Crop rotation is not commonly practised in the sugarcane industry in South Africa. It has, however, proven to be beneficial to other crops in South Africa. The objective of this study was to determine the impact of soybean-sugarcane crop rotation on selected physiological and phenological indicators of sugarcane performance and its subsequent effect on cane and estimated recoverable crystal (ERC) yields. A field trial was conducted at Mount Edgecombe, where soybean cultivar A5409RG and sugarcane cultivar NCo376 were planted under drip irrigation with different management practices. After the soybean crop, the following sugarcane crop was planted and fertilized with different levels of nitrogen (N) fertilizer (50% and 100% of the recommended N rate). The effects on sugarcane growth were recorded by taking into consideration date of emergence, plant height, tiller population, leaf N, plant performance index and chlorophyll content. Sugarcane yield and quality at harvest were also evaluated. Tiller population in all crop rotation treatments at Mount Edgecombe weresignificantly (P<0.05) higher than the monocrop treatment. There was a trend of increased leaf N in all of the cane-after-soya (crop rotation) crops compared to the cane-after-cane (monocrop) treatment, although this was not significant. A similar pattern was obtained with respect to the chlorophyll content and plant performance index. Sugarcane yields at Mount Edgecombe did not differ significantly between monocrop and crop rotation treatments. Crop rotation with soybean is beneficial for cane production, but its long term impact on soil quality and farm economy requires further investigation. / M.Sc.Agric. University of KwaZulu-Natal, Pietermaritzburg 2013.

Scarabaeid pests in South Africa and especially KwaZulu-Natal are characterised by a very long larval life cycle and short pupal and adult periods. However, it has nearly always been the adults of the species that have been identified, with very little attention paid to the larval identification of the species. This is unfortunate as it is nearly always the larval stage that is found to be associated with crop damage. Accurate identification of the species of these larvae is important for the management of scarabaeid pest species, as it unlocks the necessary information on the biology and ecology of many species, which allows the adaptation of control methods for different species. Inadequate keys for the taxonomy of larvae of these groups, as well as the lack of morphological taxonomists working on these groups have been identified as constraints. When a species is difficult to identify using traditional taxonomic methods, DNA diagnostic tools can be useful. Chapter 2 investigated the feasibility of identifying scarabaeid larvae using mitochondrial DNA data. Variation in the base pair sequence of the mitochondrial cytochrome c oxidase sub unit I (cox 1) gene was used. DNA sequences of cox 1 from scarabaeid larvae collected from sugarcane fields were compared with sequences from scarabaeid adults of known species in order to identify the species attacking sugarcane. Neighbour-joining and maximum parsimony analyses of 658 bp cox 1 sequences identified groups of larvae that linked to adult specimens. The major groupings delimited specimens belonging to the subfamilies Dynastinae, Melolonthinae and Rutelinae. Within-group sequence divergence ranged from 0 - 3.4 % and divergence between sister groups ranged from 2.6 - 25.1 %. The recorded divergence range within and between tribes was 0 - 21.3 % and 17.3 - 28.5% respectively. Similarly, the divergence range observed within and between genera was 0 - 19.2 % and 17.1 - 25.4% respectively. The maximum sequence divergence observed within subfamilies was 23.7 % and divergence between subfamilies ranged from 16.8 - 26.7 %. Examination of pairwise sequence divergence levels as well as node support allowed 68% of the unidentified larval specimens to be associated with identified adult specimens. Phylogenetic analysis matched identified adult mtDNA with unidentified larval mtDNA. This allowed the identification of those larvae through morphological characteristics unique to certain species. To create a field key to the subfamilies of Dynastinae, Melolonthinae and Rutelinae the most useful character distinguishing larvae of different species was the raster but additional morphological characteristics were included. These relationships between larval and adult scarabaeid specimens from sugarcane were examined using various phylogenetic tools. The data set included a total of 19 morphological characters as well as 166 partial cox 1 gene sequences. Maximum parsimony analyses were performed on morphological, molecular and combined data. The same morphological and molecular data sets were run both separately and as a combined analysis with MrBayes. In both types of analyses the morphological data performed poorly and crude groupings resulted, dividing taxa to tribe level only. Molecular data showed greater resolution than the morphological data and taxa were separated into groups equivalent to species and morphospecies designated in Chapter 2. A partition homogeneity test indicated that both data types could be combined. It is recommended that both morphological and molecular data be utilised in identification of scarabaeid sugarcane pests and that a character-based approach be implemented. Further molecular data from other genes should be included to test the accuracy of these results. The keys produced during this study will allow workers to focus on a single species biology, and subsequently allow an analysis of between species interactions, and within species control. These advances are a start to the improvement of knowledge of the species composition of scarabaeid larvae in sugarcane fields, thus making management and biological control of these pests a greater possibility. Further recommendations for future work are discussed in Chapter 5. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Thesis (MScConEcol)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The aim of the research presented in this dissertation was to investigate localised acridid outbreaks causing damage to sugarcane in Empangeni, Kwazulu-Natal, South Africa. Reports of outbreaks with increasing severity have occurred for the last six or seven years, which prompted this research. In general, little is known about acridid outbreaks in sugarcane due to their sporadic nature, therefore this project set out to identify morphologically and molecularly, all species associated with Empangeni sugarcane and to determine the ecology and population dynamics of the most important species, to provide baseline data for the development of an integrated pest management (IPM) plan against these crop pests. A year-long population survey was conducted on a number of affected farms and adjacent grassland sites to determine the life cycles, population density and composition of this acridid complex on these farms. Surveys showed that this complex comprised five species: Nomadacris septemfasciata, Petamella prosternalis, Ornithacris cyanea, Cyrtacanthacris aeruginosa and Cataloipus zuluensis. Observed damage was recorded throughout the year in order to correlate with species densities. It was found that damage was closely associated with two species, namely Petamella prosternalis and Nomadacris septemfasciata, therefore these two species are of particular concern due to their higher densities and large body size resulting in them being the biggest threat to Empangeni sugarcane. All five species are univoltine but two different life cycle strategies were discovered, 3 species exhibit a winter egg diapause while 2 species exhibit a winter adult reproductive diapause, an important finding considering the knowledge intensive method of control which has been proposed. Population surveys revealed a large difference in species composition among farms (sugarcane sites) and among grassland sites. Nomadacris septemfasciata and Petamella prosternalis showed a significant preference for sugarcane while species such as Cyrtacanthacris aeruginosa, Zonocerus elegans and Orthocta sp. seemed to prefer grassland sites. Feeding potential trials were completed on the two most economically important species, Nomadacris septemfasciata and Petamella prosternalis. The results showed that Petamella prosternalis has a significantly higher feeding potential (% leaf damage) compared to Nomadacris septemfasciata even though in terms of dry weight and length, it is a smaller specimen. Feeding data were used to determine the voracity of these two species under laboratory conditions. Petamella prosternalis eats roughly 1.83 grams of fresh sugarcane per day while Nomadacris septemfasciata eats approximately 1.16 grams per day. These results were then compared to observed field damage data in order to gauge their accuracy and applicability within a field setting, which showed that although sugarcane field damage is significantly correlated with the population fluctuations of both these species, it is more closely associated with Petamella prosternalis resulting in a correlation coefficient of 0.429143 while Nomadacris septemfasciata had a correlation coefficient of 0.250. Phase polyphenism in the red locust Nomadacris septemfasciata was investigated using three methods including traditional morphometrics (Elytra/Femur (E/F) ratio), hopper colouration and eye stripe data. The E/F ratio indicated that the majority of the Empangeni population sampled is in the transiens and gregarious phase with a mean E/F ratio of 2.0063 and that they seem to be becoming more gregarious over time, with populations in 2012 having a mean E/F ratio of 1.9973 and in 2013 a mean E/F ratio of 2.01315. Hopper colouration also indicates that populations are generally showing gregarious tendencies with the majority of hoppers exhibiting gregarious type colouration. Eye stripe data showed that the majority of adult specimens observed had seven eye stripes, an indication of gregarious individuals. Geometric morphometrics, a relatively new, software based technique which has not been used in phase polyphenism studies before was used as a means to accurately measure variations among populations of N. septemfasciata by measuring the variation in forewing shape according to allocated landmarks. The resulting shape variation were compared to traditional morphometrics in an attempt to relate the two techniques so that geometric morphometrics can possibly be used as a tool to study phase polyphenism in locusts in the future. The results indicate that similarities in terms of location and gender exist between the two methods, however the exact same individuals should be used for both methods which will improve the accuracy of comparisons. This study, for the first time identified the acridid complex causing damage to Empangeni sugarcane and provided a broad summary of the potential impact the complex has on the crop as well as what may be causing them to occur in this area such as optimal habitat conditions and sugarcane as a preferable host plant being two factors which are likely to be having an influence. The findings of this study provide the baseline data needed in order to develop a more integrated and sustainable approach to controlling these acridids pests. Understanding the biology of the species enables practitioners to make more effective management decisions which is clearly needed as the current techniques being used have not solved the ‘grasshopper problem’. / AFRIKAANSE OPSOMMING: Die doel van die navorsing wat in hierdie verhandeling was om ondersoek in te gelokaliseerde acridid uitbrekings veroorsaak skade aan suikerriet in Empangeni, KwaZulu-Natal, Suid-Afrika. Verslae van die uitbreek met toenemende erns plaasgevind het vir die laaste 6-7 jaar, wat gelei het tot hierdie navorsing. In die algemeen, is min bekend oor acridid uitbreek in suikerriet as gevolg van hul sporadiese aard, daarom is hierdie projek uiteengesit morfologies en molekulêre identifiseer, al die spesies wat verband hou met Empangeni suikerriet en die ekologie en bevolkingsdinamika van die belangrikste spesies te bepaal, te voorsien basislyn data vir die ontwikkeling van 'n geïntegreerde plaagbestuur (GPB) plan teen hierdie oes peste. 'N jaar lank bevolking opname is uitgevoer op 'n aantal plase wat geraak is en aangrensende grasveld plekke om die lewensiklus te bepaal, bevolkingsdigtheid en samestelling van hierdie acridid kompleks op die plase . Opnames het getoon dat hierdie komplekse bestaan uit vyf spesies: Nomadacris septemfasciata, Petamella prosternalis, Ornithacris Cyanea, Cyrtacanthacris aeruginosa en Cataloipus zuluensis Waargeneem skade is aangeteken deur die jaar ten einde te ooreenstem met spesie digtheid. Daar is gevind dat die skade was nou verbind met twee spesies, naamlik P. prosternalis en N. septemfasciata, dus is die twee spesies van besondere belang as gevolg van hul hoër digtheid en 'n groot liggaam grootte lei daartoe dat hulle die grootste bedreiging vir die Empangeni suikerriet. Al vyf spesies is univoltine maar twee verskillende lewensiklus strategieë ontdek, 3 spesies toon 'n winter eier diapouse terwyl 2 spesies toon 'n winter volwasse reproduktiewe diapouse, 'n belangrike bevinding oorweging van die kennis intensiewe metode van beheer wat is voorgestel. Bevolking opnames openbaar 'n groot verskil in spesies samestelling onder plase (suikerriet webwerwe) en onder grasveld webwerwe. Nomadacris septemfasciata en Petamella prosternalis het 'n beduidende voorkeur vir suikerriet, terwyl spesies soos Cyrtacanthacris aeruginosa, Zonocerus elegans en Orthocta SP. gelyk grasveld webwerwe te verkies. Voeding potensiaal proewe is op die twee mees ekonomies belangrike spesies voltooi, Nomadacris septemfasciata en Petamella prosternalis Die resultate het getoon dat Petamella prosternalis het 'n aansienlik hoër voeding potensiaal(% blaarskade) in vergelyking met Nomadacris septemfasciata selfs al in terme van droë gewig en lengte, is dit is 'n kleiner model. Voeding data is gebruik om die gulzig van hierdie twee spesies onder laboratorium toestande te bepaal. Petamella prosternalis eet ongeveer 1.83 gram vars suikerriet per dag, terwyl Nomadacris septemfasciata eet ongeveer 1,16 gram per dag. Hierdie resultate is dan in vergelyking met waargeneem veld skade data om die akkuraatheid en toepaslikheid in 'n veld omgewing, wat getoon het dat hoewel suikerriet veld skade beduidend gekorreleer met die bevolking skommelinge van beide hierdie spesies, is nouer dit verband hou met Petamella prosternalis te meet lei tot 'n korrelasie koëffisiënt van 0.429143 terwyl Nomadacris septemfasciata het 'n korrelasie koëffisiënt van 0.250408 Fase polyphenism in die rooisprinkaan Nomadacris septemfasciata is ondersoek met behulp van drie metodes, insluitend tradisionele Morphometricsveld (Elytra/Femur (E/F) verhouding), hopper kleur en oog streep data. Die Elytra te Femur verhouding (E/F -verhouding) het aangedui dat die meerderheid van die bevolking is Empangeni in die transiens en gesellige fase met 'n gemiddelde E/F verhouding van 2,0063 en dat dit lyk asof hulle meer kuddedier met verloop van tyd, met bevolkings in 2012 met 'n gemiddelde E/F verhouding van 1,9973 en in 2013 'n gemiddelde E/F verhouding van 2,01315 . Hopper kleur dui ook aan dat die bevolking in die algemeen toon kuddedier neigings Thye meerderheid van hoppers uitstal gesellige tipe kleur. Oog streep het getoon dat die meerderheid van die volwasse eksemplare waargeneem het sewe oog strepe: 'n aanduiding van die gesellige individue. Geometriese Morphometricsveld, 'n relatief nuwe, sagteware gebaseer tegniek wat nie gebruik is in fase polyphenism studies voor was gebruik as 'n middel tot verskille tussen bevolkings van die rooisprinkaan akkuraat te meet deur die variasie meet in voorvlerk vorm volgens toegeken landmerke Die gevolglike vorm variasie is in vergelyking met die tradisionele Morphometricsveld in 'n poging om die twee tegnieke in verband te bring , sodat meetkundige Morphometricsveld kan moontlik as 'n instrument fase polyphenism om te studeer in sprinkane in die toekoms gebruik kan word. Die resultate dui daarop dat die ooreenkomste in terme van ligging en geslag bestaan tussen die twee metodes is egter presies dieselfde individue moet gebruik word vir beide metodes wat die akkuraatheid van vergelykings verbeter. Hierdie studie, wat vir die eerste keer geïdentifiseer die acridid kompleks om skade aan Empangeni suikerriet en verskaf 'n breë opsomming van die potensiële impak van die kompleks het op die gewas sowel as wat kan veroorsaak word om hulle te kom in hierdie gebied soos optimale habitat toestande en suikerriet as 'n beter gasheer plant. Die bevindinge van hierdie studie verskaf die basislyn data wat nodig is om 'n meer geïntegreerde en volhoubare benadering tot die beheer van hulle as die begrip van die biologie van die spesie in staat stel om praktisyns meer effektiewe bestuur besluite wat duidelik nodig is as 'n die huidige tegnieke gebruik moet maak om te ontwikkel nie opgelos die "sprinkaan probleem".

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Two mathematical models are formulated in this dissertation for the population growth of an Eldana saccharina Walker infestation of sugarcane under the influence of partially sterile released insects. The first model describes the population growth of and interaction between normal and sterile E. saccharina moths in a temporally variable, but spatially homogeneous environment. The model consists of a deterministic system of difference equations subject to strictly positive initial data. The primary objective of this model is to determine suitable parameters in terms of which the above population growth and interaction may be quantified and according to which E. saccharina infestation levels and the associated sugarcane damage may be measured. The second model describes this growth and interaction under the influence of partially sterile insects which are released in a temporally variable and spatially heterogeneous environment. The model consists of a discretized reaction-diffusion system with variable diffusion coefficients, subject to strictly positive initial data and zero-flux Neumann boundary conditions on a bounded spatial domain. The primary objectives in this case are to establish a model which may be used within an area-wide integrated pest management programme for E. saccharina in order to investigate the efficiency of different sterile moth release strategies in various scenarios without having to conduct formal field experiments, and to present guidelines by which release ratios, frequencies and distributions may be estimated that are expected to lead to suppression of the pest. In addition to the mathematical models formulated, two practical applications of the models are described. The first application is the development of a user-friendly simulation tool for simulating E. saccharina infestation under the influence of sterile insect releases over differently shaped spatial domains. This tool provides the reader with a deeper understanding as to what is involved in applying mathematical models, such as the two described in this dissertation, to real-life scenarios. In the second application, an optimal diversification of sugarcane habitats is considered as an option for minimising average E. saccharina infestation levels, and as a further consequence, improving the cost-efficiency of sterile insect releases. Although many special cases of the above model classes have been used to model the sterile insect technique in the past, few of these models describe the technique for Lepidopteran species with more than one life stage and where F1-sterility is relevant. In addition, none of these models consider the technique when fully sterile females and partially sterile males are being released. The models formulated in this dissertation are also the first to describe the technique applied specifically to E. saccharina, and to consider the economic viability of applying the technique to this species. Furthermore, very few examples exist of such models which go beyond a theoretical description and analysis towards practical, real-life applications as illustrated in this dissertation. / AFRIKAANSE OPSOMMING: Twee wiskundige modelle word in hierdie proefskrif vir die populasiegroei van ’n Eldana saccha- rina Walker infestasie van suikerriet onder die invloed van gedeeltelik steriele, vrygelate insekte daargestel. Die eerste model beskryf die populasiegroei van en -interaksie tussen normale en steriele E. saccharina motte in ’n dinamiese, maar ruimtelik-homogene omgewing. Die model is ’n stelsel deterministiese verskilvergelykings onderhewig aan streng positiewe aanvangswaardes. Die primˆere doelstelling met hierdie model is om geskikte parameters te bepaal in terme waarvan die bogenoemde groei en interaksie gekwantifiseer kan word, en waarvolgens E. saccharina infestasievlakke en die gepaardgaande suikerrietskade gemeet kan word. Die tweede model beskryf hierdie groei en interaksie onder die invloed van gedeeltelik steriele insekte wat in ’n dinamiese en ruimtelik-heterogene omgewing vrygelaat word. Die model is ’n gediskretiseerde stelsel reaksie-diffusievergelykings met veranderlike diffusieko¨effisi¨ente onderhewig aan streng positiewe aanvangswaardes en zero-vloei Neumann-randwaardes op ’n begrensde ruimtelike gebied. Die primˆere doelstellings in hierdie geval is om ’n model tot stand te bring wat in ’n area-wye, ge¨ıntegreerde pesbestrydingsprogram vir E. saccharina gebruik kan word om die doeltreffendheid van verskillende steriele motvrylatingstrategie¨e te bepaal sonder om daadwerklik veldeksperimente uit te voer, en om riglyne daar te stel waarvolgens vrylatingsverhoudings, -frekwensies en -verspreidings bepaal kan word wat na verwagting na ’n onderdrukking van die pes sal lei. Bykomend tot die wiskundige modelle in hierdie proefskrif, word twee praktiese toepassings van die modelle ook beskryf. In die eerste toepassing word ’n gebruikersvriendelike simulasie hulpmiddel ontwikkel om E. saccharina infestasie onder die invloed van steriele insekvrylatings in verskillende ruimtelike gebiede te simuleer. Hierdie toepassing fasiliteer ’n dieper begrip van wat ter sprake is in die toepassing van wiskundige modelle, soos die twee modelle in hierdie tesis, tot werklike scenario’s. In die tweede toepassing word ’n optimale diversifisering van suikerriet habitats as ’n opsie vir die vermindering van die gemiddelde E. saccharina infestasie vlakke beskou, en gevolglik word die verbetering van die koste-doeltreffendheid van steriele insekvrylatings afgeskat. Alhoewel verskeie spesiale gevalle van die bogenoemde twee klasse van modelle reeds in die verlede gebruik is om die doeltreffendheid van die steriele-insektegniek te modelleer, beskryf weinig van hierdie modelle die tegniek vir Lepidopteriese spesies met meer as een lewensfase en waar F1-steriliteit ter sprake is. Verder beskryf geen van hierdie modelle die tegniek waar algeheel steriele wyfies en gedeeltelik steriele mannetjies vrygelaat word nie. Die modelle in hierdie tesis is ook die eerste waar die tegniek spesifiek op E.saccharina toegepas word, en waar die ekonomiese lewensvatbaarheid van die tegniek vir hierdie spesie oorweeg word. Verder bestaan daar min voorbeelde van soortgelyke modelle wat verder gaan as ’n teoretiese beskrywing en wiskundige ontleding na praktiese, werklike toepassings, soos in hierdie proefskrif ge¨ıllustreer.

The control of the African stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae) in sugarcane fields of KwaZulu-Natal, South Africa has proved problematical. Researchers at the South African Sugarcane Research Institute (SASRI) have since 1974 been intensively investigating various means of controlling the pest. Among the methods of control currently being investigated are biological control, chemical control, production of more resistant varieties and crop management. These investigations, however, require many years of experimentation before any conclusions can be made. In order to aid the research currently being carried out in the Entomology Department at SASRI (to investigate biological control strategies, insecticide application strategies and the carry-over decision), a simulation model of E. saccharina growth in sugarcane has been formulated. The model is cohort-based and includes the effect of temperature on the physiological development of individuals in each life-stage of the insect. It also takes into account the effect of the condition of sugarcane on the rate of E. saccharina infestation, by making use of output from the sugarcane growth model CANEGRO. Further, a crop damage index is defined that gives an indication of the history of E. saccharina infestation levels during the sugarcane’s growth period. It is linked to the physiological activity of the borer during the period spent feeding on the stalk tissue. The damage index can further be translated into length of stalks bored and hence the percentage of the stalk length bored can be calculated at each point in the simulation using the total length of stalks calculated in the CANEGRO model. Using an industry accepted relationship between percent stalks damaged and reduction in sucrose content of the crop, reductions in losses in the relative value of the crop when the various control measures are implemented can be compared. Relationships between the reduction in percent stalk length bored (and hence gains in the relative value of the crop) and the various control strategies are obtained. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermartzburg, 2008.

Five potential resistance-inducing chemicals were applied to two sugarcane varieties (N12 and N27) in a pot trial with the aim of inducing resistance to nematodes in naturally-infested soil. BION® (acibenzolar-S-methyl), methyl jasmonate, cis-jasmone and 2,6-dichloroisonicotinic acid (INA) were applied as a foliar spray and suSCon® maxi (imidacloprid) applied to the soil. All chemicals were tested at two rates and plants were sprayed one week prior to being harvested at 7, 9 and 11 weeks of age. Meloidogyne and Pratylenchus infestation of sett and shoot roots was determined at each harvest. The activity of four pathogenesis-related proteins was examined at 7, 9 and 11 weeks using separate assays, these enzymes where chitinase, β-1,3-glucanase, peroxidase and polyphenol oxidase. Methyl jasmonate treatment produced significant increases in β-1,3-glucanase, chitinase and peroxidase activity. All other elicitor treatments showed little difference in enzyme activity from the Control. The effect of each treatment on plant growth was examined by recording the dried root and shoot biomass of each plant. No significant differences were seen (p<0.05; Holm-Sidak test). However, root and shoot dried biomass was highest in the N12 variety treated by suSCon® maxi. The infection of sugarcane with Ustilago scitaminea (sugarcane smut) is commonly identified visually by the presence of a smut whip. Identification of sugarcane smut infection can be determined prior to whip development by staining tissue sections with lactophenol cotton blue and examining plant tissues microscopically. This allows for a rapid determination of smut infection which can aid breeding programs. Smut infection is achieved in vitro by soaking sugarcane setts in smut spores collected from infected whips. Four methods of inoculation were examined. The method that most consistently caused infection involved allowing setts to germinate for 24 hours, before puncturing a bud with a toothpick, followed by submerging the sett in 1x10⁸ smut spores per mℓ. An elicitor of systemic acquired resistance called BION®, and an insecticide with resistance-inducing properties called Gaucho® (imidacloprid) were used as a sett soak treatments to induce resistance to sugarcane smut. The effect of each treatment at three concentrations on plant germination and growth was examined in the NCo376 variety. Smut spore germination on agar was examined in the presence of both treatments at three concentrations. Sugarcane setts were treated with a concentration that did not significantly reduce the germination of smut spores or sugarcane setts. Plants were infected with smut post treatment and allowed to grow for approximately one month until plants were between 8 and 10 cm in height. Smut infection was assessed by cutting longitudinal sections through the base of the shoot and staining each section with cotton blue lactophenol. Treatment with BION® and Gaucho® did not reduce smut infection. / M.Sc.Agric. University of KwaZulu-Natal, Pietermaritzburg 2013.

In the KwaZulu-Natal (KZN) Midlands North region of South Africa, the importance and increased prevalence of endemic scarabaeids, particularly Hypopholis sommeri Burmeister and Schizonycha affinis Boheman (Coleoptera: Melolonthinae), as soil pests of sugarcane, and a need for their control was established. The development of a mycoinsecticide offers an environmentally friendly alternative to chemical insecticides. The identification of a diversity of white grub species, in two Scarabaeidae subfamilies, representing seven genera were collected in sugarcane as a pest complex. Hypopholis sommeri and S. affinis were the most prevalent species. The increased seasonal abundances, diversity and highly aggregated nature of these scarabaeid species in summer months, suggested that targeting and control strategies for these pests should be considered in this season. Increased rainfall, relative humidity and soil temperatures were linked to the increased occurrence of scarab adults and neonate grubs. Beauveria brongniartii (Saccardo) Petch epizootics were recorded at two sites in the KZN Midlands North on H. sommeri. Seventeen different fluorescently-labelled microsatellite PCR primers were used to target 78 isolates of Beauveria sp. DNA. Microsatellite data resolved two distinct clusters of Beauveria isolates which represented the Beauveria bassiana senso stricto (Balsamo) Vuillemin and B. brongniartii species groups. These groupings were supported by two gene regions, the nuclear ribosomal Internal Transcribed Spacer (ITS) and the nuclear B locus (Bloc) gene of which 23 exemplar Beauveria isolates were represented and sequenced. When microsatellite data were analysed, 26 haplotypes among 58 isolates of B. brongniartii were distinguished. Relatively low levels of genetic diversity were detected in B. brongniartii and isolates were shown to be closely related. There was no genetic differentiation between the two sites, Harden Heights and Canema in the KZN Midlands North. High gene flow from swarming H. sommeri beetles is the proposed mechanism for this lack of genetic differentiation between populations. Microsatellite analyses also showed that B. brongniartii conidia were being cycled from arboreal to subterranean habitats in the environment by H. sommeri beetles. This was the first record of this species of fungus causing epizootics on the larvae and adults of H. sommeri in South Africa. The virulence of 21 isolates of Beauveria brongniartii and two isolates of B. bassiana were evaluated against the adults and larvae of S. affinis and the adults of H. sommeri and Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae). Despite being closely-related, B. brongniartii isolates varied significantly in their virulence towards different hosts and highlighted the host specific nature of B. brongniartii towards S. affinis when compared to B. bassiana. Adults of S. affinis were significantly more susceptible to B. brongniartii isolates than the second (L2) or third instar (L3) grubs. The median lethal time (LT₅₀) of the most virulent B. brongniartii isolate (C13) against S. affinis adults was 7.8 days and probit analysis estimated a median lethal concentration (LC₅₀) of 4.4×10⁷ conidia/ml⁻¹. When L2 grubs were treated with a concentration of 1.0×10⁸ conidia/ml⁻¹, B. brongniartii isolates HHWG1, HHB39A and C17 caused mortality in L2 grubs within 18.4-19.8 days (LT₅₀). Beauveria brongniartii isolate HHWG1 was tested against the L3 grubs of S. affinis at four different concentrations. At the lowest concentration (1×10⁶ conidia/ml⁻¹), the LT₅₀ was 25.8 days, and at the highest concentration (1×10⁹ conidia/ml⁻¹) the LT₅₀ dropped to 15.1 days. The persistence of B. bassiana isolate 4222 formulated on rice and wheat bran and buried at eight field sites in the KZN Midlands North was evaluated by plating out a suspension of treated soil onto a selective medium. All eight field sites showed a significant decline in B. bassiana CFUs per gram of soil over time, with few conidia still present in the samples after a year. Greater declines in CFUs were observed at some sites but there were no significant differences observed in the persistence of conidia formulated on rice or wheat bran as carriers. Overall, poor persistence of B. bassiana isolate 4222 was attributed to suboptimum temperatures, rainfall, which rapidly degraded the nutritive carriers, attenuated fungal genotype and the action of antagonistic soil microbes. Growers’ perceptions of white grubs as pests and the feasibility of a mycoinsecticide market were evaluated by means of a semi-structured questionnaire. The study showed that the reduced feasibility of application, general lack of potential demand for a product, high cost factors and most importantly, the lack of pest perception, were factors which would negatively affect the adoption of a granular mycoinsecticide. Growers however exhibited a positive attitude towards mycoinsecticides, and showed all the relevant attributes for successful technology adoption. It is recommended that because B. brongniartii epizootics were recorded on target pests which indicated good host specificity, dispersal ability and persistence of the fungus in the intended environment of application; that a mycoinsecticide based on this fungal species be developed. What will likely increase adoption and success of a mycoinsecticide is collaboration between various industries partners to increases market potential in other crops such as Acacia mearnsii De Wild (Fabales: Fabaceae).

Fourteen spore-forming bacterial strains were isolated and screened for entomopathogenic activity. Five displayed toxicity towards the common mealworm, Tenebrio molitor L., (Coleoptera: Tenebrionidae). The majority of the isolates were obtained from insect larvae and insect rich environments. The three bacterial species identified were Bacillus thuringiensis Berliner, Brevibacillus laterosporus Laubach and Bacillus cereus Frankland and Frankland. Bioassays were conducted using T. molitor larvae. The one isolate of B. cereus required the highest concentration of bacterial cells to achieve its LC50, whereas one of the isolates of B. laterosporus required the lowest cell concentration to achieve its LC50. Dose response curves were generated for the five best isolates, which showed that the isolate of B. laterosporus (NDR2) was substantially more toxic than the other isolates. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009.

The Sugarcane Industry contributes approximately 400 000 jobs and ZAR 8 billion annually to South Africa’s economy. Due to climate change and the subsequent threat posed by disease, these figures have been on the decline. Brown rust, a contributor to this decline is caused by the basidiomycete Puccinia melanocephala Syd. and P. Syd., which previously resulted in 50% yield losses in susceptible varieties. This highlighted the need for improved screening and breeding techniques which will result in the replacement of susceptible varieties. The objectives of this study were to: a) Adopt and optimise a glasshouse whorl inoculation screening technique applicable for mass screening of large populations. b) Develop a rapid and cost effective rust resistance screening technique using detached leaves. c)Utilise two flanking marker sets (R12H16 and 9O20-F4-PCR primers) for the rust resistance Bru1 gene in a diagnostic polymerase chain reaction (PCR) to identify rust resistant genotypes lacking Bru1 and possessing either quantitative resistance or an alternative major qualitative resistance gene. d) Correlate rust phenotypic data to AFLP marker data for the Linkage Disequilibrium (LD2) mapping population. e) Utilise suppression subtractive hybridization (SSH) profiling on rust challenged genotypes to discover differentially expressed genes between susceptible and resistant (susceptible Bru1 negatives taken away from resistant Bru1 negatives); and resistant genotypes (resistant Bru1 positives taken away from resistant Bru1 negatives). 4 Results from the glasshouse whorl inoculation trials showed the technique could be reliably used to screen large populations, as two independently conducted pot trials showed highly correlated rust ratings. A visually assessed detached leaf assay (DLA) was developed using selected genotypes. Chlorophyll fluorescence and SPAD readings were used in the DLA to determine the leaf photochemical efficiency (PIABS) with relation to chlorophyll content, resulting in reduced assessment time of at least two days. PCR diagnostics revealed 31% of LD2 did not possess either flanking marker, 8% had one or the other marker, and 61% had both markers. The overall rust phenotypic ratings (rating scale of 0-10) and Bru1 status of the genotypes was used to group the population, with the Bru1 negative genotypes containing all three rating categories (resistant 0-3.5; intermediate 3.51-6.5; susceptible 6.51-10); while the Bru1 positive genotypes were all resistant. The phenotypic data was correlated to AFLP data using the Pearson product-moment correlation coefficient and stepwise multiple linear regression employed to build marker based models to use for predicting non-Bru1 mediated resistance. SSH analysis was then subsequently conducted on genotypes selected on the basis of Bru1 status and AFLP correlation data. Two subtraction cDNA libraries were constructed and the cDNA inserted into electro-competent Escherichia coli cells. PCR on transformed cells revealed cDNA inserts ranging from 200- 1300bp. BLAST analysis of the cDNA sequences indicated the presence of high proportions of disease and drought stress related sequences in the libraries. Analysis of the sequences in both libraries showed that the resistant Bru1 negative genotypes contained oxidative stress related sequences which were however absent in the Bru1 positive resistant genotypes. The library comparing the Bru1 negative resistant genotypes against the Bru1 negative intermediate and susceptible genotypes showed a higher proportion of differentially expressed sequences coding for putative disease resistance proteins, highlighting their presence in the resistant genotypes. Both subtraction libraries also contained high proportions of a leucine rich repeat protein coding cDNA which contained a conserved domain homologous to that of a disease resistance protein conferring resistance to Pseudomonas syringae in Arabidopsis thaliana. The outcomes of this study will subsequently enable an improved understanding of sugarcane-rust resistance mechanisms and improved breeding and screening techniques for sugarcane by identifying SSH and AFLP markers linked to rust resistance QTLs or alternative R genes. / Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

As is the case in many other regions in the world, sugarcane production in southern Africa is affected by a wide range of climatic conditions, which can vary considerably from location to location and from year to year. As a result, the season length and growth cycles of sugarcane in southern Africa differ greatly. Such conditions include the hot and dry regions of northern KwaZulu-Natal, Swaziland and Mpumalanga, where sugarcane is mostly irrigated, to the humid sub-tropical coastal belt extending from the far north coast of KwaZulu-Natal to areas in the Eastern Cape, as well as the cool frost prone midlands regions of KwaZulu-Natal. Owing to the wide range of climatic conditions in which sugarcane is grown in southern Africa, there are many different external factors that affect sugarcane production, including a range of pests and diseases, frost occurrences and variations in soil water. The objective of this research was to (1) identify a number of important variables that affect cane production in southern Africa, (2) employ suitable models to reflect these variables, and (3) simulate and map the extent and severity of these variables at a high spatial resolution over southern Africa. Such variables include the Eldana saccharina and Chilo sacchariphagus stalk borers, sugarcane rust fungus, heat units with selected base temperatures, frost, soil water content, soil compaction, irrigation water demand, conducive and non-conducive growing conditions, flowering proficiencies for sugarcane, sugarcane yields and yield increments per unit of irrigation. The distribution patterns of the above-mentioned variables relied greatly upon the various models employed to represent them, as well as the accuracy of the temperature and rainfall databases to which the various models were applied. Although not definitive, the models used to reflect the variables which had been identified were considered to be generally satisfactory. The resolution at which the variables which had been identified in this study were mapped, was also found to be adequate. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.