Spelling suggestions: "subject:"diseases anda tests"" "subject:"diseases anda pesar""
611 |
Molecular characterization of cassava brown streak viruses in MozambiqueAmisse, Jamisse Jose Goncalves 03 March 2014 (has links)
Cassava brown streak disease (CBSD) caused by two distinct ssRNA virus species (CBSV and UCBSV of genus Ipomovirus, family Potyviridae) and transmitted by whitefly (Bemisia tabaci), is a major constraint to cassava production in Africa, including Mozambique. In this research, two studies were conducted. First, in order to monitor the incidence, severity and geographical distribution of cassava brown streak disease and associated viruses in Mozambique, field surveys were performed in six cassava major growing provinces. A total of one hundred and fifteen fields and one hundred and forty six fields were surveyed in 2010 and 2012, respectively. The disease was only found in three of six provinces namely Zambezia, Nampula and Cabo Delgado. The CBSD incidence was highest (61.3% and 82.2% in 2010 and 2012, respectively) in Zambezia and lowest (23.6% and 35.1% in 2010 and 2012, respectively) in Cabo Delgado, with cultivars such as Cadri and Robero showing the highest susceptibility to CBSD, while Likonde and Amwalikampiche had relatively low CBSD incidence, illustrating some tolerance to the disease. The results, when compared to previous surveys conducted in 1999 and 2003, demonstrated that the disease is increasing, and replanting new fields with disease-affected cuttings could be responsible for the spread. The second aim of the study was to investigate the genetic diversity of Cassava brown streak viruses, based on analysis of partial sequences of the coat protein gene, in Mozambique. Collections of CBSD-symptomatic leaves were done between June 2010 and June 2012. Diagnostic RT-PCR, using specific primers to screen for the two species, revealed for the first time the presence of Uganda cassava brown streak virus (UCBSV) in Mozambique. UCBSV was found in mixed infections with CBSV, and only confined to a single province of Zambézia, while CBSV species were widely distributed. The phylogenetic analysis revealed two subgroups within CBSV, which were 6.7% divergent in nucleotide sequence. The heterogeneity observed among CBSV isolates in Mozambique suggests that in the future studies more sampling is needed to characterize strains and variants. Addtionally, sequencing of the full CP sequence of CBSaVs isolates is required, which may reveal even more diversity. Infectivity assays of cassava brown streak viruses (CBSV and UCBSV) were established using the host indicator plant Nicotiana benthamiana. Plant sap was extracted from infected cassava leaves and inoculated into N.benthamiana plants. CBSD-like symptoms were observed, and RT-PCR revealed the presence of CBSV in all samples, except for one which was co-infected with UCBSV and CBSV. This study provided further evidence that CBSaVs are efficiently transmitted to N.benthamiana. There is scanty information on alternative hosts, therefore more research is needed to identify other potential hosts of CBSaVs in order to develop an effective strategy to control CBSD.
|
612 |
Developing a sensitive, high-throughput tool for rapid detection of agronomically important seed-borne pathogens of tomatoCarmichael, Deborah Jo 31 January 2013 (has links)
The limited specificity, sensitivity and multiplex capacity of detection techniques currently available
for important seed-borne pathogens of tomato is a significant risk for the global tomato trade and
production industry. These pathogens can be associated with seed at low concentrations but, due to
their highly virulent nature, these low levels can be sufficient to infect germinating seedlings and
spread to neighbouring plants and fields, potentially causing epidemics and economic losses. In this
study, detection techniques currently available for phytodiagnostics were evaluated for the capacity
to accurately detect and identify five agronomically important seed-borne pathogens of tomato:
Pepino mosaic virus (PepMV), Tomato mosaic virus (ToMV), Clavibacter michiganensis subsp.
michiganensis (Cmm), Xanthomonas campestris pv. vesicatoria and Pseudomonas syringae pv.
tomato. A prototype diagnostic microarray was also designed in an attempt to develop a tool that
could simultaneously detect these five seed-borne pathogens from a single sample. Viral detection
based on serological techniques was rapid, accurate and reliable but only detected a single pathogen
per assay and required supplementary bioassays to indicate the viability of detected viral pathogens.
Selective media plating for bacterial detection demonstrated unreliable recovery of targeted
bacteria from infected seed and leaf samples and required supplementary tests to validate the
identity of presumptive positives. Assays were lengthy, laborious and sometimes too ambiguous for
accurate diagnosis of bacterial pathogens. Nucleic acid-based technologies demonstrated improved
sensitivity and specificity for detection of targets from pure culture, leaf and seed extracts,
compared to conventional and serological methods, yet also required supplementary bioassays or
media assays to validate the viability of detected pathogens. Amplification efficiency however, was
affected by the presence of PCR inhibitors and despite positive detection, variable banding intensity
in electrophoretic analysis of amplified products necessitated the use of reference cultures to
validate diagnosis. The developed microarray incorporated 152 pathogen-specific and control probes
to facilitate diagnosis and taxonomic classification of detected pathogens. The array was challenged
with pure culture extracts of the five target pathogens, selected related and non-target, unrelated
pathogens of tomato. Positive detection of each of the pathogens was demonstrated but the
production of hybridisation signals was highly variable and extremely sensitive to minor technical
differences. Each of the five pathogens were successfully detected in combination proving that
different classes of seed-borne pathogens could be detected from a single sample using the
developed microarray. This prototype microarray has good potential for phytodiagnostic screening
of the five targeted pathogens, and further validation, optimisation and extension for testing tomato
seed samples may facilitate incorporation of this array into standard diagnostic protocols.
|
613 |
Evaluation of resistance to tomato curly stunt virus in tomatoDias, Katia 31 January 2013 (has links)
Solanum lycopersicon (the cultivated tomato) is a commodity of great economic importance in South
Africa (SA) as well as worldwide. A destructive viral disease known as Tomato curly stunt virus,
ToCSV-[ZA:Ond:98], belonging to the genus Begomovirus has negatively impacted on tomato
production in SA. This has brought about the need to develop resistant cultivars to ToCSV. Since all
cultivated tomato cultivars are susceptible to ToCSV, resistance genes against the virus found in wild
tomato plant species have been introgressed into the cultivated tomato by plant breeding
techniques. Wild relatives of tomato were adapted to many pathogens (including viruses) as well as
stresses from the surrounding environment. During breeding for improved fruit quality and
increased yield, the gene networks giving rise to many biotic and abiotic stress resistances have been
lost leaving the domesticated tomato extremely susceptible. Plant breeders have reconstituted
some of the gene networks into the cultivated tomato that provide tolerance to stresses including
viruses. They have achieved this by the help of marker-assisted selection (MAS), where the
associated marker is used as an indirect selection criterion. This is an important process in
commercial breeding programs as it allows for a speedy selection of selected traits in the
development of tomato hybrids. The defence response to abiotic stresses in plants includes the
expression of heat shock proteins (HSPs) that function as stress response proteins, molecular
chaperones and proteases which repair or degrade damaged proteins.
The objective of this study was to elucidate the type of resistance mechanism of a tomato inbred
line (TAM), to ToCSV. Since TYLCV-IL shows 77% nucleotide identity with ToCSV, molecular markers
already established for the detection of resistance genes for TYLCV-IL were used to screen TAM.
The inbred line, TAM, was screened for the absence of any of the known resistant genes to TYLCV-IL
using molecular markers already established for the screening of TYCLV-IL resistance genes. TAM
was crossed with susceptible cultivar, Rooikhaki, to produce F1 hybrids. These F1 hybrids were
selfed to produce an F2 population. Infection trials using ToCSV were conducted using TAM inbred
line, F1 hybrids and the F2 population. Since TAM did not have any of the known resistance genes to
TYLCV-IL, a possible novel resistance source to ToCSV was speculated. A clue to the resistant
mechanism against ToCSV resistance in TAM was indicated by the segregation patterns of the F2
population after inoculation with ToCSV. The results suggest that the resistance is under the control
of partially dominant resistant genes. The level of resistance of commercial South African tomato cultivars (Tyler and Tovi-star) against
TYLCV-IL was investigated. The heat shock protein (HSP) profiles of these two SA lines including
susceptible cultivar, Rooikhaki, were treated with abiotic stresses (salt and heat) and results were
compared with a similar study conducted with TYCLV-IL resistant and susceptible tomato cultivars.
Heat shock protein 70 accumulation patterns were similar in that HSP70 was more stable in the
resistant cultivars throughout the application when abiotic stresses were applied to the SA resistant
and susceptible tomato cultivars as compared to Israel resistant and susceptible breeding lines. A
relation between infection severity and the pattern of HSP expression was found. A higher level of
HSP 70 in resistant tomato plants could contribute to a lower symptom severity phenotype.
|
614 |
Review of distribution, biology and control methods of six major insect pests of corn in the United StatesZanabria, Eulogio R January 2010 (has links)
Digitized by Kansas Correctional Industries
|
615 |
Genetic studies of field reaction to wheat soilborne mosaic virusBrunetta, Dionisio January 2011 (has links)
Photocopy of typescript. / Digitized by Kansas Correctional Industries
|
616 |
Techniques for isolating Phytophthora megasperma var. sojae from soil and plant tissueConn, Keith A January 2011 (has links)
Photocopy of typescript. / Digitized by Kansas Correctional Industries
|
617 |
Epidemiological studies on Maize chlorotic mottle virusBockelman, Donald L January 2011 (has links)
Vita. / Digitized by Kansas Correctional Industries
|
618 |
Variation in branch growth characteristics of Pinus contorta infected with Arceuthobium americanumLarsen, Lynn Anne 01 January 1981 (has links)
Arceuthobium americanum is a flowering plant which parasitizes Pinus contorta (Lodgepole pine). This study examined branch performance of P. contorta infected to varying degrees with A. americanum.
|
619 |
Shoot Structure of Boschniakia hookeri Walpers (Orobanchaceae)Babur, John Leland 18 August 1995 (has links)
Boschniakia hookeri Walpers has been found to parasitize the roots of Gaultheria shallon Pursh, Arctostaphylos uva-ursi (l.) Spreng, and Vaccinium ovatum Pursh, all members of the Ericaceae. This is the first documented report of the parasitism of Vaccinium ovatum. The subterranean shoot of B. hookeri originates endogenously from the perennial tubercle of the parasite. The shoot has an eustele, composed of collateral vascular bundles, arranged in four composite fronts and separated by four wide 'leaf gaps.' Pits on metaHylem vessels range from nearly circular to laterally elongated. Rll vessel members have simple perforations. Ouerall, the Hylem of subterranean shoots contained relatively few tracheary elements. Phloem is abundant, with radial series of sieve tube members that have simple sieve plates. Brachysclereids forming large clusters are positioned to both the inside and outside of the vascular bundles. Abundant stomata are present and frequently raised above the shoot surface. RHillary buds along subterranean shoots are capable of producing flowers or branch shoots. Considerable secondary growth occurs in maintained shoots below developing branch shoots. This manifested by the additional production of secondary Hylem and phloem, and the formation of a protective cuticular epithelium. This study of B. hookeri supports the view that the short and fleshy character of the subterranean shoot, increased presence of phloem, reduction of leaves to scales, and a perennial nature are specializations associated with the holoparasitic mode of life.
|
620 |
Celery blackheart occurrence during growth as influenced by light quality and nutrition.Guévin, José. January 1981 (has links)
No description available.
|
Page generated in 0.0504 seconds