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Greenhouse and microplot studies were conducted for understanding the effects of cover crop species/cultivars for hosts and population reduction of soybean cyst nematode (SCN; Heterodera glycines) from the fields of North Dakota. Moreover, early-maturing soybean [Glycine max (L.)] accessions from different countries of origin were screened for resistance against two common SCN populations for finding new sources of resistance. Thirty-eight cover crop species/cultivars were evaluated for their hosting ability of two SCN populations (SCN103 and SCN2W) from two fields of North Dakota in greenhouse experiments. The majority of the tested crops were non-hosts for both SCN populations. However, a few of them, such as Austrian winter pea (Pisum sativum L.), crimson clover (Trifolium incarnatum L. cv. Dixie), crambe (Crambe abyssinica, cv. BelAnn), field pea, cvs. Aragorn and Cooper, hairy vetch (Vicia villosa Roth), turnip (Brassica rapa L. cv. Purple top), and white lupine (Lupinus albus L.) were poor-hosts/hosts of both SCN populations. Furthermore, thirteen of them were tested for the SCN population reduction either or both in the greenhouse and microplot experiments. Out of 13, at least four crops, such as annual ryegrass (Lolium multiflorum L.), brown mustard (Brassica juncea L. cv. Kodiak), daikon radish (Raphanus sativus L.), and turnip cv. Pointer showed more than 50% population reduction compared with initial population densitiy, consistently in the greenhouse or microplot experiments. The resistance screening of 152 early-maturing soybean accessions showed that a majority of the accessions were susceptible/moderately susceptible to both SCN populations (SCN HG type 0 and 2.5.7), while a few (n=18) showed good resistance responses to both or either of the SCN populations. The cover crops, which were non-hosts/poor-hosts and have a greater ability for the SCN population reduction have great potential to be included in an integrated SCN management strategy. The novel resistant accessions identified in this study have the potential to be used in soybean breeding for developing SCN-resistant cultivars after confirming their resistance response and identifying the resistance genes/loci. The results obtained from this study helps in developing a sustainable SCN management strategy in the northern Great Plains.

Ninety Merino ewes, divided into three equal groups, were kept on natural highveld grazing for 42 weeks. Group M received a mineral supplement continuously, averaging 28 g per day. The other groups received commercial protein supplements, group RDP a mainly rumen degradable supplement and group RUP, a mainly rumen undegradable supplement. These supplements had crude protein (CP) levels of 29% and 28% respectively and were supplied at strategic times during the reproductive cycle, at 250 g per ewe per day for 14 days before mating, at 350 g per ewe per day for 42 days, starting 21 days before lambing and at 500 g per ewe per day for 56 days, starting 21 days after lambing. Grazing was randomized to minimize differences in nutrition and parasite challenge, and had an average CP of 8.8%. Lambing rates were: RUP 96%, RDP 89% and M 76%. Lamb survival rates at 11 and 17 weeks post lambing were 75%&63% for RUP, 64%&57% for RDP and 55% and 48% for M respectively (P< 0.05). Wool production parameters were similar for all groups, as were mean faecal egg counts: 685 (RUP), 371 (RDP) and 465 (M). Body weights, body condition scores and FAMACHA scores were also similar for all three groups. Income per ewe, calculated at 11 and 17 weeks post lambing, was highest for RUP at R147.80&R132.87, lowest for M at R117.86&R111.13, and in between for RDP (R129.85&R121.38). However, the gross margin was the highest for M at both points (R114.35&R107.77) compared to RUP (R70.43&R54.93 – P < 0.03&P < 0.008 respectively), as well as RDP (R82.96&R74.12). Strategic supplementation with protein improved performance but the additional income was not sufficient to cover feed costs under prevailing conditions and neither supplement could therefore be economically justified. / Dissertation (MMedVet)--University of Pretoria, 2002. / Production Animal Studies / unrestricted

Thesis(M.Sc.(Plant Protection))-- University of Limpopo,2019 / Previously, cucurbitacin-containing phytonematicides that were drench-applied in black plastic containers filled with pasteurised loam soil when placed on the soil surface had no effect on suppression of population densities of root-knot (Meloidogyne species) nematodes. The active ingredients of cucurbitacin-containing phytonematicides, namely, the cucurbitacins, had been shown to be thermophilic, with the failure of the products explained from the view of the variability induced by container-type and aboveground positioning. The view was investigated further using Nemarioc-AL and Nemafric-BL phytonematicides as influenced by container-type and positioning on growth of tomato (Solanum lycopersicum L.) plants and suppression of M. incognita population densities. Tomato cv. ′Floradade′ seedlings were transplanted into 30-cm-diameter brown pot belowground, brown pot aboveground, black pot belowground, black pot aboveground, 5 L polyethylene plastic bag belowground and 5 L polyethylene plastic bag aboveground, each containing 5-dm3 steam-pasteurised sandy loam soil amended with Hygromix at 3:1 (v/v) ratio. Seedlings were inoculated with 2000 eggs and second-stage juveniles (J2) of M. incognita race 2, with Nemarioc-AL and Nemafric-BL phytonematicides applied once 17 days after inoculation in both Experiment 1 and Experiment 2. Also, standard cultural practices were applied throughout the trial. At 56 days after inoculation, container-type and positioning had significant effects on various plant growth and essential nutrient element variables in Experiment 1 and Experiment 2, except that the six treatments did not have significant effects on nutrient elements and nematode population densities in Experiment 2. Relative to brown plastic pot belowground, treatments either increased or decreased plant growth, essential nutrient elements and nematode densities in Experiment 1, with selective similaritiesin Experiment 2. Specifically, nematode variables except for J2 in soil and total nematode population densities were significantly affected by the treatments in Experiment 2. Relative to the standard, plastic bag belowground increased J2 in soil and total population in soil by 18%. In conclusion, both container-type and positioning had effects on the efficacy of phytonematicides on plant growth, accumulation of essential nutrient elements and suppression of nematode population densities. Consequently, in trials where cucurbitacin-containing phytonematicides are conducted in microplots, brown plastic pots with the belowground positioning should be used to enhance the efficacy of the phytonematicides in stimulating plant growth and suppression of nematode population densities.

Thesis(M.Sc.( Agriculture, Horticulture)) -- University of Limpopo, 2019 / Worldwide, tomato (Solanum lycopersicum L.) is one of the most important crops grown for nutritional value and health benefits, and are highly susceptible to root-knot (Meloidogyne species) nematodes. Following the withdrawal of synthetic chemical nematicides, Nemarioc-AL and Nemafric-BL phytonematicides have been researched and developed as alternatives to synthetic chemical nematicides. However, Nemarioc-AL and Nemafric-BL phytonematicides contains allelochemicals namely, cucurbitacin A (C32H46O9) and cucurbitacin B (C32H46O8) as their active ingredients. Therefore, the objective of this study was to determine whether increasing concentration of Nemarioc AL and Nemafric-BL phytonematicides would result in cucurbitacin residues in tomato plant, to generate mean concentration stimulation point (MCSP) values, overall sensitivity (∑k) and selected foliar mineral elements of tomato plant. Two parallel trials of Nemarioc AL and Nemafric-BL phytonematicides were conducted under field conditions, with each validated the next season. Each trial had seven treatments, namely, 0, 2, 4, 8, 16, 32 and 64% of Nemarioc-AL or Nemafric-BL phytonematicide concentrations, arranged in a randomised complete block design (RCBD), with five replications. In each trial, the seasonal interaction on variables was not significant and therefore data were pooled across the two seasons (n = 70). In both phytonematicides, the cucurbitacin residues were not detected in soil and tomato fruit. Plant variables and selected foliar nutrient elements were subjected to the Curve-fitting Allelochemical Response Data (CARD) model to generate biological indices which allowed for the calculation of MCSP of phytonematicides on tomato and their ∑k values of tomato to Nemarioc-AL and Nemafric BL phytonematicides. In Nemarioc-AL phytonematicide experiment, MCSP for tomato plant variables was at 1.13%, with the ∑k of 60 units, while the MCSP for selected tomato nutrient elements in leaf tissues was at 2.49%, with the ∑k of 21 units. Plant height, chlorophyll content, stem diameter, number of fruit, dry fruit mass, dry shoot mass and dry root mass each with increasing concentration of Nemarioc-AL phytonematicide exhibited positive quadratic relations with a model explained by 95, 82, 96, 89, 83, 83 and 92%, respectively. Similarly, K, Na and Zn each with increasing Nemarioc-AL phytonematicide concentration exhibited positive quadratic relations with a model explaining a strong relationship by 91, 96 and 89%. In Nemafric-BL phytonematicide experiment, MSCP for tomato plant variables was at 1.75%, with the ∑k of 45 units, whereas MCSP for selected tomato nutrient elements in leaf tissues was at 3.72% with the ∑k of 33 units. Plant height, chlorophyll content, stem diameter, number of fruit, dry fruit mass, dry shoot mass and dry root mass and increasing Nemafric-BL phytonematicide concentration exhibited positive quadratic relations with the model explaining a strong relationship by 92, 83, 97, 96, 87, 94 and 96%. Likewise, Na and Zn each with increasing Nemafric-BL phytonematicide concentration exhibited positive quadratic relations with a model explaining their relationship by 93 and 83%, respectively. In contrast, K with increasing Nemafric-BL phytonematicide concentration exhibited negative quadratic relations with a model explaining the relationship by 96%. In conclusion, tomato plant variables and selected foliar nutrient elements over increasing concentration of phytonematicides exhibited DDG patterns, characterised by three phases, namely, stimulation, neutral and inhibition. The developed non-phytotoxic concentration would be suitable for successful tomato production under field conditions.

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Soybean (Glycine max [L.] Merr.) is one of the most important crops in the world. The average annual yield losses due to soybean diseases and pests are estimated to be around 11% in the United States. Soybean yield losses due to sudden death syndrome (SDS), caused by the fungus Fusarium virguliforme O'Donnell & T. Aoki have been problematic in majority of the soybean producing states. In recent years, reniform nematode (RN, Rotylenchulus reniformis Linford and Oliveira) and frogeye leaf spot (FLS), caused by the fungus Cercospora sojina K. Hara have emerged as a major problem in the southern soybean producing states. Planting resistant cultivars is one of the most cost-efficient methods in managing SDS, RN, and FLS, therefore it would be critical to identify and map the quantitative trait loci (QTL) that underlie their resistances. Two soybean populations were evaluated in this study. The ‘Essex’ × ‘Forrest’ 77 near-isogenic lines were screened in the field to evaluate the disease index of SDS. The Essex × Forrest and ‘Flyer’ × ‘Hartwig’ recombinant inbred lines were screened in the greenhouse to assess the reproduction index of RN and the disease severity of FLS. The BARCSoySNP6k chip was used to genotype the two populations. Four QTL that underlie SDS resistances were mapped in the same region as Rfv06-01, Rfv06-02, Rfv13-01, and Rfv19-01. The Rfv06-02 interval in this study was smaller than the one previously reported. Rrr08-01, Rrr13-01, Rrr15-01, Rrr18-01, and Rrr18-02 were reported to confer resistances to RN. Rrr08-01, Rrr13-01 and Rrr15-01 were novel whereas Rrr18-01, and Rrr18-02 were mapped in previous studies. cqSCN-001 (soybean cyst nematode, Heterodera glycines Ichinohe) was identified in the same region as Rrr18-01, and Rrr18-02 whereas cqSCN-006 was identified in the same region as Rrr15-01. These findings provide further evidence that there are common sources of genetic resistances to RN and SCN. Rcs15-01 and Rcs15-02 were reported to confer resistances to FLS. Rcs15-01 was novel and Rcs15-02 was mapped at the same region as an Rcs mapped in a previous study. This indicated that Rcs15-02 has dual resistances to C. sojina races. Candidate genes were inferred in this study. The QTL mapped in this study could potentially be used in soybean breeding programs that aim to introgress genetic resources that confer resistances to SDS, RN, and FLS.

Heterodera glycines, soybean cyst nematode (SCN) causes more than one billion dollars soyben production loss in the U.S. annually. SCN is an obligate parasite of specialized feeding cells within the host root known as syncytium. The SCN resistance genes and signaling pathways in soybean have not been fully characterized. Gene expression analysis in syncytium from compatible and incompatible interactions identified candidate genes that might involve conferring resistance to SCN. This dissertation aimed to investigate the biological functions of the candidate resistance genes to confirm the roles of these genes in resistance to SCN. The study demonstrated a role of syntaxin 31-like genes (Gm-SYP38) in resistance to SCN. Overexpression of Gm-SYP38 induced the transcriptional activity of the cytoplasmic receptor-like kinase BOTRYTIS INDUCED KINASE 1 (Gm-BIK1-6). Overexpression of Gm-BIK1-6 rescued the resistant phenotype. In contrast, Gm-BIK1-6 RNAi increased parasitism. In another experiment, the expression of a Glycine max homolog of LESION SIMULATING DISEASE1 (LSD1) resulted in the transcriptional activation of ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) and NONEXPRESSOR OF PR1 (NPR1), that function in salicylic acid (SA) signaling, implicating the involvement of the antiapoptotic, environmental response gene LESION SIMULATING DISEASE1 (LSD1) in defense that is demonstrated here. The study also investigated the role of SNARE components (genes functioning in membrane fusion) in resistance to SCN. Experiments showed that SNARE functions in concert with a beta-glucosidase having homology to PEN2 and an ATP binding cassette transporter having homology to PEN3. This study provides novel information for the genetic improvement of soybean for enhanced disease resistance.

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Evaluating soil health using bioindicator organisms has been suggested as a method of analyzing the long-term sustainability of agricultural management practices. The main objective of this study was to determine the effects of vineyard management strategies on soil food web structure and function, using nematodes as bioindicators by calculating established nematode ecological indices. Three field trials were conducted in a commercial Pinot Noir vineyard in San Luis Obispo, California; the effects of (i) fertilizer type (organic and inorganic), (ii) weed management (herbicide and tillage), and (iii) cover crops (high or low water requirements) on nematode community structure, soil nutrient content, and crop quality and yield were analyzed. Overall, although nematode ecological indices indicated that all plots had disturbed soil food webs, the indices proved to be less useful for measuring subtle differences in soil management over the short-term than anticipated. They showed few differences treatments. In general, the most pronounced differences were seen by sample location (under the vine or in the tractor row) and sample date, rather than treatment. None of the evaluated strategies affected crop quality, although fertilizer had a slight effect on yield. However, several indices were correlated with soil chemical parameters, including pH, nitrogen, carbon, and, to a lesser extent, EC. These results indicate that while nematode indices can be useful for comparing the state of the soil food web under long-term soil conditions, they may not be a robust measure of how agricultural management practices change soil health over a single growing season.