京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第17830号 / 農博第2015号 / 新制||農||1016(附属図書館) / 学位論文||H25||N4787(農学部図書室) / 30645 / 京都大学大学院農学研究科農学専攻 / (主査)教授 稲村 達也, 教授 冨永 達, 教授 奥本 裕 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

The resistance of Palmer amaranth (PA) and the tolerance (natural resistance) of pitted morningglory (PM) to glyphosate have made these species among the most common and troublesome weeds in the southeastern U.S. since the adoption of glyphosate-resistant (GR) crops. Populations of GR PA (R1 and R2) were identified in Mississippi. The inheritance of glyphosate resistance was examined in reciprocal crosses (RC) between glyphosate-resistant (R) and -susceptible (S) parents (Female-S × Male-R, S/R, and Female-R × Male-S, R/S), and second reciprocal crosses (2RC) (Female-S/R × Male-S/R, S/R//S/R, and Female-R/S × Male-R/S, R/S//R/S). Dose-response assays resulted in 17- to 4old resistance to glyphosate compared with S. Population S accumulated 325- and 8-times more shikimate at the highest glyphosate dose than in R1 and R2, respectively. cDNA sequence analysis of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene indicated no target site mutation. Genomes of R1, R2, RC, and 2RC contained from 1- to 59old more copies of EPSPS gene than S; EPSPS was highly expressed in R1 and R/S, but was poorly expressed in S, S/R, and R2. EPSPS activity was lower in S and S/R than in R and R/S, glyphosate absent; all were inhibited by glyphosate. Western Blot analysis confirmed an increased EPSPS protein level to EPSPS copy number correlation. Thus, the level of resistance was decidedly influenced by the direction of the cross. R and S female plants were reproductively isolated and seed were still produced, suggesting that PA can produce seed both apomictically and sexually (facultative apomixis). This mode of reproduction determined the low copy number inheritance, as well as guaranteeing the GR trait stability in the R populations. Dose-response assays resulted in 2.6old variability in tolerance to glyphosate between the most tolerant (MT) and the least tolerant (LT) PM populations. The level of tolerance positively correlated with the time of exposure to GR-crop system. Less shikimate was recovered in MT as compared to LT. Levels of aminomethylphosphonic acid (AMPA) were not different between populations and sarcosine was not present in either populations. Consequently, metabolism of glyphosate to AMPA or sarcosine is not a common factor in explaining natural resistance levels.

<I>Bean pod mottle virus </I>(BPMV, Genus <I>Comovirus</I>, Family: <I>Comoviridae</I>)is an important virus in soybean (<I>Glycine max</I> (L.) Merrill), causing quality and yield loss due to seed coat mottling and seed weight reduction. Although BPMV has been known in Virginia since 1958 and has always been regarded as causing negligible losses, its impact is changing as BPMV incidence has increased in many soybean growing areas of Virginia and the USA in general. From 1997 to 2001, a total of five BPMV isolates (V-W1, V-W2, V-S98-1, V-S98-15 and V-S01-10) were collected in Virginia and characterized. In this study, the effects of these isolates were studied, alone or with Soybean mosaic virus (SMV, Genus Potyvirus, Family Potyviridae) strain SMV G1, and isolates S98-51 and S98-52, on selected soybean cultivars. Individual isolates of BPMV showed variable symptom severity, and resulted in yield loss of between 40.4 to 58.1%, while SMV caused 23.7% in the most severe interactions. Up to 100% yield loss was realized from double inoculations of selected BPMV and SMV isolates, BPMV V-S98-1 + SMV S98-52 and BPMV S98-15 + SMV S98-52 on Hutcheson and Hutcheson Roundup Ready&#174; (BC5) soybeans, respectively. Time of inoculation, a critical factor in the impact of many virus diseases, affected seed coat mottling in four cultivars and seed weight in two cultivars, in tests with four BPMV isolates and three stages of soybean development. All BPMV isolates inoculated to plants at vegetative stage V1-V3 severely increased seed coat mottling and reduced seed weight than those inoculated at V4-V6 and reproductive stage R1-R3. Seedlings grown from non-mottled seeds germinated more uniformly had fewer thin-stemmed seedlings and grew faster than those grown from mottled seeds. Inoculation of various cultivars and breeding lines showed that there was no correlation between the severity of virus-induced foliar symptoms, relative accumulation of SMV, and extent of seed coat mottling. Thus, by avoiding the presence of BPMV at an early growth stage through proper timing of planting to avoid vectors, proper cultural practices like weed control, use of SMV free seeds, and chemical control, it is possible to greatly improve seed quality and reduce yield losses in soybean. / Ph. D.

No description available.

Italian ryegrass (Lolium multiflorum Lam.) is a competitive weed in small grain production areas throughout the northwestern and southeastern US. In small grains, Italian ryegrass has generally been controlled with postemergence treatments of diclofop, or diclofop-methyl, a member of the subfamily of the aromatic carboxylic acid family, the aryloxyphenoxypropionates. The first incidence of diclofop resistance in Italian ryegrass was reported in Virginia in 1995. Experiments to characterize diclofop resistance in several Virginia biotypes of Italian ryegrass included the following objectives: (1) evaluation of the presence of diclofop resistance in several Italian ryegrass biotypes collected across Virginia, (2) evaluation of alternative herbicide efficacy for diclofop resistant Italian ryegrass control, and (3) characterization of the aryloxyphenoxypropionate (APP) resistance mechanism in resistant Italian ryegrass biotypes. The response of 32 biotypes to diclofop collected from various locations statewide with varying histories of diclofop applications confirmed diclofop resistance in Virginian Italian ryegrass populations. At 4-times the label-recommended application rate, only 50% of biotypes previously exposed to diclofop in a cropping situation were adequately controlled versus 94% of the biotypes not previously treated with diclofop. Tralkoxydim provided the most effective control of four of the biotypes. No postemergence treatment effectively controlled one biotype previously exposed to diclofop applications. Effective preemergence herbicide treatments for Italian ryegrass control in the greenhouse included acetochlor (two formulations) and flufenacet plus metribuzin. In the field, flufenacet plus metribuzin resulted in excellent Italian ryegrass control, little crop injury, and acceptable barley yields. Acetyl-coenzyme A carboxylase (ACCase) assays and herbicide absorption, translocation, and metabolism studies were conducted to investigate resistant mechanism(s) to two APP herbicides, diclofop and quizalofop. ACCase assays indicated no differences in enzyme activity between the two biotypes of Italian ryegrass evaluated. Furthermore, no significant differences in the specific activity of ACCase were detected between the two biotypes in the absence of diclofop. [14C]Quizalofop-P absorption, translocation, and metabolism did not differ between resistant and susceptible Italian ryegrass biotypes. Lack of a significant biotype effect suggests that differential metabolism does not explain the differential response to diclofop treatments observed in the herbicide dose-plant response experiment. / Ph. D.

The purpose of this research was to evaluate a common lambsquarters (Chenopodium album) collection from Westmoreland County, Virginia, which exhibited a differential response to glyphosate treatments as compared to most other common lambsquarters. Plants from this site that survived glyphosate applications were collected in both 2002 and 2004. Greenhouse studies were conducted on F1, F2, and F3 progeny from this collection and compared to a wild type collection from Montgomery County, Virginia. Evaluations were conducted on these plants treated with a range of glyphosate rates. F1 progeny of the Westmoreland plants from both 2002 and 2004 collections showed reduced response to glyphosate relative to the Montgomery collection. Vigor reduction of F1 progeny from three 2004 Westmoreland source plants with 0.84 kg ae/ha of glyphosate ranged from 66 to 85% at 28 days after treatment (DAT), compared to 89% for the Montgomery collection. Evaluation of four Westmoreland F2 common lambsquarters lines derived from 2002 collections indicated significant differences in glyphosate sensitivity. Fifteen F2 lines were generated from 2004 collections from each of three Westmoreland source plants and from the Montgomery source. For the least sensitive Westmoreland source, vigor reduction ranged from only 24 to 36% across F2 lines in response to 1.68 kg/ha of glyphosate at 28 DAT, relative to 55 to 100% for the Montgomery source. I50 estimates for fresh weight reduction were 0.91 and 0.32 kg/ha, for these sources, respectively. Sequential treatments of 0.42, 1.26, and 1.68 kg/ha applied at three-week intervals to the least susceptible 2004 Westmoreland F2 line resulted in only 37% vigor reduction and no mortality among 360 treated plants. Growth chamber studies were also conducted on the F2 progeny of these sources to determine if differential growth responses occur in noncompetitive environments and in the absence of glyphosate treatment. Generally, few differences were observed among the Westmoreland and Montgomery collections in growth parameters including height, leaf number, leaf area, leaf size, shoot weight, and reproductive output. However, significant differences were observed with regard to root weight, root length, and root density. In germination studies, it was determined that the Montgomery source had significantly faster and greater seed germination than the Westmoreland source. The susceptibility of F3 seedlings to glyphosate varied significantly with respect to F2 parent line and glyphosate rate. Mortality of 100% was observed in F3 seedlings from the Montgomery source in response to the 3.36 kg ae/ha glyphosate rate, while no mortality was observed in Westmoreland F3 seedlings in response to this glyphosate rate. / Master of Science

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

Common ragweed (Ambrosia artemisiifolia L., Asteraceae) is an annual herbacious weed that is a troublesome pest in carrot fields of Southwestern Quebec. Over the past decade, ragweed has shown resistance to linuron, the only herbicide that is registered for post-emergence control of this weed in carrots. In this research, the degree of resistance to linuron was investigated for a ragweed biotype collected from a carrot field in Sherrington, Quebec, where a decreased performance of linuron had been noted. This biotype showed a linuron resistance ratio (I50) of 9.09, when compared with ragweed plants collected from a field never sprayed with this herbicide. The fungal pathogen Phoma sp., which had been initially isolated from diseased ragweed leaves in 1993, was considered as a potentially effective biological agent for the control of common ragweed. The pathogenicity of Phoma sp. was re-evaluated during the current research. This fungus was found not to have any appreciable virulence towards common ragweed; it is likely that virulence was lost during storage. Hence, twenty other fungal species were isolated from diseased common ragweed plants and assayed to determine their potential as biological agents against this noxious weed. Varying dew periods, temperatures, spore concentrations, host growth stages, and different types of carrier were evaluated. Only isolates ATT#9, INNA4a, INNA4b, ATT#10, ISO#65, and ISO#68 were able to induce lesions on ragweed foliage at spore concentrations of 106 to 107 spores ml-1, but only after an extended dew period of 48 hrs. No interaction effects on the degree of ragweed control were found when combining five fungal isolates and the insect, Ophraella communa LeSage. However, a possible interactive effect was detected when the fungal isolate ISO#65 and linuron were used in combination.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22080号 / 農博第2372号 / 新制||農||1072(附属図書館) / 学位論文||R1||N5234(農学部図書室) / 京都大学大学院農学研究科農学専攻 / (主査)教授 冨永 達, 教授 奥本 裕, 教授 白岩 立彦 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

<p>  </p> <p>Giant ragweed (<em>Ambrosia trifida</em> L.) is an annual broadleaf plant capable of emergence throughout the cropping season, opportune colonization of disturbed soil, rapid biomass accumulation, and a propensity to evolve mutations that endow resistance to herbicides, all of which contribute to giant ragweed being one of the most challenging weeds to control in row-crop production. Many soybean growers rely on acetolactate synthase (ALS)-inhibiting herbicides such as cloransulam for control of giant ragweed prior to its emergence, though the spread of biotypes resistant to ALS inhibitors can render these herbicides largely ineffective. Mesotrione inhibits the 4-hydroxyphenylpyruvate dioxygenase (HPPD) enzyme, and applications of this herbicide have recently been approved for use in mesotrione-resistant soybean varieties. Field experiments demonstrated that preemergence applications of mesotrione resulted in greater control of giant ragweed populations segregating for ALS-inhibitor resistance than several other commonly used herbicide combinations. Where mesotrione was applied, giant ragweed biomass was reduced by an average of 84% relative to the nontreated, while treatments without mesotrione increased biomass by an average of 34% by suppressing competition from other weed species. Additionally, both soil- and agar-based bioassays demonstrated that combinations of mesotrione and metribuzin can be synergistic for control of giant ragweed. </p> <p>Cloransulam was shown to result in strong selection for giant ragweed individuals with ALS-inhibitor resistance, increasing the proportion of resistant plants that emerged at one field site from 15% to greater than 90% after a single preemergence application. This selection pressure was reduced when mesotrione was co-applied with cloransulam. However, no herbicide combination, including sequential applications of non-ALS-inhibiting herbicides, consistently resulted in a resistance frequency similar to the baseline if an ALS inhibitor was applied preemergence. Resistance to cloransulam and other ALS inhibitors is expressed in giant ragweed plants possessing at least one mutant (Trp574Leu) <em>ALS</em> allele. The distribution of this allele in one field violated the Hardy-Weinberg Equilibrium, despite the fact that <em>ALS</em> is a nuclear gene and the Trp574Leu mutation does not incur a fitness penalty. We suspected that the inheritance of this mutation may be linked with a gene or genes responsible for self-incompatibility (SI) in giant ragweed, and that linkage drag was disrupting pollination in resistant plants. This research provided evidence that giant ragweed does possess SI, as greater pollen retention, pollen tube growth, and seed set were observed in cross-pollinated plants compared with self-pollinated plants. Non-Mendelian inheritance of the Trp574Leu mutation was documented in crosses between plants from three different giant ragweed populations, indicating that the mutant <em>ALS</em> allele may be linked with an SI allele common to many plants because of a shared resistant ancestor.  In crosses between plants from one population, production of resistant F1 seeds was 33% greater on average compared with the expectation under Mendelian inheritance. </p> <p>Collectively, this research demonstrated that mesotrione may become a highly effective tool for control of giant ragweed in soybean. Applications of mesotrione can also reduce the selection for an increased frequency of ALS inhibitor-resistant biotypes induced by cloransulam, though a more robust weed management strategy may be necessary to maintain the long-term viability of ALS inhibitors.  The need for sound weed management practices is underscored by the impact of the linkage of SI and <em>ALS</em> genes, which may be encouraging a more rapid spread of herbicide-resistance than was previously anticipated.</p>