The association between individual plant performance and seed yield variability within and between field pea crops was investigated. In 1988/89 six F8 genotypes with morphologically distinct characteristics were selected from a yield evaluation trial. Analysis of the individual plant performance within these crops indicated an association between low seed yields and the location and dispersion of plant harvest index (PHI) and plant weight (PWT) distributions. The analyses also showed there was a strong linear relationship between the seed weight (SWT) and PWT of the individual plants within each crop, and that the smallest plants tended to have the lowest PHI values. A series of 20 simulations was used to formalize the relationships between SWT, PWT and PHI values within a crop into a principal axis model (PAM). The PAM was based on a principal axis which represented the linear relationship between SWT and PWT, and an ellipse which represented the scatter of data points around this line. When the principal axis passed through the origin, the PHI of a plant was independent of its PWT and the mean PHI was equal to the gradient of the axis. However, when the principal axis had a negative intercept then the PHI was dependent on PWT and a MPW was calculated. In 1989/90 four genotypes were sown at five plant populations, ranging from 9 to 400 plants m⁻². Significant seed and biological yield differences were detected among genotypes at 225 and 400 plants m⁻². The plasticity of yield components was highlighted, with significant genotype by environment interactions detected for each yield component. No relationship was found between results for yield components from spaced plants and those found at higher plant populations. The two highest yielding genotypes (CLU and SLU) showed either greater stability or higher genotypic means for PHI than genotypes CVN and SVU. Despite significant skewness and kurtosis in the SWT, PWT, and PHI distributions from the crops in this experiment, the assumptions of the PAM held. The lower seed yield and increased variability in PHI values for genotype CVN were explained by its higher MPW and the positioning of the ellipse closer to the PWT axis intercept than in other genotypes. For genotype SVU, the lower seed yield and mean PHI values were explained by a lower slope for the principal axis. Both low yielding genotypes were originally classified as having vigorous seedling growth and this characteristic may be detrimental to crop yields. A method for selection of field pea genotypes based on the PAM is proposed. This method enables the identification of weak competitors as single plants, which may have an advantage over vigorous plants when grown in a crop situation.

Isolates of Monilinia fructicola (Wint.) Honey obtained from stone fruit orchards in Hawkes Bay, North Island and from Californian fruit exported to New Zealand, were tested for resistance to methyl benzimidazole carbamate (MBC). Resistant isolates from the North Island had EC₅₀ values of >30,000, and most isolates from the imported fruit had of values approximately 1.5 mg a.i./l carbendazim. Sensitive isolates failed to grow on 1 mg a.i./l carbendazim. A detached peach shoot system was used in controlled conditions for estimation of values for incubation period, latent period and rate of spore production on flowers (cv Glohaven). The same variables and the rate of colonisation of host tissue were measured on fruit (cv Fantasia) in controlled conditions. An inoculum density of 1x10⁴ spore/flower or fruit greatly increased fitness in vivo compared to an inoculum density of 1x10² spore/flower (fruit). Isolates varied considerably, but there was no consistent relationship between the degrees of resistance and fitness. This was in contrast to earlier studies with dicarboximide resistant strains of M. fructicola. The survival in the field of 10 isolates resistant or sensitive to MBC or dicarboximide fungicides on twig cankers and mummified fruit was compared. The ability to produce conidia on twig cankers inoculated in late spring 1989 was maintained by all sensitive and MBC resistant isolates for at least 1 year. The production of conidia on mummified fruit inoculated in February 1990 decreased after 2-3 months in the field but some conidia were still produced on all fruit in the following spring. Dicarboximide resistant isolates produced less conidia than either the MBC resistant and the sensitive isolates. The pathogenicity and fitness of all isolates were similar to the original values after survival for 1 year. A technique was developed to produce apothecia reliably from inoculated peach (cv Black Boy) and nectarine (cv Fantasia) fruit in controlled conditions in the laboratory. The fruit were inoculated with resistant or sensitive isolates, or combinations, and were incubated for 8 weeks at 25°C (±1°C) with 12 hours photoperiod of fluorescent light (Sylvania 2x65 W, daylight) to produce mummified fruit. The fruit were then buried in moist autoclaved peat moss for 10 weeks at 25°C (±1°C) in the dark to form stromata. These fruit were then hydrated with running tap-water (total hardness (CaCO₃) = 47 g/m³ and conductivity at 20°C = 12.7 mS/m) for 72 hours. The hydrated mummified fruit were placed in moist peat moss and were incubated for 13-14 weeks at 8°C (±0.5°C) in the dark. At the end of this period, stipe initials were visible. Differentiation of stipe initials into mature apothecia occurred within 15-20 days after transfer to 12°C (±2 °C) with a 12 hour photoperiod of fluorescent and incandescent light. All isolates produced apothecia when treated in this way. A technique for isolation of ascospore sets in linear arrangement was developed for tetrad analysis of the inheritance of resistance. At least 3 hours of fluorescent and incandescent light at 12°C (±2°C) was essential to allow ascospore ejection from individual asci taken from apothecia previously maintained in a 12 hour photoperiod at 12°C (±1°C). A water film on the surface of water agar was necessary to hold a set of ejected ascospores in linear sequence. Single ascospores were obtained in sequence with the aid of a micromanipulator. Genetic analysis of MBC resistant isolates was carried out on ascospores derived from apothecia produced in the laboratory. Analysis of ascospore sets in linear arrangement and ascospore populations indicated that resistance to >30,000 mg a.i./l carbendazim (high-resistant) is governed by a single major gene and is affected by gene conversion mechanisms. Crossing over was frequent, suggesting that recombination of resistance with other characters, such as pathogenicity and fitness, may occur readily. The segregation ratio (1:1) from most resistant isolates revealed that heterokaryons containing both resistant and sensitive alleles were common in resistant populations and that resistance is dominant. Allozyme analysis of ascospore progeny through electrophoresis revealed a narrow genetic base of M. fructicola in New Zealand. The technique for reliable apothecial production in controlled conditions developed in this study provided an important step for the determination of the biology of M. fructicola strains resistant to MBC fungicides, and the complexity of its life cycle. Genetic heterogeneity in field populations can be conserved in one isolate through heterokaryosis, thus providing for adaptability of the pathogen to the changing environmental conditions. Knowledge on genetic variability, overwintering ability, pathogenicity and fitness factors may be useful for future management strategies of stone fruit brown rot. Special emphasis should be made in particular to prevent primary infection on blossoms, which would delay the establishment of recombinant strains of M. fructicola and the onset of brown rot epidemics.

Although New Zealand is fortunate in having a climate mild enough to allow some growth of pasture in winter even in the extreme south of the South Island (Duffy, 1971), growth is nevertheless considerably less than in spring and summer. O’Connor et al, (1968) point out that at Lincoln, Canterbury, winter production from a New Zealand Certified Grasslands Ruanui Perennial ryegrass (Lolium perenne c.v.) and New Zealand Certified Grasslands Huia white clover (Trifolium repens c.v.) sward is at best only 8% of the mean total annual dry matter (D.M.) production. A similar seasonal pattern is shown by irrigated pastures (Rickard, 1968), as well as pastures in the milder North Island of New Zealand (O’Connor and Vartha, pers comm.). Stocking of grazing animals is normally related to the growth rate of pastures in the spring, with conserved hay or silage, plus specially grown greenfeed or root crops being fed if necessary to offset the winter feed deficit. However on hill country too steep for tractor cultivation, cropping and conservation are not possible. Animals have to rely upon in situ grazing of native or dominant browntop (Agrostis tenuis) swards which may not have been improved by the aerial introduction of clovers. In an unimproved state, the quality and quantity of the herbage grown on such areas are low, Molloy (1966) have discussed clover introduction into native swards and the notably beneficial result this has on stock thrift, particularly during the winter period. Considerably better growth rates of stock grazing legumes rather than grasses have been noted by many authors including Ulyatt, (1971), and McLean et al (1962); this superiority being due largely to the greater digestible organic matter intake and higher ratio of soluble to insoluble carbohydrate associated with the herbage of legumes (Ulyatt, 1971). Consequently the presence of clover, and the winter activity of this, have an important influence on the productivity of steep hill country during winter. An increase of winter activity is also desirable, but not essential, in clover associated with flat or gently rolling pastures. The main pasture legume used in New Zealand has, in the past, been the white clover cultivar Huia. Whilst since 1945 selection and breeding of ryegrasses has brought about a very considerable improvement in the winter or cool season activity of these (Corkill, 1966), no legume cultivar having an increased level of cool-season activity has been released to commerce in New Zealand over the same period to date. Breeding for increased winter growth has been an objective of the Grasslands Division Plant Breeding Section for many years (Barclay, 1960). Since 1957, breeding and selection work has been proceeding with the objective of increasing the winter growth of the New Zealand Certified Grasslands white clover cultivar – Huia (henceforth to be referred to as Huia) without sacrificing the moderately good summer growth of this strain, (Barclay, 1969). Seed of a promising cultivar selected during the course of this work – New Zealand Grasslands 4700 white clover, (henceforth to be referred to as 4700) became available for testing in 1967. The investigation to be reported here aimed to measure the cool-season activity of 4700 by comparison with that of Huia, at the same time elucidating if possible the factors controlling this growth.

No description available.

Univ., Diss.--Zürich, 2005.

The Russian wheat aphid (RWA) (Diuraphis noxia Kurdjumov) is one of the important insect pests of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and other grasses. To date, there are four RWA biotypes identified in South Africa. The virulent biotypes emerged, partly due to climate change and new genetic variations within populations of RWA; hence there is a need to improve host-plant resistance, as an effective control measure. Bread wheat (Triticum aestivum L.) accession Cereal Introduction (CItr) 2401 is known to be resistant to all RWA biotypes worldwide. The goal of this study was to use a backcrossed near-isogenic line (NIL) BC5F5 mapping population, developed from a cross between CItr 2401 and susceptible Kavkaz, to identify and validate single nucleotide polymorphism (SNP) markers linked to the resistance phenotype in CItr 2401. This was achieved by (i) conducting a preliminary study that evaluated the suitability of simple sequence repeat (SSR) markers previously reported in literature for discriminating stacked RWA resistance genes and, (ii) employing SNP markers for the first time in a RWA resistance study as a future alternative to the widely used SSR markers. None of the tested SSR markers showed potential use in marker-assisted selection (MAS). The mapping population was phenotypically evaluated for RWA resistance using the four South African biotypes, viz. RWASA1, RWASA2, RWASA3 and RWASA4. Analysis of variance (ANOVA) showed significant (P<0.001) differences of genotypes after confirming the normality of residuals and homogeneity of variance. The Illumina iSelect 9,000 wheat SNP platform was used to genotype the two crossing parents and a selection of 24 NIL genotypes from the mapping population. Eight SNP markers found to be linked to the phenotype were converted to breeder-friendly and high-throughput Kompetitive allele-specific polymerase chain reaction (KASP) markers. The designed KASP markers were validated on the two crossing parents, the 24 NIL sent for SNP genotyping, on the mapping population and on the preliminary study genotypes for their effectiveness. The KASP assays developed in this study will be useful for stacking the RWA resistance from CItr 2401 with other Dn genes effective against the RWA. / Life and Consumer Sciences / M. Sc. (Life Sciences)

Un nouveau facteur de transcription, appartenant à la famille des protéines à domaine bHLH, a récemment été isolé dans notre laboratoire. Initialement appelé « clone bc8 » puis HRT1, ce facteur présentait des similitudes avec les protéines Hairy and Enhancer of split qui interviennent notamment dans le phénomène d’inhibition latérale lors de la formation du tissu neural. Des études d’hybridation in situ réalisées chez l'embryon de xénope ont suggéré un rôle important de XHRT1, la protéine HRT1 de xénope, dans le développement neural. Nous avons recherché les partenaires protéiques de XHRT1 par la technique du double-hybride afin de mieux comprendre son mécanisme d’action moléculaire dans la neurogenèse.<p>Tout d’abord nous avons construit les outils appropriés pour l’élaboration du travail, à savoir, les clones de levures exprimant les appâts spécifiques des domaines de la protéine étudiée et la création d’une banque d’ADNc du xénope au stade de la neurulation. Ensuite, trois criblages ont été réalisés. Dans le premier cas, nous avons recherché les partenaires des domaines bHLH et Orange (bHLH-O). Le domaine bHLH est en effet responsable de la dimérisation de ce type de protéine. Le domaine Orange qui suit le domaine bHLH, pourrait participer dans le choix du partenaire d’hétérodimérisation. Nous avons isolé deux facteurs de type bHLH-Orange apparentés à HRT1, XHairy1 et XHairy2b et confirmé leur interaction avec XHRT1. Les domaines impliqués dans ces interactions sont les bHLH-O pour les trois facteurs. Ce même criblage nous a permis d’isoler un nouvel ADNc qui code une protéine sans domaine apparent connu actuellement. Nous avons montré que cette protéine reconnaissait spécifiquement le domaine Orange de HRT1 mais pas celui des autres facteurs de type bHLH-O. Elle a été baptisée BOIP pour Bc8 Orange Interacting Protein. Le rôle physiologique de cette interaction n’a pu être démontré. Nous avons établi que la protéine BOIP pouvait aussi s’homodimériser. Nous avons aussi déterminé son profil d’expression chez le xénope et la souris. Son transcrit est hautement présent dans les testicules adultes. La protéine pourrait donc jouer un rôle important dans la spermatogenèse. Les deux autres criblages, utilisant les domaines situés dans la partie C-terminale de XHRT1, ont apporté des nouveaux partenaires potentiels, mais ces interactions n’ont pu être confirmées dans un système indépendant. <p>Enfin, en étudiant plus en détail les interactions entre XHRT1 et XHairy1 ou XHairy2b, nous avons mis à jour une possible fonction de spécificité dans le choix du partenaire dans la région C-terminale de HRT1. La formation de ces dimères pourrait jouer un rôle dans la formation du tube neural mais également dans d’autres différenciations tissulaires.<p> / Doctorat en sciences, Spécialisation biologie moléculaire / info:eu-repo/semantics/nonPublished

Genetically modified (GM) white and yellow maize, Zea mays, has been commercially released and cultivated in South Africa since 1997/1998. The traits expressed are insect resistance and herbicide tolerance conferred by the bacteria Bacillus thuringiensis (Bt) Cry genes and Agrobacterium 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase gene, respectively. The Cry genes have been used widely to control lepidopteran insect pests but insect resistance to GM Bt crops has been a concern since the introduction of this technology. A management strategy includes refugia planting of 5% non-Bt plants, with no insecticide application, and 20%, where insecticide application is allowed. These refugia are designed to allow the survival of insect pests within restricted planted zones. However, in South Africa there are reports of Bt-resistant stem borer (Busseola fusca) (Fuller) (Lepidoptera: Noctuidae) and non-compliance with refuge planting. The aims of this study were two-fold: 1. To conduct a survey among KwaZulu-Natal (KZN) GM maize growers to ascertain information such as level of compliance with refuge planting and to determine which refugia were predominantly planted and reasons thereof; 2. To conduct a replicated field trial to determine yield, insect borer damage and economic benefit of the 5% unsprayed and 20% sprayed refuge options (including three configurations namely strip, perimeter and block and a 5 and 20% ‘refuge-in-a-bag’ option). The survey indicated that 28 out of 29 (96.6%) KZN Bt maize growers plant the 5% non-sprayed refuge with 27 (96.4%) of those respondents planting the strip configuration for the purpose of insect management (75%) and ease of planting (32.2%). The survey also showed that 7 (seven) i.e. 21.9% of KZN Bt maize growers observed borer damage and although growers are now fully compliant with refugia planting requirements, initially 7 respondents (24.1%) did not comply with or plant refugia correctly. Furthermore, 7 respondents reported insect borer damage in their maize with 4 of the 7 instances (57.1%) likely stemming from incorrectly planted refugia. vii No significant differences in yield or insect damage were observed between the 5 and 20% refugia for any of the planting configurations in the field trial. However due to costs involved with insecticide application and labour required for the operation in the 20% option, these treatments were less economically advantageous than the non-Bt control. The 20% block and strip configurations had a cost benefit ratio of ZAR 7.21 and ZAR 6.67 respectively, earned per R1 spent by the grower compared with ZAR 7.76 in the sprayed control. The cost-benefit comparison for the 5% block and strip configurations was ZAR 8.48 and ZAR 7.71, respectively compared with ZAR 9.44 in the unsprayed control. In addition, the 20% seed mixture limited borer damage to 4.95% when compared with 15.77% damage in the sprayed control (ANOVA, F pr = 0.124). The seed mixtures are not available commercially and the results from the survey indicated that some education and marketing by the seed companies would be advisable prior to their release to the farming community. In order to determine which of the refuge options between 5 and 20% would be more advantageous for growers overall, regardless of the planting configuration; data were grouped and analysed. There were no significant differences in either the yield or insect damage for the 5 and 20% refugia, but the cost-benefit calculations indicated that the 5% option was more cost effective – for the 5 and 20% refugia, ZAR 7.97 and ZAR 7.15 respectively, earned per ZAR 1 spent by the grower (ANOVA, F pr. = 0.03). This is because no insecticide was used in the 5% treatments. Mean ear damage comparisons between the 5 and 20% refugia showed that the 20% refuge in the perimeter configuration incurred the least damage (2.65% ear damage) compared with 5% perimeter (10.86% ear damage), although the reasons for this are not clear. While the results of the field trials showed no significant differences in insect damage and yield with regard to choice of refuge configuration, monitoring insect resistance management remains an integral part of Bt maize crops in South Africa, in order to delay further resistance development and to prolong the viability of Bt technology. / Agriculture and  Animal Health / M. Sc. (Agriculture)

Derived from and inspired by the adaptive immune system of bacteria, CRISPR has gone from basic biology knowledge to a revolutionizing biotechnological tool, applicable in many research areas such as medicine, industry and agriculture. The full mechanism of CRISPR-Cas9 was first published in 2012 and various CRISPR-Cas systems have already passed the first stages of clinical trials as new gene therapies. The immense research has resulted in continuously growing knowledge of CRISPR systems and the technique seems to have the potential to greatly impact all life on our planet. Therefore, this literature study aims to thoroughly describe the CRISPR-Cas system, and further suggest an undergraduate laboratory exercise involving gene editing with the CRISPR-Cas9 tool. In this paper, we describe the fundamental technical background of the CRISPR-Cas system, especially emphasizing the most studied CRISPR-Cas9 system, its development and applications areas, as well as highlighting its current limitations and ethical concerns. The history of genetic engineering and the discovery of the CRISPR system is also described, along with a comparison with other established gene editing techniques.  This study concludes that a deeper knowledge about CRISPR is important and required since the technique is applicable in many research areas. A laboratory exercise will not only inspire but also provide extended theoretical and practical knowledge for undergraduate students.

In early 2003, a persistent drought threatened about 15 million people in the Southern African region (SADC) with starvation as farmers in this region were not able to produce enough food. A similar threat was experienced in the United States of America (USA). The Americans responded by introducing GM technology, which thankfully stabilised corn production and food security. It was against this backdrop that the South African government legalised and supported GM technology in the farming industry. However, the technology became a contentious issue amongst scholars, politicians and policy makers as well as farmers. Therefore, this study analysed the perceptions of small-scale and large-scale farmers, located in Paarl, Western Cape, South Africa, on the adoption of GM technology. This qualitative study, using a case study design, collected primary data from thirty (30) farmers: fifteen (15) small-scale and fifteen (15) large-scale farmers. The findings revealed complex factors influencing farmers’ adoption decisions and that Adopter perception (AP) and Consumer perception (CP) play a key role in their adoption of GM technology. These commercially and profit-driven farmers avoid using GM technology because public opinion and the markets weigh heavily against it. It was concluded that the farmers regarded GM technology as just one of many agricultural technologies and not as an exception. It was also considered unaffordable and detrimental to the environment, the economy and their livelihoods.The study recommends that the government should fully investigate public perceptions with regard to the adoption of any new agricultural innovation prior to making policy decisions. / Development Studies / M.A. (Development Studies)