Letteratura scientifica selezionata sul tema "Tobacco Diseases and pests Control"

Tobacco is one of the most important plants which were cultivated by Farmers Groups "Darma Mukti Tani I" and "Karya Tani" of Wangon District, Banyumas Regency. However, several obstacles often interfere with the production of tobacco, including quite high tobacco pests and diseases. Socialization of plant pests diseases management by using Trichoderma sp. and Pseudomonas fluorescens biopesticides, needs to be done. The activity aimed was to increase knowledge and skills of farmers on pests and diseases in tobacco and their management measures with biological pesticides. Issues addressed farmers partners with several technology solution, which was conducted by the transfer of technology through education, training, demonstration plots, and mentoring. Dissemination activities were able to increase their knowledge of pests and diseases, their control, and the control of environmental friendly as 58,82, 62,5, and 67.67%, respectively. The training activities of P. fluorescens exploration was able to improve their ability as 166.67%. Propagation activity and application training could improve their ability for 100 and 73,33%, respectively. The training activities of Trichoderma sp. exploration were able to improve their ability as 94,44%, while the propagation and application training could improve their ability, respectively, as 73,33 and 88.23%. Application of biological pesticides P. fluorescens and Trichoderma sp. at demonstration plot was able to increase growth and reduced the intensity of bacterial and fusarium wilt disease by 40-50%.Keywords: Tobacco, technology transfer, pests and diseases, biological control.

Tobacco Deli" Sumatra, the belle of the European cigar tobacco is an economically valuable commodity exports as a source of foreign exchange. Deli tobacco leaf wrapper cigar known as the number one in the world, so it is still needed by plants producing high-quality cigars. Approach to literacy method in the inventory of the tobacco plant pest and disease appropriately in order to improve tobacco produktiviats to foreign countries. The main pests of tobacco plants were identified from the source of literacy is Thrips parvispinus, Spodoptera litura, Helicoperva armigera, Myzus persicae, Agrotis ipsilon, Heliothis, Meloydogyinae, Aphis sp, Thrips sp, Bemisia sp. While the types of diseases that often attack the tobacco plant was charred trunks, black shank, homeopathic leaf, spotting coelat, late blight and viruses. Preparation of seed healthy and productive; tillage seeding and planting land; Biological Control Agents consumption (BCA), rice husk ash, ash kitchen, liquid organic fertilizer and weed-free treatment that is an appropriate way to improve the productivity of tobacco as a commodity exporting country Indonesia.

Introduction Tobacco farming exposes workers to various health risks due to the high application of pesticides needed to control pests, weeds and fungal diseases that prevent the tobacco plant growth. Objective To analyze the perception of the quality of life of tobacco growers exposed to pesticides, with emphasis on general health, hearing, and working conditions. Method This is a descriptive, cross-sectional study using a quantitative approach with farmers from southern Brazil. Data were collected from November of 2012 to November of 2014. For data collection, we opted for the 36-item short form health survey (SF-36) questionnaire, and a questionnaire with closed questions about health, hearing and working conditions. We evaluated a total of 78 subjects; the study group, made up of 40 tobacco farmers exposed to pesticides, and a control group of 38 participants without occupational exposure to pesticides. Both groups are residents of the same municipality, and users of the federal public health system. Results The results showed that tobacco growers had lower quality of life scores compared with the control group. Significant differences were observed in the areas of pain and general health. There were correlations between physical elements and chronic diseases; hearing complaints and a lack of personal protective equipment use, occupation and hearing complaints, as well as general health and hearing complaints. Conclusion Tobacco farming is a risky activity for general and hearing health, and it can impact the quality of life of those working in this field.

ABSTRACT Spodoptera litura F. is a pest that causes a decrease in production at various plant phases. S litura attacks the leaves and fruit of the plant, causing leaves to be slightly whitish because only the upper leaves are left behind. The cause of the high attack of pests is resistance to the use of chemical insecticides that are used continuously. The negative impact of the use of chemical insecticides can be reduced by the use of vegetal insecticides made from neem seeds and tobacco leaf waste. The study was conducted in May to June 2017, through two stages. The first stage is preparation includes the multiplication and maintenance of S litura, tool sterilization, and extraction of vegetal insecticides in the Laboratory of Pests and Diseases. The second stage of preparation includes the application of vegetal insecticides to S litura. The application of the treatment uses factorial Randomized Complete Design (RAL) with the first factor, which is neem seed (M), and vegetal insecticides made from tobacco leaf waste (T) and the second factor Concentration (D) includes 5 concentrations namely 15%, 12.5%, 10%, 7.5%, 5% plus controls as a comparison with an accuracy value of 95% and continued Duncan test 95%. The combination of treatment was the concentration of pulp seeds of 15%, neem seed concentration of 12.5%, neem seed concentration of 10%, neem seed concentration of 7.5%, pulp concentration of 5%, tobacco leaf waste concentration of 15%, tobacco leaf waste concentration of 12.5 %, 10% tobacco leaf waste concentration, 7.5% tobacco leaf waste concentration, 5% tobacco leaf waste concentration. Neem seeds are the best vegetal insecticides to control as many as S litura pests. The best concentration to increase production is 15%. Keywords : Tabacco Leaf Waste, Neem Seeds, Concentration, S. litura F. ABSTRAK Spodoptera litura F. merupakan hama pemakan daun hingga habis, sehingga hanya tertinggal bagian epidermis daun dan tulang-tulang daun saja (Kurmia, 2017). Penyebab tingginya serangan hama ini dikarenakan karena resistensi hama akibat penggunaan insektisida kimia yang digunakan secara terus menerus. Penelitian dilakukan pada bulan Mei sampai Juni 2017, melalui dua tahap. Tahap pertama adalah persiapan meliputi perbanyakan dan pemeliharaan S litura, sterilisasi alat, dan ektraksi insektisda nabati Labolatorium Hama dan Penyakit. Tahap kedua persiapanya meliputi aplikasi insektisida nabati pada S litura. Pengaplikasian perlakuan menggunakan Rancangan Acak Lengkap (RAL) faktorial dengan faktor pertama yaitu insketisida nabati berbahan biji mimba (M), dan insektisida nabati berbahan limbah daun tembakau (T) dan faktor kedua Konsentrasi (D) meliputi 5 konsentrasi yaitu 15%, 12,5%, 10%, 7,5%, 5% ditambah kontrol sebagai pembanding dengan nilai ketepatan 95% dan dilanjutkan uji Duncan 95%. Kombinasi perlakuan yaitu konsentrasi biji mimba 15%, konsentrasi biji mimba 12,5%, konsentrasi biji mimba 10%, konsentrasi biji mimba 7,5%, konsentrasi mimba 5%, konsentrasi limbah daun tembakau 15%, konsentrasi limbah daun tembakau 12,5%, konsentrasi limbah daun tembakau 10%, konsentrasi limbah daun tembakau 7,5%, konsentrasi limbah daun tembakau 5%. Kata Kunci : Limbah Daun Tembakau, Biji Mimba, Konsentrasi, dan S. litura F

Tea is a popular beverage made from the leaves of evergreen shrub or tree Camellia sinensis, under the family Theaceae. Tea plant is subjected to the attack of insects, mites, nematodes and some plant pathogenic diseases. Tea production is greatly hindered due to these maladies. About 10-15% crop loss occurred by these pests per annum. In severe cases, it would be 100%. To combat these problems different groups of pesticides have been used in the tea fields since 1960. As tea is a consumable commodity, the effect of residue of pesticides in made tea is harmful to human health. In this context, biopesticides are being considered as environmentally safe, selective, biodegradable, economical and renewable alternatives for use in IPM programmes. Biopesticides are natural plant products and may be grown by the planters with minimum cost and extracted by indigenous methods. Biopesticides are secondary metabolites, which include alkaloids, terpenoids, phenolics, and minor secondary chemicals. It is estimated that as many as 2121 plant species have been reported to posses’ pest control properties. Botanicals like neem, ghora-neem, mahogoni, karanja, adathoda, sweet flag, tobacco, derris, annona, smart weed, bar weed, datura, calotropis, bidens, lantana, chrysanthemum, artemisia, marigold, clerodendrum, wild sunflower and many others may be grown by planters with minimum expense and extracted by indigenous methods. These botanical materials can be used as an alternative to chemical pesticides. These botanical extracts will help in controlling major pests of tea such as Helopeltis, red spider mite, aphids, thrips, jassid, flushworm, termites, nematodes etc. The present note reviews the information of most widely available indigenous plants that may be used for the control of insect pests of tea as a component of IPM. DOI: http://dx.doi.org/10.3329/ijarit.v1i1-2.13924 Int. J. Agril. Res. Innov. & Tech. 1 (1&2): 16-23, December, 2011

<p>Penerapan teknologi ramah lingkungan budi daya tanaman pada suatu lahan akan dapat mempertahankan kelestarian lingkungan. Penciptaan teknologi budi daya tanaman tembakau, serat, dan minyak industri di-arahkan pada teknologi yang dapat meningkatkan produktivitas dan mutu hasil, efisiensi biaya usaha tani, dan ramah lingkungan. Teknologi ramah lingkungan difokuskan pada penemuan komponen teknologi prapa-nen yang mempunyai dampak minimal terhadap pencemaran atau perusakan lingkungan, yang meliputi va-rietas-varietas unggul, teknik pengendalian hama dan penyakit, teknik konservasi lahan tembakau. Varietas-varietas unggul tersebut adalah varietas-varietas yang mempunyai ketahanan terhadap hama dan penyakit, yaitu tembakau Prancak 95, Prancak N1, Prancak N2, Kemloko 2, dan Grompol Jatim 1; kapas: Kanesia 11–Kanesia 13; kenaf: Karangploso 14–Karangploso 15; wijen: Sumberrejo 4; dan jarak kepyar: Asembagus 81. Teknik pengendalian hama dan penyakit yang ramah lingkungan adalah teknologi pengendalian hama yang membatasi atau meniadakan penggunaan insektisida kimia sintetik dan menerapkan teknik pengendalian de-ngan memanfaatkan peran musuh alami serangga hama atau antagonis patogen penyebab penyakit, dan penggunaan pestisida nabati. Teknik konservasi lahan untuk mengendalikan erosi dan penyakit lincat dikem-bangkan pada lahan tembakau temanggung dengan menerapkan penggunaan varietas tahan penyakit, pem-buatan terassering dan penguatnya, pengolahan lahan minimal, dan aplikasi mikroba antagonis. Teknologi ramah lingkungan tersebut telah diterapkan di tingkat petani dan memberikan dampak yang positif terhadap pengembangan komoditas.</p><p>Technology innovations for tobacco, fibers, and industrial-oil crops are directed to increase production and quality of the products, efficiency, and environmentally-friendly technologies. The efficiency and environ-menttally-friendly technologies are focused on the pre-harvest technology innovations that have minimal im-pacts on environmental damages. The technologies include superior varieties, pest control, and land conser-vation. The superior varieties are those that resistant to either insect pests or diseases, i.e. tobacco: Prancak 95, Prancak N1, Prancak N2, Kemloko 2, and Grompol Jatim 1; cotton: Kanesia 11–Kanesia 13; kenaf: Ka-rangploso 14–Karangploso 15; sesame: Sumberrejo 4; and castor: Asembagus 81. Environmentally-friendly pest control is to limit or no use synthetic-chemical pesticides in pest control, but optimally make use the role of natural enemies and antagonists and use biopesticides. Land conservation technique to control erosi-on as well as ”lincat’ disease has been developed in fields of temanggung tobacco by using tobacco variety resistant to the disease, terracering, minimum tillage, and application of antagonist microbes. Those techno-logies has been implemented in the farmers’ fields and has a positive impacts for the commodity develop-ment.</p><p> </p>

The rod-shaped nanoparticles of the widespread plant pathogentobacco mosaic virus(TMV) have been a matter of intense debates and cutting-edge research for more than a hundred years. During the late 19th century, their behavior in filtration tests applied to the agent causing the 'plant mosaic disease' eventually led to the discrimination of viruses from bacteria. Thereafter, they promoted the development of biophysical cornerstone techniques such as electron microscopy and ultracentrifugation. Since the 1950s, the robust, helically arranged nucleoprotein complexes consisting of a single RNA and more than 2100 identical coat protein subunits have enabled molecular studies which have pioneered the understanding of viral replication and self-assembly, and elucidated major aspects of virus–host interplay, which can lead to agronomically relevant diseases. However, during the last decades, TMV has acquired a new reputation as a well-defined high-yield nanotemplate with multivalent protein surfaces, allowing for an ordered high-density presentation of multiple active molecules or synthetic compounds. Amino acid side chains exposed on the viral coat may be tailored genetically or biochemically to meet the demands for selective conjugation reactions, or to directly engineer novel functionality on TMV-derived nanosticks. The natural TMV size (length: 300 nm) in combination with functional ligands such as peptides, enzymes, dyes, drugs or inorganic materials is advantageous for applications ranging from biomedical imaging and therapy approaches over surface enlargement of battery electrodes to the immobilization of enzymes. TMV building blocks are also amenable to external control of in vitro assembly and re-organization into technically expedient new shapes or arrays, which bears a unique potential for the development of 'smart' functional 3D structures. Among those, materials designed for enzyme-based biodetection layouts, which are routinely applied, e.g., for monitoring blood sugar concentrations, might profit particularly from the presence of TMV rods: Their surfaces were recently shown to stabilize enzymatic activities upon repeated consecutive uses and over several weeks. This review gives the reader a ride through strikingly diverse achievements obtained with TMV-based particles, compares them to the progress with related viruses, and focuses on latest results revealing special advantages for enzyme-based biosensing formats, which might be of high interest for diagnostics employing 'systems-on-a-chip'.

<p>Nematisida nabati adalah salah satu jenis nematisida alami yang saat ini sedang banyak dipelajari peranan-nya dalam mengendalikan nematoda. Nematisida ini relatif aman bagi lingkungan dan organisme hidup karena bahan aktifnya berasal dari senyawa metabolit sekunder tanaman yang mudah terurai. Pemanfaatan senyawa metabolit sekunder tanaman sebagai bahan aktif nematisida nabati didasarkan pada fungsinya bagi tanaman, di antaranya sebagai sarana untuk perlindungan diri dari serangan hama dan penyakit. Salah satu tanaman yang berpotensi untuk dikembangkan adalah tembakau (Nicotiana tabacum). Daun tembakau mengandung senyawa nikotin dan secara in vivo mampu membunuh nematoda Meloidogyne incognita dengan nilai LC50 dan LC90 berturut-turut sebesar 1,9 dan 3,6 mg ekstrak/ml air. Nematoda yang mati terpapar ekstrak daun tembakau berbentuk keriting (curly), menyerupai bentuk nematoda yang mati terpapar insektisida organo-fosfat dan karbamat yang menghambat pembentukan senyawa acetylcholine dalam sistem syaraf organisme hidup. Fenomena ini dapat dijadikan salah satu indikator untuk mendeteksi cara kerja berbagai senyawa se-kunder tanaman dalam membunuh hama yang hingga kini masih belum banyak diketahui. Tujuan dari penu-lisan tinjauan ini adalah untuk mengkaji prospek ekstrak daun tembakau sebagai nematisida nabati, juga sebagai alternatif diversifikasi pemanfaatan tembakau selain untuk bahan baku rokok.</p><p> </p><p>Botanical nematicide is one type of natural pesticide, which is currently being studied for its role in the control of nematodes. This nematicide is safer for the environment and living organisms as the active ingredient de-rived from secondary metabolite of plants is biodegradable. Utilization of this compound as active ingredients of botanical nematicide is based on naturally used as a mean of self-protection against pests and diseases. One plant that potentially to be used as nematicide is tobacco (Nicotiana tabacum). Tobacco leaves extract is able to kill the root knot nematode, Meloidogyne incognita, with LC50 and LC90 values are 1.9 and 3.6 mg extract/ml of water, respectively. Body of the dead nematodes exposed by this extract shows curly shape similar to that of exposed by an organophosphate and carbamate groups, which acts as acetyl cholinesterase inhibitors. Meanwhile the body of naturally dead nematode shows straight shape. This phenomenon can be used as an indicator to detect the mode of action of plant secondary metabolite compounds that have not been widely known. This paper would discuss about possibility of using extracted tobacco leaf as botanical nematicide, and also alternatife of tobacco diversification usage except cigarette.</p>

English Lavender (Lavandula angustifolia Mill.) has been considered an alternative crop to tobacco in Hatay Province of Turkey because of its great production potential. As a new, nonnative crop, diseases and pests of lavender are not well known in the region. In summer 2010, root rot symptoms were observed with an average incidence of 45% in a 2-year-old lavender nursery in Hatay. Initial symptoms of chlorosis and wilting were followed by progressive death of the plants starting at the shoot tips. An oomycetous species was isolated consistently from the stems and roots of diseased plants on potato dextrose agar (PDA) amended with several fungicides and antibiotics. The culture of the single-zoospore isolate produced arachnoid growth on PDA. Chlamydospores of the isolate were approximately 35.0 μm in diameter. The isolate produced papillate, caduceus, hyaline sporangia in different shapes ranging from spherical to ellipsoidal. Sporangia with short pedicels (5 μm) were 35.0 to 57.5 × 27.5 to 42.5 μm with a length/width ratio of 1.2 to 1.8. On the basis of symptoms and morphology of the organism, the pathogen was identified as Phytophthora palmivora (E.J. Butler) E.J. Butler (3). Identification of the isolate was also confirmed by comparison of the sequence of the nuclear ribosomal internal transcribed spacer (ITS) region with reference isolates. The ITS region of rDNA was amplified by PCR with primers ITS1/ITS4 and sequenced (GenBank Accession No. JF777117). BLAST analysis of the sequence obtained showed a 99 to 100% homology with P. palmivora. Pathogenicity tests were performed on 12 greenhouse-grown 2-year-old lavender plants in 2-liter pots containing a steamed sand/peat/soil mixture. After rooting, the plants were inoculated by placing mycelial plugs from a 1-week-old culture of the isolate into an incision made at the base of each plant. Control plants were treated with plugs of sterile PDA. Inoculated plants were kept at 27°C for 5 weeks. Similar symptoms developed on the inoculated plants within 4 weeks after inoculation. P. palmivora was consistently reisolated from symptomatic plants. No symptoms developed on control plants. P. palmivora attacks a wide range of crop species including lavenders (1,2,4). To our knowledge, this is the first report of a root rot caused by P. palmivora, a new pathogen of lavender in Turkey. References: (1) S. Davino et al. Plant Dis. 86:561, 2002. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996. (3) D. J. Stamps. C.M.I. Descr. Fungi Bact. 831:1, 1985. (4) G. A. Torres et al. Plant Dis. 94:1163, 2010.

Viral diseases caused by begomoviruses are economically important for their depressing impact on common bean production in Cuba. Mayabeque is a Cuban province where this crop is significantly grown and affectations by Bean golden yellow mosaic virus (BGYMV) have been detected in the last 30 years. Integrated pest management (IPM) programs in this crop have allowed controlling the disease for a long time. However, in prospections of the last years, an increase of the incidence of various yellowing symptoms typical of begomoviruses has been observed in common bean production areas. DNA was extracted from leaf samples taken from symptomatic plants. Non-radioactive nucleic acid hybridization and a specific PCR assay were used to detect BGYMV, Common bean severe mosaic virus, Common bean mottle virus, and Tobacco leaf curl Cuba virus. Of the 218 bean plants sampled, 89.5 % was positive to BGYMV; the presence of the rest of the begomovirus species was between 3 and 4% (3.08% of CBMoV, 3.08% of TbLCCuV and 4.32% of CBSMV). The viral DNA from some samples was analyzed by rolling circle amplification (RCA), by restriction fragment length polymorphism analysis using restriction enzymes, and by cloning and sequencing of the viral components. The DNA sequences from BGYMV isolates showed 98% of identity with the isolates reported in Cuba in 2003. The infection by Tobacco leaf curl Cuba virus (TbLCCuV) was confirmed also in fields in the Cuban western region. This is the first work where the DNA-B of TbLCCuV is identified. These studies will help to strengthen phytosanitary surveillance and management programs implemented in the country to control the whitefly-begomovirus complex in this economically important crop.

The Wheeler Orchid Collection is home to some of the most endangered species of orchids in the world. This fantastic reservoir of endangered species has been enhanced and broadened by its function as a plant rescue station for the U.S. customs service. Unfortunately, this responsibility increases the risk of bringing orchids, which harbor contageous diseases, into the greenhouse where sap transmitted diseases such as the Tobacco Mosaic Virus (TMV), can run rampant. Although manipulation of orchid characteristics is typically done by classical plant breeding techniques, genetic engineering is emerging as a useful technique for the introduction of desirable traits into the orchid genome. Through the use of genetic engineering techniques it may be possible to mitigate the symptoms associated with this destructive virus. Virus resistance may be achieved through the expression of either the sense or antisense viral coat protein gene in orchid tissues if an efficient means of orchid transformation is developed. In this research two transformation protocols were examined for their ability to efficiently transform orchid tissue. The first transformation protocol explored utilized the native ability of Aq bacterium tumefaciens to incorporate DNA into host plants to achieve transformation. The second mechanism explored was particle bombardment transformation.Many strains of A. tumefaciens were employed using direct exposure of Cattleya_ orchid protocorm and callus tissue. Particle bombardment using DNA coated 0.5 um diameter tungsten particles and high pressure helium tank acceleration was employed. The particle bombardment procedure employed the pG35barB plasmid which confers herbicide resistance to the herbicide basta when integrated and expressed in plant tissues.GUS fluorescence assays and PCR analysis indicate that T-DNA is present in orchid tissues, while Southern blot analysis was unable to display that integration had occurred. Particle bombardment yielded herbicide resistant orchid tissues which have yet to be analyzed by Southern blot analysis to confirm integration due to limited tissue quantities.
Department of Biology

This research was an attempt to use a dicot transformation vector to transform a monocot. The initial purpose of this thesis was to transform orchids with the sense and antisense coat protein genes from the Odontoglossum ringspot virus (ORSV) in an effort to mitigate viral symptoms in transgenic plants using the transformation vector, Agrobacterium tumefaciens. However, it soon became apparent that much time would be needed to develop a transformation protocol. The transformation vectors used included the Agrobacterium tumefaciens disarmed strain LBA4404 with the binary plasmid pB1121, the disarmed strain At699 with the binary plasmid pCNL65, and the wild-type strain Chry5. The marker gene on the binary plasmids of both disarmed strains was p-glucuronidase (GUS).Several transformation protocols were used in an effort to determine if this transformation system would work on orchids. Transformation was not achieved even though a number of experimental conditions were varied. These included using two different types of orchid tissue, callus and protocorms; using two different species of orchids, Cattleya Chocolate Drop x Cattleytonia Kieth Roth and Cymbidium maudidum; varying the time the plant tissue was exposed to the bacteria from 1 hour to 96 hours; performing experiments with and without the wound signal molecule acetosyringone; and exposing the tissue to the virulent strains of A. tumefaciens mentioned previously.This research also developed GUS assay conditions necessary to decrease the number of false positives due to bacterial contamination. These conditions included chloramphenicol in the GUS assay buffer.
Department of Biology

Thesis (MSc)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: Seed germination is the most vulnerable time in a plant's life cycle, since the thick protective seed coat ruptures and the moist and humid soil environment not only favours seed germination, but also the growth and development of plant pathogens. Infection of plant seeds during germination, however, is the exception rather than the rule. Plant seeds have - - -developed a--cemplex preformed defense mechanism that includes anttfungal agents thatdiffuse into the surrounding environment to form a protective layer around the seed. This protective layer prevents fungal and bacterial pathogens from infecting the young seedling. Over the last decade, scientists have studied the defense mechanisms of different seeds in an effort to understand and ultimately to introduce and/or manipulate these mechanisms in plants as part of the plant's endogenous disease resistance to pathogens. Various chemical compounds, peptides and proteins that showed strong in vitro activities against various fungi were isolated in these efforts. The mere demonstration of in vitro activity alone, however, is not sufficient to assign a defense role to these antifungal agents. Typically, mutant plants that have lost the ability to produce the antifungal agent, or mutants that are overproducing the agent, have been used to correlate the mutant phenotype to either a decline or increase in disease resistance respectively. Genetic transformation and the subsequent development of transgenic plants have made an unprecedented impact in this regard, specifically in understanding the role of specific defense-related proteins and their interaction with plant pathogens. In this study, the antifungal peptide, Hs-AFP1, from Heuchera sanguinea, a plant defensin, was evaluated in a heterologous in planta environment as a defense protein with potential for engineering disease resistant crops. The in vitro assays performed with Hs-AFP1 against Botrytis cinerea showed antifungal activities of 88% growth inhibition at a concentration of 8 J,lg/ml of the purified peptide, while inducing a characteristic hyperbranching effect on the Botrytis hyphae. Tobacco was subsequently transformed with a construct, pFAJ3068, expressing Hs-AFP1 under the strong constitutive 35S promoter. The peptide was targeted to the apoplastic region with the signal peptide from Mj-AMP2, an antimicrobial peptide from Mirabilis jalapa. Due to reports of peptide instability in transgenic plant systems, two additional constructs were prepared and transformed into tobacco to anticipate possible Hs-AFP1 instability in the heterologous tobacco environment. A putative peptide stabilization construct, pHs-EXG1, consisted of a fusion between Hs-AFP1 and the antifungal exo-glucanase (encoded by EXG1) from Saccharomyces cerevisiae. A control construct, pMj-EXG1, expressing EXG1 targeted to the apoplastic region with the Mj-AMP2 signal peptide, was also prepared and transformed into tobacco to normalize the background antifungal activity as a result of the exoglucanase in the fusion construct lines. Tobacco was successfully transformed with pFAJ3068, pHs-EXG1 and pMj-EXG1, resulting in transgenic tobacco lines designated THs, THE and TME respectively. Transgene expression was confirmed for the THs and THE transgenic lines. The translation of these transcripts into proteins was also confirmed with Western blot analysis. Moreover, the heterologous production of Hs-AFP1 in tobacco led to an increase in disease resistance to B. cinerea in the THs lines in comparison with the untransformed tobacco controls. An increase of up to 42% in disease resistance was observed in an in planta detached leaf assay. Crude protein extracts from the THs lines were also analyzed in an in vitro quantitative fungal growth assay. This assay confirmed the results obtained with the disease resistance assay, with crude protein extracts exhibiting up to 40% fungal growth inhibition. The incubation of B. cinerea in the presence of crude protein extracts from THs lines resulted in hyperbranching of the fungal hyphae, which is characteristic of Hs-AFP1 activity. From these analyses it was clear that the heterologously expressed Hs-AFP1 was quite stable in the transgenic environment. The fusion between Hs-AFP1 and EXG1 did not increase the stability of Hs-AFP1, but rather led to a loss of the Hs-AFP1 activity. All the analyses performed showed the THE lines to be reduced in their ability to inhibit fungal infection in comparison to the THs line. Also, microscopic analysis of the effects of the crude THE extracts on B. cinerea growth showed no hyperbranching activity, again confirming the loss of peptide activity due to the fusion to EXG1. This is in agreement with previous work, in which sarcotoxin 1A was fused to a reporter gene and also lost activity. Although integration of the Mj-EXG1 expression cassette was confirmed, no mRNA levels could be detected with Northern blot or RT-PCR analysis of the TME lines. These lines also did not show any in vitro antifungal activities, probably indicating post-transcriptional gene silencing. This silencing was overcome in the fusion constructs that were expressed in the THE plant lines. These lines also showed EXG1 protein activity, as measured by ~-glucosidase assays. Although the THE lines did not serve the functions originally envisaged, they fortuitously showed that a fusion strategy might stabilize glucanase expression in a transgenic environment. A variety of glucanases have been shown to be prone to gene silencing when overexpressed in a plant environment and the yeast glucanase can now be added to that list if it is not present as a fusion protein. Overall, this study confirmed that Hs-AFP1 is involved in plant defense systems and provided valuable information on the stability of small peptides in a heterologous environment. The positive results obtained with overexpressed Hs-AFP1 on fungal inhibition in this study merits further investigations into the use of this peptide in the engineering of disease-resistant crops.
AFRIKAANSE OPSOMMING: Saadontkieming is die mees vatbare tyd vir siekteontwikkeling gedurende 'n plant se lewenssiklus. Die saadhuid bars en die vogtige grondkondisies bevoordeel nie net saadontkieming nie, maar ook die groei en ontwikkeling van plantpatogene. Infeksie van plantsade tydens ontkieming is egter die uitsondering eerder as die reël. Plantsade besit komplekse -veraeaigingsfueganfsmes-reen moontlike - patoqeeninteksies. Die meqanismes sluit die produksie van antifungiese agense, wat tydens saadontkieming na die omliggende omgewing diffundeer om 'n beskermende sone om die ontkiemende saad te vorm, in. Die gevolglike antifungiese sone beskerm die saad teen infeksie deur bakterieë en swamme. Gedurende die laaste dekade het navorsers baie aandag aan die bestudering van plantsaadverdedigingsmeganismes gegee. Dié kennis word gebruik om die verdedigingsmeganismes beter te verstaan, asook om dié meganismes te manipuleer en/of oor te dra aan plantspesies met inherente swak weerstandsmeganismes wat gereeld aan plantpatogeeninfeksies onderhewig is. Navorsing op plantsade het tot die isolasie van verskeie chemiese agense, peptiede en proteïene, wat sterk in vitro aktiwiteite teen 'n wye reeks swampatogene vertoon, gelei. Die vermoë van dié agense om swamme in 'n in vitro omgewing te inhibeer, is alleen egter nie 'n bewys dat hulle 'n rol in plantverdeging speel nie. Studies waar mutante gebruik word, is gewens om addisionele bewys te lewer dat die substanse 'n rol in plantverdediging vervul. Sodanige mutante sluit plantlyne, waarin die geen van belang gemuteer is of ooruitgedruk word om so die rol van die geen in 'n in planta omgewing te bepaal in. In hierdie toepassings het genetiese transformasie en die daarstelling van transgeniese plante 'n ongeëwenaarde bydrae gelewer. In dié studie is die antifungiese peptied, Hs-AFP1, wat aan die peptiedgroep van plant- "defensins" behoort en van Heuchera sanguine a afkomstig is, in 'n heteroloë in planta omgewing geëvalueer as 'n verdedigingspeptied met die potensiaal om in die generering van transgeniese siektebestande gewasse gebruik te word. Die antifungiese aktiwiteit van Hs-AFP1 is teen Botrytis cinerea in 'n in vitro reaksie geëvalueer, waar die toediening van 8 ,",g/mlgesuiwerde Hs-AFP1 peptied aanleiding gegee het tot 'n 88% afname in hifegroei van B. cinerea. Hipervertakkings van swamhifes, 'n kenmerkende eienskap van Hs-AFP1 aktiwiteit, kon duidelik waargeneem word. Tabakplante is voorts getransformeer met 'n konstruk, pFAJ3068, wat die koderende geen van Hs-AFP1 onder die sterk konstitutiewe CaMV 35S promotor bevat het. Die peptied is met behulp van die seinpeptied wat afkomstig is van die Mirabilis jalapa antimikrobiese peptied, Mj-AMP2, na die apoplastiese omgewing geteiken. Voorheen is gerapporteer dat transgeniese peptiede in die heteroloë omgewing soms onstabiel is. Dit het gelei tot die generering van twee addisionele konstrukte om die moontlikheid van peptiedonstabiliteit te ondervang. 'n Stabiliseringskonstruk, pHs-EXG1, bestaande uit In versmelting tussen Hs-AFP1 en In antifungiese eksoglukanase van Saccharomyces cerevisiae, gekodeer deur EXG1, is in tabakplante getransformeer. In Kontrolekonstruk, pMj-EXG1, met die EXG1-geen saam met die Mj-AMP2-seinpeptied, is ook voorberei en in tabakplante getransformeer. Dit is gebruik om die antifungiese aktiwiteit van die eksoglukanase in die antifungiese aktiwiteitstoetse van die stabiliseringskonstruk te kwantifiseer en te normaliseer. Tabak is suksesvol met pFAJ3068, pHs-EXG1 en pMj-EXG1 getransformeer, wat onderskeidelik gelei het tot die sogenaamde THs, THE en TME transgeniese tabaklyne. Transgeentranskripsie en -translasie in die THs en THE tabaklyne is onderskeidelik deur Noordelike- en Westelike-kladanalises bevestig. Die aktiewe uitdrukking van Hs-AFP1 het die vermoë van tabakplante om B. cinerea infeksies te weerstaan, met tot 42% verhoog in vergelyking met ongetransformeerde kontrole tabakplante tydens 'n in planta siekteweerstandstoets. Totale proteïenekstrakte van THs tabaklyne is voorts ook in In in vitro inhibisietoets geëvalueer, wat gelei het tot resultate wat goed met dié van die in planta toetse ooreenstem. Die totale proteïenekstrakte het swamgroei met 40% geïnhibeer en die kenmerkende hipervertakking van Hs-AFP1-aktiwiteit is ook mikroskopies waargeneem. Resultate wat verkry is vanaf al die analises wat op die transgeniese THs tabaklyne uitgevoer is, het aangedui dat Hs-AFP1 baie stabiel in die heteroloë tabakomgewing is en peptiedstabiliteit was dus nie In probleem, soos verwag is nie. Die fusie tussen Hs-AFP1 en EXG1 het dus nie die stabiliteit van die reeds stabiele Hs-AFP1 peptied verder verbeter nie, maar het wel tot die verlies van Hs-AFP1 aktiwiteit gelei. Die antifungiese analises van die THE tabaklyne het verder bevestig dat dié lyne selfs swakker inhibisie van B. cinereainfeksies tot gevolg gehad het, as ongetransformeerde tabakplante. Mikroskopiese analises van totale THE proteïenekstrakte het voorts ook geen kenmerkende hipervertakkings in die swamhifes vertoon nie, wat alles daarop dui dat die Hs-AFP1-deel van die fusieproteïen as gevolg van die fusie met EXG1 geïnaktiveer is. Dié resultaat is in lyn met vorige navorsing, wat getoon het dat In ander peptied, sarcotoxin 1A, sy antifungiese aktiwiteit verloor indien dit met In verklikkergeen versmelt word. Alhoewel integrasie van die pMj-EXG1-konstruk in die TME-tabaklyne bevestig is, kon geen mRNA met Noordelike-klad- of trutranskriptase-PKR (RT-PKR)-analises waargeneem word nie. Die TME plant het ook geen antifungiese aktiwiteit in in vitro toetse getoon nie en dit het geblyk dat die pMj-EXG1-konstruk aan geenafskakeling in die heteroloë tabakomgewing onderworpe was. Dié afskakelingseffek is egter in die THE plante oorkom, aangesien laasgenoemde sterk EXG1 proteïenaktiwiteit met J3-glukosidase aktiwiteitstoetse vertoon het. Alhoewel die THE plante nie die stabiliteit van Hs-AFP1 verbeter het nie, het dit onwerwags tot die stabilisering van EXG1 in In heteroloë omgewing gelei. Versmeltingstegnologie kan dus moontlik gebruik word as 'n strategie om ander glukanases, wat bekend is vir geenafskakeling in transgeniese omgewings, heteroloog uit te druk. In die geheel gesien, het dié studie getoon dat Hs-AFP1 'n onbetwiste rol in plantverdedigingsmeganismes speel en daar is voorts ook meer kennis oor die stabiliteit van peptiede in 'n heteraloë plantomgewing ingewin. Die positiewe resultate t.o.v. die verhoogde siekteweerstand in die transgeniese THs plantlyne regverdig ook die verdere bestudering van dié peptied om transgeniese siekteweerstand in gewasse te bewerkstellig.

The objective of this study was to transform sweet pepper ferredoxin-like protein (PFLP) gene, which has antimicrobial properties, to tobacco and investigate the disease resistance abilities of transgenic tobacco. This protein interacts with another protein, harpin that is produced by the bacteria which is invading the plant tissues, and stimulates hypersensitivity response in plants, thus the spreading of disease is limited. Gene transfer was achieved to tobacco by Agrobacterium- mediated method and with indirect organogenesis
the explants were grown on selective media and then transferred to jars and pots respectively. Molecular and genetic analyses such as PCR, RT-PCR, Sequence Analysis and Northern Blot, were performed with plants which their seeds survived and grew on selective medium and also gave positive reactions for GUS histochemical assay. Finally, with putative transgenic plants, some hypersensitive response assays were carried out with Pseudomonas syringae and it was observed that the recovered plants showed hypersensitive response (HR) in the preliminary tests. These results indicated that putative transgenic tobacco plants which carry pflp transgene, can be used in disease resistance studies.

A two year study was conducted to measure the impact of tobacco aphid, Myzus nicotianae Blackman, colonization and cumulative aphid-days on flue-cured tobacco, Nicotiana tabacum (L.). The objectives of the study included quantifying the response of tobacco production variables, cured leaf quality, and cured leaf chemical analysis to the level of cumulative aphid-days. Aphid populations and tobacco plant responses were recorded on an individual plant basis. A gradient in cumulative aphid-days was obtained through the use of temporally distributed aphid colonizations and selective insecticide use. Tobacco aphid populations resulted in yield reductions as great as 22 and 27% in 1988 and 1989, respectively, while gross economic returns were reduced 27 and 32% in the respective years. The responses of tobacco production variables were characterized by a decreasing negative slope; therefore, incremental losses were greatest at low levels of cumulative aphid-days. Regression models were developed to describe crop production responses as a function of cumulative aphiddays. The quality of the cured leaves (grade index) was also responsive to the level of cumulative aphid-days. Changes in both tobacco grade group and quality within a given group occurred with increasing cumulative aphid-days. The occurrence of nondescript tobacco was associated with large aphid populations. The chemical quality of the cured tobacco was also influenced by cumulative aphid-days. The total alkaloid content followed a linear function, while the level of reducing sugars was a nonlinear relationship with cumulative aphid-days. The study also reported on the disproportionate impact of aphid populations upon the within-plant responses of tobacco. A study was conducted to evaluate the impact of tobacco aphid management using eight different action thresholds. Comparison of the two most commonly recommended treatment thresholds (10 and 20% of plants with 50 or more aphids per leaf) revealed no significant differences in the number of remedial treatments required or the yield and gross economic returns. However, use of the latter threshold resulted in a delay of approximately one week for the first treatment and the retreatment interval.
Ph. D.

Tobacco rattle virus (TRY) and trichodorid vector nematodes were found to be widespread in bulb growing areas in The Netherlands. Indications, obtained from pot bait tests, that associations between serotypes of tobacco rattle virus and Paratrichodorus and Trichodorus vector species occurred were confirmed in bait tests using individual trichodorid nematodes. Whereas different Paratrichodorus vector species each transmitted a serologically distinct TRV-isolate, different Trichodorus vector species transmitted serologically indistinguishable TRV-isolates. It remains to be studied whether a particular Trichodorus species is able to transmit all isolates serologically indistinguishable from the one with which it was naturally associated. A TRV-isolate transmitted by T. cylindricus from Scryne, Scotland and isolates transmitted by P. teres from Julianadorp, The Netherlands were considered anomalous TRV-isolates as they serologically resembled pea early-browning virus but had RNA-1 sequences typical of TRV. Virus-free P. pachydermus from Scotland and from The Netherlands acquired and subsequently transmitted TRV-isolates originally obtained from bait-plants infected by P. pachydermus from Scotland or The Netherlands. They failed to transmit a serologically similar isolate obtained from an infected potato tuber. Virus-free P. pachydermus did not acquire and transmit a pseudorecombinant TRV-isolate with the RNA-2 from a non-transmissible isolate, but efficiently transmitted a pseudorecombinant isolate in which the RNA-2 was derived from a efficiently transmitted isolate. This indicated that transmissibility is most likely determined by the virus coat-protein. Transgenic tobacco plants, expressing TRV coat-protein were resistant to mechanical inoculation but susceptible to nematode transmission of the virus. A possible low level of coat-protein expression in the roots could not fully explain this result as the nematodes also transmitted TRV directly to detached leaves of such transgenic plants.

Dissertation (PhD (Agric))--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: Fungi belonging to the genus Botryosphaeria are heterotrophic micromycetes that can be pathogens on woody plants. They cause serious, and in some cases devastating losses to crops through leaf necrosis, stem cankers and plant death. The Proteaceae cut-flower industry in South Africa accounts for 70% of the national cut-flower enterprise. Botryosphaeria diseases are a major impediment to production and trade of Proteaceae and there is an urgent need to investigate the etiology, epidemiology and control of these diseases. Losses of one of the most important proteas, P. magnifica, amount to 50% or more, locally. The main aims of this study were therefore to establish the etiology and aspects of epidemiology of Botryosphaeria stem cankers on P. magnifica and other Proteaceae, and to investigate methods of disease control. Although there is a vast body of information pertaining to this fungus, which was reviewed in Chapter 1, there is relatively little information available on Botryosphaeria on Proteaceae. The taxonomy of Botryosphaeria requires thorough review, and molecular techniques need to be employed to resolve species identities. In Chapter 2, it was found that Phyllachora proteae, a leaf pathogen of proteas, produced a Fusicoccum anamorph, which is described as F. proteae. A sphaeropsis-like synanamorph was associated with F. proteae and a new combination for P. proteae is proposed in Botryosphaeria, as B. proteae. The taxonomy of Botryosphaeria is in disarray at both the generic and the specific level. In Chapter 3 the taxonomic history of Botryosphaeria is reviewed, and the genus circumscribed and distinguished from other morphologically similar genera. Although several anamorph genera have been linked to Botryosphaeria, based on morphological observations and phylogenetic analysis of lTS rDNA sequence data, two anamorph genera are now recognised, those with pigmented conidia (Diplodia), and those with hyaline conidia (Fusicoccum). Botryosphaeria proteae should thus be excluded from Botryosphaeria. Several pathogenic Botryosphaeria spp. have an endophytic phase within their hosts. They are therefore imported unwittingly into other countries where they may pose a risk to agriculture and indigenous vegetation. The current global distribution of Botryosphaeria spp. associated with Proteaceae is clarified and a key to these taxa associated with Proteaceae is provided in Chapter 4. Five Botryosphaeria spp. are associated with cut-flower Proteaceae worldwide viz. B. lute a, B. obtusa, B. protearum, B. proteae and B. rib is. B. protearum is described as a new species. A thorough understanding of disease epidemiology is essential to effect a reduction of losses. In Chapter 5, I show that on P. magnifica, lesions caused by Botryosphaeria protearum, which lead to the formation of stem cankers, are initiated in the mid-rib vein or margin of leaves. Koch's postulates were satisfied and it was found that the number of lesions that developed from artificial inoculations correlated with starch levels present in leaves at the time of inoculation. In Chapter 6 it is shown that B. protearum exists as an endophyte in leaves of P. magnifica in naturally occurring as well as cultivated plants. In natural stands of proteas stem cankers are rare, but in cultivated plantations the incidence is high. Nutritional analyses indicate that higher levels of nitrogen occur in leaves of cultivated plants in spring, which could enhance disease development. High levels of sodium in the leaves of wild plants may restrict disease development. The severe economic losses caused by B. protearum make the search for improved methods of disease control essential. Fungicide applications form an important component of an integrated approach to disease management. In Chapter 7, in vitro tests demonstrate that tebuconazole, benomyl, prochloraz me, iprodione and fenarimol reduce the mycelial growth of B. protearum effectively. In the field there was a 25-85% reduction in the occurrence of stem cankers by applying fungicides or sanitation pruning. The best control was achieved by using benomyl, bitertanol, fenarimol, iprodione, prochloraz manganese chloride alternated with mancozeb and tebuconazole prophylactically. If sanitation pruning is combined with regular applications of fungicides, disease can be combated.
AFRIKAANSE OPSOMMING: Mikrofungi wat tot die genus Botryosphaeria behoort, is heterotrofiese organismes, wat patogenies op houtagtige plante kan wees. Hulle veroorsaak ernstige, en in sommige gevalle, verwoestende verliese, deur blaarnekrose, stamkankers en plantafsterwing. Die Proteaceae snyblom-industrie in Suid-Afrika maak 70% van die nasionale snyblomindustrie uit. Botryosphaeria siektes is 'n belangrike struikelblok in die produksie en handeldryf van Proteaceae, en daar is 'n ernstige behoefte om die etiologie, epidemiologie en beheer van siektes te ondersoek. Verliese van een van die belangrikste proteas, P. magnifica, beloop plaaslik 50% of meer. Die hoof doelstellings van hierdie studie was dus om die etiologie en epidemiologie van Botryosphaeria stamkankers op P. magnifica en ander Proteaceae vas te stel en metodes van siektebeheer te ondersoek. Hoewel daar 'n wye hoeveelheid inligting rakende die swam bestaan, wat in Hoofstuk I hersien is, is daar relatief min inligting oor Botryosphaeria op Proteaceae beskikbaar. Die taksonomie van Botryosphaeria benodig deeglike hersiening, en molekulêre tegnieke word benodig om spesie-identiteite op te klaar. In Hoofstuk 2 is gevind dat Phyllachora proteae, 'n blaarpatogeen van proteas, 'n Fusicoccum anamorf produseer, wat as F. proteae beskryf word. 'n Sphaeropsis-agtige synanamorf is met F. proteae geassosieer en 'n nuwe kombinasie vir P. proteae is as B. proteae in Botryosphaeria voorgestel. Die taksonomie van Botryosphaeria is, beide op die genus- as die spesievlak, in wanorde. In Hoofstuk 3 word die taksonomiese geskiedenis van Botryosphaeria hersien, en die genus word omskryf en van ander morfologies soortgelyke genera onderskei. Hoewel verskeie anamorf genera al met Botryosphaeria op grond van morfologiese waarnemings en filogenetiese analise van ITS rDNA volgorde data verbind is, word twee anamorf genera nou herken, dié met gepigmenteerde konidia (Diplodia), en dié met deurskynende konidia (Fusicoccum). Botryosphaeria proteae moet dus van Botryosphaeria uitgesluit word. Verskeie patogeniese Botryosphaeria spp. het 'n endofitiese fase in hul lewenssiklus. Hulle word dus onwetend in ander lande ingevoer waar hulle 'n gevaar vir landbou en inheemse plantegroei kan inhou. Die huidige wêreldverspreiding van Botryosphaeria spp. wat met Proteaceae geassosieer word is opgeklaar, en in Hoofstuk 4 word 'n sleutel tot die taksa wat met Proteaceae geassosieer word verskaf. Vyf Botryosphaeria spp. word met snyblom Proteaceae wêreldwyd geassosieer, naamlik B. lutea, B. protearum, B. proteae, B. ribis en B. obtusa. B. protearum word as 'n nuwe spesie beskryf. 'n Deeglike kennis van siekte-epidemiologie is noodsaaklik ten einde verliese te verminder. In Hoofstuk 5 dui ek aan dat letsels wat lei tot stamkankers, veroorsaak deur Botryosphaeria protearum op P. magnifica, in die hoofnerf of rant van blare ontstaan. Koch se postulate is uitgevoer en daar is vasgestel dat die aantal letsels wat vanuit kunsmatige inokulasies ontwikkel het korreleer met die styselvlakke teenwoordig in die blare ten tye van die inokulasie. In Hoofstuk 6 word getoon dat B. protearum as 'n endofiet in die blare van P. magnifica. In natuurlike standplase van proteas is stamkankers skaars, maar in verboude plantasies is die voorkoms hoog. Voedingsanalises dui aan dat hoër vlakke van stikstof in die blare van verboude plante in die lente voorkom, wat siekte-ontwikkeling moontlik kan bevorder. Hoë vlakke van natrium in die blare van natuurlike plante mag siekteontwikkeling beperk. Die ernstige ekonomiese verliese wat deur B. protearum veroorsaak word, maak die soektog na verbeterde metodes van siektebeheer noodsaaklik. Fungisiedtoedienings maak 'n belangrike deel uit van 'n geïntegreerde benadering tot siektebeheer. In Hoofstuk 7 dui in vitro toetse aan dat tebuconazole, benomyl, prochloraz me, iprodione en fenarimol die miseliumgroei van B. protearum effektief verminder. 'n Vermindering van 25-85% is aangetoon in die voorkoms van stamkankers in die veld, deur die toediening van fungisiedes en sanitasiesnoei. Die beste beheer is verkry deur die voorkomende toediening van benomyl, bitertanol, fenarimol, iprodione en prochloraz manganese chloride, afgewissel met mancozeb en tebuconazole, op plante in die veld. Indien sanitasiesnoei met gereelde toedienings van fungisiedes gekombineer word, kan die siekte bekamp word.

Thesis (PhD)--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: The population density of the white wax scale, Ceroplastes destructor Newstead, has increased since 1994 in certain areas of Western and parts of Eastern Cape Provinces of South Africa where citrus is grown, particularly on Citrus reticulata (Blanco). A study was conducted to investigate its morphology, biology and ecology as contributions to the development of a sound integrated management programme. Characteristics of the immature stages and adult females were described and illustrated from field-collected and slide-mounted specimens. A key to the different stages and morphometeric characteristics useful for separating them are provided. No significant differences in female fecundity were found between orchards (P > 0.05). However, fecundity varied significantly between female size classes from the same orchard (P < 0.001). Female body-size also differed significantly between orchards (P < 0.05) and was significantly positively correlated with fecundity (P < 0.01). C. destructor has one discrete generation per year in South Africa. Oviposition commenced in November and continued through to the end of December with a few females ovipositing until mid January. Population density of the second instar peaked in February while the third instar extended from March to the end of July, followed by a peak population of adults in August. Seven primary and three secondary parasitoids, as well as four predator species attacking C. destructor were identified. Aprostocetus (= Tetrastichus) ceroplastae (Girault) was the dominant species, accounting for 78.87% of the total primary parasitoids reared. Peak numbers of parasitoids and predators were synchronized with peak emergence of susceptible scale stages, indicating that the host-parasitoid/predator system contained a density-dependent regulatory mechanism. Key mortality factors varied slightly between two of the orchards. Key stage mortality determined from a cohort life table was generally in the third instar (LIlI) and preovipositional female (POF) stage. Significant density-dependent mortality factors were demonstrated for the first instar (LI) and PDF stage. Dispersal of C. destructor is by first instar nymphs and the numbers caught on a series of yellow sticky traps varied significantly between crawler densities at the source, trap distances and trap directions from the source (P < 0.001). The numbers caught were positively correlated to the initial crawler density at the source (P < 0.01), suggesting that dispersal was density dependent. Trap distance and the numbers caught were inversely correlated (P < 0.01). Evaluation of effects of different densities of C. destructor on growth, survivorship and reproduction of scales as well as on leaf bearing ability of trees and area of leaf surface covered with sooty mould fungus was carried out on naturally infested Syzygium (= Eugenia) malaccensis (L.) plants. Scale body size and fecundity were inversely related to scale density (P < 0.01), suggesting density-dependent intraspecific competition. Scale survivorship generally declined with increasing density whereas scale parasitism and predation were positively correlated with density (P < 0.05). At high scale densities production of new leaves was significantly reduced (P < 0.01), reducing the resource base for subsequent generations of scale. Scale density and leaf area covered with sooty mould fungus were significantly positively correlated (P < 0.05). The toxicity of four synthetic insecticides against the three immature stages of C. destructor and of eight insecticides against the parasitoid A. ceroplastae was evaluated. Development of the first and second instars of C. destructor was completely arrested by the chemicals. Female fecundity, fertility and body sizes of survivors of treatments applied at the LIII stage were not significantly affected by any of the chemicals (P > 0.05). All the chemicals exhibited high toxicity to A. ceroplastae and hence are not recommended for integrated management of C. destructor in citrus orchards where A. ceroplastae plays an important role.
AFRIKAANSE OPSOMMING: Die populasiedigtheid van die witwasdopluis, Ceroplastes destructor Newstead, het sedert 1994 toegeneem in sekere gebiede van die Weskaap en Ooskaap provinsies van Suid-Afrika waar sitrus verbou word, veralop Citrus reticulata (Blanco). 'n Studie van hierdie insek se morfologie, biologie en ekologie is onderneem as bydrae tot die ontwikkeling van 'n geïntegreerde bestuursprogram. Die karaktertrekke van die onvolwasse stadia en die volwasse wyfies is beskryf en geïllustreer vanaf eksemplare wat in die veld versamel is en op g1asplaatjies gemonteer is. 'n Sleutel vir die verskillende stadia en morfometriese kenmerke wat nuttig is om hulle te onderskei, word voorsien. Geen beduidende verskille in die vrugbaarheid van wyfies van verskillende boorde is gevind nie (P < 0.05). Vrugbaarheid het egter betekenisvol verskil by die verskillende grootteklasse van wyfies uit dieselfde boord (P < 0.001). Die liggaamsgrootte van wyfies uit verskillende boorde het betekenisvol verskil (P < 0.05) en was betekenisvol positief gekorreleer met vrugbaarheid (P < 0.01). C. destructor het een generasie per jaar in Suid-Afrika. Eierlegging het in November begin en aangehou tot aan die einde van Desember, met enkele wyfies wat nog tot in middel Januarie eiers gelê het. Die populasiedigtheid van die tweede instar het 'n hoogtepunt in Februarie bereik, terwyl die derde instar van Maart tot aan die einde van Julie geduur het, gevolg deur 'n piekbevolking van volwassenes in Augustus. Sewe primêre en drie sekondêre parasitoïde asook vier predator spesies wat C destructor aanval, is geïdentifiseer. Aprostocetus (=Tetrastichus) ceroplastae (Girault) was die dominante spesies wat 78.87% van die totale aantal primêre parasitoïde wat uitgeteel is, uitgemaak het. Die pieke in die getalle van parasitoïde en predatore was gesinchroniseer met pieke in die verskyning van die gevoelige stadia, wat dui op die aanwesigheid van 'n digtheidsafhanklike regulatoriese meganisme. Die sleutel mortaliteitsfaktore het effens gevarieer tussen twee van die boorde. Die sleutelstadium van mortaliteit, soos bepaal m.b.v. 'n kohort lewenstabel, was gewoonlik die derde instar (LIlI) en die preoviposisionele wyfie (POW). Betekenisvolle digtheidsafhanklike mortaliteitsfaktore IS aangetoon vir die eerste instar (LI) en die POW. Die verspreiding van C.destructor vind plaas deur die eerste instar nimfe en die getalle wat op 'n reeks van taai geel valle gevang is, het betekenisvol gewissel volgens kruiperdigthede by die bron, asook die afstand en rigting van die valle vanaf die bron (P < 0.001). Die getalle wat gevang is, was positief gekorreleer met die aanvanklike kruiperdigtheid by die bron (P < 0.01), wat daarop dui dat verspreiding digtheidsafhanklik was. Die afstand van die valle en die aantal wat gevang is, was omgekeerd gekorreleer (P < 0.01). 'n Evaluering van die invloed van verskillende digthede van C. destructor op die groei, oorlewing en reproduksie van dopluise, asook die vermoë van bome om blare te dra en die area van die blaaroppervlak wat met roetskimmel besmet is, is uitgevoer op plante van Syzygium (= Eugenia) malaccensis (L.) met 'n natuurlike besmetting. Die liggaamsgrootte en vrugbaarheid van die dopluise was omgekeerd gekorreleer met hulle digtheid (P < 0.01), wat dui op digtheidsafhanklike intraspesifieke kompetisie. Die oorlewing van die dopluise het oor die algemeen afgeneem met toenemende digtheid, terwyl parasitisme en predasie positief gekorreleer was met digtheid (P < 0.05). By hoë dopluisdigthede het die produksie van nuwe blare betekenisvol afgeneem (P < 0.01), wat die hulpbronbasis vir daaropvolgende generasies van dopluise verswak. Die dopluisdigtheid en blaaroppervlak wat met roetskimmel bedek was, was positief gekorreleer (P < 0.05). Die toksisiteit van vier sintetiese insektemiddels teenoor die drie onvolwasse stadia van C. destructor en van agt insektemiddels teenoor die parasitoïd A. ceroplastae is geëvalueer. Die ontwikkeling van die eerste en tweede instars van C. destructor is heeltemal stopgesit deur die middels. Die fekunditeit, fertiliteit en liggaamsgrootte van wyfies wat toedienings op die LIIl stadium oorleef het, is nie betekenisvol ge-affekteer deur enige van die middels nie (P < 0.05). Al die middels was baie toksies teenoor A. ceroplastae en word dus nie aanbeveel vir die geïntegreerde bestuur van C. destructor waar A. ceroplastae 'n belangrike rol speel nie.

A new selective medium (TB-CEN) was developed for isolating Thielaviopsis basicola, cause of black root rot of tobacco, from soil. TB-CEN medium contains etridiazol and nystatin to inhibit the growth of undesired fungi, and unautoclaved extract from carrot to selectively enhance for the growth of T. basicola. Inoculum and/or population densities of T. basicola in five burley tobacco fields were 74-166 propagules per g of soil, and 0-12 propagules per g of soil in three other burley fields. Inoculum and/or population densities of T. basicola in 12 flue-cured and 2 sun-cured tobacco fields were 0-26 propagules per g of soil, and 101 and 402 propagules per g of soil in two other flue-cured fields. Environmental factors apparently had a strong effect on black root rot development, since root rot and plant stunting were severe in two burley fields that had 148 and 158 propagules per g of soil, but were not severe in the two flue-cured fields that had 101 and 402 propagules per g of soil. All of the cultivars planted in the four fields were susceptible. Black root rot was the major disease associated with the stunting of tobacco plants in the burley region of Virginia, but not in the flue- and sun-cured regions. No evidence was found to indicate that endomycorrhizae were involved in tobacco stunting in Virginia. T basicola inoculum density-disease severity studies were conducted both in soil-temperature tanks and in the field. Tobacco seedlings were grown in temperature tanks (20-23 C) for 30-31 days in naturally infested field soil (pH 6.5). For all cultivars tested (Burley 21, NC95, and Va Gold), the mean percent of roots that were rotted increased significantly (P=0.001) as inoculum density increased (R² range for regressions=0.93-0.97). Severe levels of root rot occurred at inoculum densities of 50-200 propagules per g of soil. Significant (P=0.01) reductions in plant growth occurred at inoculum densities as low as 5-10 propagules per g of soil. In a study conducted on a commercial burley tobacco (cv. B21-Ky10) field, inoculum densities of 150 and 683 propagules per g of soil were associated with moderate and severe levels of black root rot, respectively. Differences between soil-temperature tank and field studies appeared to be due to variations in environmental- and host-related factors. In another burley field study, the fungicide imazalil, which completely inhibited the growth of T. basicola when amended into agar media at a concentration of 1.0 μg a.i./ml, failed to control black root rot when it was added to transplanting water (50 ml/plant) at concentrations as high as 1,500 μg a.i./ml.
Ph. D.
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Abstract This chapter describes the different diseases and pests that affect yams and various methods for their control. It particularly covers the following aspects: field fungal diseases; postharvest fungal diseases; specific fungal diseases; control of fungal diseases; bacterial diseases; viral diseases; physiological disorders; insect pests; and nematode pests.

This working paper predicts the fiscal and public health outcomes from a change in the excise tax structure for cigarettes in Ghana. More than 5,000 people are killed by diseases caused by tobacco every year in Ghana (Tobacco Atlas 2018). Currently the country has a unitary tax administration approach, with a uniform ad valorem tax structure on all excisable products, including tobacco. However, the ECOWAS directive on tobacco control, in line with the WHO Framework Convention on Tobacco Control (WHO 2003), recommends a simple tax structure – using a mixed excise system with a minimum specific tax floor to overcome the limitations of an ad valorem system on tobacco products, especially cigarettes. The study therefore simulates mixed tax policy interventions, and assesses their effect on government revenue and public health relative to the current ad valorem tax system. Primary data collection of tobacco prices in three geographical zones of the country was conducted in February 2020, across both rural and urban localities. This was supported with secondary data from national and international databases. Based on the assumption that Ghana adopts a mixed tax structure, the simulation shows that, if the government imposes a specific excise tax of GH₵4.00 (US$0.80) per pack in addition to the current ad valorem rate of 175 per cent of the CIF value, the average retail price of a cigarette pack would increase by 128 per cent, cigarette consumption decrease by 27 per cent, tobacco excise tax revenue increase by 627 per cent, and overall tobacco-related government tax revenue increase by 201 per cent.1 Additionally, there would be significant declines in smoking prevalence (3.3%), smoking intensity (1,448 cigarettes per year), and 3,526 premature smoking-related deaths would be avoided. The paper advocates for a strong tax administration and technical capacity, with continuous commitment by the government to adjust the tax rate in line with the rate of inflation and per capita income growth.