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.

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.

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.

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).

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.

Not available

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.

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.

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.

Not available