the genetic basis of glyphosate resistance in kochia, specifically to study 1) the inheritance of glyphosate resistance and 2) determine the chromosomal distribution of EPSPS gene copies. Homozygous resistant (R) and susceptible (S) parental lines of kochia were identified. Using these parents, reciprocal crosses were performed to produce F₁ progeny. As expected for a nuclear encoded EPSPS gene, F₁ plants from both crosses survived various doses of glyphosate application. However, F1 plants showed intermediate shikimate accumulation and EPSPS gene copies (relative to ALS reference gene) compared to parents. F₂ progeny were produced by selfing F₁ plants. In response to 870 g ae ha⁻¹ glyphosate, F₂ plants (n=115) segregated into 3:1 (R:S) implying a Mendelian monogenic segregation of glyphosate resistance in kochia. Additionally, relative EPSPS gene copies ranged from 1-10 in the F₂ progeny (n=51) with a genotypic segregation of 40:11 (plants with 3 or more EPSPS gene copies: plants with 1 EPSPS gene copy). In F₂ dose-response, a correlation between the level of resistance and relative EPSPS gene copies was observed. Genomic organization of the amplified copies using fluorescent in situ hybridization (FISH) displayed a single and larger hybridization site of the EPSPS gene on one pair of homologous chromosomes in R compared to a faint hybridization site in S samples of kochia. These results suggest possibility of amplification of EPSPS gene mediated via unequal recombination leading to the evolution of the glyphosate resistance in kochia.

Doctor of Philosophy / Department of Agronomy / Mithila Jugulam / Kochia (Kochia scoparia (L.) Schrad), one of the most troublesome weeds in the North American Great Plains, including Kansas (KS), has become a significant concern in croplands ever since the evolution and spread of glyphosate resistance in this weed. Dicamba, an important synthetic auxin herbicide, is a useful substitute for managing glyphosate-resistant (GR) broadleaf weeds. As a result of extensive and intensive use, kochia populations have also developed resistance to dicamba. However, the precise mechanism(s) of dicamba resistance in kochia is still unknown. In the first part of this dissertation, the physiological, biochemical and genetic basis of dicamba resistance in dicamba-resistant (DR) kochia from KS was investigated. The results suggest that the mechanism of dicamba resistance in this kochia is not due to decreased absorption, reduced translocation or enhanced detoxification of dicamba. In contrary, reduced translocation of dicamba was found to contribute to the dicamba resistance in DR kochia from Colorado (CO). Further investigation of DR kochia from KS revealed a possible role of single nucleotide polymorphism (SNP) in TIR1 (the receptor gene of auxin) in the dicamba resistance evolution. Genetic analyses of data from inheritance studies demonstrated that an incomplete dominant nuclear gene controls the dicamba resistance in kochia from KS. Also, it was found that the genes controlling dicamba resistance in kochia from KS and CO are not linked. Similarly, although, GR and DR traits were found to be controlled by two distinct single dominant genes, they appear to co-exist in many kochia populations from KS. Nonetheless, these two genes were also found not to be linked. The second part of this dissertation focused on the development of reliable tools for the management of DR and/or GR kochia. The following experiments were conducted under greenhouse and field conditions in KS: a) the effect of temperature stress on the efficacy of dicamba or glyphosate; b) efficacy of dicamba and glyphosate when applied in combination; and c) efficacy of dicamba when used as pre-emergence (PRE) herbicide. The results suggest that the efficacy of both dicamba and glyphosate on kochia can be improved when applied at cooler temperature conditions. Also, it was found that the dicamba and glyphosate tank-mix should not be recommended to manage kochia, especially DR kochia, due to significant antagonistic interaction when applied in combination. On the other hand, application of dicamba as PRE compared to the postemergence application, was found to improve kochia control including DR kochia. Overall, this dissertation provided several novel outcomes both in basic and applied aspects of dicamba resistance in kochia.

Master of Science / Department of Agronomy / Johanna A. Dille / No-till producers can manage weeds by including cover crops during the fallow phase as part of an integrated weed management plan. Field experiments were conducted between 2007 and 2009 to quantify the influence of cover crops on weed emergence, biomass accumulation, and seed production. Field experiments were established near Garden City, KS with winter wheat or fallow as main plots and cover crop treatments as subplots including five spring- and five fall-sown individual or mixtures of crop species and a no-cover chemical fallow. Separate1-m2 quadrats were seeded with kochia or downy brome at 500 seed/m2. Kochia density was reduced by 75% and biomass reduced by 88% in fall-sown cover crops compared to chemical fallow across growing seasons. Spring-sown cover crop mixtures reduced kochia biomass in 2009 when kochia emergence was delayed. Downy brome biomass decreased exponentially as cover crop biomass increased. A second field experiment was established near Manhattan, KS with soybean, winter wheat, or grain sorghum phases of the rotation as main plots and six cover crop treatments as subplots sown after winter wheat harvest. Paired Palmer amaranth 1-m2 quadrats were seeded with 500 seed/m2 in each cover crop subplot. One quadrat was protected from any herbicide application made to the cover crop or to the grain sorghum. Combining burndown application with high biomass-producing cover crops reduced Palmer amaranth emergence and biomass. Influence of cover crop presence reduced early season Palmer amaranth emergence in the subsequent grain sorghum phase. Optimal seeding rate of forage soybean sown in winter wheat stubble and its impact on Palmer amaranth and downy brome emergence and growth were evaluated in field studies established near Manhattan and Hesston, KS in 2008 and 2009. Soybean was no-till drilled after wheat harvest at five rates ranging from 100,000 to 600,000 seeds/ha. A no-cover chemical fallow treatment was included. Separate 0.5-m2 quadrats were seeded with Palmer amaranth at 100 seed/0.5 m2 or with downy brome at 250 seed/0.5 m2. Three termination methods evaluated were killing frost, glyphosate application, or crop rolling. Palmer amaranth density was not affected by treatments but biomass decreased as soybean seeding rate and crop biomass increased. Downy brome emergence was less with rolled or sprayed termination methods in one site year as timing of termination was optimal. High biomass producing cover crops sown during the fallow phase of a crop rotation reduced weed emergence, density, and biomass accumulation. Cover crops can be part of an integrated weed management plan in Kansas.

Master of Science / Department of Agronomy / Anita Dille / A better understanding of kochia (Kochia scoparia) seed characteristics is necessary for long term management of this increasingly troublesome weed. The objectives were to evaluate maternal environmental factors influencing kochia seed produced in the field and to document variability in dormancy and seed viability produced within a single kochia plant grown in the greenhouse or field. Field experiments were conducted in 2012 and 2013 at the Kansas State Agricultural Research Center in Hays. Two different kochia biotypes from Hays were planted with and without five canopy types, namely corn, soybean, grain sorghum, wheat stubble, and kochia plants. A greenhouse experiment with two generations (F1 and F2) of self-pollination was conducted with the same kochia biotypes. Date of initial flowering and final plant heights were recorded. Plants were harvested when seed was mature and divided into three equal parts (top, middle, and bottom). Seeds were cold treated or not, and approximately 50 seeds were placed in petri dishes with water for germination counts taken over six weeks. Viability of remaining seeds were then tested. For field-grown kochia, plants were taller in corn, sorghum and weedy canopies compared to the absence of a canopy. Seed germination from field grown kochia ranged between 77 and 100% for both treatments. There was reduced germination in the presence of a weedy canopy for both treatments and biotypes (77 to 82%) compared to the absence (93 to 99%), with an increase in hard viable seed in the presence of weedy canopy (5 to 14%). In the greenhouse, the F2 generation produced more immediately germinable seed compared to the F1 generation which had more seed with delayed germinability. Seed from bottom third of F1 and F2 plants had greater total germination (73 and 70%, respectively) compared to the middle (61 and 65%) and top (50 and 59%) thirds of the plant. There was a maternal environmental effect on kochia seed characteristics with implications on generating persistent seed for the future seedbank.

Kochia scoparia (L.) Schrad. has had limited use as a forage crop during the past fifteen. years in parts of the western United States, Canada, and Argentina. Erickson and Moxon (1947) reported kochia* to be a good emergency feed for sheep and cattle during dry years in South Dakota. Salguero (1946) said that this species could be utilized in Argentina as silage or pasturage if harvested before flowering. Bell, et al. (1952) in Saskatoon, Canada studied this species in a comparison with other introduced plants and reported that it seemed to have desirable nutrient characteristics for livestock roughage. Plummer (1949) reported beef cattle in Ephraim, Utah had eaten and gained normally on kochia hay.