Spelling suggestions: "subject:"agroclimatic factors.both africa."" "subject:"agroclimatic factors.both affrica.""
1 |
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.
|
2 |
Simulating the effects of nitrogen and phosphorus on the growth and yield of maize in Vhembe District, Limpopo ProvinceMakhaga, Ngeletshedzo Superior 25 February 2013 (has links)
MSCAGR / Department of Soil Science
|
3 |
Climate change awareness: a case study of small scale maize farmers in Mpumalanga province, South AfricaOduniyi, Oluwaseun Samuel 07 1900 (has links)
This study was conducted in the Nkangala district, in the province of Mpumalanga in South Africa. This province remains the largest forestry production region in South Africa. The majority of people living in Mpumalanga are farmers and they have contributed immensely to promote food security. The objective of the study was to determine the level of climate change awareness among small scale maize producers in Mpumalanga province. Random sampling techniques was used to select two hundred and fifty one (251) farmers to be interviewed. A pre-tested questionnaire was administered to maize farmers, focusing on matters relating to climate change awareness in maize production. Data was captured and analysed using software package for social science (SPSS version 20 of 2012). Descriptive statistics were applied to analyse and describe the data. Logistic regression analysis followed to demonstrate the significance of the independent variables on climate change awareness. The results of the analysis indicated that the information received and the size of the farm had an impact on climate change awareness in the area of study. It was therefore recommended that the majority of farmers in Mpumalanga needed to be made aware of climate change in order to assist them to build the adaptive capacity, increase resilience and reduce vulnerability. Information on climate change awareness should be disseminated well to ensure that it will attract the attention of the farmers / Agriculture and Animal Health / M.Sc. (Agriculture)
|
4 |
Climate change awareness: a case study of small scale maize farmers in Mpumalanga province, South AfricaOduniyi, Oluwaseun Samuel 07 1900 (has links)
This study was conducted in the Nkangala district, in the province of Mpumalanga in South Africa. This province remains the largest forestry production region in South Africa. The majority of people living in Mpumalanga are farmers and they have contributed immensely to promote food security. The objective of the study was to determine the level of climate change awareness among small scale maize producers in Mpumalanga province. Random sampling techniques was used to select two hundred and fifty one (251) farmers to be interviewed. A pre-tested questionnaire was administered to maize farmers, focusing on matters relating to climate change awareness in maize production. Data was captured and analysed using software package for social science (SPSS version 20 of 2012). Descriptive statistics were applied to analyse and describe the data. Logistic regression analysis followed to demonstrate the significance of the independent variables on climate change awareness. The results of the analysis indicated that the information received and the size of the farm had an impact on climate change awareness in the area of study. It was therefore recommended that the majority of farmers in Mpumalanga needed to be made aware of climate change in order to assist them to build the adaptive capacity, increase resilience and reduce vulnerability. Information on climate change awareness should be disseminated well to ensure that it will attract the attention of the farmers / Agriculture and Animal Health / M. Sc. (Agriculture)
|
5 |
Drought analysis with reference to rain-fed maize for past and future climate conditions over the Luvuvhu River catchment in South AfricaMasupha, Elisa Teboho 02 1900 (has links)
Recurring drought conditions have always been an endemic feature of climate in South Africa, limiting maize development and production. However, recent projections of the future climate by the Intergovernmental Panel on Climate Change suggest that due to an increase of atmospheric greenhouse gases, the frequency and severity of droughts will increase in drought-prone areas, mostly in subtropical climates. This has raised major concern for the agricultural sector, particularly the vulnerable small-scale farmers who merely rely on rain for crop production. Farmers in the Luvuvhu River catchment are not an exception, as this area is considered economically poor, whereby a significant number of people are dependent on rain-fed farming for subsistence. This study was therefore conducted in order to improve agricultural productivity in the area and thus help in the development of measures to secure livelihoods of those vulnerable small-scale farmers.
Two drought indices viz. Standardized Precipitation Evapotranspiration Index (SPEI) and Water Requirement Satisfaction Index (WRSI) were used to quantify drought. A 120-day maturing maize crop was considered and three consecutive planting dates were staggered based on the average start of the rainy season. Frequencies and probabilities during each growing stage of maize were calculated based on the results of the two indices. Temporal variations of drought severity from 1975 to 2015 were evaluated and trends were analyzed using the non-parametric Spearman’s Rank Correlation test at α (0.05) significance level. For assessing climate change impact on droughts, SPEI and WRSI were computed using an output from downscaled projections of CSIRO Mark3.5 under the SRES A2 emission scenario for the period 1980/81 – 2099/100. The frequency of drought was calculated and the difference of SPEI and WRSI means between future climate periods and the base period were assessed using the independent t-test at α (0.10) significance level in STATISTICA software.
The study revealed that planting a 120-day maturing maize crop in December would pose a high risk of frequent severe-extreme droughts during the flowering to the grain-filling stage at Levubu, Lwamondo, Thohoyandou, and Tshiombo; while planting in October could place crops at a lower risk of reduced yield and even total crop failure. In contrast, stations located in the low-lying plains of the catchment (Punda Maria, Sigonde, and Pafuri) were exposed to frequent moderate droughts following planting in October, with favorable conditions noted following the December planting date. Further analysis on the performance of the crop under various drought conditions revealed that WRSI values corresponding to more intense drought conditions were detected during the December planting date for all stations. Moreover, at Punda Maria, Sigonde and Pafuri, it was observed that extreme drought (WRSI <50) occurred once in five seasons, regardless of the planting date.
Temporal analysis on historical droughts in the area indicated that there had been eight agricultural seasons subjected to extreme widespread droughts resulting in total crop failure i.e. 1983/84, 1988/89, 1991/92, 1993/94, 2001/02, 2002/03, 2004/05 and 2014/15. Results of Spearman’s rank correlation test revealed weak increasing drought trends at Thohoyandou (ρ = of 0.5 for WRSI) and at Levubu and Lwamondo (ρ = of 0.4 for SPEI), with no significant trends at the other stations. The study further revealed that climate change would enhance the severity of drought across the catchment. This was statistically significant (at 10% significance level) for the near-future and intermediate-future climates, relative to the base period.
Drought remains a threat to rain-fed maize production in the Luvuvhu River catchment area of South Africa. In order to mitigate the possible effects of droughts under climate change, optimal planting dates were recommended for each region. The use of seasonal forecasts during drought seasons would also be useful for local rain-fed maize growers especially in regions where moisture is available for a short period during the growing season. It was further recommended that the Government ensure proper support such as effective early warning systems and inputs to the farmers. Moreover, essential communication between scientists, decision makers, and the farmers can help in planning and decision making ahead of and during the occurrence of droughts. / Agriculture, Animal Health and Human Ecology / M. Sc. (Agriculture)
|
Page generated in 0.0696 seconds