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EVALUATION OF BAMBARA GROUNDNUT (Vigna subterranea) FOR YIELD STABILITY AND YIELD RELATED CHARACTERISTICSMasindeni, Dimakatso Roselina 26 January 2007 (has links)
This study was undertaken to evaluate genotype x environment interaction
(gxe) and yield stability of eight bambara groundnut genotypes in three
locations at two planting dates; to compare the stability parameters used
in determining stable yields, to correlate yield and related characters of the
crop, to determine the effect of planting date on yield and yield
components; and to assess the effect of location and genotype on protein
content.
Field trials were planted with two different planting dates in three localities.
A randomized complete block design with three replications was used.
Data collected was days to 50% flower, number of pods per plant, grain
yield, haulm yield, 100 seed weight, and maturity days.
Data was subjected to simple ANOVAâs for all measured characteristics.
Significant differences were found for most of these characteristics.
Combined analyses of variance were computed across locations to
determine the performance of yield and related characteristic. Significant
differences were found for genotype, environment and Gxe interactions.
The best genotype was SB4-4 across locations.
Four stability parameters namely Eberhart and Russell regression model,
Lin and Binnsâ Cultivar Superiority Measure (Pi), Wricke ecovalence (Wi)
and Additive Main Effects and Multiplicative Interaction (AMMI) were
performed to determine yield stability. SB16-5A was regarded the most stable by Eberhart and Russell, SB19-3 by Wricke ecovalence, SB7-1 by
ASV and SB4-4 by cultivar superiority and yield rankings The results
showed that SB19-3 was the third most stable genotype according to
Eberhart and Russell and Lin and Binns yield ranking; and the first and
second most stable genotypes by the Wricke and AMMI model. Therefore
SB19-3 proved to be the most stable genotype. ASV and Wricke
ecovalence value ranked SB4-4 and SB1-1 to be the first and second
most stable genotypes for 100 seed weight, while ranking SB19-3 first and
second respectively for number of pods per plant. The AMMI model
summarizes patterns and relationship between gxe interactions and helps
to obtain a good yield estimates. The results for stability of yields are not
conclusive since the data is for one season, therefore the trials must be
repeated to validate the results.
Correlation analyses were first computed for separate trials and then for
combined trials across locations. Hundred seed weight, haulm yield,
number of pods per plant and root weight were positively correlated with
grain yield with haulm yield and 100 seed weight having strong positive
correlations to grain yield. Planting date did not significantly affect yield
and protein content was also not significantly affected by gxe interactions.
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PYRAMIDING WHEAT RUST RESISTANCE GENES USING MARKER-ASSISTED SELECTIONSydenham, Scott Lloyd 05 February 2009 (has links)
Wheat (Triticum aestivum L.) is widely cultivated over large areas and is an
important food crop worldwide. Wheat is extensively used during the production
of many different types of foods. Wheat rusts (leaf, stem and stripe rust) are
important foliar diseases of wheat worldwide, causing large losses and damage
to the wheat industry. The ability of these rust pathogens to change and be
dispersed over long distances pose a continual global threat. Annually millions
around the world are spent on fungicides in an attempt to control wheat rusts.
Resistant cultivars have proven to be the most effective, economical and
environmentally friendly form of rust control. Although many resistant cultivars
have been developed historically, a need for more durable resistance exists.
The application of molecular markers and marker-assisted selection (MAS)
strategies in breeding programmes can support plant breeders in accomplishing
pyramiding of several rust resistant genes into new cultivars.
The aim of this study was to pyramid seven rust resistant genes/QTL (leaf,
stripe and stem rust) into a single genotype using five SSR, three STS and two
AFLP markers. The study focused on wheat genes applicable to the local wheat
industry and markers used and/or developed in South African breeding
programmes. In this study four bread wheat cultivars or lines (AvocetYrsp,
Blade, CSLr19-149-299 and Kariega) were used as parental sources of five
resistance genes (Sr2, Sr26, YrSp, Lr19 and Lr34) and two QTL (QYr.sgi-7D
and QYr.sgi-2B). Selection after each cross was done using a MAS approach
with SSR and STS markers linked to the different resistant genes/QTL. The
study was conducted over a two year period, involving the development of two
different sets of F1 offspring and one double cross generation from a series of
directional crosses.
Before crosses were made, the presence of the expected rust resistance genes
was confirmed in the parental lines using specific SSR, STS and AFLP markers.
The SSR and STS markers amplified the expected allele sizes in the parental
lines, except for the unexpected detection of the Lr34 gene in AvocetYrSp. Results indicated that the Sr2 marker was not consistently present in Blade,
suggesting the Blade cultivar was heterogeneous for Sr2. The AFLP markers
linked to the YrSp resistance gene did not detect differences between the
parental lines and were excluded from further experiments. The F1 generations
were screened with one SSR or STS marker each to identify successful
crosses. Genotyping of the F1 generations indicated than on average, 85.5% of
the tested F1âs were true hybrids. Phenotypic screening was done on the
parental lines and F1 individuals for the three rust types and confirmed the
presence of the expected genes in the parental lines as well as selected F1
individuals.
A total of 900 individuals of the double cross generation were screened with five
SSR and three STS markers associated with resistance genes and QTL to
identify whether gene pyramiding within a single genotype was successful. The
number of individual plants of the double cross population containing markers
linked to the desired resistance gene(s)/QTL ranged from two individuals
containing none of the markers to three individuals containing all eight markers.
The three individuals containing eight markers confirmed the presence of
markers associated to the presence of the four single genes (Sr2, Sr26, Lr19
and Lr34) and two QTL (QYr.sgi-7D and QYr.sgi-2B.1). Due to the inefficiency
of the AFLP markers, the presence of the seventh gene (YrSp) could not be
confirmed on genotypic level. The future uses of the developed rust resistance
gene pyramided lines of this study are countless. The use of these lines in
combating the continual threat of wheat rusts in some manner should be helpful
in future.
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TARGETING QUANTITATIVE TRAIT LOCI FOR ADULT PLANT STRIPE RUST RESISTANCE IN WHEATPhilippou, Onoufrios Agathoclis 05 February 2009 (has links)
Stripe rust, caused by Puccinia striiformis West. f. sp. tritici is one of the most damaging
diseases of wheat (Triticum aestivum L.) globally. The South African wheat cultivar Kariega
expresses APR and has retained yield levels acceptable for commercial production, which is
of great importance to plant breeders. A Kariega x Avocet S partial linkage map has made a
significant contribution to understanding the genetics underlying APR to stripe rust (Yr) in
Kariega. Two major YrQTL with indications of different resistance mechanisms were
identified on chromosomes 2B and 7D.
In this study we investigated the effectiveness of identifying AFLP markers closely linked to
the YrQTL using a targeted bulk segregant analysis (tBSA) approach in F1 doubled haploid
(DH) individuals. Individual Kariega x Avocet S DH lines were characterised and bulked
based on stripe rust phenotypes and DNA marker allele profiles. In agreement with standard
BSA, an extreme resistant bulk (both QTL present: +7D+2B) and extreme susceptible bulk
(both QTL absent: -7D-2B) were constructed based on phenotypic data and verified with
marker allele data. Three additional bulks (+7D-2B; -7D+2B and narrow down +7D±2B with
marker recombinations in 7D QTL interval) were constructed based on a combination of
phenotypic and marker data, with a strong emphasis on the presence or absence of marker
alleles representing a specific QTL interval as required by a specific bulk.
A total of 184 AFLP primer combinations (SseI and MseI) were tested on the two parental
lines and five bulks. Thirty-one of these primer combinations detected 32 putative markers
that could discriminate between the extreme resistant and susceptible bulks and that were
putatively linked to either the 7D or 2B QTL regions. After validation of these markers on all
individuals used in the extreme resistant and extreme susceptible bulks, nine markers were
identified that were present in the extreme resistant and the specific -7D+2B bulk, but absent
in the extreme susceptible bulk. Another two markers were identified that were present in the
extreme resistant, +7D-2B and narrow down +7D±2B bulks, but absent in the extreme
susceptible bulk. These markers were mapped onto the existing Kariega x Avocet S partial linkage map using Map Manager QTXb20. Six AFLP markers mapped within or close to the
QYr.sgi.2B and one close to the QYr.sgi.7D QTL regions.
The tBSA approach was efficient since 10 of the 11 markers (91%) putatively identified after
screening of the individuals constituting the bulk samples mapped to either chromosome 2B
or 7D. AFLP analysis in combination with tBSA was shown to be reproducible, faster and a
more cost effective approach compared to a traditional BSA since tBSA lead to a reduction
of 28.2% of primers that need to be tested. Following the tBSA approach, marker s23m53d
mapped 3 cM from marker gwm148 previously shown to be significantly associated with
mean host reaction type for final field data as well as leaf area infected of the QYr.sgi-2B
QTL region. This resulted in an increase in LOD score from 20.1 to 23.9 using interval
mapping. Even though two markers were added to the 7D chromosome, both mapped outside
the QYr.sgi-7D QTL region. Marker s20m38b mapped 9 cM from the SSR marker gwm295
and 20 cM from the Ltn gene previously shown to be associated with the trait of interest on
chromosome 7D.
In summary, the combination of AFLP analysis and a tBSA approach has proved to be useful
in the identification of QTL, the placement of closely linked markers to known QTLs and
targeting chromosome areas with low marker numbers. Indications are that a large number of
AFLP primer combinations need to be screened to successfully target a specific QTL interval
for increased map resolution.
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INHERITANCE OF NITROGEN USE EFFICIENCY COMPONENTS IN SOUTH AFRICAN IRRIGATED WHEATOtto, Willem Morkel 06 February 2009 (has links)
In a second experiment, the NUE components of seven parental irrigation cultivars and
their F2-offspring were studied in 2004 at a cooler (Bethlehem) and a warmer (Vaalharts)
irrigation environment. The genotypes were tested at two N treatments; a control (LN)
and 180 kg N/ha (HN) applied. Agronomic characteristics, N uptake and NUE
components were measured.
From the analysis of variance, the agronomic characteristics (BM, grain yield, HM, TKM
and GP) showed significant genotypic variation. Harvest index, BM, HM and TKM
showed no significant genotypic variation at the N treatment. The N uptake and NUE
components showed significant genotypic variation with the exception of NutEYld. The
HN treatment resulted in significant variation in Ngrain, Ntotal NHI, NUEYld and NutEYld.
The HN treatment increased BM, grain yield and GP values, but reduced the HM, TKM,
HI and NHI values of the genotypes. The NUE components NupE%, NUEYld and
NutEYld were also reduced by the HN treatment. Cultivars responded differently at the two N treatments in measured and calculated
agronomic and NUE components. Olifants, Kariega and Marico showed good responses
for the agronomic components at the HN treatment. Inia, SST 806, SST 822, Olifants,
Kariega and Marico showed high values for NUE components. The crosses Olifants x
Steenbras, SST 806 x SST 822, Marico x Steenbras, Olifants x SST 822 and Marico x
SST 806 showed positive responses in the measured agronomical and NUE
components.
The correlation coefficients were calculated to study the phenotypic resemblance
between characteristics. The calculated correlation matrixes for the environments
indicated positive correlation coefficients between several of the agronomic and
calculated components. Biomass and grain yield was highly correlated with the NUE
components, NupE%, NUEYld, Ngrain and Ntotal at both environments. Grain protein
was negatively correlated to NutEYld, while NHI was positively correlated to this
component. This points to the first order importance of grain yield production before
grain protein under limiting N availability conditions. The correlation coefficients of
components BM, grain yield, NPE, NRE and NUEYld increased at the HN treatment.
The effect of N treatments on the calculated GCA and SCA effects was studied from a
diallel analysis. Significant GCA effects for the parental cultivars were found for the
majority of the agronomic and NUE components at both N treatments. Significant SCA
effects for the tested hybrids were also found at BM, grain yield, Ngrain, Ntotal, NupE%,
NUEYld, NAEYld, PHE and NRE. The application of N fertilizer (LN versus HN
treatments) affected the significance of the calculated combining abilities.
For the agronomic characteristics that were measured at Bethlehem, GCA effects for
BM, HM, TKM, GP and HI were significant at the HN treatment. Significant GCA effects
were found at the LN treatment for TKM and GP. The N uptake components Ngrain,
Ntotal and NHI showed significant GCA effects at the HN treatment. For the NUE
efficiency components significant GCA effects were calculated for NupE%, NUEYld and
NutEYld at the HN treatment. No significant cultivar differences were found for the N
uptake and NUE components at the LN treatment. For the agronomic components SST
822, Inia and Kariega generally had the highest GCA values. The cultivars Marico,
Olifants, SST 806 and Inia showed the highest GCA values at the HN treatment for the
agronomic, N uptake and NUE components. At Vaalharts significant variability for GCA effects for the agronomic components BM,
grain yield, HM, TKM and HI were found at both N treatments. For the N uptake
components, significant GCA effects were calculated for Ngrain and Ntotal at both N
treatments and for NHI at the HN treatment. Significant GCA effects were found for the
NUE components NupE%, NUEYld at both N treatments and for NutEYld at the HN
treatment. The cultivars Kariega, Olifants, Inia, Steenbras and SST 806 had the highest
GCA values for the agronomic, N uptake and NUE components at the LN treatment. At
the HN treatment Olifants, SST 806 and Inia had the highest GCA values for these
components, as well as for the N uptake and NUE components.
The calculated SCA effects at Bethlehem were significant for BM, grain yield, Ngrain,
Ntotal, NUEYld at both N treatments, and for NAEYld, NPE, NRE, HM and NupE% at the
HN treatment. At Vaalharts significant SCA effects were calculated for BM, grain yield,
Ngrain, Ntotal, NupE%, NUEYld at both N treatments and for NHI at the HN treatment.
The calculated GCA:SCA ratios for the respective components at Bethlehem showed
that the values for most of the components increased at the HN treatment, with only
grain yield, Ngrain and NUEYld at values less than one. The calculated NUE
components NAEYld, NPE and NRE also showed non-additive gene action. At
Vaalharts all the components showed additive gene action at both the LN and HN
treatments, except for GP, NHI and NutEYld at the LN treatment. Also, in contrast to the
response calculated at Bethlehem, the calculated NAEYld, NPE and NRE showed
additive gene action. These differences in responses between the two environments can
be attributed to the different growing conditions and N availability scenarios inducing the
changes in response of agronomic and NUE components.
High broad-sense heritabilities were calculated for BM, grain yield, HM, TKM and HI at
the LN and HN treatments at both environments. At Vaalharts the heritability value for
GP was high at the HN treatment, and at Bethlehem at both the LN and HN treatments.
Broad-sense heritability estimates improved at the HN treatment except for TKM
compared to the LN treatment. The heritability values for the N uptake components,
Ngrain, Ntotal and NHI were high, and were increased at the HN treatment. With the
exception of the NutEYld component at the LN treatment at Vaalharts, the broad-sense
heritability values of all the NUE components were high and increased by the HN
treatment. At Bethlehem the narrow-sense heritability value of TKM was high at both N treatments,
and values of GP, NHI and NutEYld at the HN treatment. At Vaalharts high narrowsense
heritability values were found for HM, TKM, NAEYld and NPE at the LN treatment.
All the agronomic characteristics and calculated components showed increased narrowsense
heritability values at the HN treatment. These responses indicate that the
estimation of heritability of the studied components were improved when N were
sufficiently available.
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THE INFLUENCE OF HEAT AND COLD STRESS ON GLUTEN PROTEIN AND STARCH IN WHEATOskar, Elago 06 February 2009 (has links)
The ability of wheat flour to be processed into bread and other products is largely
determined by the gluten proteins, which confer unique visco-elastic properties to
dough. These proteins are influenced by genetic make up and the environment in
which the plants are grown. The objective of this study was to gain a better
understanding of the influence of extreme temperatures on the gluten proteins,
quality characteristics, starch and starch components. Two bread wheat cultivars,
a soft biscuit wheat and a durum wheat were grown two plants to a pot, with 12
pots for each replication, with three replications in a greenhouse for two
consecutive years. Cold and heat treatments were applied during grain filling.
Size exclusion and reverse phase HPLC were used to measure the different
protein fractions. Starch, amylose, amylopectin and various quality
characteristics were measured on all entries after harvest in both years.
The results from this study showed that in both years the softest cultivar, Snack
showed the largest reaction to low temperature stress specifically, where the
monomeric proteins were significantly increased, and the polymeric proteins
were significantly decreased. In the second year SST86 showed the same trend
as Snack under cold stress conditions. Oranje, the durum wheat cultivar, reacted
to both heat and cold stress in the second year, where the small polymeric
proteins (SDS soluble) were significantly reduced, and the small monomeric
proteins were increased with stress, and the SDS insoluble large monomeric
proteins were increased only under heat stress. The protein fractions of the
tetraploid Oranje were very different from that of the other three hexaploid
cultivars. The soft wheat Snack had significantly lower large polymeric protein,
and higher large monomeric protein fractions (SDS insoluble) than the bread
wheat cultivars for both years. Summed over cultivars, per treatment for the two
years, all the fractions, except for the small polymeric and small monomeric
proteins (SDS insoluble) were affected by the cold treatment. The monomeric
proteins were consistently increased, and the polymeric proteins decreased. Only the SDS soluble large polymeric proteins were significantly affected by the heat
treatment, where it was significantly decreased.
Both kernel weight and diameter were significantly decreased at both stress
treatments for the two bread wheat cultivars, indicating that their kernel
characteristics were sensitive to extreme temperatures. Across the two seasons,
the starch content in Kariega was significantly reduced by both heat and cold
temperatures, as is also reflected in the reduction of kernel weight and diameter.
Amylose content and the amylose:amylopectin ratio increased under heat and
cold treatment. There were highly significant positive and negative correlations
between certain RP-HPLC peaks and quality characteristics for all three the
temperature treatments in both years. The number of significant correlations was
reduced under the two stress conditions, but there is a possibility to use certain
peaks for quality selection. The profiles must, however, be standardised so that
peaks can be scored and compared on any gel according to their elution times.
Stepwise regression also emphasized the importance of some of the RP-HPLC
peaks in explaining variation in flour protein content and SDS sedimentation for
all three temperature treatments.
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HYDROPONICS AS A TOOL IN WHEAT BREEDING.du Toit, Andreas Gerhardus Adriaan 14 February 2006 (has links)
The aims of this study were to evaluate the functionality and the practicality
of hydroponics in the process of wheat breeding compared to a conventional
glasshouse cultivation method. Furthermore for assessing the screening
capability of drought tolerance in wheat cultivars using a hydroponic system
was used and morphological yield components were measured and protein
concentration fluctuations by means of SE-HPLC were analyzed.
x In the first study, five South African wheat cultivars, SST 88, Baviaans,
Steenbras, SST 876 and Kariega, were planted into two identical hydroponic
systems. A second set of the five cultivars where planted two months after
the first planting to separate the two stress periods, the first being drought
stress before seed fill and in the second planting, stress was induced at
seedling stage. This was done simultaneously.
x When maturity was reached, several yield component measurements were
taken.
x The influences of the drought treatment on the different yield components
were established.
x Protein extracts of wheat flour were analyzed by SE-HPLC.
x SDS was used for the first protein extraction step, and the rest of the
proteins were extracted by sonication.
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x The SE-HPLC method fractionated the storage proteins (both SDS-soluble
and SDS-insoluble) into four distinct peaks of decreasing molecular size
range, representing mainly larger polymeric proteins (mainly HMWglutenins),
smaller polymeric proteins (mainly LMW-glutenins), larger
monomeric proteins (mainly gliadins), and smaller monomeric proteins
(mainly albumins and globulins).
x Relationships between the amount and size-distribution of polymeric and
monomeric proteins and flour quality properties were established.
x The influence of the drought treatment on protein fractions and quality
characteristics was also determined by SE-HPLC.
x The results showed that both the genotype and drought conditions had a
significant influence on the yield components and protein characteristics.
x The use of a hydroponic cultivation method for the induction of drought
conditions at any stage of development of wheat can be done at a highly
significant level, not only for inducing stresses but for re-establishing and
maintaining optimum conditions as well.
x SE-HPLC provided a simple and an objective test for measuring the relative
size-distributions of wheat storage proteins.
x In the second study two South African wheat cultivars, Baviaans and
Steenbras, were planted into two identical hydroponic systems (differing
only in the makeup of the nutrient solution) and in pots.
x Emergence percentages and dates were recorded for a one month period
after the emergence of the first seedling in the experiment.
x When maturity was reached several yield component measurements were
taken.
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x The two hydroponic systems provided a better emergence environment
compared to the potting solution, indicating that there is already a higher
potential number of crosses that can be made in the breeding program using
a hydroponic cultivation method.
x The effect of treatment was highly significant for most of the yield
characteristics, indicating that the effectiveness of the treatments played a
significant role in the yield potential of each cultivar.
x Findings indicated that by using a hydroponic cultivation method instead of
the potting method for growing wheat, parent lines can increase the amount
of crosses that can potentially be made, thus increasing the amount, potential
success and quality of the crosses made, together with the potential of
producing seeds that will have the potential of a higher emergence rate.
x The hydroponic cultivation method using the chemicult solution proved to be the most effective method of cultivation during this study.
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EVALUATION OF GROUNDNUT (ARACHIS HYPOGAEA L.) GERMPLASM FOR RESISTANCE TO LEAF DISEASES AND RELATED CYTOPLASMIC FACTORS, TESTA COLOUR AND CUP LEAFPretorius, Alana Elmarie 28 February 2007 (has links)
Early leaf spot (ELS) caused by Cercospora arachidicola, late leaf spot (LLS) caused by
Cercosporidium personatum, web blotch (WB) caused by Phoma arachidicola and rust
caused by Puccinia arachidis, are serious diseases of groundnut in South Africa. The
aims of this study were to evaluate ARC-GCI germplasm for resistance to the important
foliar diseases such as ELS, LLS, WB, and rust and to ascertain if cytoplasmic factors
influence the pattern of inheritance of resistance to ELS, LLS, and WB, testa colour and
mutations such as the one responsible for cupleaf phenotypes.
Twenty-one reciprocal crosses were made to study the cytoplasmic factors but the F1
progenies gave no evidence of cytoplasmic factors directly responsible for any of the
above-mentioned traits.
During 2003/04, 138 ARC-GCI germplasm entries were evaluated for resistance to ELS,
LLS, WB and rust at Potchefstroom (North West Province; Highveld), Burgershall
(Mpumalanga Province), Brits (North West Province), Vaalharts (Northern Cape
Province) and Cedara (Kwazulu Natal Province). No fungicides were used to control the
foliar diseases. In trials at Vaalharts, Cedara, and Burgershall entries 1, 10-13, 18-21, 23,
30, 52 and 56-58 were resistant to two of the three (LLS, WB, and rust) foliar diseases
and entries 18, 19 and 20 (best) to LLS, WB and rust. At Brits, Elite (E) and ICRISAT (I)
short/medium growth entries 8I and 7E, were resistant to LLS and WB and the long
growth entries 1E and 3E were resistant to WB, LLS and rust. In micro-plots at
Potchefstroom entries 6, 9, 10 and 13-15 were resistant to LLS and WB and in the brick
plots 1-3, 6 and 7 to ELS and LLS.
Entries with resistance to ELS, LLS, WB, and rust as well as other favourable traits, such
as a high yield and oleic acid percentage, from the 2003/04 trials were included in the
2004/05 trials for further assessment. All the entries were evaluated for resistance to ELS,
LLS, WB and rust, were graded and grouped by using the Canonical Variate Analysis
(CVA). From the results on the five locality trials (2004/05) medium growth entries 1, 3, 7, 10, 14, 15, 20-22, 26, 27, 30, 32 and 33 were resistant to three or four of the foliar
diseases, gave good yields and choice grade kernels. The CVA identified separate groups,
containing entries 3, 20, 21 and 32, with resistance to two or more foliar diseases and
with high yield. No choice grade entries were reported for unsound blemished and soiled
(UBS) kernels with an UBS>13%.
In the Elite short/medium trials at Brits (2004/05) entries 3 and 8 were resistant to rust, 1,
2, 4, 7, 11-13, 15, 17, 19-22, 24 and 25 gave choice grade kernels, and 10, 13 and 12 the
highest yield. Entries 1-6, and 8-15 (Elite long) were resistant to LLS, 1-15 to WB, and 1,
4 and 15 to rust, 4, 10 and 12 gave choice grade kernels and 4, 1 and 10 the highest
yields. ICRISAT (long) entries 5 and 7 gave choice grade kernels, and 1, 6 and 3 the
highest yields. The CVA identified the groups containing medium growth entries 10, 12,
13, 22 and 23, Elite long 1, 4, 10 and 15 and ICRISAT long 5, 8 and 9 as groups with
resistance to two or more foliar diseases (ELS, LLS, WB, and rust) and good yield.
Twenty-three medium and 11 long growth entries in the Elite trials at Vaalharts (an extra
trial planted where fungicides were used to control foliar diseases) gave choice grade
kernels and good yields.
In this study, some ARC-GCI germplasm entries were resistant to ELS, LLS, WB, and
rust, but climatic factors influenced the severity of infection. Foliar diseases lowered the
quality and grade of the kernels and resulted in lower yields. CVA simplifies the
evaluation and grouping of new germplasm entries and will save valuable research
resources.
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THE ABILITY OF A NOVEL COMPOUND TO ENHANCE THE EFFECT OF UREA ON NITROGEN DEFICIENT TOMATOESPretorius, Hendri 22 March 2011 (has links)
A company, Elementol (Pty) Ltd, requested the evaluation of their novel product,
Pheroids. Pheroids can apparently facilitate the transport of phytological beneficial
substances over membranes. Information regarding the chemical attributes was
withheld as patent registration is still pending. Pheroids is apparently a microemulsion
containing free fatty acids (FFAâs) and or fatty acid derivatives. It
apparently encapsulates a substance and facilitates its transport over the
membrane. The exact mechanism involving encapsulation, transport and release of
the substances inside the cells is still vague due to little information available on it.
The aim of this study was to evaluate the ability of Pheroids to facilitate the transport
of additional nitrogen, urea in this case, in tomatoes grown under nitrogen limiting
conditions. Tomatoes (Lycopersicon esculentum cv. Rodade Star) were cultivated in
a greenhouse using a circulating ebb and flow hydroponic setup, which supplied the
plants with either a control- or nitrogen limiting nutrient solutions. The plants
cultivated in the nitrogen limiting conditions showed a remarkable reduction in
vegetative development and yield. To alleviate the effect of nitrogen limiting
conditions on yield, the plants were foliarly sprayed with 0.5% and 1% urea
solutions, singly or mixed with Pheroids, once every two weeks. The purpose of
these foliar treatments was to determine whether Pheroids can further enhance the
absorption and transport of urea across membranes of the leaves to alleviate the
effect of limiting nitrogen supply. Plants grown under nitrogen adequate conditions
(control) were also foliarly treated with a 0.5% urea solution, singly and mixed with
Pheroids, to determine to which extent control plants react to the additional nitrogen
supplied. The reduction in yield, as a result of limited nitrogen supply, was partially alleviated
by spraying nitrogen deficient plants with the 0.5% and 1% urea solutions. However,
mixing the 0.5% and 1% urea solutions with Pheroids, not only improved vegetative
growth and generative development, but also improved yield, suggesting that
Pheroids indeed has the ability to improve the uptake of urea. The 0.5% urea /
Pheroids solution specifically proved to have the best ability in alleviating the effect
of nitrogen limiting conditions on yield without compromising fruit quality. Although
the reducing effect was not completely alleviated, the yield and loss in income as a
result of nitrogen limiting conditions was prevented to a large extent.
Spraying control plants with 0.5% urea, singly or mixed with Pheroids, also improved
yield, without compromising fruit quality. In addition, Pheroids itself, without mixing it
with any substance, also resulted in increased yields in both control- and plants
grown under nitrogen limiting conditions.
In summary, it appeared that Pheroids has the ability to facilitate the transport of
phytological beneficial substances, in this case urea, over plant membranes and
enhances cellular nitrogen content, but this needs further detailed analyses. This
phenomenon was more evident in plants grown under nitrogen limiting conditions
than in plants grown under control conditions. Taking into consideration that most
crops frequently may suffer from nitrogen limiting conditions in standard agricultural
practices, Pheroids may have numerous potential applications in the agricultural
industry.
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THE INFLUENCE OF ENVIRONMENT ON THE EXPRESSION OF RUSSIAN WHEAT APHID; Diuraphis noxia (KURDJUMOV) RESISTANCELindeque, Robert Crowther 08 April 2009 (has links)
The purpose of this study was to investigate the effect of variations in climatic factors
such as vernalization periods, minimum- and maximum temperatures and rainfall on
the expression of host plant resistance to RWASA1 (original biotype) and RWASA2
(newly identified biotype) in the eastern Free State of South Africa between 2003 and
2006. Climatic records indicate above-average temperatures and reduced rainfall
occurred in the Eastern Free State in 2003 to 2005 probably contributing to
widespread RWA damage on dryland wheat crops. Greenhouse experiments
confirmed that vernalization did not alter RWA plant resistance ranking of wheat
entries. However, infestation did produce significant damage by RWASA2 on Elands,
Gariep and Limpopo but not on CItr 2401 (containing Dn-4 and another unidentified
Dn-gene) and Halt (Dn-4). Resistance rating to RWASA1 of Halt, Komati and
Matlabas in greenhouse tests at 18°C/12°C, 22°C/16°C and 26°C/22°C shifted to
less resistant- or susceptible categories and changed the ranking of SST 966 as
temperature increased. Also, RWASA2 ratings at increased temperature shifted Halt
to a more resistant category and changed rankings of Komati and SST 399. Komati,
Matlabas, SST 966 or SST 399 did not express any host plant resistance to
RWASA2 through leaf area or leaf roll and chlorosis supporting the susceptible
ratings that were given to the same varieties in the visual screening test. Seeddressing
in AMMI results for 2003 to 2006 were able to increase yields under higheryielding
conditions in seasons when moisture- and heat stress occured and the yield
performance of cultivars was stabilized irrespective of whether they contained
genetic resistance to RWA. Identifying new RWA resistance donors provide an
excellent opportunity to exploit novel germplasm with potential new genetic variance
for RWA resistance, as well as other beneficial traits such as drought-tolerance.
Three germplasm pools were evaluated for this purpose. Twenty-one entries from the
Stillwater, Oklahoma/SGI RWA resistance pool expressed resistance against
RWASA2 in the seedling test and where generally well adapted to local conditions.
Seedling evaluation of the CIMMYT pool revealed twenty entries with acceptable
resistance to RWASA2 though field adaptability particularly to biotic stress was
occasionally lacking. Twenty entries from the Iranian pool were resistant to RWASA2
though unadapted for resistance to stripe rust; Puccinia striiformis Westend f.sp tritici
Eriks., occurring in the Eastern Free State.
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METABOLIC ASPECTS OF THE EARLY RESPONSE OF LEAF RUST-INFECTED WHEATHuang, Ju-Chi 08 April 2009 (has links)
The aim of this study was to study various aspects of the defence response of wheat infected by Puccinia triticina. SSH was used to isolate differentially expressed cDNA fragments from P. triticina infected wheat. Once sequenced, two cDNA clones were selected for further analysis. One of the cDNA clones, LRW268, showed similarity to an EST derived from de-etiolated wheat. It showed a 16.5 fold induced expression at 9 hpi in the P. triticina infected wheat. In P. striiformis infected wheat, an induced expression was found in the resistant Avoset-Yr1 plants. Application of chemical elicitors showed an induction of LRW268 expression for plants treated with H2O2, MeJA and menadione. To obtain the full length gene, 5â-RACE was attempted, but it was unsuccessful. However, a contig was assembled using ESTs present in the GenBank database. This yielded a 603 bp contig encoding a 96 amino acid sequence that showed good homology to a RLK interacting protein. The presence of a putative MAPK docking motif and a phosphorylation site indicated that LRW268 could play a role in cell signalling. The presence of LRW268 in different wheat cultivars signified that it could form part of the general defence response of wheat. The second cDNA clone, LRW222, which was similar to an EST from wheat infected with powdery mildew, showed a 4.6 fold induction of expression at 15 hpi in wheat infected with P. triticina, while the susceptible Thatcher cultivar showed an induction at an earlier time interval. P. striiformis infected wheat showed a more constant expression of LRW222. Putative induced expression of LRW222 was observed in H2O2, MeJA and menadione treated wheat. Assembly of a contig using published ESTs yielded a 668 bp contig which encoded an 89 amino acid polypeptide showing homology to various wound-induced protease inhibitors. The presence of a putative MAPK docking motif on LRW222 suggested that it could be a general or pathogen specific protease inhibitor.
The effect of light on the wheat defence response was also examined. The photosynthetic capacity of all treatments was measured and fluorescence microscopy performed. Infection caused a decrease in the photosynthetic capacity of the susceptible plants with the resistant plants showing less fluctuation. The infected resistant plants recovered faster and better than the infected resistant plants after the dark incubation. Plants that were additionally dark incubated showed a lower photosynthetic capacity compared to the control treatments. This difference in photosynthetic capacity was not observed on molecular level with photosynthesis related genes showing unaltered expression. The putative expression of certain defence related genes did however show a light dependency. An induced defence was observed in the uninfected plants, confirming a putative volatile signalling event that was detected during an earlier study involving this particular plant/pathogen interaction. The importance of light in wheat resistant towards P. triticina could thus be attributed to the ability of plant to photosynthesise optimally. It must however be emphasized that the expression of all tested genes were not quantitatively determined, since end-point analysis using RT-PCR was used. Future research will include the use of techniques that allows quantitative measurement of gene expression.
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