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<p>Thesis submission for Caleb Kell</p>

MSCAGR / Department of Plant Production

Thesis (M.Sc. (Agriculture in Horticulture)) -- University of Limpopo, 2017. / Butternut squash (Cucurbita pepo) is highly susceptible to root-knot (Meloidogyne species) nematodes. Nemafric-BL and Nemarioc-AL phytonematicides were being researched and developed for use in various crop farming systems for managing nematode numbers. However, the two products when not properly quantified are highly phytotoxic to crops. The Curve-fitting Allelochemical Response Dosage (CARD) computer based model was adopted to compute the Mean Concentration Stimulation Point (MCSP), which is a non-phytotoxic concentration. The objective of the study, therefore, was to determine whether the MCSP values of Nemarioc-AL and Nemafric-BL phytonematicides on squash under greenhouse, microplot and field conditions exist. Seedling were raised in 25-cm plastic bags filled with loam, pasteurised sand and Hygromix 2:1:1 (v/v) in the greenhouse , raised in 25-cm pots with pasteurised sand and loam 3:1 (v/v) on the microplot, and raised under field with Hutton sandy loam (65% sand, 30% clay and 5% silt). After establishment each plant was inoculated with 5 000 eggs and second-stage juveniles (J2) of M. incognita. Treatments comprised 0, 2, 4, 8, 16 and 32% concentration of Nemarioc-AL and Nemafric-BL phytonematicides with ten replicates. For greenhouse, treatments comprised 0.0, 0.8, 1.6, 3.2, 6.4 and 12.8% concentration of both Nemarioc-AL and Nemafric-BL phytonematicide with 10 replicates. For micro-plot and for field experiment treatments comprised 2.4, 4.8, 9.6, 19.2 and 38.4% of both Nemarioc-AL and Nemafric-BL with nine replicates. In all experiments, treatments were arranged in a randomised complete block design with ten replicates. In the greenhouse, Nemafric-BL phytonematicide had highly significant effects on dry fruit mass and significant on fruit number, but had no effect other plant variables recorded. xxii Treatments contributed 51 to 71% in total treatment variation (TTV) of dry fruit mass and fruit number, respectively. However, at higher concentrations the same phytonematicide decreased fruit number by 66 to 137% and dry fruit mass by 6 to 14%. In the greenhouse, MCSP value for Nemafric-BL phytonematicide was 2.83% of which the overall Σk was 3 units. Plant variables and increasing concentration of phytonematicide exhibited quadratic relations. In microplot, Nemarioc-AL was highly significant for dry shoot mass and dry fruit mass with treatment contribution of 15 to 63% in TTV. At lower concentrations Nemarioc-AL phytonematicide increased dry shoot mass by 5%. However, with increasing concentrations dry shoot mass decreased from 7 to 30%. Phytonematicide increased dry shoot mass from 41 to 81% and decreased root galls from 3 to 73%. In microplot, MCSP value was 11.85%, with the Σk zero. Plant variables and increasing concentration of phytonematicide exhibited quadratic relations. In field experiment, Nemarioc-AL and Nemafric-BL phytonematicide treatment effect were not significant on any plant variables. In conclusion, the MCSP and Σk values appear to be location-specific since they were not similar in various locations.

<div>Anthropogenically driven global change is disrupting ecosystems and habitats of many plant species, straining the ability of native species to survive and reproduce. The overarching goal of this research was to holistically work towards restoration of a threatened tree species by connecting research from different disciplines. In order to do so, the threatened butternut tree (<i>Juglans cinerea</i>) and its hybrids were used as a case study. Hybridization can incorporate stress tolerance in plants and could be a potential restoration tool. Evidence in some wild butternut populations indicates that naturalized hybrids of butternut with Japanese walnut (<i>Juglans ailantifolia</i>) may be more tolerant to butternut canker disease (BCD) than butternut, but this has not been formally tested. Thus, chapter 2 examined potential BCD tolerance within and between unadmixed and hybrid butternut inoculated with two BCD fungal isolates. Differences in canker growth were observed by fungal isolate, which could help to explain some differences in BCD severity found among butternut populations. Smaller and fewer cankers and greater genetic gains were detected in hybrid families, demonstrating that hybrids warrant further evaluation as a possible breeding tool for developing BCD-resistant butternut trees.</div><div>However, even with increased disease tolerance, hybrids must possess similar ecophysiological tolerances to their native progenitor to be an effective replacement. Butternut is extremely cold hardy, but Japanese walnuts are native to a warmer ecosystem, indicating potential disparities in extreme temperature tolerances between the two species and their hybrids. Thus, samples from mature trees were subjected to cold and heat treatments to compare relative extreme temperature tolerances within butternut and between butternut, Japanese walnut, and their hybrids. Within butternut, trees from colder areas exhibited less cold damage than those from warmer areas. Differences in heat damage among provenances occurred but did not follow a clear trend. Butternut exhibited greatest cold tolerance, Japanese walnut exhibited greatest heat tolerance, and hybrids were intermediate. Thus, the utility of hybrids for restoration could be limited at the extremes of the species’ distributions.</div><div>A second, but different type of freeze test was conducted for chapter 4 using seedlings to gain a more nuanced understanding of cold tolerance within butternut and between butternut and its hybrids. No survival or damage differences were detected in butternut provenances, although seedlings from the coldest provenances experienced more delayed budbreak at the two warmest treatments than those from warmer provenances. Interspecific differences were not observed in dieback but were detected in survival and budbreak. The hybrids had greater survival than butternut from warmer provenances at the lowest temperature treatment (-38 °C), but given that temperatures that low are extremely unlikely to occur in those provenances, it is not anticipated to give the hybrids an advantage if planted in those areas. However, the hybrids’ earlier budbreak could limit the success of restoration with these hybrids in the coldest extents of butternut’s range. </div><div>If hybrids, as well as genetically modified (GM) trees, are successfully developed for effective disease tolerance and to serve as an ecologically suitable replacement, success of restoration using hybrids will ultimately depend on those directly responsible for replanting efforts. A survey was administered to land managers in 46 organizations in Indiana to gauge perceptions of hybrid and GM trees, as well as current use of hybrid trees. Land managers had stronger concern for ecological, rather than economic, issues. Agreement was highest for using hybrid and GM trees for “conservation and restoration of at-risk species”, “timber production”, and “non-timber products (fruit, syrup, etc.)”. However, perceptions varied by characteristics, such as concern type, age, and the type of land they managed. Ecological concern and the type of land being managed most strongly predicted current hybrid use. Overall, results indicate the majority of land managers in Indiana would likely be agreeable to recommendations towards using hybrids. However, most nonetheless had strong ecological concerns about their suitability as a native replacement. It is important to note, though, that consistent with the results of previous studies, great variation was seen within the performance and characteristics of the butternut hybrids in chapters 2-4. Thus, it may be possible with careful selection and breeding to harness this variation to develop disease tolerant and ecologically similar hybrids acceptable to land managers.</div>

Effective microorganisms (EM), a commercial concoction of microbes that includes yeasts, fungi, bacteria and actinomycetes, have been found to be effective in enhancing crop growth by a number of scholars. It is registered in South Africa, but it had not been thoroughly investigated. The present study investigated the effects of EM on growth, yield and quality of tomato (Lycopersicon esculentum Mill), butternut (Curcurbita moschata) and Swiss chard (Beta vulgaris), along with selected soil properties. In field-grown tomato it was observed that the application of EM caused a significant increase in the number of fruits at seven weeks after transplanting. However, plants treated with EM alone, or EM in combination with other amendments, subsequently produced lower yields owing to an outbreak of early and late blights which affected them the most severely. Combined applications of EM with organic amendments improved plant N content and increased soil N content above initial levels. The application of compost resulted in soil N and P concentrations higher than those of the control presumably due to nutrients being slowly released from the compost material. In a follow up greenhouse trial EM application had a negative effect on tomato leaf dry matter yield, number of leaves, number of trusses, fruit yield and number of fruits. The negative effects of EM were ascribed to N immobilization by the EM that could have resulted in reduced N availability to plants. The lower number of fruits associated with EM application resulted in improved average fruit weight of tomatoes grown in the greenhouse, possibly as a result of more assimilates being partitioned to the few fruits EM application also had a negative effect on field grown butternut as reflected by lower total yield, lower marketable yield and lower first grade yield. The results were attributed to immobilization of N induced by application of EM, and to the inability of EM to control pumpkin fly that attacked very young fruit, resulting in their failure to develop or resulting in the down grading of mature fruits. The application of EM alone had a positive but non significant effect on the yields of both the first and second harvests of Swiss chard. However, when applied with compost or goat manure, a non significant negative effect on yield was observed. When applied with inorganic fertilizer, EM had no effect on yield but tended to increase the uptake of nitrogen by Swiss chard. Though goat manure had a narrower C: N ratio than compost, it did not result in greater EM effectiveness as had been hoped. However, goat manure had a more positive effect on soil properties than compost. It increased the N, P, and K contents of the soil and resulted in a narrower C: N ratio of the soil compared to compost. Generally, the results of the four trials conducted with three different crops indicated that EM had inconsistent effects on crop performance.