Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2000. / Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1988.

abstract / Biological Sciences / Master / Master of Philosophy

<p> Glyphosate-resistant Palmer amaranth (<i>Amaranthus palmeri</i> [S.] Wats) is an economically troublesome weed to southeastern United States soybean (<i>Glycine max</i> [L.] Merr.) growers. Palmer amaranth is troublesome due to its evolution of resistance to multiple herbicide modes of action, competiveness, and prolific seed production. Greenhouse studies were conducted at the Delta Research and Extension Center in Stoneville, MS to evaluate different rates of 2,4-dichlorophenoxyacetic acid (2,4-D) for control of Palmer amaranth. Field experiments were conducted at the Delta Research and Extension Center in Stoneville, MS in 2013 and 2014 to evaluate Palmer amaranth emergence using a cultural practice and a residual herbicide. Field experiments were also conducted at the Delta Research and Extension Center in Stoneville, MS in 2013 and 2014 to evaluate Palmer amaranth control with applications of glyphosate, glufosinate, and 2,4-D alone and in mixtures.</p>

Guayule (Parthenium argentatum Gray) is a natural rubber producing plant presently being commercialized for production in arid and semi-arid regions of the world. Inconsistent seed (achenes) quality and the lack of methods to discriminate between good and bad seed lots are significant problems, allowing commercial stands to be established only by transplants, rather than by more cost effective direct-seeding. The objective of this study was to investigate why guayule seed and seed lots vary significantly in quality. The laboratory and greenhouse experiments involved separation of seed based on physical attributes (diameter, color and weight) and the confirmation of internal structures (embryo and endosperm) by x-ray analysis. The effect of different conditioning treatments on seed lots was also tested. Separation of seed by size (diameter) was shown to be less efficient than separation by color. Color was the most effective means of separating heavier and darker (opaque-black and gray color grades) seed, and these seed were confirmed to be filled, containing internal structures by x-ray analysis. Germination percentage and rate were greater for seed with these characteristics than for yellow and bright-black seed, which are lighter and predominately partially filled or unfilled. Conditioning treatments used for guayule seed older than two years had no effect on seed germination and emergence percentage or rate. However, differences in germination and emergence were found among lines, therefore, differences among seed lots appear to be due to variation in the number of filled seed. The quality of seed lots was significantly improved when seed were separated based on color first, then by weight. The separation of good quality seed (filled) from poor quality seed (unfilled) is crucial to lower the costs of stand establishment by direct seeding. Therefore, the quality of seed lots can be improved significantly (higher proportion of filled seed) by separating first by color, then by weight.

(+)-Pisatin, ([+]-[6aR,11aR]-6a-hydroxy-3-methoxy-8,9-methylenedioxypterocarpan) is the major phytoalexin of the garden pea (Pisum sativum L.). Despite being the first phytoalexin to be chemically characterized, its biosynthesis remains to be fully elucidated. RNA-mediated genetic interference (RNAi) was used to gain further insights into the (+)-pisatin biosynthetic pathway. The expression of three genes, isoflavone reductase (IFR) catalyzing the reduction of 7,2'-dihydroxy-4',5'-methylenedioxyisoflavone to (-)-sophorol, sophorol reductase (SOR) involved in reducing (-)-sophorol to (-)-7,2'-dihydroxy-4',5'-methylenedioxyisoflavanol and hydroxymaackiain-3-O methyltransferase (HMM) involved in methylation of (+)-6a-hydroxymaackiain to (+)-pisatin was silenced. The genes are transcriptionally co-regulated during (+)-pisatin biosynthesis, with the IFR and SOR proposed to function upstream of the HMM gene.Hairy roots expressing the HMM RNAi construct, deficient in (+)-pisatin biosynthesis were identified. However, these did not accumulate (+)-6a-hydroxymaackiain, precursor to (+)-pisatin. Instead they accumulated 2,7,4'-trihydroxyisoflavanone, daidzein, liquiritigenin and isoformononetin. The amino acid sequence of HMM is very similar to that of another methyltransferase, hydroxyisoflavanone-4'-O-methyltransferase (HI4MOT), found in most legumes. HI4?MOT catalyzes the methylation of 2,7,4'-trihydroxyisoflavanone (THI) to 2,7-dihydroxy-4'-methoxyisoflavanone, one of the earliest enzymatic steps in isoflavonoid biosynthesis. In pea, HI4OMT may be the same enzyme as "HMM" catalyzing the methylation of both THI and (+)-6a-hydroxymaackiain. Preventing the methylation of THI could divert pea intermediates to the production of daidzein and isoformononetin instead of (+)-pisatin.None of the transgenic hairy roots expressing the IFR RNAi construct were totally deficient in (+)-pisatin biosynthesis. However, all produced reduced amounts of (+)-pisatin, with one culture accumulating 7,2'-dihydroxy-4',5'-methylenedioxyisoflavone, the substrate for IFR. Hairy roots expressing the SOR RNAi construct deficient in (+)-pisatin biosynthesis were identified. These accumulated (-)-sophorol, the substrate for SOR. These data provide evidence for the involvement of these genes and the intermediates with (-)-optical activity in (+)-pisatin biosynthesis.The elicitation of the biosynthesis of secondary metabolites in plant cell and tissue cultures by electric current was explored. Electric current was demonstrated to elicit the biosynthesis of secondary metabolites in pea hairy and intact roots, seedling, root and cell suspension cultures of various plant species. Electric current has potential for use as an elicitor of secondary metabolites in basic and commercial research ventures.

The aims of this study were to identify sources of drought tolerance in a common bean reference collection, to improve genetic and physiological understanding of drought tolerance in different gene pools of common bean, to establish the role of rooting characteristics in improving grain yield under drought conditions, to determine the genetic structure and diversity in the reference collection using SSR marker data, and to identify simply inherited markers in close proximity to genes affecting drought tolerance. Field experiments were laid out as 11x11 Mesoamerican and 9x9 Andean lattices with three replicates under irrigated and rainfed treatments at CIAT-Palmira and Harare Research Station. Yield was significantly correlated with total shoot biomass at mid pod fill, 100-seed weight, number of pods per plant and days to maturity under both treatments at both locations. Based on geometric means and drought sensitivity indices, BAT477, G11721, G4017, DOR390 (Mesoamerican) and SAB645, PVA1111, SEQ1003, SEQ1027, G17076 and G5142 (Andean) genotypes had high and stable yields across treatments in both locations and could serve as sources of drought tolerance in common bean. Two greenhouse experiments were conducted at CIAT-Palmira using the soil cylinder system, in a randomised complete block design with three replicates. Well watered and water stressed treatments were applied in each trial. In 2009 a total of 33 Andean landraces and three Mesoamerican checks were evaluated for deep rooting and other root properties. In 2010 phenotypic differences were determined between elite genotypes in root development under water stress. A total of 40 elite Andean and Mesoamerican genotypes commonly used as parents in many breeding programmes, were evaluated. Variability of root traits under water stress was expressed either as adaptive or constitutive traits depending on genotype. It was found that deep rooting alone may not be adequate for drought tolerance in common bean, as some deep rooted genotypes had poor yields under field conditions. SSR and SNP markers were used for molecular characterisation of the reference collection to determine the population structure and identify statistically significant marker-trait associations relevant for drought tolerance in the reference collection. The reference collection is strongly structured following the geographical origins of the genotypes. TOG896943-500, TOG918200- 347 and TOG 910860-634 were significantly associated with 100-seed weight and total shoot biomass across locations and treatments. In conclusion, all findings in the current study need to be integrated to develop drought tolerant common bean varieties in future. Mapping studies should be extended to candidate gene analysis for the identified marker-trait associations.

The nature of host susceptibility to phytopathogenic parasites, especially the obligates, remains one of the major problems in plant pathology even though it has been investigated extensively from the early part of the present century until the late thirties. Studies on the genetics of the pathogens and breeding for resistant varieties have predominated since that time. There is at present a revival of interest in the physiology of disease resistance. [...]

Verticillium wilt is often the cause of serious losses in potatoes in Eastern Canada and Northern United States. It is of minor importance in field tomatoes except in California and Utah. The disease is not uncommon in greenhouse tomatoes in North America and in Europe. [...]

Hay is the most important crop in Quebec. According to the annual report of the Quebec Bureau of Statistics for 1961, of a total cultivated area of 7,864,176 acres in Quebec, 3,458,000 acres were in hay. The value of the hay crop in 1961 was 55.8 percent of the value of all field crops in the province. Since alfalfa, birdsfoot trefoil, red, alsike, and ladino clovers are cominant in this hay crop, their agricultural importance is apparent. This, together with the fact that some of these forage legumes, mainly red clover and alfalfa, are the most common rotation crops, led to the choice of these plants for study.