Thesis (MScAgric)--University of Stellenbosch, 1994 / 127 Leaves printed single pages, preliminary pages i-viii and numberd pages 1-118.Includes bibliography,tables and figures. / Date on t.p.: Dec. 1994. / ENGLISH ABSTRACT: Effects of pH,sucrose, boric acid and temperature on in vitro germination of pollen of Protea repens (L.) L. cv. 'Embers' were investigated in hanging-drop culture to establish optimum conditions for germination. Optimum values were found within ranges pH: 5 - 8, sucroseconcentration:0.4 - 0.7 M, boric acid concentration:50 - 500 mg.e-1 , and incubation temperature: 5 - 30°C. Storage temperature and humidity on pollen viability was studied in four Pro tea clones. Pollen was stored at a range of temperatures and relative humidities for up to one year and tested for ability to germinate in vitro. Pollen of P. repens cv. 'Sneyd', P. eximia cv. 'Fiery Duchess' andP. magnifica clone 'T 84 07 OS', stored in liquid nitrogen (-196°C) and in a freezer (-14° to -18°C), retained a germination percentage as high as that of fresh pollen regardless of humidity. The study showed that long-term storage of protea pollen is not feasible at temperatures above O°C. The correlations between the fluorochromatic reaction (FCR) and germinability were found to be low and nonsignificant. Fifteen month old cryopreserved 'Sneyd' pollen was shown to retain its ability to fertilize and set seed equal to that of fresh pollen. 'Sneyd', 'Fiery Duchess' and 'T 84 07 OS' pollen could be repeatedly thawed and frozen in liquid nitrogen before its germinability in vitro decreased. The morphology and size of Protea pollen was studied, using light and scanning electron microscopy. Polymorphic grains were observed in two interspecific hybrids. Very small differences in pollen grain size were recorded between clones/species. The male fertility of 25 interspecific Pro tea hybrids, based on in vitro pollen germinability, was investigated. The majority of hybrids were found to be sufficiently fertile to be used in a breeding programme. Pistil structure and pollen tube pathways were investigated in 'Sneyd' using light and scanning electron microscopy. The pistil had four distinct regions, consisting of the stigma, the vertebra-shaped upper style, the heart-shaped lower style, and the ovary. The pistil had a stylar canal along its entire length and this canal was also the route by which pollen tubes grew to the ovary. Very low numbers of pollen tubes reached the ovary. The breeding system of 'Sneyd' and 'Fiery Duchess' were determined from pollen tube and seed set data, after controlled hand-pollinations. Both clones were found to be fully selfcompatible. Very low percentages autogamous seed set were recorded. Interspecific crosses had a low success rate. An incompatibility reaction probably occurred on the stigma and/or in the upper style regions.The attainment of maximum stigma receptivity of two Protea cultivars was investigated by means of seed set experiments, pollen tube growth observations and measurement of the degree of opening and closing of the stigmatic groove. Both cultivars were found to be protandrous. The maximum stigmatic groove width of both cultivars never exceeded the pollen grain diameter. It was concluded that Protea spp. must be hand-pollinated two to six days after anthesis in order to obtain maximum seed set; while for the observations of pollen tubes in the ovary, inflorescences must not be harvested before seven days after pollination. / AFRIKAANSE OPSOMMING: Ten einde 'n optimale medium vir die in vitro-ontkieming van Protea-stuifmeel te ontwikkel, is die effek van pH, sukrose, boorsuur, en temperatuur op die in vitro-ontkieming van Protea repens (L.) L. cv. 'Embers'-stuifmeel deur middel van die hangdruppel-metode ondersoek. Die volgende reekse van veranderlikes wat getoets is, is as optimaal gevind; pH: 5 - 8, sukrosekonsentrasie: 0.4 - 0.7 M, boorsuurkonsentrasie: 50 - 500 mg.e-1 en inkubasietemperatuur: 5 - 30°C. Die invloed van bergingstemperatuur en humiditeit op stuifmeel-Iewenskragtigheid is in vier Protea-klone ondersoek. Stuifmeel is gestoor by 'n reeks temperature en relatiewe humiditeite vir tot eenjaar, en vir in vitro-ontkiemingsvermoe getoets.' Stuifmeel van P. repens <?v. 'Sneyd', P. eximia cv. 'Fiery Duchess', en P. magnifica kloon'T 84 07 OS', in vloeibare stikstof (-196°C) en in 'n vrieskas (-14° tot - 18°C) geberg, het 'n ontkiemingspersentasie gelykstaande aan die van vars stuifmeel gehandhaaf, ongeag van die humiditeit. Hierdie studie het verder aangetoon dat langtermynberging van Protea-stuifmeel bokant O°C me die moeite werd is me. Die korrelasie tussen die fluorochromatiese reaksie (FCR) en ontkieming was laag en me betekemsvol me. 'Sneyd' -stuifmeel wat vir 15 maande in vloeibare stikstof gestoor is, het die bevrugtings- en saadsetvermoe gelykstaande aan vars stuifmeel behou. 'Sneyd', 'Fiery Duchess' en 'T 84 07 OS'-stuifmeel kon herhaaldelik in vloeibare stikstof gevries en ontdooi word voordat hul ontkiemingsvermoe afgeneem het. Die morfologie en grootte van Proteastuifmeel is deur middel van lig- en skandeerelektronmikroskopie bestudeer. Polimorfiese stuifmeelkorrels is in twee interspesie-hibriede waargeneem. Baie klein verskille in stuifmeelkorrelgroottes het tussen klone/spesies voorgekom. Die manlike vrugbaarheid van 25 Protea-interspesiehibriede, gebaseer op die in vitro-ontkiembaarheid, is ondersoek. Dit is gevind dat die meerderheid hibriede 'n voldoende graad van vrugbaarheid het om in 'n teelprogram te gebruik. Die stamperstruktuur en stuifmeelbuiswee in P. repens is deur middel van lig- en skandeer-elektronmikroskopie ondersoek. Die stamper bestaan uit vier kenmerkende gebiede, naamlik die stempel, die werwelvormige bo-styl, die hartvormige onderstyl, en die vrugbeginsel. Die stamper het 'n stylkanaal regdeur die totale lengte van die stamper, en hierdie kanaal is ook die weg waarvolgens stuifmeelbuise na die vrugbeginsel gegroei het. Min stuifmeelbuise het die vrugbeginsel bereik. Die teelsisteem van 'Sneyd' en 'Fiery Duchess' is deur middel van stuifmeelbuis- en saadsetdata na gekontroleerde handbestuiwings ondersoek. Beide kIone was ten volle selfverenigbaar. Die persentasie outogame saadset was baie laag. Interspesiekruisings het 'n baie lae sukses gehad. Dit is voorgestel dat die onverenigbaarheidsreaksie in die stempel en/of in die bopunt van die styl plaasvind. Die bereiking van maksimum stempelontvanklikheid van twee Protea-cultivars is deur middel van saadseteksperimente, stuifmeelbuisdata en waarnemings van die oop- en toemaak van die stempelgroef ondersoek. Beide cultivars was protandries. Die maksimum stempelgroefwydte het nooit die stuifmeelkorreldeursnee oorskry nie. Dit is afgelei dat Protea-spesies twee tot ses dae na antese handbestuif moet word vir optimale saadset. Vir die waarneming van stuifmeelbuise in die vrugbeginsel, moet bloeiwyses nie voor sewe dae na bestuiwing geoes word nie.

Sweetpotato (Ipomoea batatas, L.) is one of the important sources of carbohydrates and economic income in Mozambique. As with most of the food crops in Mozambique, it is usually produced by small-scale farmers under dryland conditions. Despite the importance of the crop, the storage root yields are still low and it is difficult to keep planting material (vines) for the next planting season. One of the major challenges to production is drought stress. Drought stress affects sweetpotato by retarding aboveground growth, reducing total root yield, percentage of dry mass, and reducing the quality of the roots as a result of the increase in damage caused by the sweetpotato weevil (Cylas formicarius). The objective of this study was to identify sweetpotato genotypes tolerant to drought particularly amongst the orange fleshed types which can be used in breeding programmes to improve the drought tolerance of genotypes grown in Mozambique. To this end, 48 genotypes were evaluated in both field and greenhouse studies conducted at Umbeluzi Research Station (26º 03’ S, 32ºC 23’ E; 12 masl) located about 30 km from Maputo city. The field trial was a three replicate, α-design with split-plots. Genotypes were the wholeplot treatment factor and irrigation levels were the sub-plot treatment factor. The three irrigation levels imposed were: nonstressed plants irrigated from planting to 120 DAP; moderately stressed, plants irrigated until 60 DAP; and severely stressed, plants irrigated until 30 DAP. In the greenhouse trial the 48 genotypes were grown in wooden boxes arranged in a two replicate, randomized complete block design. The plants were exposed to water stress from 10 DAP to the end of experiment at 60 DAP. Genotypes were significantly different for all traits, namely: survival %, vine vigour, aboveground biomass, total and commercial root yield, total fresh biomass, harvest index, β-carotene content, % dry mass, dry mass yield, incidence of sweetpotato virus disease, and incidence of weevil damage. Irrigation levels were significant for the traits: survival %, vine vigour, aboveground biomass, total and commercial root yield, total fresh biomass, harvest index, β-carotene content, % dry mass, and dry mass yield. Irrigation levels were not significant for incidence of sweetpotato virus disease and incidence of weevil damage. The genotypes x irrigation levels interaction was significant for: total and commercial root yield, and incidence of weevil damage; and not significant for: survival %, vine vigour, aboveground biomass, total fresh biomass, harvest index, β-carotene content, % dry mass composition, dry mass yield and incidence of sweetpotato virus disease. The mean dry mass yields across irrigation levels of the national breeding lines and introduced genotypes were higher than the landrace genotypes. Most of the national breeding lines had higher β-carotene content than the introduced and landrace genotypes. The landrace genotypes had relatively higher % dry mass composition compared to the national breeding lines. The stress tolerance index (STI) separated the 48 sweetpotato genotypes evaluated in the field trial into three groups: drought tolerant (high STI); moderate drought tolerant (intermediate STI); and drought sensitive (low STI). Under moderate stress, yield potential (Yp) and yield in a stress environment (Ys) were highly significant, positively correlated with Mean productivity (MP), Geometric mean productivity (GMP), Stress tolerance index (STI) and Tolerance index (TOL). Under severe stress the same correlations were reported. Under moderate and severe stress, the correlation between stress tolerance index (STI) and Stress susceptibility index (SSI) was significant and negative. In the greenhouse trial, differences between genotypes in vine length increment, vine diameter increment, leaf width increment and number of nodes vine-1 were significant (P<0.05). Vine length, vine diameter, leaf width and length increments either increased or were reduced due to water stress. Less than 10% increment in vine length (between 25 and 50 DAP) was recorded in MGCl01, Atacama, Cordner, Beauregard, and CN1448-49. Higher than 40% vine length increment was recorded in Jonathan and UNK-Malawi, Naspot, MUSG0614-24, Resisto, K566632, Tainung64, Ejumula and MUSG0623-09. Vine diameter decreased in Manhissane and MUSG0616-18. No change in leaf length in Tacna and Jonathan and in leaf width in Xihetamakote and Resisto-Nairobi was recorded. The longest petiole length at 30 DAP was recorded by Tacna and the shortest by Nhacutse4. The longest internode length was recorded in 199062.1. Similar to petiole length, Nhacuste4 reported the shortest internode length. The highest number of primary vines was recorded by MUSG0608-61 and lowest by Beauregard. Of the 48 genotypes exposed to water stress, 18 survived until the end of the greenhouse experiment at 60 DAP and were therefore considered to be drought tolerant. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, 2011.

A study was undertaken to compare growth potential of three Eucalyptus species of natural origin in South Eastern Australia, with commercially grown species on mid and high altitude temperate sites in the summer rainfall growing zones in South Africa. The three species were Eucalyptus globulus subsp. bicostata (E. bicostata), Eucalyptus cypellocarpa and Eucalyptus nobilis. Nine sites were selected to represent the growing areas of South Africa experiencing cold winter drought with occasional snow falls. Improved, commercially grown pure Eucalyptus species and interspecific hybrid clones were included as controls in the trials to give comparative growth performances on specific sites. Both balanced and unbalanced lattice designs were used to evaluate the growth potential of the unimproved Australian species and the improved commercial controls incorporated into the trials. Volume production and basal area growth were assessed for the three species at all sites. However, only three sub species E.globulus (E. bicostata, E. maidenii and E. globulus) showed varying levels of disease (Mychosphaerella nobilosa) infestation and this was therefore assessed in trials at 12 and 30 months respectively, and correlation analysis was used to study the relationship between the impact of disease infestation and growth performance. It was found that negative phenotypic correlations existed between the levels of infection and tree growth. ie greater infection slower growth. Evaluation of genotype x environment interaction (GXE) revealed that this did not exist in the E. bicostata nor E. nobilis populations, and therefore one population of each species can be developed for all the sites tested. E. cypellocarpa was the only species that showed some GXE interaction implying that separate populations to be developed for different sites. Contrary to what was expected, unimproved Eucalyptus species being investigated performed equally as well as the improved commercial species included as controls, thus providing potential for commercial deployment with selection and breeding. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Groundnut (Arachis hypogaea L.) is one of the most important legume crops in Malawi. However, production among smallholder farmers has declined in recent years. One of the constraints affecting groundnut production is groundnut rosette disease (GRD). Therefore, the main objective of this study was to develop appropriate groundnut cultivars that are resistant to GRD, combined with other traits preferred by farmers, in order to improve income and food security of smallholder farmers in Malawi and beyond. The specific aims were; (i) to assess groundnut cropping systems used by smallholder farmers in Malawi, their varietal preferences, and production challenges (ii) to assess the genetic diversity among groundnut germplasm collected from ICRISAT, the Chitedze gene bank and farmers (iii) to identify sources of resistance to GRD and to its aphid vector (iv) and to understand the type of gene action governing GRD resistance, and to identify groundnut genotypes suitable for use as parents in breeding for GRD resistance. Assessment of groundnut cropping systems used by smallholder farmers, their varietal preferences, and production challenges was done by using a field survey and participatory rural appraisal (PRA) tools. The field survey was done in Lilongwe, Mchinji and Salima while the PRA was done in Kasungu, Lilongwe, and Salima. The assessment of genetic diversity among 106 groundnut genotypes collected from ICRISAT, Chitedze gene bank and farmers was done using 19 SSR markers. High throughput DNA extraction was done followed by polymerase chain reactions (PCR) after which the amplified products were analyzed. Evaluation of genotypes to identify new sources of resistance to GRD and its aphid vector was conducted under two test situations, one with high inoculum levels and one with low inoculum levels. Under high inoculum level, the infector row technique developed by Bock and Nigam (1990) which employs a susceptible variety as a disease spreader was used. While under low inoculum level, an aphid resistant variety instead of the infector row was used to control the aphids. Aphid resistance was studied under field and glasshouse conditions. Plants were planted in rows and at 14 DAS, 2 aphids were place on each plant. Aphid resistance was determined by observing the increase in number of the aphid population on the test plants. Gene action governing inheritance of resistance to GRD was studied under high disease pressure created by using viruliferous aphids. Parents and F2 generations and their reciprocals were used in the study. The trials were laid out in a glasshouse and aphids were infested a week after germination and were killed after 7 days using Dimethoate. Disease data was collected at 7, 14, 21 and 28 days after aphid infestation. The study on groundnut cropping systems, varietal preferences and production challenges revealed that most farmers grew groundnut alongside maize (Zea mayis L.) and beans (Phaseolus vulgaris L.) as food crops and tobacco (Nicotiana tabacum L.) and cotton (Gossypium hirsutum L.) as cash crops. The most preferred groundnut varieties grown by farmers were Chalimbana and CG 7. GRD was observed in half of the fields visited. However, 98% of the farmers interviwed had experienced it in their fields at some point, and 63.3% of the farmers believed that GRD was a major problem. Other challenges noted by farmers included lack of quality seed, poor extension support, lack of inputs, manipulation of the markets by buyers, and the failure of groundnut crops to meet the high standards required by the market. The examination of genetic diversity among 106 groundnut genotypes revealed a total number of 316 alleles with a mean of 17 alleles per locus. Polymorphic information content (PIC) and gene diversity values were high, which indicated that genetic diversity among the groundnut genotypes was high. The analysis of molecular variance indicated that 72.9% of the genetic variation observed in the genotypes was due to the variation between individuals within rather than between specific population groups. The evaluation of genotypes for resistance to GRD revealed five highly resistant genotypes namely ICG 9449, ICG 14705, ICGV-SM 05701, MW 2672 and MW 2694. Farmer preferred genotypes were rated as either moderately resistant or susceptible to GRD. Aphid resistance was only recorded in ICG 12991. Yield and GRD incidence were negatively and moderately correlated, which confirmed that GRD has the potential to reduce yield in groundnuts. The highly resistant genotypes were also high yielding except for genotype ICG 9449. Farmer preferred genotypes CG 7, Chalimbana and Tchayilosi, also gave above average yields, despite high disease incidence levels, which showed that these genotypes have tolerance to GRD. The study on gene action governing GRD resistance revealed information on combining ability effects of GRD resistance. The diallel analysis showed that GCA, SCA, reciprocal, maternal and non-maternal effects were all significant, which indicated that both additive and non-additive gene effects played a role in governing GRD resistance. The significance of SCA and reciprocal effects indicated that maternal parents played an important role in the expression of GRD resistance. However, the additive effects were predominant over non-additive gene effects. Four of the resistant genotypes, ICG 14705, MW 2694, ICGV-SM 05701, and MW 2672, were the best combiners for GRD resistance. Generally, the study indicates that there is still a need to develop new varieties with resistance to GRD having traits preferred by farmers to enhance adoption. There is also a need for breeders to work with extension staff in promoting new varieties and also there is need for extension staff to actively provide information to farmers on production and marketing of groundnut. Groundnut is widely known to have a narrow genetic base which has been a bottleneck to its improvement. However, the high genetic diversity observed in this study provides a basis for selection of appropriate parental genotypes for breeding programmes which can enhance further the broadening of the groundnut genetic base. Identification of the genotypes with high resistance to GRD in this study provides an opportunity to breed more GRD resistant materials. The observation that additive gene effects are predominant in governing GRD resistance means that GRD resistant materials can be improved by introgressing additive genes using recurrent selection breeding procedures. There is also a need to employ molecular techniques which can help in shortening the entire breeding process. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Understanding direct and indirect defense mechanisms that enhance host plant resistance (HPR) and biological control is critical for successful development of an integrated pest management (IPM) approach. Cassava green mite (CGM) (Mononychellus tanajoa Bondar (Acari: Tetranychidae)) is a major arthropod pest of cassava (Manihot esculenta Crantz) in Africa. Strategies to control CGM include HPR and biological control by use of exotic natural enemies particularly the predatory mite Typhlodromalus aripo DeLeon (Acari: Phytoseiidae). The success of the latter depends on continuous survival of the natural enemy which requires suitable host plants and weather conditions. Various plant morphological traits have been recognized as indirect defense mechanisms that enhance HPR to CGM, and/or attract T. aripo in cassava. It was envisaged that integration of HPR and classical biological control approaches through manipulation of such indirect defense traits would lead to a more sustainable management of CGM in view of anticipated climate change. Lack of information on farmers’ perception of CGM and preferred varietal attributes, and gene action controlling the inheritance of CGM resistance also limits success of resistance breeding and adoption of varieties. This research was undertaken to gather information on farmers’ perceptions of cassava varietal attributes and cultural practices in relation to CGM resistance, identify suitable sources of resistance and environments for future breeding; and to determine the nature of gene action controlling CGM resistance and the inheritance of plant morphological traits that enhance the ability of cassava to host and support continuous survival of natural enemies. High fresh storage root yield (FSRY), high storage root dry mass percentage (SRDM%), earliness combined with extended underground storability, and resistance to foliar pests and diseases are the major factors that influence adoption and retention of genotypes by farmers. Moles, termites and CGM are the most widespread and most damaging pests. However, due to the non-conspicuous nature of CGM, its effects are under-estimated and are given limited attention by farmers. The majority of the farmers are familiar with CGM leaf damage symptoms but they cannot associate them with the actual pest. Participation of farmers in field training and field research activities helps them to know CGM. Crop rotation, intercropping, removal of shoot tips, selective pruning of infested shoots, and burning of cassava fields are some of the ways used by farmers to manage CGM. Farmers associate hairy broad-leaved, tall cassava genotypes and pink leaf pigmentation (anthocyanin) with low CGM damage. There is substantial genetic variability in the Zambian cassava germplasm for CGM resistance and associated plant morphological traits such as leaf pubescence (Pbs), leaf retention (LR), stay green (SG), tip size (TS), tip compactness, and plant height (PH), stem diameter (StD), SRDM% and FSRY. Genotypes with wide or specific adaptability for these traits have been identified, and should be recommended for general or localized production and for use as sources of desired genes in crop improvement. Genotypes L9.304/147, 92/000, TME2, 4(2)1425, I60/42 and L9.304/175 combine wide adaptability with high levels of resistance to CGM. Genotypes Kapeza, L9.304/147 and 4(2)1425 are able to produce 13-15 t ha ¯¹ at 9 months after planting suggesting their potential for early bulking. This study has shown that both additive and non-additive gene effects play a role in the expression of CGM resistance and associated plant morphological traits. The best combinations of parents for resistance against CGM were 4(2)1425 x L9.304/147 and Mweru x L9.304/147, while L9.304/147 x I92/000 displayed combined resistance to CGM and cassava mosaic disease (CMD). The resistance of cassava to CGM is positively correlated with Pbs, LR, and TS, SG, PH, StD. Overall, the study has shown that there is wide diversity in the expression of valuable indirect defense traits among genotypes, indicating that there is scope for integration of biological control and host plant resistance for CGM in Zambia. The release of genotypes that exhibit high level of intra-season and inter-season stability for enhanced expression of LR, SG, and Pbs will minimize the impact of CGM on FSRY and SRDM% that results from seasonal effects. Such genotypes should also provide habitat for and thus help to ensure the survival of T. aripo in cassava fields. The study has contributed to the promotion of food security through identification of early-bulking genotypes which also have good potential for extended underground storability of roots. Early-bulking, high FSRY and SRDM% and SRR resistance are farmer-preferred traits. Therefore, enhancement of such traits through plant breeding is likely to increase the adoption of new genotypes by farmers. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Abstract not available. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Quality protein maize (QPM) has high nutritional value, but production is threatened by downy mildew (DM) and maize streak virus disease (MSVD) among other constraints. There are few studies of DM and MSVD resistance in QPM cultivars. The objective of this study was to improve resistance to DM and MSVD in three QPM populations. This was realized through ascertaining farmers’ key production constraints and special preferences for cultivars; determining the utility of recurrent selection method for improvement of three QPM populations (SussumaS2, ZM521Q and Pop62SRQ); and determining grain yield potential. The study was conducted in Mozambique for DM and in Zimbabwe for MSV, during 2003 to 2006. Surveys were conducted in Manica and Angonia districts in Mozambique to ascertain farmers’ perceptions and preferences for maize varieties, especially QPM. Participatory rural appraisal tools that included semi-structured questionnaires and focus group discussions were used to collect data. Results showed that farmers predominantly grew open pollinated varieties and fewer normal maize hybrids (non-QPM), and grain yield was estimated to be very low (0.2 to 0.6 t ha-1). Results showed that drought and insect pests were the dominant constraints to maize productivity in Mozambique, while diseases were ranked third. Downy mildew disease and MSVD were considered to be the most important diseases reducing maize productivity. Farmers also showed high preference for high yielding and early maturity cultivars in all areas. Predominantly, farmers were still using their local landraces because of sweet taste, particularly for home consumption and flint grain for storage. Farmers’ access to improved cultivars was limited due to high seed prices on the local market. Research priorities as perceived by the farmers included breeding for resistance to drought, grain weevils and diseases and sweetness. Generally, farmers showed little knowledge of QPM varieties and the importance of this trait, but they observed that the few QPM varieties they knew had some weaknesses such as poor storability and susceptibility to DM and MSVD which required improvement. These results should be considered in breeding new cultivars, both normal and QPM. To improve DM and MSV disease resistance in QPM varieties, S1 recurrent selection was conducted in three QPM populations, Sussuma, ZM521Q and Pop62SRQ at Umbeluzi Research Station in Mozambique and at CIMMYT-Harare Research Quality protein maize (QPM) has high nutritional value, but production is threatened by downy mildew (DM) and maize streak virus disease (MSVD) among other constraints. There are few studies of DM and MSVD resistance in QPM cultivars. The objective of this study was to improve resistance to DM and MSVD in three QPM populations. This was realized through ascertaining farmers’ key production constraints and special preferences for cultivars; determining the utility of recurrent selection method for improvement of three QPM populations (SussumaS2, ZM521Q and Pop62SRQ); and determining grain yield potential. The study was conducted in Mozambique for DM and in Zimbabwe for MSV, during 2003 to 2006. Surveys were conducted in Manica and Angonia districts in Mozambique to ascertain farmers’ perceptions and preferences for maize varieties, especially QPM. Participatory rural appraisal tools that included semi-structured questionnaires and focus group discussions were used to collect data. Results showed that farmers predominantly grew open pollinated varieties and fewer normal maize hybrids (non-QPM), and grain yield was estimated to be very low (0.2 to 0.6 t ha-1). Results showed that drought and insect pests were the dominant constraints to maize productivity in Mozambique, while diseases were ranked third. Downy mildew disease and MSVD were considered to be the most important diseases reducing maize productivity. Farmers also showed high preference for high yielding and early maturity cultivars in all areas. Predominantly, farmers were still using their local landraces because of sweet taste, particularly for home consumption and flint grain for storage. Farmers’ access to improved cultivars was limited due to high seed prices on the local market. Research priorities as perceived by the farmers included breeding for resistance to drought, grain weevils and diseases and sweetness. Generally, farmers showed little knowledge of QPM varieties and the importance of this trait, but they observed that the few QPM varieties they knew had some weaknesses such as poor storability and susceptibility to DM and MSVD which required improvement. These results should be considered in breeding new cultivars, both normal and QPM. To improve DM and MSV disease resistance in QPM varieties, S1 recurrent selection was conducted in three QPM populations, Sussuma, ZM521Q and Pop62SRQ at Umbeluzi Research Station in Mozambique and at CIMMYT-Harare Research. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Cassava (Manihot esculenta Crantz ssp. esculenta) is the second most important food crop and a main source of income for the rural communities with potential for industrial use in the coastal region of Kenya. However, its productivity of 5 to 9 t ha-1 is low due to the low yield potential of the local cassava landraces caused by cassava brown streak disease (CBSD) among other biotic and abiotic constraints. Breeding for CBSD resistant varieties with farmer desired characteristics is hampered by limited information on the current status of the disease and farmers’ preferred characteristics of new CBSD resistant genotypes. In addition, there is a lack of an effective inoculation technique for cassava brown streak virus (CBSV) for screening genotypes for CBSD resistance. Information about the general combining ability (GCA) and specific combining ability (SCA) for CBSD above and below ground symptoms, fresh biomass yield (FBY) and fresh storage root yield (FSRY) (kg plant-1), harvest index (HI), dry matter % (DM %) and picrate score (PS) is limited and conflicting especially for the cassava germplasm in Kenya. These studies were carried out to update information on the status of CBSD, farmer’s preferences for cassava genotypes, and identify the most effective CBSV inoculation technique. In addition, the studies aimed to: determine the GCA and SCA for, and gene action controlling, the incidence and severity of above ground CBSD, root necrosis, FBY, FSRY, HI, DM %, and PS; and identify CBSD resistant progeny with farmers’ desired characteristics. A survey carried out in three major cassava-growing divisions in Kilifi, Kwale and Malindi Districts indicated that there was potential to increase production and productivity by increasing the area under cassava production and developing CBSD resistant genotypes that are early maturing, high yielding and sweet. In addition, CBSD was widely distributed, being present in 98.0% of the farms surveyed at a mean incidence of 61.2%. However, 99.0% of farmers interviewed lacked awareness and correct information about the disease. The genetic variability of cassava within the farms was low as the majority of farmers grew one or two landraces. Highly significant differences (P < 0.01) were observed among inoculation techniques for CBSV for which the highest infection rate of up to 92.0% was observed in plants inoculated by wedge grafting infected scion. Highly significant differences (P < 0.01) were observed among genotypes, between sites and their interaction for incidence of CBSD and root necrosis, while the differences among genotypes and the interaction between genotypes and the period of ratings were highly significant (P < 0.01) for the severity of CBSD and root necrosis. Above ground CBSD symptoms were not always associated with below ground CBSD symptoms and below ground CBSD symptoms were more severe at 12 months after planting (MAP) than at 6 MAP. Therefore, selecting cassava genotypes with resistance to below ground CBSD is more important than selection based on resistance to above ground CBSD and should be done after 12 months. Genotypes 5318/3 (exotic) followed by Msa140 and Plot4 (both local) had high resistance and can be used as new sources of resistance to root necrosis. Both GCA and SCA effects were highly significant with GCA sums of squares (SS) predominant over the SCA SS for most traits evaluated except for DM % at the clonal stage. These results indicate that although additive and non-additive genetic effects are involved in the inheritance of these traits, the additive genetic effects are more important except for DM %. Therefore breeding for CBSD-resistant genotypes that have characteristics desired by farmers in the coastal region of Kenya can be achieved through recurrent selection and gene pyramiding followed by participatory selection or use of a selection index that incorporates characteristics considered important by farmers. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Low soil nitrogen (N) and drought impede maize production in the small-scale farming sector in Zambia; and adoption of new cultivars with improved tolerance might enhance production. This study: a) assessed farmer preferences for maize cultivars; b) determined genotype x environment interaction effects among popular maize cultivars under contrasting soil fertility levels and; c) investigated landraces for tolerance to low N and drought using S1 selection. The study was carried out in Zambia from 2004-07. Farmer preference influencing the adoption of maize cultivars was investigated using both formal and informal surveys in Luangwa, Chibombo and Lufwanyama rural districts representing the three agro-ecological regions of Zambia. Focus group discussions and personal interviews were used to collect data on issues that affected maize production in these areas. It has been found that although farmers perceived landraces to be low yielding, they believed that they were superior to improved cultivars for: tolerance to drought; tolerance to low soil fertility; grain palatability; grain storability; and poundability. The need for food security, their inability to apply fertiliser, and their need for drought tolerant cultivars significantly (p ≤ 0.05) influenced farmers in adopting cultivars. The farmers would readily adopt cultivars that address these concerns. The predominant use of certain landraces (76%) reflected their superiority in meeting some of these needs. The performance of nine popular cultivars (three for each of hybrids, OPVs and landraces) under contrasting levels of soil fertility, across six environments (ENVs) in the three agro-eological regions, was evaluated. An ENV was defined as season x location combination. The fertilizer treatments were full fertilization, basal dressing, top dressing and nil fertilization. The cultivars exhibited significant non-crossover type of genotype x fertilisation interaction effects at three ENVs, while the genotype x fertilisation interaction effects, were non-significant at the other three ENVs. The cultivars exhibited dynamic stability by increasing grain yield (GY) when fertilization was increased. Landraces yielded higher than all open pollinated varieties and were generally higher yielding than two hybrids. Based on average rank for GY, the five highest yielding cultivars were MRI724, Gankata, MM603, Kazungula and Pandawe. Superiority of landraces revealed their genetic potential for GY under low soil fertility and they should be used as germplasm in developing cultivars targeting such environments. Ninety-six local landraces were selfed to generate S1 lines (2004/05 season) which were crossed to a tester (2005/06 season). Testcrosses were evaluated under optimal, low N, and drought conditions (2006/07 season). Data on GY, anthesis-silking interval, number of ears per plant, leaf senescence, leaf rolling, tassel size and grain texture were recorded in all the trials during the study period. Testcrosses, their S1 parents and landraces that were superior under low N, drought, optimal conditions and across environments were identified; these should be used to develop varieties targeted to a particular environment. Selection for tolerance to drought also selected for tolerance to low N. Selection for low N tolerance also selected for GY under drought and optimal conditions. Therefore, in selecting for tolerance to abiotic stresses, use of optimal and managed stress environments was effective. The following landraces were superior at 10% selection intensity: LR38, LR84 and LR86 (optimal, low N and drought conditions); LR11, LR35 and LR76 (low N and drought conditions); LR12 (optimal and drought conditions); LR40 and LR93 (low N conditions only); LR79 (drought conditions only) and; LR74 and LR85 (optimal conditions only). These landraces should be used as source germplasm targeting respective environments. Significant (p ≤ 0.05) positive general combining ability effects for GY under both low N and drought conditions were found implying that additive gene action conditioned GY under the abiotic stresses. The heritability for GY under low N (0.38), and drought (0.17) conditions, was low suggesting that selection based on GY alone was not effective. The genetic correlation for GY between optimal, and either low N (rG=0.458), or drought (rG = 0.03) environments, was low (rG < 0.5) suggesting that indirect selection would not be effective either. Therefore, use of secondary traits for selection is discussed. The study established that most farmers depended on local landraces for seed and would adopt low input improved varieties that yield higher than the landraces. Some landraces were found superior to some improved cultivars under contrasting fertilisation regimes. The study also found that landraces had genetic variation for tolerance to low N and drought. Landraces, S1 lines and testcrosses superior under low N, drought, optimal conditions and across environments were selected and they should be used to develop cultivars targeting respective environments. Policy implications of these results are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Pigeon pea [Cajanus cajan (L.) Millspaugh] is a very important grain legume crop for food, cash and firewood in Malawi. However, its production is affected by Fusarium wilt (Fusarium udum Butler), which causes up to 100% yield loss. The deployment of resistant varieties would be an economical way to manage the disease, and for this, more information is needed on farmers' preferences for local landraces, how farmers and consumers can be involved in developing new varieties resistant to wilt disease, and the genetics of inheritance of resistance. This information would be used to devise a breeding strategy. A participatory rural appraisal was used in the southern region of Malawi to identify pigeonpea production and marketing constraints. Results showed that Fusarium wilt was the most prevalent and destructive disease of pigeonpea in the area. Other constraints included pests, flower abortion, low yields, and low soil fertility. Local landraces accounted for 84% of the pigeonpea production in Malawi. Local landraces were preferred due to their fast cooking time, taste, and the high prices they earn the farmer. Participatory variety selection was used to identify landraces with desirable traits that could be used in the breeding programme. Farmers and buyers selected ten local landraces which were used in the genetic improvement programme. Pigeonpea local landraces and international Crops Research Institute for the Semi-Arid Tropics (ICRISAT) genotypes were evaluated for wilt resistance, yield, and secondary traits at three sites over three seasons. Most of the landraces were susceptible to wilt and late maturing. However, AP10, a local landrace, was high yielding and resistant to wilt and outperformed ICRISAT varieties. This local landrace showed promise for use as a source material for Fusarium wilt resistance in other locally adapted farmer-preferred varieties lacking resistance. The local landraces needed genetic improvement in wilt resistance, yield, early maturity, number of branches and seeds pod. Laboratory and screenhouse studies were performed to develop a new Fusarium wilt screening technique. Grains of finger millet, sorghum, and wheat were tested as media for multiplying F. udum isolates. Pathogenicity tests were done on Bunda College and Bvumbwe Research Station isolates. The Bunda isolate was then used in an infested-seed inoculation technique against eight differential cultivars. The results showed that finger millet, sorghum and wheat were equally effective for rapid multiplication of F. udum isolates. Wheat grain showed the best results for pathogen multiplication and inoculation, due to the large seed size for easy handling. The inoculation process involved placing infested wheat grain on bruised pigeonpea roots and transplanting into soil in pots. The infested seed inoculation technique, which is the first of its kind for pigeonpea, was effective in screening pigeonpea for wilt resistance. The selected landraces were crossed with wilt resistant testers in a 12 lines x 4 testers mating scheme, and 48 F1 crosses were generated. These F1 crosses were evaluated for wilt resistance, yield, and secondary traits. The variations among F1 crosses for wilt and secondary traits were due to additive gene action in both parents and the dominance effects arising from the interactions of parents. Parental lines, with good combining ability effects for wilt resistance (AP2, AP3, and AP4), days to 50% flowering, seed pod, plant height, stem diameter, and number of primary and secondary branches were identified, while ICEAP00554 (tester) was a good general combiner for wilt resistance and days to 50% flowering. These lines would be useful in breeding for Fusarium wilt resistance in farmer-preferred pigeonpea genotypes in Malawi or similar environments. Specific F1 crosses were identified with significant SCAs for wilt resistance, days to 50% flowering, and secondary branches. The significance of GCA and SCA effects, which indicated importance of both additive and non-additive gene effects, respectively, suggested that both selection and hybridisation would be useful to improve the resistance in farmer-preferred varieties. Segregation analyses were conducted on F2 populations to determine the resistance to susceptibility phenotypic ratios. The Chi-square analyses showed that resistance to wilt was dominant over susceptibility in most F2 populations. The segregation ratios of 3:1, 13:3, 15:1, and 9:7 (R:S) indicated that either one dominant gene, or two inhibitory genes, or two independent dominant genes, or two complementary genes, respectively, were conferring wilt resistance in these crosses. Involvement of only a few genes governing wilt resistance suggested few complications, if any, in breeding for this trait in these locally adapted pigeonpeas. The Pedigree breeding method would be recommended for incorporating these traits. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.