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    Aspects of herbicide resistance in three New Zealand weed species : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatu, New Zealand
    (Massey University, 2015) Ghani Zadeh, Hossein
    Herbicide resistant weeds have become a challenge in agricultural systems globally. In this thesis, aspects have been studied of three weed species which have evolved resistance to herbicides from different chemical families within New Zealand. Dicamba-resistant fathen (Chenopodium album) was recently reported by researchers in Waikato. In this thesis, the level of resistance to dicamba in two of these populations of fathen was investigated using a whole plant dose-response experiments and it ranged from 5- to 20-fold. Also, a seed-test for rapidly and reliably detecting dicamba resistant fathen has been developed. Seed tests have seldom been used for detecting resistance within weeds to auxinic herbicides. The thesis also investigated aspects of the first reported cases of glyphosate resistance in New Zealand, found in both Italian ryegrass (Lolium multiflorum) and perennial ryegrass (Lolium perenne) from vineyards. Resistance to glyphosate in two populations of Italian ryegrass (Populations A and P) and two populations of perennial ryegrass (Populations J and N) was found to be almost 10-fold, whereas it was almost 30-fold for one perennial ryegrass population (Population O). Three different quick tests (seed assays, excised tiller bioassays and shikimic acid assays) were developed for detecting glyphosate resistance in Italian ryegrass and perennial ryegrass. Of the five populations of ryegrass studied, only Population O had a target site modification at Codon 106 of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Translocation of radiolabelled glyphosate was studied in four of the populations (Populations A, J, O and P), and movement from treated leaves was significantly reduced in them all compared with susceptible populations (non-target site mechanism of resistance). Therefore, Population O had two mechanisms of resistance, possibly explaining the 30-fold resistance. The studied glyphosate-resistant ryegrass populations were all found to be resistant to glufosinate. Populations A, J and O were also found to be resistant to amitrole. Genetic studies showed that the restricted glyphosate translocation trait is incompletely dominant and can be transmitted via pollen. The restricted herbicide translocation was suppressed under cool conditions in experiments, suggesting that application of glyphosate during winter might improve control of glyphosate-resistant Italian ryegrass and perennial ryegrass infestations. KEYWORDs: Chenopodium album, dicamba, glyphosate, Lolium multiflorum, Lolium perenne, amitrole, glufosinate, glyphosate mechanisms of resistance, target site mechanism of resistance, restricted herbicide translocation.
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    Herbicide resistance of transgenic plants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Breeding and Genetics, Department of Plant Science, Massey University, Palmerston North, New Zealand
    (Massey University, 1994) Naderi Shahab, Mohebbat Ali
    A cloned dehalogenase gene, conferring the ability to degrade the herbicide dalapon, was introduced into white clover and tobacco using Agrobacterium-mediated transformation. The objectives of this study can be divided into three parts. The first part consists of the evaluation of genetically transformed white clover and tobacco plants for their level of resistance to dalapon, determination of the heritability of the introduced transgene at different stages of growth, and identification of the segregation pattern of the transgene. The second part consists of the study of the quantitative inheritance of the transgene in transgenic tobacco plants. The third part consists of a determination of the number of copies of the transgene integrated into the genome of a transgenic tobacco line, inheritance of the transgene over successive generations and analysis of steady slate levels of mRNA of the transgene in leaf tissue. Relationships between the levels of transgene mRNA and the degree of resistance of these plants to dalapon were also assessed. The resistance of genetically transformed white clover and tobacco plants to dalapon was studied under both in vitro and greenhouse conditions using different experimental designs. In the in vitro studies, both white clover callus lines and tobacco seedlings showed resistance to high concentrations of dalapon. The level of resistance of the tobacco plants to dalapon was studied under greenhouse conditions using six transgenic lines and one non-transgenic control line. The non-transgenic line was unable to grow at dalapon levels greater than 6.0 kg ha-1, while the majority of the transgenic lines were able to grow at a herbicide level of 48.0 kg ha-1. There were significant differences between the transgenic tobacco lines in their resistance to the dalapon. The heritability of necrosis, leaf length, leaf width and stem height characters were estimated at various levels of dalapon. The heritability of dalapon resistance for developed transgenic tobacco plants at various levels of dalapon was high. The heritability of dalapon resistance for the characters under study decreased with increasing dalapon levels, with the lowest values of heritability occurring at the highest level of dalapon (48 kg ha-1). The leaf length and leaf width characters had the highest heritabilities, while the necrosis and stem height characters had the lowest heritabilities. The effect of time and the interaction between time and herbicide concentration as environmental factors where lowest for the leaf length and leaf width characters, while the time effect was highest for the stem height character. The interaction between time and the effects of dalapon were highest for the necrosis character. The heritability of dalapon resistance in transgenic tobacco seedlings grown in vitro was significantly lower than in plants, indicating either a low expression of the transgene or a high effect of environmental factors for plants at an early stage of growth. The segregation ratio (resistant:susceptible phenotype) for the transgenic lines was 3:1, and x2 test results demonstrated the involvement of single gene inheritance for the lines. Quantitative inheritance studies of the transgene in tobacco plants using generation mean with six generations and 9x9 full diallel mating designs revealed that the additive component of variation was greater than the dominance (hemizygosity) component of variation. The hemizygosity effect was partial and towards the dalapon resistant phenotype. There was significant inter-allelic interaction (epistasis), either between the host plant allele(s) and the dehalogenase transgene or between copies of the transgene. The non-significance of reciprocal effects in the diallel table analysis revealed a lack of maternal or cytoplasmic effects. The analysis of general combining ability and specific combining ability in the diallel table indicated that the majority of transgenic parents had significant general combining ability effect (g.c.a. effects) towards the resistant phenotype, while the non-transgenic parents showed significant g.c.a. effects towards the susceptible phenotype. The progeny derived from crosses between resistant transgenic parents and susceptible, non-transgenic parents showed significant s.c.a. effects towards the resistant phenotype. In contrast, progeny derived from crosses between the susceptible, transgenic parent and non-transgenic parents, as well as progeny derived from crosses between non-transgenic parents showed significant s.c.a. effects towards the susceptible phenotype. In molecular studies of the copy number of the transgene at different generations of one transgenic tobacco line, the transgenic plants were shown to contain two closely linked copies of the transgene at a single locus, whereas the non-transgenic plants were shown to lack the transgene. It was also shown that the transgene was stably integrated into the plant genome in successive generations and that rearrangement of the integrated transgene did not occur. A dehalogenase-specific mRNA was detected in total RNA extracted from leaves of the transgenic plants. Although all of the transgenic plants contained tne same gene, they showed significant variation in the accumulation of dehalogenase-specific mRNA. In control, non-transgenic plants no dehalogenase-specific mRNA was detected. Although the level of the dehalogenase-specific mRNA in transformed plants varied considerably between the lines, was no significant differences between the individual plants within the lines. In a two phase selection experiment, some transgenic callus lines exhibited a dissimilarity in expression of the dehalogenase gene and the neomycin phosphotransferase II gene, conferring kanamycin resistance, used in these experiments as a second selectable marker. Some of the genetically transformed cells selected on medium containing kanamycin, when transferred onto medium containing dalapon, did not show resistance to dalapon. Similarly, when transformed cells selected on medium containing dalapon were transferred onto medium containing kanamycin, some of the callus lines did not show resistance to kanamycin. These results show that in some cases selection for one of the transferred genes does not result in expression of the other, non-selected, transferred gene.
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    Aspects of resistance to phenoxy herbicides in nodding thistle (Carduus nutans L.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1992) Harrington, Kerry Charles
    A nodding thistle (Carduus nutans L.) population had been reported from Argyll in Hawkes Bay, New Zealand, which had poor susceptibility to MCPA and 2,4-D. Plants from the Argyll population were grown beside another Hawkes Bay nodding thistle population in a glasshouse and their dose response curves for MCPA were compared in three separate experiments. The Argyll population was significantly less susceptible to MCPA in all experiments, though the magnitude of resistance varied between experiments from 5-fold to 14-fold. When grown beside each other in the field, the Argyll population was 7 times more resistant to MCPA than the other population. A range of other herbicides was applied to the Argyll nodding thistle population. Cross-resistance was detected for 2,4-D and MCPB, but no significant decreases in susceptibility were detected with mecoprop, clopyralid, picloram, dicamba, paraquat/diquat or glyphosate. A significant reduction in susceptibility to tribenuron-methyl was measured in a field experiment, but this difference was not apparent when the experiment was repeated in a glasshouse. The cross-resistance to MCPA, MCPB and 2,4-D meant selective control of nodding thistle at Argyll in clover-based pastures was now very difficult to achieve. Nodding thistle populations from 20 Hawkes Bay and 7 Waikato properties were tested for resistance to MCPA, and significant levels of resistance were detected in 14 of these populations. Interviews of property owners indicated that resistance had developed where 2,4-D or MCPA had been applied annually for many years, whereas properties without resistance had been sprayed less regularly. Resistant and susceptible nodding thistle seedlings were grown together at a 1:1 ratio under conditions of nutrient stress to determine whether herbicide-resistant nodding thistle plants are less competitive than normal. No difference was detected between the resistant and susceptible biotypes used. Under some conditions, susceptible plants were more likely to have high trichome densities on their leaves, but this trait was found to be too variable and not correlated closely enough with herbicide susceptibility to be useful in distinguishing between resistant and susceptible biotypes. Significant differences in susceptibility to MCPA were maintained between resistant and susceptible biotypes even when leaf surfaces were damaged to allow better foliar penetration of the herbicide, or when herbicide was applied to plants via the root system. Thus the mode of resistance did not appear to involve difficulties with foliar uptake. Studies with radiolabelled 2,4-D confirmed that resistance did not relate to poor leaf penetration. These experiments indicated that 2,4-D was broken down more rapidly in resistant plants. Other findings were that 2,4-D or its metabolites were released in greater quantities from the root systems of susceptible plants, and that herbicide molecules were more difficult to extract from the interior of susceptible plants, possibly due to increased binding. Reasons why resistance to phenoxy herbicides has developed in nodding thistle are discussed, and techniques for controlling resistant populations selectively in pastures and preventing further resistance from developing are also analysed.