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HETEROTIC PATTERNS AND COMBINING ABILITY OF CIMMYT EARLY MAIZE (ZEA MAYS L.) LINES UNDER MOISTURE AND NITROGEN STRESS AND OPTIMAL CONDITIONSMawere, Sebastian Shangwa 08 April 2009 (has links)
Since the initiation of a product oriented breeding programme aimed at improving maize for
drought prone mid altitudes of southern Africa, CIMMYT developed several inbred lines and
single cross hybrids using pedigree selection methods, with emphasis on earliness, drought
and low nitrogen stress tolerance. This resulted in increased volumes of seed inventories.
Sixteen inbred lines and 71 single cross hybrids were crossed to three (single cross) testers,
CML312/CML442 and CML505/CML509 (heterotic group A) and CML395/CML444
(heterotic group B) and evaluated as two separate experiments for general and specific
combining ability in contrasting environments (optimal, managed drought and nitrogen
stressed). The objective was to asses the relative importance of general combining ability
(GCA) and specific combining ability (SCA) in identifying promising early maturing maize
lines, single crosses and testers that could tolerate drought and nitrogen stress conditions,
thus simulating prevailing conditions in most resource poor farmersâ fields in the mid
altitude environments of southern Africa.
The first experiment consisted of 48 experimental crosses and 24 additional crosses. Six
trails were planted in a lattice (Alpha 0,1) with eight plots per incomplete block. The second
experiment consisted of 213 experimental crosses and additional 27 double crosses and
synthetics. Five trials were planted in a lattice (Alpha 0,1) with 12 plots per incomplete
block. Trials were planted under optimal conditions at ART farm, Rattray Arnold and
Kadoma, nitrogen stressed conditions at Harare and drought stressed conditions at Chiredzi
in Zimbabwe in 2006.
Data was collected on grain yield (GY), anthesis dates (AD), anthesis silking interval (ASI),
plant heights (PH), ears per plant (EPP), and leaf senescence (SEN). Data was analysed first
according to Lattice (alpha 0.01) design using computer software Fieldbook, for the general
performances of all crosses for all traits. Line x tester analysis for general combining ability and specific combining ability was performed using SAS and AGROBASE II computer
software. The first experiment identified heterotic group B line 15 as superior with a GCA value of
0.56. The line had a SCA value of 0.21 with early maturing (heterotic group A tester)
CML505/CML509. The hybrid had grain yield of 7.9t/ha and 1.3t/ha across optimal and
stress environments respectively and was early maturing (69 days) (silking anthesis days).
In the second set of materials heterotic group A single crosses 51, 37, 55, and 7 had good
general combining ability above 0.64. Heterotic group B single crosses 11, 38, 39 and 22 had
good specific combing ability with CML505/CML509. The hybrid combinations ranged
between 6.1-7.4 t/ha across optimal environments and 0.8-1.4 t/ha across stressed
environments. These hybrids were very early (AD 64-66 days), could be evaluated in wide
environments for GCA with heterotic group A lines and single crosses in order to identify an
early maturing group B tester. CML505/CML509 classified the early maturing lines and
single crosses into heterotic groups better than CML312/CML442.
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VEGETATION CLASSIFICATION OF THE UNIVERSITY OF THE FREE STATE CAMPUS, BLOEMFONTEINNthejane, Maboee 16 May 2008 (has links)
The aims of this study were to survey, classify, describe and ecologically interpret the
natural plant communities of the University of the Free State campus in Bloemfontein. A further aim was to apply the urban biotope mapping technique to the campus so that
ecological information may be availed to decision makers at the University in an easily
accessible format.
The phytosociological study was based on Braun-Blanquet procedures. A total of 222
reléves were classified using TURBOVEG, TWINSPAN and MEGATAB. Ordination
using the DECORANA ordination algorithm was also applied to the floristic data in order
to determine the relationship between the vegetation units and environmental variables.
The vegetation was classified into 5 Major Grassland Communities and 2 Major Wetland
Communities. All the vegetation units and sub-units were ecologically interpreted and
described.
Biotope mapping was conducted on the campus using a German technique that has
been used in the city of Potchefstroom after being customized to South African
conditions. The resultant biotope map showed that most of the space on the campus is
taken up by 3 biotope types, namely the built-up area with its intensively managed lawns
and gardens and planted trees mainly on the eastern side of the campus, the extensively
managed open spaces (natural grassland) mainly in the middle and to the west and the
intensively managed sports fields. This study also contributes to the building up of
scientific knowledge about the Grassland Biome.
Recommendations are made as to how the vegetation on the campus and in other
increasingly urbanizing areas of the Grassland Biome may be managed in a manner that
is ecologically sound and that meets amenity needs as well.
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GENETIC VARIATION IN CLIVIA MINIATA VAR. CITRINAGagiano, Anthia 13 June 2007 (has links)
The genus Clivia is from the African tribe Haemanthaceae and a member of the
family Amaryllidaceae. Clivia is endemic to southern Africa. Yellow Clivia are
mutations of the orange-red standard forms that have appeared spontaneously in both
wild and garden populations. Yellow Clivia plants are rare and desirable and were
described as Clivia miniata var. citrina. Hobbyists from around the world trade in
these ornamental plants initiating entire enterprises. Although the yellow form occurs
naturally, many yellow clones have arisen through cultivation. Clones passed on from
breeder to breeder have acquired different names. For directed breeding purposes in a
thriving industry it is important to identify genetically similar plants. The aims of this
study were to evaluate existing microsatellites for Clivia miniata var. citrina, to
determine if AFLP analysis can distinguish among different plants within the genus
Clivia and to determine genetic relatedness between different plants of âVicoâ,
âGiddyâ and âNatal Yellowâ cultivars.
Previous studies done on Clivia include RAPD analysis and SSR analysis for Clivia.
Work done in this study presents a first report of AFLP and SSR fingerprint analyses
on C. miniata var. citrina. SSR fingerprint analysis revealed that the existing four
SSR primer combinations were not applicable for studies on C. miniata var. citrina.
AFLP analysis was optimised using a total of 28 EcoRI / MseI primer combinations.
Primer combinations were evaluated using six randomly selected Clivia plants based
on number of generated fragments, ability to score generated fragments, ability to
detect polymorphism and level of polymorphic fragments. Fragments generated using
EcoRI+3 primers in combination with Mse+4 primer combinations conformed to the chosen criteria. Primer combinations E-ACC with M-CATC, E-AGC with M-CATC
and E-AGC with M-CTGG were selected for further studies on Clivia.
AFLP analysis using three preselected primer combinations on 72 Clivia plants was
successful in detecting genetic diversity and determining genetic relationships within
closely related cultivated Clivia plants. Relatively high levels of genetic diversity
(35%), as expected from known pedigree and species data, existed among Clivia
plants. Genetic diversity within C. miniata and C. miniata var. citrina plants was high
at 27%. Plants available for scrutiny were all genetically distinct. However, based on
known pedigree data, names allocated to plants might not be truly representative of
the true origin of the plants (e.g. Vico Meristem plants). Material obtained from
different breeders could be distinguished at DNA level (e.g. âGiddyâ and âNatal
Yellowâ cultivars).
AFLP analysis revealed that different flower coloured plants (Apricot, Blush, Peach,
Orange and Yellow) as well as plants from the same geographic areas were distributed
together throughout the dendrogram with only a few of a certain colour grouping
together. Known Group 1 Yellow and Group 2 Yellow were also present throughout
the entire dendrogram, although the majority of known Group 1 Yellow plants
grouped together.
Clustering of the different species of the genus Clivia agreed with known pedigree
data and hybrids included with their parents clustered according to known pedigree
data. The phylogenetic relationships of natural populations of C. miniata indicated that all
C. miniata plants shared a common ancestor. Clivia miniata from the same
geographical area grouped together in the cladogram. More data would be required to
prove these observations for all Clivia. Taxonomic status of the C. miniata var. citrina
would depend on the monophyly of yellow Clivia plants. Orange flowered forms
should be included to determine the validity of the current taxonomic status of these
groups.
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INHERITANCE OF FREEZING STRESS IN SOUTH AFRICAN POTATO (SOLANUM TUBEROSUM) GERMPLASMVenter, Carien 13 June 2007 (has links)
a) Frost damage caused by freezing stress is a major problem for potato
growers in some parts of South Africa. In this study two South African potato
cultivars, Darius and BP1, were compared for yield loss due to freezing stress
during the late vegetative, early reproductive and late reproductive growth
stages. The cultivars were subjected to temperatures of -2°C and -4°C for three
and six hours. Significant genotype x treatment interactions were observed for
stem and leaf damage in both cultivars. Genotype x treatment interactions were
also significant for yield and some of the yield components. The cultivars were
shown to be the most sensitive to freezing stress during the early reproductive
growth stage, followed by the late reproductive growth stage. BP1 was identified
to be more sensitive to freezing stress in the early and late reproductive growth
stages. Stem damage was positively associated with tuber number, whereas
leaf damage correlated with tuber mass.
b) Electrophoretic separations of proteins were done to study the polymorphisms
as a result of freezing stress at -2°C and -4°C for three and six hours. The plants
were treated during the late vegetative, early reproductive and late reproductive
growth stages. The freezing treatments caused large variability in the protein
profiles of Darius. Various new protein bands developed while others
disappeared. Differences in the intensity of the bands were also recovered. A
protein band of approximately 29/33 kDa developed consistently at -2°C
treatment during the early reproductive growth stage. Plants subjected to -4°C
for three and six hours developed protein bands of approximately 40/49 kDa
during the three growth stages tested.
c) In this study fourteen selected C1 progenies of a Caren x Bravo cross with the
two parents were included, subjected to freezing temperatures of -4°C for four
hours to study the heritability of potato yield under freezing stress conditions.
The plants were treated during the early reproductive growth stage (the most
sensitive growth stage). Freezing stress (-4°C) treatment during the early
reproductive growth stage reduced potato yield, tuber diameter, tuber mass and
number of tubers significantly. Significant genetic variability was found among
offspring for leaf damage, yield, tuber diameter, tuber mass and number of tubers
under freezing stress conditions. Tuber diameter (r=0.56), tuber mass (r=0.86)
and number of tubers (r=0.75) were significantly correlated with yield for
percentage damage caused by freezing stress. The freezing treatment had no
significant effect on the correlation coefficients between potato yield and yield
components. Relatively high broad sence heritabilities were recorded for potato
yield (h2 =0.74) tuber diameter (h2=0.91), tuber mass (h2=0.87) and number of
tubers (h2=0.79).
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Genetic variability for Russian wheat aphid, Diuraphis noxia resistance in South African wheat genotypesTolmay, Vicki Louise 13 June 2007 (has links)
Near-isogenic genotypes 1684/Tugela and 2199/Tugela containing D. noxia resistance ex SA1684
[PI 137739 (Dn1)] and SA 2199 [PI 262660 (Dn2)] were studied in terms of antibiosis, antixenosis
and tolerance, population development of D. noxia under field conditions and the probing behaviour
of D. noxia. The susceptible cultivars Betta and Tugela were included for comparison. A sister line
of 1684/Tugela, the commercial cultivar TugelaDn, was used to characterise the constitutive and
induced components of the resistance to D. noxia. Mechanism of resistance studies showed
antibiosis present in both resistant genotypes. No antixenosis was recorded in 2199/Tugela, with
only low levels present in 1684/Tugela. 1684/Tugela was able to retain the same leaf area and
plant dry mass as 2199/Tugela under a much higher aphid infestation level and both lines were
significantly more tolerant than Betta, but did not differ from Tugela. Betta and Tugela showed
higher infestation levels, both in terms of percentage tillers infested and number of D. noxia per
tiller, and lower yields than the resistant genotypes. The initial rapid increase of D. noxia
populations started in the beginning of October and peak aphid numbers were in early to mid-
November. EPG data reflecting the probing behaviour of D. noxia revealed distinct differences
between the resistant cultivars and the susceptible Betta and Tugela. The influence of resistance
in 1684/Tugela and 2199/Tugela on the probing behaviour of D. noxia is different indicating that
they contain two different genes, with different modes of action. While resistance in 1684/Tugela
was generally reflected by disturbances in phloem activity, the resistance in 2199/Tugela was
associated with a high number of short probes denoting some host recognition or epidermal factor
involved in the resistance. Constitutive resistance in TugelaDn influenced the time taken by D.
noxia to reach sustained phloem feeding. There was no evidence of surface or epidermal factors
influencing probing behaviour in this genotype. D. noxia probing on induced resistant TugelaDn
was characterised by a reduction in phloem activities on preinfested plants. D. noxia feeding on five
day induced resistant plants showed more E2 fractions shorter than ten minutes and fewer E2
fractions longer than 60 minutes indicating a reduction in the ingestion of nutrients. In the case of
both constitutive and induced resistance, initiation of phloem ingestion appears easier on
susceptible Tugela with a higher number of single phloem salivation periods on the resistant
genotype. Yield data for five susceptible and 15 resistant cultivars was analysed quantifying the
percentage yield retained under severe infestation. Cultivars with D. noxia resistance from the
same donor accession did not react in a similar way, neither was there any indication that they
show the same measure of compensation for D. noxia damage. Compensation for aphid
infestation was observed in some of the cultivars where higher yields were recorded from some
infested cultivars than from cultivars kept aphid free throughout the trial. In the 2000 season, the
variation in percentage yield retained between resistant cultivars equalled 63.2%, in the 2001
season 85.0 % and in the 2003 season 41.3%. This study confirms that the interaction between
the aphid and each host genotype is unique. The expression of host plant resistance is not only
dependent on the donor accession utilised, but also the genetic background in which it is deployed.
Furthermore, environmental factors can also significantly influence the performance of host plant
resistance to D. noxia.
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BIOCHEMICAL AND MOLECULAR ANALYSIS OF THE EARLY RESPONSE OF TRITICUM AESTIVUM INFECTED WITH PUCCINIA STRIIFORMIS F.SP TRITICIvan Zyl, PJL 28 June 2006 (has links)
Not available
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ASSESSMENT OF CUP QUALITY, MORPHOLOGICAL, BIOCHEMICAL AND MOLECULAR DIVERSITY OF COFFEA ARABICA L. GENOTYPES OF ETHIOPIABekele, Yigsaw Dessalen 04 July 2006 (has links)
The genetic diversity of C. arabica genotypes collected from the northwestern and
southwestern parts of Ethiopia was evaluated using morphological, biochemical and
molecular (AFLP and SSR) markers. The objectives of the study were to (1) estimate
the level of genetic variation among currently grown C. arabica genotypes, (2)
estimate the level of associations among agro-morphological characters, coffee
quality traits and green bean biochemical compounds, (3) compare the level of genetic
variation between coffee genotypes collected from the northwestern and southwestern
parts of Ethiopia and (4) compare the efficiency of AFLP and SSR markers in
detecting genetic variation in C. arabica.
Results of diversity analysis using nine qualitative and 18 quantitative morphological
characters indicated the presence of substantial variability among evaluated coffee
genotypes. Genotypes were significantly different for all 18 quantitative
morphological characters. Higher Shannon-Weaver diversity indices ranging from
0.401 to 0.989 were recorded for nine qualitative morphological characters. Cluster
analysis using qualitative, quantitative and a combination of qualitative and
quantitative characters classified genotypes into two groups. Qualitative characters
failed to independently distinguish seven of the genotypes. Principal component
analysis grouped 18 quantitative characters into 15 principal components and the first
four explained 82.3% of the entire variability among genotypes. Average green bean
yield per tree and bean length were important for the variation explained in three of
the first four principal components.
Correlation analysis performed among 18 agro-morphological characters indicated
positive associations between average green bean yield per tree and all other
characters. Average green bean yield per tree had statistically significant correlations
with percentage of bearing primary branches per tree, bean weight, canopy and trunk
diameters, tree height, bean length and thickness, internode lengths of orthotropic and
primary branches and fruit and petiole lengths. Broad sense heritability varied from 38% for bean thickness to 94% for bean weight and number of secondary branches
per tree. Average green bean yield per tree, canopy diameter, tree height and bean
weight had higher genetic coefficients of variation and broad sense heritabilities.
These characters were positively and significantly correlated, allowing simultaneous
improvement of these traits.
Genotypes were evaluated for variability in four cup quality traits (acidity, body,
flavour and overall standard) and four green bean physical characters (bean shape,
size, uniformity and weight). Considerable variation was observed among genotypes
both for cup quality as well as green bean physical characters. Of all the genotypes,
AD0691 and AD1691 had both desirable cup quality and green bean physical
characters. Cluster analysis performed using cup quality and green bean physical
characters, classified genotypes into two groups. Genotypes were not clustered
according to collection regions. All cup quality traits were positively and significantly
correlated and correlation coefficients ranged from 0.69 to 0.93. Positive correlations
were observed among desirable cup quality and green bean physical characters
indicating that cup quality and green bean physical characters can be improved
simultaneously.
Genotypes were evaluated for green bean caffeine, chlorogenic acids, sucrose and
trigonelline content variability. Analysis of variance indicated significant differences
among genotypes for all biochemical compounds. Green bean caffeine, chlorogenic
acids, sucrose and trigonelline contents ranged between 0.91-1.32%, 2.34-4.67%,
5.30-8.98% and 1.04-1.71%, respectively on dry matter basis. Cluster analysis
classified coffee genotypes into eight groups and genotypes were not clustered
according to collection regions. Coffee genotypes collected from northwestern
Ethiopia were more diverse in green bean caffeine, chlorogenic acids and sucrose
contents compared to southwestern Ethiopia genotypes. On average, southwestern
Ethiopia coffee genotypes had higher green bean caffeine, chlorogenic acids, sucrose
and trigonelline contents compared to northwestern Ethiopia genotypes. Green bean
caffeine content showed negative and statistically significant associations with all
desirable cup quality attributes and correlation coefficients ranged from -0.305 to -0.
407. Desirable cup quality traits and low green bean caffeine content can be selected
simultaneously. Green bean sucrose content showed positive associations with all desirable cup quality and green bean physical characters. Higher green bean sucrose
content, desirable cup quality as well as green bean physical characters can be
improved together.
The genetic diversity of coffee genotypes was investigated using 10 AFLP primer
combinations. Results revealed differences among AFLP primer combinations in
detecting genetic variation among genotypes. Of the 10 primer combinations EcoRI-ACA/
MseI-CAA, EcoRI-ACC/MseI-CAG, EcoRI-ACT/MseI-CAG and EcoRI-AAC/
MseI-CAA were superior in detecting genetic variation. Almost all primer
combinations were positively correlated in estimating pair-wise genetic similarity
coefficients, indicating the similarity of primer combinations in detecting genetic
variation among genotypes. All genotypes were independently distinguished and pair-wise
genetic similarity coefficients ranged from 0.851 to 0.982 with an average of
0.915. Ten genotypes had 18 specific AFLP markers which could be utilised for
genotype fingerprinting. AD1291 and AD1491 were the most dissimilar while
AD3591 and AD3991 were the most similar genotypes. Genotypes were classified
into two groups using UPGMA method of cluster analysis. Genotypes did not cluster
according to collection regions. Results unveiled the presence of genetic variation
among genotypes collected in each region and the presence of close genetic similarity
among some coffee genotypes collected from different regions. The genetic diversity
among coffee genotypes from southwestern Ethiopia was higher compared to those
from northwestern Ethiopia.
Genetic diversity analysis performed using six SSR primer pairs indicated the
presence of considerable genetic variation among some of the genotypes collected
from northwestern and southwestern Ethiopia. Twenty polymorphic SSR markers
were amplified of which two were specific to genotypes AD1491 and AD2991. Using
20 polymorphic SSR markers, 64.3% of the genotypes were independently
distinguished. Pair-wise genetic distances ranged from 0.286 to 1.000. The lowest
pair-wise genetic similarity coefficient was recorded between AD0591 and AD1491
as well as AD1491 and AD4591. Genotypes from southwestern Ethiopia were more
diverse compared to those from northwestern Ethiopia. Molecular markers differ in the amount of information generated per PCR reaction.
The efficiency of 10 AFLP primer combinations and six SSR primer pairs in detecting
genetic variation was compared using 28 C. arabica genotypes. AFLP primer
combinations amplified 220 and SSR primer pairs 20 polymorphic alleles among
evaluated genotypes. AFLP markers independently distinguished all evaluated coffee
genotypes whereas SSR markers distinguished 64.3% of the genotypes. Moreover, 18
genotype specific AFLP markers compared to two SSR genotype specific markers
were identified. The assay efficiency index of AFLP markers (22) was far superior to
that of SSR markers (3.3). AFLP markers surpassed SSR markers in detecting genetic
variation among evaluated arabica coffee genotypes. Results of this study indicated
the presence of good congruence between the two genetic markers in estimating pair-wise
genetic similarity coefficients among genotypes.
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CHARACTERISATION OF MALAWIAN CASSAVA GERMPLASM FOR DIVERSITY, STARCH EXTRACTION AND ITS NATIVE AND MODIFIED PROPERTIESBenesi, Ibrahim Robeni Matete 04 July 2006 (has links)
Cassava has been neglected and considered as a primitive crop, food for the poor and a crop with poor nutritional value for a long time. Cassava provides more dietary energy per unit area than any staple crop. Population increase, multiplicity of cassava uses, unusual climatic variations and prospects of global warming highlight advantages of possible uses of this hardy drought tolerant crop. Policy makers realised the importance of cassava and are encouraging its promotion through research, production and utilisation. Since the crop has lagged behind for a long time, there exist knowledge gaps in many areas.
Commercialisation of cassava, and biotic and abiotic factors encourage genetic erosion.
Management and use of germplasm in production and breeding programmes need knowledge of
genetic diversity. Hence, there existed a need to collect, characterise, evaluate, conserve and use Malawian cassava germplasm. Indigenous knowledge revealed wide genetic diversity because farmers reported a wide range of quantitative and quality attributes, which they preferred or disliked in existing Malawian cassava germplasm. Morphological markers failed to uniquely distinguish all analysed accessions. Manyokola5 and Mbundumali1, Gomani1 and 2, and Matuvi and Depwete were morphologically identical. However, morphological markers revealed high levels of genetic diversity with Dice genetic similarity (GS) ranging between 0.083-1.000. The most distant accessions were Beatrice (local cultivar) and Yizaso (CH92/112; locally screened). AFLP characterisation using cluster analysis indicated narrow genetic diversity with a GS range between 0.778-0.946 and uniquely differentiated all analysed accessions. The closest accessions were Mabundumali1 and Manyokola5 (GS=0.946), and Gomani1 and 2 (GS=0.938). PCA analysis for AFLP markers revealed that PCA axis 1 displayed narrow genetic diversity but PCA axes 2 and 3 displayed wide genetic diversity. AFLP analysis of cassava germplasm grouped accessions according to pedigree and geographical origins. Morphological and AFLP markers were not similar but significantly correlated, indicating the need to use both markers in characterisation of cassava
germplasm. Screening of AFLP primers revealed that M-CAA/E-ACA, M-CAA/E-AAC, M-CAT/E-ACA,
M-CAT/E-AAC, M-CTT/E-ACT and M-CTT/E-ACC were convenient and efficient in analysing
cassava. Further analysis indicated that a combination of four primer pairs was more cost and time efficient and gave similar resolution compared to a combination of six primer pairs, the best being M-CAA/E-ACA+M-CAA/E-AAC+M-CTT/E-ACT+M-CTT/E-ACC. Evaluation of genotypes for starch extraction was done just before or at onset of the rainy season
(October-November), within the rainy season (January) and towards the end of the rainy season (March-April). Results indicated that the best genotypes were Mkondezi, Silira, Mbundumali and CH92/082. Starch extraction done just before or at onset of the rainy season gave the highest starch extraction rates compared to the middle of the rainy season. Apart from high recovery of starch in October-November, it is convenient for drying starch using open-air method and releases land for other crops in the following rainy season. Makoka was the best site for growing cassava for starch extraction. Starch extraction rate on fresh root weight basis had a direct relationship with starch yield as opposed to starch extraction on dry root weight basis. Cassava starch from different genotypes were characterised for physical and functional properties. Results indicated that Silira, 81/00015, Mbundumali and Sauti were easily dextrinised and 80% solubility was achieved within 60min of dextrinisation at 100 o C after acidification with 0.1M HCl. Pyrodextrin from Mkondezi variety after dextrinisation for 40min turned out to be similar in functional properties to amylmaize starch. Cassava starches had lower gelatinisation temperatures desired for hot-setting adhesives since less heating is required to gelatinise cassava starch, which leads to energy saving. Functional properties of 83350 native starch was different from the rest of the genotypes but was very close to amylmaize starch as revealed by DSC.
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CLONING OF GENES INVOLVED IN THE EARLY RESPONSE OF WHEAT TOWARDS RUSSIAN WHEAT APHID INFESTATION.Huang, Ju-Chi 05 July 2005 (has links)
The interaction between wheat (Triticum aestivum) and the Russian
wheat aphid (Diuraphis noxia) was investigated on a molecular level. The
resistant cultivar, Tugela DN1, was infested with the Russian wheat aphid
and tissue harvested at 3 hour time intervals for 24 hours. Differential
display RT-PCR was used to clone genes that were inducibly expressed using
primers specific to the conserved subdomain VIb of the kinase domain of
protein kinases. Differentially expressed genes were found as early as three
hours after infestation. These fragments were cloned and sequenced.
A total of 11 differentially expressed cDNA fragments were analyzed.
Four showed homology to genes encoding proteins involved in normal
cellular metabolism, such as the Rubisco large subunit, indole-3-gylcerol
phosphate lyase that produces indole that could act as a volatile messenger
molecule, triose-phosphate isomerase that is involved in glycolysis and 2-isopropylmalate
synthase that is involved in leucine biosynthesis.
Of the other cDNAs, three clones showed homology to several
hypothetical proteins with no defined functions, while the other three
showed no homology at all with any other known genes.
One of the unknown clones (D20) was selected for further analysis.
The gene was inducibly expressed only in the infested resistant plants, but
not in the infested susceptible plants. The expression of the gene was
induced within 3 h after infestation reaching a maximum expression level 6
h.p.i. The gene is present as a single copy within the genomes of susceptible
and 5 different resistance lines. An attempt to clone the full length gene
was only partially successful since after the sequences were combined
homology was found with several hypothetical genes from rice and maize.
However, no identity and function could be given.
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THE GENETIC, MORPHOLOGICAL AND PHYSIOLOGICAL EVALUATION OF AFRICAN COWPEA GENOTYPESMagloire, Nkouannessi 27 July 2006 (has links)
Not available
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