John Horton Conway was a British mathematician in the twentieth century. He made notable achievements in fields such as algebra, number theory, and knot theory. He was a renowned professor at Cambridge University and later Princeton. His contributions to algebra include his discovery of the Conway group, a group in twenty-four dimensions, and the Conway Constellation. He contributed to number theory with his development of the surreal numbers. His Game of Life earned him long-lasting fame. He contributed to knot theory with his developments of the Conway polynomial, Conway sphere, and Conway notation.

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Plant MAP3Ks have expanded significantly compared to their metazoan counterparts. A new, sequential workflow combining multispecies ortholog clustering and newly built, family-specific HMMs is used to identify the MAP3K gene family within seven plant species, allowing for a refinement of previously proposed gene family cladding and the novel identification of the MAP3K gene families in the allotetraploid cotton Gossypium hirsutum and newly sequenced monocot seagrass Zostera marina. The MAP3K gene family architecture is further refined and validated using bioinformatics analyses before the recently characterized Arabidopsis Raf-like MAP3K ILK1 is identified and characterized in upland cotton. Transient gene silencing reveals an increase in RKN susceptibility following GhILK1.1 silencing in the susceptible TM1 cultivar. No changes in susceptibility were seen in the resistant M240 cultivar or against reniform nematodes. GhILK1.1 is only the second cotton gene characterized to have a direct role in mediating RKN resistance.

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Thesis (M.A. Agricultural Management (Plant Production)) -- University of Limpopo, 2017 / Nemafric-BL and Nemarioc-AL phytonematicides, which are being researched and developed to serve as alternatives to methyl bromide, have not been tested against plant growth and accumulation of essential nutrient elements in watermelon (Citrullus lanatus) cultivars. The objectives of this study were two fold, to determine the (1) overall growth responses and accumulation of selected essential nutrient elements in watermelon cultivars ‘Congo’ and ‘Charleston Gray’ and suppression of Meloidogyne javanica in response to increasing concentrations of Nemafric-BL and Nemarioc-AL phytonematicides, and (2) efficacy of Velum, Nemafric-BL and Nemarioc-AL phytonematicides on growth of watermelon, accumulation of selected essential nutrient elements in leaf tissues of cv. ‘Congo’ and the suppression of population densities of Meloidogyne species. Objective 1 and Objective 2 were achieved under greenhouse and field conditions, respectively. At 56 and 90 days after initiating the greenhouse and field treatments, respectively, the data were collected and subjected to statistical analyses. Nemafric-BL phytonematicide significantly affected growth of watermelon cultivars ‘Charleston Gray’ and ‘Congo’, whereas Nemarioc-AL phytonematicide did not have any significant effects on the plant variables of both cultivars. Generally, plant growth variables and increasing concentrations of Nemafric-BL phytonematicide had density-dependent growth (DDG) patterns, which were quantified through either positive or quadratic equations (Chapter 3). In contrast, both phytonematicides had significant effects on selected nutrient elements in leaf tissues of both watermelon cultivars. The affected nutrient elements, P, Mn and Na versus increasing concentrations of phytonematicides exhibited the DDG patterns, which were also quantified through either positive or quadratic equations (Chapter 3). The phytonematicides were consistent in suppressing nematode numbers in both watermelon cultivars. Comparison of synthetic nematicide Velum and the two phytonematicides under field conditions suggested that, relative to untreated control, the three products each stimulated growth of watermelon cv. ‘Congo’. The efficacy of Nemafric-BL and Nemarioc-AL phytonematicides on suppression of population densities of Meloidogyne species was comparable to that of Velum. In conclusion, Nemafric-BL and Nemarioc-BL phytonematicides were highly effective in managing population densities of Meloidogyne species in watermelon cultivars and also affected the partitioning of selected nutrient elements in tissues. The study provided essential information that could assist in decision-making in nematode management in watermelon production, particularly in fertiliser application.

Upland cotton (Gossypium hirsutum ) is an important fiber crop grown throughout the southern United States. Plant-pathogenic nematodes are worm-like animals that feed on the roots of most agronomic crops, including cotton. The southern root-knot nematode (Meloidogyne incognita, RKN) and the reniform nematode (Rotylenchulus reniformis, RN) cause significant yield losses in cotton every year. Current sources of resistance are effective but limited, therefore historical screenings of cotton accessions were revisited in search for novel resistance sources. None were identified but many of the screened accessions possessed markers of known root-knot nematode and reniform nematode resistance. The emerging guava root-knot nematode (Meloidogyne enterolobii, GRKN) is a risk for upland cotton production, and identifying host plant resistance would greatly reduce the yield losses for growers. Assays were conducted on the currently available RN and RKN resistance sources inoculated with GRKN. No known nematode resistance gene suppressed GRKN infection, indicating that work must be done to protect crops from the eventual discovery of GRKN in Mississippi fields. Using the same resistance sources, tests were conducted to determine if the currently available resistances to RKN and RN offer any suppression of secondary infection of non-target nematode species for resistance. This is referred to as systemic acquired resistance, which is the induction of non-specific plant defense. Assays found that early inoculation with the nematode targeted by resistance did not effect infection by a secondary nematode species.

Thesis (M.Sc. Agriculture (Horticulture)) -- University of Limpopo, 2017 / Phytonematicides, mainly due to their allelopathic nature, might be highly phytotoxic to crops protected against nematode damage. Phytotoxicity issues are compounded by the fact that the efficacy of plant extracts on nematode suppression depended much on their concentration and duration of exposure to the nematodes. Phytotoxicity could result in low crop yield and/or even in the eventual death of the protected crops. Concentrations that were suppressive to nematode numbers, but phytotoxic to the tested crop would not be useful when applied as a post-planting phytonematicides. The Mean Concentration Stimulation Point (MCSP) values were developed from the Curve fitting Allelochemical Response Dosage (CARD)computer based model to ensure that a non-phytotoxic concentration was applied for each crop. The objective of this study was to determine whether a series of Nemarioc-AL and Nemafric-BL phytonematicide concentrations would provide the MCSP for beetroot (Beta vulgaris) under greenhouse, microplot and field conditions. The greenhouse treatments included 0, 2, 4, 8, 16 and 32% for each phytonematicide. The microplot treatments were 0, 0.8, 1.6, 3.2, 6.4 and 12.8% concentrations, whereas in the field trial treatments were 0, 2.4, 4.8, 9.6, 19.2 and 38.4%. Under each condition, treatments of Nemarioc-AL and Nemafric-BL phytonematicides were, in separate experiments arranged in a randomised complete block design, with the greenhouse, microplot and field trials having 15, 10 and 9 replications, respectively. In the greenhouse, seedlings were raised in 20cm diameter plastic pots, containing pasteurised river sand and commercial seedling growing medium Hygromix® at 3:1 (v/v) ratio. Each seeding was inoculated with 5000 eggs and second-stage juveniles (J2) of Meloidogyne incognita. Seedlings were irrigated with chlorine free tapwater every other day using 250 ml/plant, with irrigation substituted by the treatment once weekly. On the microplot, the procedures were as in the greenhouse except that they growing mixture comprised pasteurised soil collected from the site. In the field, seedlings were directly transplanted into the soil. At 56 days after inoculation, in the greenhouse trial, the effects of Nemarioc-AL and Nemafric-BL phytonematicides were highly significant (P ≤ 0.01) on root galls, contributing 77 and 72% in total treatment variation (TTV) of root galls, respectively. Relative to untreated control, the respective products reduced root galls by 28-72% and 43-67%. Nemarioc-AL and Nemafric-BL phytonematicides had MCSP values on beetroot of 18.1 and 6.4%, respectively, with overall sensitivity values of 0 and 1, respectively.There was no treatment effect on nematode since there was absence of nematode in untreated control.Under microplottrials,Nemafric-BL phytonematicide had significant (P≤ 0.05) effects on fresh root mass, dry root mass and root galls, contributing 20, 19 and 57% in TTV of the three variables, with relative increases for fresh root mass and dry root mass of 65-159% and 63-143%, respectively, whereas root galls were reduced by 82-100%. Nemafric-BL phytonematicide had MCSP value on beetroot of 10.2%, with overall sensitivity value of 4 units. There was no treatment effect on nematode since there was absence of nematode in untreated control. In microplots, Nemarioc-AL phytonematicide did not have significant effects on all plant variables. Under field conditions, the treatments did not have significant effects on plant variables. In conclusion, results of the current study suggested that under greenhouse and microplot conditions the MCSP values of the phytonematicides ranged from 6.4 to 18.1%, with a wide range of overall sensitivities of phytonematicides to the test of beetroot cultivar / National Research Foundation (NRF) and Land Bank Chair of Agriculture - University of Limpopo and the Agricultural Research Council Universities Collaboration Centre

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