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Heterosis, genetic distance and path coefficient analysis in dent, flint and popcorn hybrids.Mhoswa, Lorraine. January 2013 (has links)
Maize (Zea mays L.) is one of the most important food crops in sub-Saharan Africa (SSA);
however its production is constrained by many factors. Grain yield is compromised by poor
genetic performance and poor agronomic management. This calls for need to develop
hybrids and exploiting heterosis of single crosses which are adapted to challenging
environments. Currently, there is no popcorn hybrids developed in South Africa which is
adapted to local conditions. As such, there is need to develop hybrids that cater for smallscale
farmers in marginal environments. The objectives of the study were to determine i)
standard heterosis, levels of variation and heritability for phenotypic traits in dent and flint
maize hybrids; ii) the association between genetic distances and phenotypic traits in dent and
flint maize hybrids; iii) mid-parent heterosis in popcorn hybrids, iv) the effect of secondary
traits on grain yield in dent, flint and popcorn hybrids; v) genetic diversity and the relationship
between traits in widely grown selected hybrids in Southern Africa; and vii) to compare
effectiveness of phenotypic analysis models for determining genetic distances between
hybrids. Popcorn, dent and flint hybrids were evaluated at two sites. The data was analysed
using SAS, Genstat and Power marker statistical packages. The results revealed that the
relationship between genetic distance and heterosis is dependent on the environment.
Hybrids in top 10 at both sites were different indicating that there was a significant genotype x
environment interaction. 13 new heterotic patterns that performed better than the controls can
be utilized in heterosis breeding; however there is need to test them in different environments
to check on their stability. Grain texture cannot be used to discriminate hybrids for yield
because all patterns of dent x dent, dent x flint and flint x flint were present in the top 10
hybrids. Lines DXL124 and DXL158 dominated parentage of the top 10 hybrid rank for yield
qualifying them as potential testers for specific combining ability in future studies. Heterosis in
popcorn hybrids that performed better than the mid-parent can be utilized in heterosis
breeding to exploit vigour, though there is need to test the hybrids in a number of different
environments. The main direct factors contributing to yield were ear prolificacy, ear aspect,
number of plants and shelling percentages qualifying them to be selected to boost grain yield.
Phenotypic data and 91 SNP markers were used to estimate the genetic distance between
the hybrids. The results indicated that hybrids that were in the same cluster belong to the
same brand and were related in origin and pedigree. Both molecular and phenotypic data
were effective in discriminating the hybrids into different clusters according to genetic
background. SNP markers revealed nine clusters of hybrids, 12-trait model revealed eight
clusters and five-trait model revealed six clusters at 85% genetic distance. The study
indicates strategies that can be adopted to boost grain yield in dent, flint and popcorn hybrids. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Genetic diversity, stability, and combining ability of maize genotypes for grain yield and resistance to NCLB in the mid-altitude sub-humid agro ecologies of Ethiopia.Mengesha, Wende Abera. January 2013 (has links)
Maize (Zea mays L.) is the third most important cereal crops in the world after wheat
and rice. In Ethiopia, maize remains the second largest food security crop after tef
[Eragrostis tef (Zucc.) Trotter.]. The mid-altitude, sub-humid agro-ecology (1000 to 1800
m above sea level) is the most important maize producing environment in Ethiopia.
However, productivity of maize is low, due to several biotic and abiotic constraints.
Among the biotic constraints, Turcicum leaf blight disease of maize caused by
Exserohilum turcicum Pass Leonard & Suggs shows high incidence of 95-100% and
inflicts significant grain losses in the country. Therefore, high yielding, Turcicum leaf
blight resistant and farmers-preferred maize varieties and their production technologies
should be developed and made available to growers to enhance maize production and
to achieve food security.
The objectives of this study were to: (1) assess farmer’s preferences, and production
constraints for maize in the mid-altitude, sub-humid agro-ecology of western Ethiopia,
(2) determine the genetic variability among elite maize inbred lines and select promising
parents for resistance to E. turcicum, (3) determine diversity among the elite germplasm
lines using SSR markers, (4) determine combining ability and heterosis among elite
maize inbred lines and their hybrids, and (5) investigate genotype x environment
interaction and yield stability of experimental maize hybrids developed for the midaltitude
sub-humid agro-ecology of Ethiopia.
A participatory rural appraisal (PRA) research was conducted involving 240 maize
farmers in three representative maize growing zones of western Ethiopia; West Shoa,
East Wollega and West Wollega, each represented by two districts and two subdistricts.
Maize was ranked number one both as food and cash crop by 82.9% of
respondents. Turcicum leaf blight was ranked as number one devastating leaf disease
by 46% of respondents. Breeding for improved disease resistance and grain yield,
enhancing the availability of crop input and stabilizing market price during harvest time
were recommended as the most important strategies to increase maize production by
small-scale farmers in western Ethiopia. Fifty inbred lines were evaluated for reaction to Turcicum leaf blight during the main
cropping seasons of 2011 and 2012. Inbred lines were clustered into resistant
(CML202, 144-7b, 136-a, 139-5j, 30H83-7-1, ILOO’E-1-9, SZYNA-99-F2, and 142-1-e),
and susceptible (CML197, CML464, A7033 , Kuleni C1-101-1-1, CML443, SC22-430
(63), (DRB-F2-60-1-2) – B-1-B-B-B, Pool9A-4-4-1-1-1). Inbred lines (CML312, CML445,
Gibe-1-158-1-1-1-1, CML395, and 124-b (113)) had intermediate response to the
disease. Overall, inbred lines such as CML202, 30H83-7-1, ILOO’E-1-9-1, CML312,
CML395 CML445 and 142-1-e were selected with better agronomic performance and
resistance to leaf blight for breeding. Twenty selected elite parental inbred lines were
genotyped with 20 polymorphic SSR markers. The genotypes used were clustered into
five groups consistent with the known pedigrees. The greatest genetic distance was
identified between the clusters of lines CML-202 and Gibe-1-91.
Eighteen selected inbred lines were crossed using the factorial mating scheme and 81
hybrids developed to determine combining ability effects and heterosis. Inbred lines with
high GCA effect (CML 202, CML395, 124-b (113), ILOO’E-1-9 and CML 197) were
selected as best combiners for hybrid development. Additionally five high yielding novel
single cross hybrids with grain yield of > 8 t ha-1 and high SCA effects were identified
such as CML395 X CML442, DE-78-Z-126-3-2-2-1-1 X CML442, ILOO’E-1-9-1-1-1-1-1
X CML312, X1264DW-1-2-2-2-2 X CML464 and SC22 X Gibe-1-91-1-1-1-1. These
experimental hybrids are recommended for direct production or as hybrid testers for
hybrid development.
Genotype x environment interaction (GEI) effects of 81 newly developed and three
check maize hybrids were evaluated across 10 locations in the mid-altitude sub-humid
agro-ecologies of Ethiopia. The AMMI-3 and GGE biplot models were used to determine
stability. Hybrids such as G68, G39, G37, G77, G34 and G2 were identified as the most
stable and high yielding at favorable environments such as Bako, Jima, Arsi Negelle
and Pawe in Ethiopia. The genotype and genotype by environment interaction (GGE)
biplot clustered the 10 environments into three unique mega-environments. Environment I included Bako, Jima, Asossa, Ambo, Finote Selam, Haramaya and Pawe
while environment II represented by Arsi-Negelle and environment III Areka and
Hawassa.
In general, the study identified valuable maize inbred lines with high combining ability
for breeding and novel single cross hybrids for large-scale production or as testers for
hybrid development at the mid-altitude, sub-humid agro-ecologies of Ethiopia or similar
environments in sub-Saharan Africa. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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IRRIGATION, ADAPTATION, AND WATER SCARCITYIman Haqiqi (7481798) 17 October 2019 (has links)
<p>Economics is about the management
of scare resources. In agricultural production, water stress and excess heat
are the main constraints. The three essays of this dissertation try to improve
our understandings of how climate and water resources interact with agricultural
markets, and how global changes in agricultural markets may affect water
resources. I construct empirical and simulation models to explain the interplay
between agriculture and water. These models integrate economic theories with environmental
sciences to analyze the hydroclimatic and economic information at different
geospatial scales in a changing climate. </p>
<p>In the first essay, I illustrate
how irrigation, as a potential adaptation channel, can reduce the volatility of
crop yields and year-on-year variations caused by the projected heat stress.
This work includes estimation of yield response to climate variation for
irrigated and rainfed crops; and global projections of change in the mean and
the variation of crop yields. I use my estimated response function to project
future yield variations using NASA NEX-GDDP climate data. I show that the
impact of heat stress on rainfed corn is around twice as big as irrigated
practices. </p>
<p>In the second essay, I establish
a framework for estimating the value of soil moisture for rainfed production. This
framework is an extension of Schlenker and Roberts (2009) model enabled by the
detailed soil moisture information available from the Water Balance Model (WBM).
An important contribution is the introduction of a cumulative yield production
function considering the daily interaction of heat and soil moisture. I use
this framework to investigate the impacts of soil moisture on corn yields in
the United States. However, this framework can be used for the valuation of
other ecosystem services at daily basis.</p>
<p>In the third essay, I have
constructed a model that explains how the global market economy interacts with
local land and water resources. This helps us to broaden the scope of global to
local analysis of systems sustainability. I have employed SIMPLE-G-W (a
Simplified International Model of agricultural Prices, Land use, and the
Environment- Gridded Water version) to explain the reallocation across regions.
The model is based on a cost minimization behavior for irrigation technology
choice for around 75,000 grid cells in the United States constrained by water
rights, water availability, and quasi-irreversibility of groundwater supply. This
model is used to examine the vulnerability of US land and water resources from
global changes.</p>
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Genetic variation and associations among adaptive traits in a recombinant maize inbred line population.Sithole, Mxolisi Percival Sibongeleni. 05 November 2013 (has links)
Maize production in Africa is constrained by abiotic and biotic stresses. Breeders need to
have information on the nature of combining ability of parents, their traits and performance
in hybrid combination. This requires careful determination of genetic variability of parents,
and studying associations between grain yield and adaptive traits to breed superior cultivars
which are better able to withstand such stresses. Therefore, this study was aimed at
selecting parental testers with best combining ability in hybrid combination with
recombinant inbred lines (RILs); and studying the correlation between grain yield and its
components in eastern and western South Africa. It was also aimed at determining genetic
variation and associations among adaptive traits in hybrids involving RILs. The final
objectives of the study were to determine cultivar superiority of testcrosses involving RILs,
and to select the best cultivars within and across four different environments.
The 42 RILs were crossed to 9 Zimbabwean tropical testers resulting in 1009 hybrids with
sufficient seed for planting in trials. From these a sample of 87 hybrids with adequate seed
were selected and planted at four sites for combining ability analysis. The hybrids were
evaluated at four sites in two regions; western region (Potchefstroom research station) and
eastern region (Cedara, Ukulinga and Dundee research stations), during 2011/12 season.
The experiments were laid out as augmented alpha lattice design. Trials were managed in
accordance with production culture for each region. All quantitative data was subjected to
GenStat and SAS statistical softwares.
The results from combining ability study indicated that the line general combining ability
(GCA) effects played a non-significant role (p > 0.05) in determining grain yield, grain
moisture and anthesis date, while they were significant (p ≤ 0.05) for the other traits such as
ear prolificacy. The tester main effects were significant for all the traits except ear
prolificacy and plant height. Results also revealed that all the traits were controlled by both
additive and non-additive genes, where additive gene action had the most contribution to
the traits. The non-additive gene action played a minor role suggesting the total GCA effects
attributed to both lines and testers predominantly higher over the specific combining ability
(SCA) for all traits. In general the additive effects were preponderant over the non-additive
gene effects. One cross (L114 x T12) had a significant and positive SCA effect for grain yield.
The correlation between grain yield and secondary traits (number of ears per plant, grain
moisture content, ear height, plant height, ear position and anthesis date) suggested that
indirect selection can be employed to enhance grain yield by breeding for these particular
adaptive traits. Path analysis showed that plant height had the highest direct and indirect
effect on grain yield indicating its importance among other secondary traits for grain yield
enhancement. Phenotypic coefficient of variation (PCV) was higher than genotypic
coefficient of variation (GCV) for all the studied traits across all the four environments. All
the traits displayed high heritability at Potchefstroom except anthesis date which was highly
heritable at Ukulinga. Cedara was the second best site for heritability of all the traits except
for the number of ears per plant. The genetic advance for grain yield was the highest at
Cedara followed by Potchefstroom, Dundee and Ukulinga. The hybrids exhibited different
patterns of variation and distribution for all the traits. This indicated that selection
strategies to exploit GCA should be emphasised.
Association studies among grain yield and secondary traits such as ear length, number of
ears per plant, plant height, anthesis date, silking date and ear leaf area revealed that there
were significant phenotypic correlations between grain yield and secondary traits, and
among the secondary traits. Ear length had the highest direct effect on grain yield at
Ukulinga; number of ears per plant had the highest direct effect on grain yield at Cedara and
Potchefstroom; whereas plant height had the highest direct effect on grain yield at Dundee.
Grain yield was least affected by indirect factors at all the sites except Ukulinga, where
anthesis date had the highest indirect effect on grain yield through silking date followed by
plant height through leaf area. The study reveals that there is significant variation among
the hybrids for mean performance, indicating that there is opportunity for selection. Overall
the findings suggest that direct selection would be appropriate to enhance grain yield. Path
analysis revealed that plant height had the highest direct and indirect effects on grain yield,
indicating that plant height can be further exploited as the main trait in future breeding programmes for grain yield increment.
Hybrid 10MAK10-1/N3 was the best hybrid at Ukulinga in terms of grain yield, relative yield
and economic traits. Whereas hybrid T17/L83 was the best hybrid at Cedara in terms of
grain yield and relative yield; however, T11/L102 was selected as the most elite hybrid with
respect to grain yield, relative yield and economic traits. Hybrid T3/L48 was identified as thebest hybrid at Dundee with respect to grain yield, relative yield and prolificacy. At Potchefstroom the standard check PAN6611 was identified as the best hybrid in terms of grain yield and relative yield followed by developmental hybrid T1/L28; however,
developmental hybrid T1/L28 was the best in terms of earliness, prolificacy and ear aspect.
Stability coefficients and cultivar superiority index across the sites revealed that four
developmental hybrids were identified as best hybrids and they performed better than the
standard check. These hybrids will be recommended for further testing in advanced trials.
With respect to cultivar superiority, the desired hybrids are required to combine high grain
yield with economic and adaptive traits such as high ear prolificacy, low grain moisture, and
low ear aspect score (desired) for them to adapt to production environments in South
Africa. There was significant variation among the top 25 yielding hybrids. At least 5 hybrids
combined high grain yield with the desired complimentary adaptive traits such as quick
moisture dry down, prolificacy and ear aspect. The results showed that there is variation in
the performance of high yielding genotypes within all the sites, and that agronomically superior cultivars can be identified.
The study shows that there is significant variation among the RILs since they interacted
differently with the 9 tropical testers. Even among the top 25 selections of RILs in each
environment there was still variation for combinations of the desired traits. Significant
associations among grain yield and other economic and adaptive traits were observed with
implications for breeding strategy. Above all the significant variation gives large score for future breeding of new unique lines. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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Soil nitrate and ammonia levels as affected by no-till and conventional tillage, monoculture corn and soybean, corn-soybean and corn- soybean-alfalfa rotations, and added NGaliano, Norma Graciela. January 1996 (has links)
Corn (Zea mays L.) production under monoculture and conventional tillage systems may land to soil degradation and nitrate (NO$ sb3 sp-$) pollution of surface and groundwater. This study evaluated the impact of no-till and conventional tillage, monoculture corn and soybean, corn-soybean rotations and corn-soybean-alfalfa rotations, and three fertilizer N rates applied to monoculture corn or soybean, and corn in rotation, on soil NO$ sb3$-N and NH$ sb4$-N levels. Experimental sites were a Ste-Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Results obtained from fall 1992 to spring 1995 showed that tillage had no effect on soil N levels under corn. Soil N levels under corn showed a linear response to added N, specially in the fall. Soil N levels under corn did not change considerably during the non-growing season. Higher spring NO$ sb3$-N levels, particularly in plots under conventional tillage and alfalfa or soybean, compared to fall values indicated greater nitrification and/or mineralization than denitrification, immobilization or leaching. Low NH$ sb4$-N levels indicated that nitrification processes were active. No consistent estimation could be made of fertilizer N credits for corn from either soybean or alfalfa based on NO$ sb3$-N levels in soil.
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Yield response of Fusarium infected maize seed treated with biological control agent formulationsGerber, Johan,1961- 11 1900 (has links)
Potential vegetative and reproductive increases in yield, as well as the biological efficacy against Fusarium verticillioides and F. proliferatum causing ear and stem rot in maize crops of commercially-formulated micro-organism formulation T-Gro (Trichoderma harzianum isolate DB103 WP) combined with Spartacus (Beauveria bassiana isolate DB 105 WP), T-Gro combined with Armenius (Bacillus subtilis isolate DB 109 WP), T-Gro combined with Maximus (Bacillus subtilis isolate DB 108 WP), T-Gro combined with Shelter (Bacillus subtilis isolate DB 101), T-Gro combined with Bismarck (Microbacterium maritypicum isolate DB 107 WP), as well as individual treatments of T-Gro, Armenius, Bismarck, Maximus and Shelter, were investigated when applied to maize seed and soil under field conditions. All the micro-organism treatments were compared with Thiram 750WP (750g/kg thiram WP) and an untreated control.
The micro-organism treatments showed an increase in vegetative as well as reproductive yields when compared to the reference product Thiram 750 WP and the untreated control. There were no observations of adverse effects on the germination of maize seed in all the treatments that were applied. The three isolates B. subtilis, T. harzianum, and M. maritypicum, showed a significant reduction in vascular tissue discolouration of the main and ear stems, indicating a potential to be used in the reduction and control of diseases caused by Fusarium spp. Results also showed poor to very good increases of stem and foliage biomass as well as cob yield per plant produced by the micro-organism treatments when compared to the untreated control. The highest cob yield per plant that differed significantly from the untreated control was produced by T-Gro and Shelter.
No phytotoxicity of any kind was observed with the application of the micro-organism formulations and they could therefore be deemed suitable to be used for the treatment of maize seed. The micro-organism formulations containing fungal and bacterial biological control agents have the potential to be used in commercial maize production to increase vegetative and reproductive yields and reduce the severity of ear and stem rot in maize. / Agriculture Animal Health and Human Ecology / M.Sc. (Agriculture)
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Soil nitrate and ammonia levels as affected by no-till and conventional tillage, monoculture corn and soybean, corn-soybean and corn- soybean-alfalfa rotations, and added NGaliano, Norma Graciela. January 1996 (has links)
No description available.
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Cover crop biomass production and effects on weeds and soil fertility in a maize-based conservation agriculture systemMuzangwa, Lindah January 2011 (has links)
Low cover crop biomass production is a major obstacle to the success of conservation agriculture currently promoted as panacea to the inherent problem of soil erosion and loss of soil productivity in the Eastern Cape (EC). Therefore, this study evaluated cover crop management strategies for optimizing biomass production for better soil cover, soil nitrogen (N) and phosphorus (P) fertility, weed control and maize yields. The strategies tested are cover crop bicultures, selection of an adapted lupin cultivar and seeding rate, and the feasibility of rain fed winter cover cropping. The cover crop experiments were carried in rotation with summer maize between the winter of 2009 and summer of 2010/2011. Biculture trial was carried out by seeding oat (Avena sativa) and vetch (Vicia dasycarpa) at three mixture ratios and as sole crops under irrigation. On a separate irrigated trial, two lupin cultivars (Lupinus angustifolius var Mandelup & Qualinock) were seeded to a range of seeding rate, 40 to 220 kg ha-1. To study the feasibility of rain fed winter cover cropping, oat, vetch, rye (Lolium multiflorum), barley (Hordeum vulgare), radish (Raphanus sativa) and triticale (Triticale secale) were relayed into a maize crop in February, March and April of 2010. The irrigated trials were followed with SC701 maize cultivar, whilst the rain fed trial was followed with DKC61-25 maize cultivar. Bicultures gave higher cover crop biomass than sole vetch, increasing with an increase in the oat component of the mixture. Increased N and P uptake was observed with bicultures compared to sole oat, however, the levels were comparable to sole vetch. Sole vetch increased soil inorganic N and P at maize planting, whilst the slow decomposition by sole oat residue resulted in mineral lock up. Bicultured cover crop residues had intermediate decomposition rates and resulted in optimum levels of inorganic N and P for prolonged periods compared to sole crops. Weed suppression by the bicultures was comparable to sole cover crops. Biculturing technology significantly (P<0.05) increased maize grain yield compared to sole oat and the yields were comparable to those from sole vetch. For lupins, 206 kg ha-1 seeding rate gave the optimum biomass yield. Weed dry weights in both cover crop and maize crop decreased with an increase in lupin biomass. Comparable soil total N and inorganic P values at maize planting, were observed from plots planted to 120, 180 and 220 kg ha-1. Maize grain yield increased with an increase in lupin seeding rate. The study on rain fed winter cover cropping had most cover crop species’ biomass decreasing with each delay in planting except for radish, which increased. Vetch produced the highest amounts of biomass from February and March planting whilst radish had the highest biomass in April planting. The two species resulted in the greatest N improvement compared to the other species. Regardless of the grazing, the grass specie residues managed to persist to the next cropping season and the residue remaining were comparable to that of radish and vetch. Late-planted cover crops had the greatest residue remaining than early-planted, as a result, April planted cover crops provided better weed suppression than March and April planted. Vetch provided the highest maize grain yield (4005 kg ha-1) whilst all other species tested had comparable grain yields. The results suggested that bicultures could be grown to give sufficient biomass for both weed suppression and soil fertility improvement. Furthermore, increasing lupin plant densities improve its function as a cover crop with respect to weed suppression, soil fertility improvement and maize yields. The study also showed that for dry land systems, February and March planted vetch and April planted radish can provide the greatest biomass and maize yield improvement.
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Strategies for Optimizing Nitrogen Use in Corn with and without Subsurface DrainageTwedt, Evan Jacob January 2011 (has links)
Excessive soil moisture can impact planting date, plant establishment, and N availability, resulting in reduced yields and N use efficiency. Nitrogen management practices such as use of urease and nitrification inhibitors, and split applications may be used to reduce N lost during the growing season, improving N use efficiency and crop productivity. The objective of this study was to determine whether N management practices could improve corn (Zea mays L.) productivity with or without subsurface drainage on a fine-textured clay soil in eastern North Dakota. Five field trials were conducted in 2009 and 2010 in eastern North Dakota. Treatments consisted of a factorial combination of N management practices [urease inhibitor n-(n-butyl) thiophosphoric triamide (NBPT), starter fertilizer, nitrification inhibitor 2-Chloro-6-(trichloromethyl) pyridine (nitrapyrin), and split applications], N rates (56, 112, 168, and 224 kg N ha-1), and the presence of subsurface drainage (two environments). In both 2009 and 2010 there was no grain yield differences among drainage treatments. Differences in grain yield were observed with different N rates. Nitrogen management practices also affected grain yield. The interactions between N management practices and drainage were not significant. End of season stalk nitrate content showed differences in N availability with different N rates, but not N management practices. Neither NBPT nor the starter fertilizer significantly increased yield over the untreated check in any environment. Nitrapyrin significantly increased yield over the untreated check at Fargo in 2010. Increased N rates resulted in greater corn grain protein.
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Effectiveness of varied refugia configurations for the genetically modified maize (Zea mays L.) in Kwa-Zulu-Natal midlandsMoodley, Odeshnee 11 1900 (has links)
Genetically modified (GM) white and yellow maize, Zea mays, has been commercially released and cultivated in South Africa since 1997/1998. The traits expressed are insect resistance and herbicide tolerance conferred by the bacteria Bacillus thuringiensis (Bt) Cry genes and Agrobacterium 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase gene, respectively. The Cry genes have been used widely to control lepidopteran insect pests but insect resistance to GM Bt crops has been a concern since the introduction of this technology. A management strategy includes refugia planting of 5% non-Bt plants, with no insecticide application, and 20%, where insecticide application is allowed. These refugia are designed to allow the survival of insect pests within restricted planted zones. However, in South Africa there are reports of Bt-resistant stem borer (Busseola fusca) (Fuller) (Lepidoptera: Noctuidae) and non-compliance with refuge planting. The aims of this study were two-fold: 1. To conduct a survey among KwaZulu-Natal (KZN) GM maize growers to ascertain information such as level of compliance with refuge planting and to determine which refugia were predominantly planted and reasons thereof; 2. To conduct a replicated field trial to determine yield, insect borer damage and economic benefit of the 5% unsprayed and 20% sprayed refuge options (including three configurations namely strip, perimeter and block and a 5 and 20% ‘refuge-in-a-bag’ option). The survey indicated that 28 out of 29 (96.6%) KZN Bt maize growers plant the 5% non-sprayed refuge with 27 (96.4%) of those respondents planting the strip configuration for the purpose of insect management (75%) and ease of planting (32.2%). The survey also showed that 7 (seven) i.e. 21.9% of KZN Bt maize growers observed borer damage and although growers are now fully compliant with refugia planting requirements, initially 7 respondents (24.1%) did not comply with or plant refugia correctly. Furthermore, 7 respondents reported insect borer damage in their maize with 4 of the 7 instances (57.1%) likely stemming from incorrectly planted refugia.
vii
No significant differences in yield or insect damage were observed between the 5 and 20% refugia for any of the planting configurations in the field trial. However due to costs involved with insecticide application and labour required for the operation in the 20% option, these treatments were less economically advantageous than the non-Bt control. The 20% block and strip configurations had a cost benefit ratio of ZAR 7.21 and ZAR 6.67 respectively, earned per R1 spent by the grower compared with ZAR 7.76 in the sprayed control. The cost-benefit comparison for the 5% block and strip configurations was ZAR 8.48 and ZAR 7.71, respectively compared with ZAR 9.44 in the unsprayed control. In addition, the 20% seed mixture limited borer damage to 4.95% when compared with 15.77% damage in the sprayed control (ANOVA, F pr = 0.124). The seed mixtures are not available commercially and the results from the survey indicated that some education and marketing by the seed companies would be advisable prior to their release to the farming community.
In order to determine which of the refuge options between 5 and 20% would be more advantageous for growers overall, regardless of the planting configuration; data were grouped and analysed. There were no significant differences in either the yield or insect damage for the 5 and 20% refugia, but the cost-benefit calculations indicated that the 5% option was more cost effective – for the 5 and 20% refugia, ZAR 7.97 and ZAR 7.15 respectively, earned per ZAR 1 spent by the grower (ANOVA, F pr. = 0.03). This is because no insecticide was used in the 5% treatments. Mean ear damage comparisons between the 5 and 20% refugia showed that the 20% refuge in the perimeter configuration incurred the least damage (2.65% ear damage) compared with 5% perimeter (10.86% ear damage), although the reasons for this are not clear.
While the results of the field trials showed no significant differences in insect damage and yield with regard to choice of refuge configuration, monitoring insect resistance management remains an integral part of Bt maize crops in South Africa, in order to delay further resistance development and to prolong the viability of Bt technology. / Agriculture and Animal Health / M. Sc. (Agriculture)
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