Please read the abstract in the section 00front of this document / Dissertation (MSc Agric (Agronomy))--University of Pretoria, 2005. / Plant Production and Soil Science / unrestricted

Insects are considered to be responsible for 80-85% of all pollination, with honeybees being well known for their pollination services for many crops. The effect of managed honeybee pollination on sunflower seed yield and quality (germination percentage and oil content) was investigated at the University of Pretoria experimental farm and in commercial sunflower fields at Settlers. This was done through pollinator exclusion and pollinator surveys on sunflower field plots located at different distances from managed honeybee colonies. Observations on the foraging behaviour and activity of honeybees throughout the day were also made. The data presented in this thesis reveal that seed quantity and quality of sunflower increased significantly as a result of insect visits. Insect pollination improved the mass of 100 seeds (by 38%), as well as their germination percentage (by 38%) and oil content (by 36%). Moreover, visitation frequency, seed yield and quality were negatively correlated with distance to the honeybee hives, suggesting that the distribution of honeybee colonies is not enough to maintain an adequate pollination service throughout the large sunflower fields at Settlers. Honeybee foraging activity varied throughout the day, the highest activity being from 9h00 until 16h00, and activity was correlated with temperature. The results of this study suggest that the use of managed honeybees in sunflower crop production can effectively increase the seed quality and quantity, but additional management measures should be considered to improve production in large monocropping farms that are currently isolated from pollinator sources. Additional provision of honeybee colonies is needed in sunflower production areas during the flowering period. Furthermore, as our results show that in the presence of pollinators other than honeybees seed yield was also improved, management measures that promote the biodiversity of sunflower visitors may also have an important contribution. / Dissertation (MScAgric)--University of Pretoria, 2010. / Zoology and Entomology / unrestricted

Germination of plants is one of the most important stages during their growth which is often influenced by environmental stresses, especially drought and salinity. This study was conducted to investigate the effects of salinity and drought on seed germination and growth of Lathyrus sativa. The experiment was laid out in a completely randomized design with factorial arrangement in 4 replications. Salinity treatments were 0, 2, and 4 dS/m and drought treatments included 0, 0.4, 0.8, 1.2 MPa. Salinity and drought treatments were prepared by using sodium chloride and polyethylene glycol 6000, respectively. The results showed that salinity and drought stresses decreased germination percentage, root and radicle length.

Field experiments were conducted in two different growing environments to evaluate the spread and movement of Dickeya dadantii. A procedure to inoculate seed potatoes with Dickeya dadantii was developed to use during this study. Spread of Dickeya dadantii from inoculated potato seed to healthy potato seed during the handling, cutting and planting procedures was not detected at either location. Spread of Dickeya dadantii from inoculated seed to surrounding progeny tubers in the field was documented in both locations. In Florida, 33% of progeny tubers tested positive for Dickeya using PCR, and in North Dakota, 13% of the progeny tubers tested positive. Stunting was observed in plants grown from Dickeya dadantii inoculated seed tubers in North Dakota, but not in Florida. These results indicate that Dickeya dadantii may spread during the seed handling and cutting processes and can spread in the field from infected seed tubers to progeny tubers.

Witchweeds and broomrapes are root parasitic weeds that represent one of the main threats to global food security. By drastically reducing host crops’ yield, the parasites are often responsible for enormous economic losses estimated in billions of dollars annually. Parasitic plants rely on a chemical cue in the rhizosphere, indicating the presence of a host plant in proximity. Using this host dependency, research in parasitic plants focuses on understanding the necessary triggers for parasitic seeds germination, to either reduce their germination in presence of crops or provoke germination without hosts (i.e. suicidal germination). For this purpose, a number of synthetic analogs and inhibitors have been developed and their biological activities studied on parasitic plants around the world using various protocols. Current studies are using germination-based bioassays, where pre-conditioned parasitic seeds are placed in the presence of a chemical or plant root exudates, from which the germination ratio is assessed. Although these protocols are very sensitive at the chemical level, the germination rate recording is time consuming, represents a challenging task for researchers, and could easily be sped up leveraging automated seeds detection algorithms. In order to accelerate such protocols, we propose an automatic seed censing tool using computer vision latest development. We use a deep learning approach for object detection with the algorithm Faster R-CNN to count and discriminate germinated from non-germinated seeds. Our method has shown an accuracy of 95% in counting seeds on completely new images, and reduces the counting time by a significant margin, from 5 min to a fraction of second per image. We believe our proposed software 5 “SeedQuant” will be of great help for lab bioassays to perform large scale chemicals screening for parasitic seeds applications.

L’objectif de cette thèse est de définir l’effet de l’environnement maternel sur la qualité des graines de A.thaliana, H.annuus, B.oleracea et H.vulgare, caractériser deux mutants d’A.thaliana affectés au niveau d’enzymes de la membrane plasmique et caractériser l’activité de ces deux protéines. Des dosages de O₂•⁻ et de radicaux ont été faits sur des graines issues de plantes ayant subi des stress thermique et/ou hydrique et n’ont pas montré d’effet des stress. Des traitements de vieillissement accéléré ont eu des effets négatifs sur la vigueur et la viabilité des graines. Des radicaux ont été identifiés par RPE haut champ au niveau de l’enveloppe et du péricarpe. Etant donné la localisation de ces radicaux, ils ne sont pas de bons marqueurs de la qualité des graines. Des mutants KO d’A.thaliana de quinones réductases (QR) et de AIR12 ont été caractérisés. Les QR sont des enzymes cytosoliques ayant une affinité pour la membrane. Elles catalysent la réduction de quinones en dihydroquinones et jouent un rôle protecteur contre le stress oxydatif. A pH alcalin par contre, les dihydroquinones se déprotonent et s’autooxydent entrainant la formation de semiquinones et de O₂•⁻. AIR12 est un cytochrome b 561 ancré à la membrane du côté de l’apoplaste réductible par l’ascorbate et le O₂•⁻. Ces protéines pourraient être impliquées dans un transfert d’électrons à travers la membrane via la vitamine K1. Les protéines recombinantes NQR et AIR12 ont été produites. A pH alcalin, AIR12 est réduit par les semiquinones et pourrait donc récupérer les électrons du produit de NQR. En présence de membrane plasmique, la production de O₂•⁻ est augmentée avec NQR et diminuée avec NQR et AIR12. Les QR semblent avoir un rôle anti- et pro-oxydant selon les cas et AIR12 un rôle anti-oxydant. Le transfert d’électrons entre les deux protéines pourrait se faire via les semiquinones à pH alcalin et via O₂•⁻. / The aim of this work is to define the effects of adverse environmental conditions on seed quality of A.thaliana, H.annuus, B.oleracea et H.vulgare), characterize two A.thaliana mutants affected in plasma membrane proteins and characterize the activity of the two proteins. Seeds were harvested from plants subjected to drought and/or thermal stress. Then O₂•⁻ and organic radicals in seeds were measured showing no impact of the stress. Accelerated ageing had a negative effect on seed vigor and viability. Radicals have been identified by high field EPR: epi-catechin and Mn(II) in the testa and melanin in the pericarp. There was no correlation between these radicals and the seed quality, therefore these radicals were not found to be good markers of seed quality. A.thaliana KO mutants of quinone reductase (QR) and AIR12 have been characterized. QR are cytosolic enzymes that have an affinity for the membrane. QR catalyze the reduction of quinone to dihydroquinone. Thus they are known to be protective enzymes against oxidative stress. However, at alkaline pH, dihydroquinone deprotonize and form semiquinones and O₂•⁻. AIR12 is a b561 cytochrome anchored to the apoplastic side of the membrane. These proteins could be implied in a transmembrane electron transport via vitamin K1. Recombinant proteins and NQR and AIR12 were produced. At alkaline pH, AIR 12 was reduced by the semiquinone, AIR12 could form a redox couple with vitamin K1 as electron shuttle across the membrane. In the presence of plasma membrane, the production O₂•⁻ was increased with NQR and reduced with NQR and AIR12. QR appear to have an anti- and pro-oxidant according to the conditions and AIR12 an anti-oxidant role. Electron transfer between the two proteins could be done via the semiquinone at alkaline pH and via O₂•⁻.

The use of coated seed to establish crops is not a novel practice. Seed coatings have been used on small seeded crops to improve the handling ability by making the seed unit larger and heavier. Producers can therefore calibrate their sowing equipment more efficiently and wind will not cause as much drift at sowing. Seed coating can have an added benefit for leguminous crops if the symbiotic inoculant (Rhizobium) is added to the coating. This saves the producer time and allows peace of mind that inoculation was done by trained professionals. Other than the inoculation, there are some other constituents in the seed coating that can have benefits to the plant. It can, however, be theorized that added nutrients or pesticides will be beneficial to the plants only if these nutrients are deficient in the growth medium or when pests are present. This study evaluated the effect of seed coating on the life stages of germination, emergence and survival, seedling growth and ultimate yield of mature lucerne (Medicago sativa L.) plants, comparing the results with non-coated seed. Two cultivars were used in the evaluation, SA Standard and SuperCuf, to determine if the effects would be similar, or would genetic differences between the cultivar play a significant role. These life stages (germination, emergence and seedling growth) were chosen due to the importance of these stages to the success of establishment. Fast and uniform germination will result in a uniform stand with strong competition against weed infestation. The effect of growth medium on the emergence of seedlings and the interaction between the seed coating and the growth medium was important to determine to identify limitations in the use of seed coating. Changes in the growth of seedlings in terms of some physio-morphological characteristics will assist in identifying parameters influenced by the coating. It was, however, essential to not only do these trials under ideal agricultural conditions, but to identify if similar results would be obtained from stressed conditions, such as salinity, which is a growing concern for crop production areas. The question of whether seed coating will influence the ultimate production of the crop could then be answered. It was found that the method in which germination is tested can have a significant outcome for the results obtained. When the Jacobsen apparatus was compared with the use of petri dishes, using specification according to ISTA, it was found that the water movement in the Jacobsen apparatus overcomes concentrated nutrient conditions, especially for SuperCuf. Under saline conditions the coated SA Standard seed had higher germination than the non-coated seed, therefore overcoming inhibitions imposed by the salinity. It is clear that the coating influences germination of lucerne and the interaction with the seed environment is significant. It is also clear that the genetic differences between cultivars are significant and results should not be applied across all lucerne cultivars. When the emergence percentage had been determined in different growth media, namely a commercial growth media, a sandy loam soil and silica medium, it was found that the emergence was influenced by the media. Even though the emergence of seedlings are mostly determined by the nutrients in the cotyledons, some growing conditions did cause lower emergence for non-coated SA Standard seeds and was overcome by the use of coated seed. When the growing conditions were manipulated with saline irrigation it was found that coated SuperCuf had a higher emergence % than the non-coated treatments when irrigated with the 750 μS.cm-1 water. From the data collected from this trial, it can be concluded that, even though the use of seed coating does not always influence the emergence of lucerne seedlings, seed coating does have an influence on the emergence, but it is dependent on the growth medium quality in terms of nutrient composition and salinity. Similar to the germination trial, the genetic influence of the different cultivars was noticeable. To determine the differences caused by seed coating to the physio-morphological characteristics (stem height, leaf area etc.) of lucerne, a pot trial was conducted using different irrigation treatments, municipal water (180 μS.cm-1), 500 and 750 μS.cm-1 water, created with NaCl. It was found that the physio-morphological characteristics were highly correlated, i.e. the stem height, leaf area, number of leaves and dry matter production changed in relation to each other. There were, however, differences in this correlation coated and non-coated seed treatments, when irrigated with 500 μS.cm-1 water. For the seedlings grown from coated seed, the correlation between shoot dry matter yield and the other parameters were low, while the seedlings growth from non-coated seed, leaf area was not correlated with the other parameters. It was concluded that the tolerance mechanism for salinity for plants irrigated with 500 μS.cm-1 water, caused more differences than the other water treatments. Taking into consideration that coating influences the germination and emergence of lucerne and that the two cultivars react differently to the seed coating, the yields obtained from field trials could then be interpreted if differences were observed. Three field trials were established, namely a trial established in autumn (established in 2009) and second trial established in spring (established in 2010) which were sown at 25 kg.ha-1, while a third trial established spring (established in 2010) was sown at 5 different sowing densities, namely 80%, 90%, 100%, 110% and 120% of recommended sowing density (25 kg.ha-1). It was found that the pasture stands established with SA Standard, did not show many differences between the coated and non-coated seed treatments and were mostly restricted to the second growing season, where the non-coated seed treatments had significantly higher dry matter yield than the coated seed treatments. Stands established with SuperCuf, displayed more variation between the seed treatments and the non-coated seed treatments had higher yields in the first season. It was, however, found that the stands established with coated SuperCuf seed had lower stem: leaf ratio’s, indicating that a better quality fodder can be produced from coated seed. The data from the sowing density trial showed very little difference between the yields of the stands established with coated and non-coated SA Standard seed. Differences were, however, observed between seed treatments at 90% and 120% of the recommended sowing density, where the stands established with non-coated seed had higher yields than the stands established with coated seed. It can be concluded that under these trial conditions, the use of coated seed had very little influence on the yield of the lucerne stands. The observed differences suggest that the lucerne growth under these few conditions, the stands established from non-coated seed had better yield, but the stands established from coated seed had better quality. It is, however, more likely that there will be no differences between the seed treatments. Data from the sowing density trial also led to the conclusion that stands established at 20% less seed will not result in lower yields if the stand establishment is successful. The similarity between the seed treatments and the sowing densities suggests that the number of plants per area were the same, caused by seedling mortality during the high growth rate in the early growing stage, or the morphological characteristics, such as number of stems per plant and number of leaves per stem, adapted to result in similar yields and quality. / Dissertation (MSc Agric)--University of Pretoria, 2013. / gm2014 / Plant Production and Soil Science / unrestricted

The Plant Breeder’s Right (PBR), also known as Plant Variety Protection (PVP), is a form of intellectual property afforded to breeders of newly bred plant varieties. In South Africa, intellectual protection of new plant varieties is afforded through the Plant Breeders’ Rights Act, 1976 (Act No. 15 of 1976) as amended in 1996. / The writer has been Registrar: Plant Breeders’ Rights since November 2007. Over the years the writer has interacted with several stakeholders with interest in plant breeders’ rights, including breeders, farmers, patent attorneys, growers, plant breeders’ rights administrators from other countries and civil society organisations. Although South Africa has had Plant Breeders’ Rights legislation since 1976, it has been observed that this piece of legislation is relatively unknown and often misunderstood even by the users of the system. In engagements with various stakeholders, it has been established that there are conflicting views amongst the stakeholders on pertinent issues related to the plant breeders’ rights system. There are views, among others, include: that the plant breeders’ rights system is only relevant and benefits breeders from big multinational companies such as Monsanto and farmers can never benefit in such a system; that the Plant Breeders’ Rights Act is synonymous with genetically modified organisms; that indigenous plants are neglected, and that the system only promotes protection of foreign varieties. The most contentious issue is however around the impact of plant breeders’ rights on the tradition of farmers to save, sell and exchange seed. / Very little is documented on the South Africa plant breeders’ rights system, more so from the administrator’s perspective. This study explored some aspects of the plant breeders’ rights system that may need policy interventions and legislation amendments, such as matters around the plant breeders’ rights system in relation to farmers’ rights, possible dual protection of Genetically Modified varieties in terms of the Plant Breeders’ Rights Act 1976 and the Patents Act 1978, as well as the participation of indigenous ornamental crops in the plant breeders’ rights system. / On the issue of the farmers’ rights: results of this work show that the current provision in the Plant Breeders’ Rights Act deals with Farmers’ Rights in a narrow sense, i.e. with the rights of farmers to save seed. It was established that this provision is inadequate for both the breeders and the farmers. A survey was also conducted among smallholder farmers from four provinces, namely Eastern Cape, Free State, Limpopo, and Western Cape. The interesting finding was that although there is so much debate around the impact of the plant breeders’ rights system on farmers’ rights, the majority of the farmers from this study group have never heard of the Plant Breeders’ Rights Act. There are farmers who are continuing with the practice of seed saving; however some farmers have indicated that they do not save seed they believe that this practice lowers yield. Those who do save seed mostly save their traditional seed, i.e. locally adapted seed lacking formal crop improvement as opposed to modern commercial seed. Some farmers have indicated that they do develop varieties through their own selections and believe that their varieties could qualify for protection in terms of the Plant Breeders’ Rights Act. It is evident that both government and the civil society organisations need to do more to educate smallholder farmers about laws and policies that impact their livelihood. Based on this study, a proposal was made to have the farmers’ privilege provisions in the current Plant Breeders’ Right Act amended to allow the Minister responsible for Agriculture to prescribe among others: the crops in which this provision will apply; the category or categories of farmers that would benefit; the circumstances under which royalties should be paid. This proposal was welcomed by most stakeholders and has since been incorporated in the draft Plant Breeders’ Rights Bill. It is envisaged that specific details around these factors will be included in the Regulations to the Act after extensive consultations with all relevant stakeholders. / There is a gap in policy and legislation with regard to the recognition of Farmers’ Rights as envisaged in the International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA). As such there are calls from some stakeholders including the civil society organisations that legislation on plant breeders’ rights must address these gaps and/or an alternative sui generis (of its own kind) system should be explored as the International Union for the Protection of New Plant Varieties (UPOV) system is not tailored for developing © University of Pretoria vii countries. In South Africa, legislation dealing with some aspects pertaining to Farmers’ Rights is spread over different government departments, e.g. Department of Agriculture, Forestry & Fisheries dealing with intellectual property protection only in as far as plant breeders’ rights; Department of Trade & Industry being custodians of intellectual property laws in South Africa and administrators of, among others the Patents Act; Department of Environmental Affairs dealing with Access and Benefit Sharing matters; Department of Science and Technology dealing with Indigenous Knowledge Systems and intellectual property protection emanating from publicly funded research institutions. More discussions are needed on South Africa becoming a member of the ITPGRFA as these will pave the way for further discussions and policy interventions addressing Farmers’ Rights in a broad sense. / As far as the Genetically Modified Organisms are concerned, South Africa has approved only three Genetically Modified (GM) crops for commercialization in terms of the GMO Act, 1997, namely cotton, maize, and soybean. This is contrary to some statements made by members of the public that much more crops, including pumpkin, potato, banana and tomato are genetically modified. In terms of intellectual property protection, of the total number of GM varieties protected by plant breeders’ rights per crop: 60% of varieties are GM for cotton, 61% for yellow maize, 34% for white maize and 63% for soybean. Currently there are no GM events used in these crops protected in terms of the Patents Act 1978, which effectively means that there is currently no dual protection for these crops. Dual protection is however one of the most hotly debated issues because of the impact it might have on the rights of farmers to save seed. It has been argued that in South Africa dual protection is possible. Scrutiny of the Plant Breeders’ Rights Act 1976, the Patents Act 1978 and the draft National Policy on Intellectual Property shows that all are silent on the issue of dual protection of plant varieties. The Departments of Agriculture, Forestry & Fisheries together with the Department of Trade and Industry need to initiate discussions around dual protection as well the use of Technology Agreements, between technology holders and technology users, in protecting GM varieties and the impact thereof for all role players in the value-chain in order to come up with the country position in this regard. / This study showed that ornamental plants attract the highest number of plant breeders’ rights applications. Of the applications received between 2000 and 2010 about 20% are of varieties developed from indigenous plants. Of plant breeders’ rights in ornamental plants, 84% are owned by foreign entities. Of the 16% owned by local entities, 12% are privately owned and 4% are owned by public research institutions. Some of the challenges facing this industry include the fact that there is inadequate turnover to allow for breeding programs and research initiatives; this is exacerbated by plant breeder’s rights infringements which lead to further revenue losses. Other challenges the industry face include high labor costs and lack of market information. The national Department of Agriculture, Forestry and Fisheries together with the other relevant departments, e.g. the Department of Labour and the Department of Trade and Industry need to engage more with the floricultural industry stakeholders to discuss the challenges facing the industry and come up with policies that would be conducive for the further development of the industry in order for South Africa to benefit from its unique biodiversity. Literature study has also established that breeders are keen on developing varieties of medicinal plants that are uniform and stable. This would call for domestic legislation on intellectual property protection that is aligned with legislation on Biodiversity and Access and Benefit-Sharing. / This study highlights the importance of engaging stakeholders from both the formal and informal sector and brings attention to gaps in our policies and legislation. This study has already made a major contribution in the draft Plant Breeders’ Rights Bill through the inclusion of the revised provision on farmers’ privilege. This revision is aimed at ensuring that the legitimate interests of the breeder are protected whilst the rights of the farmers are recognized. It is hoped that this study will make a positive contribution to future policy developments and will lay a foundation for future studies pertaining to the plant breeders’ rights system and its impact in the agricultural sector. / Thesis (PhD)--University of Pretoria, 2016. / Department of Agriculture, Forestry & Fisheries / Paraclinical Sciences / PhD / Unrestricted

Dectes texanus LeConte (Coleoptera: Cerambycidae) is a longhorn beetle species endemic to eastern United States. Originally described as a pest of weeds from the family Asteraceae, D. texanus has expanded its host range and is found infesting the stems of soybeans, Glycine max (L.) through the southwestern and middle United States. Female D. texanus chews a hole in the epidermis of a petiole and oviposits on it. Then, the D. texanus larva depletes all the pith of the stem making a tunnel down to the base of the plant and girdle the stem about 5 cm above the soil line. When a force is applied to the girdling point, generally weather related (i.e. strong winds), the plant lodges. While D. texanus phenology has been described for some states, this topic has yet to be explored in Kentucky. The objectives of this study were: 1) to describe the life cycle and behavior of D. texanus in soybeans in Western Kentucky, 2) to study the effect of the stem diameter on the incidence of D. texanus infestations, 3) to evaluate the susceptibility of full-season and double-crop soybeans to D.texanus infestations, 4) investigate the efficacy of seed treatment in reducing D. texanus infestations, 5) to determine effects of D. texanus larval feeding in the physiological yield of soybeans. The results of these studies showed that: 1) there was no distinct peak of D. texanus emergence detected in the 2018 and 2019 growing seasons and pupation period varied with year and location; the best sampling period for D. texanus population should occur between 1000 and 1600 hours during the peak season with either a 5-gallon white plastic bucket or sweep net; 2) the probability of finding D. texanus infesting soybeans was higher when the stem diameter is larger than 9 mm, and smaller than 11 mm; 3) double-crop soybeans had reduced infestations of D. texanus because these soybean plants are not a suitable host when D. texanus was active ovipositing and the pith was not fully developed; 4) seeds treated with imidacloprid did not influence D. texanus infestation on soybeans, larvae presence in main and lateral stems, and parasitism occurrences; and 5) D. texanus did not affect seeds and pods attributes (pod width, length, height and weight), and yield. The latter may occur because feeding of D. texanus larva does not interfere on photosynthesis or nutrient transportation during seed fill.

The Janzen-Connell mechanism is proposed to maintain plant diversity: predators and diseases of seeds reduce the number of seeds that survive near a parent tree, but allow seeds far from the parent tree to grow into adulthood. In the area where seeds don’t survive, seedlings from other tree species which are not affected by the seed consumer can grow. At large scales, this effect is thought to increase overall plant diversity. Soil-borne pathogens can contribute to seed mortality in this way, but we don’t know how important different parts of their lifecycle are in creating Janzen-Connell patterns. To determine the role of soil-borne pathogens in the development of Janzen-Connell patterns, we constructed a simulation model to examine how tree and pathogen characteristics affect plant spatial patterns. Under specific combinations of tree and pathogen characteristics, we found that pathogens could create Janzen-Connell patterns. The most important parameters were how far trees dispersed their seeds, and how many seeds a tree produced in a year. These characteristics determined how much of an impact the pathogens were able to have on the tree population because they rely on the density of seeds to determine how far they can spread and how many spores they will produce.