Maize (Zea mays L.) streak virus disease (MSD) is the most important virus disease in Africa but farmers are unaware of its status. A project was initiated to assess the current status of MSD and to breed for its resistance. Four populations comprised of two BC1F1 and two F2 progenies developed by backcrossing and selfing the F1 progenies of two crosses between a donor line (CMl 202) and two susceptible lines (CMl 321 and CMl 384) were developed. Conventional and molecular marker assisted selection (MAS) methods were used to screen for resistance to MSD in each of the four populations. To facilitate unbiased comparison, separate screening nurseries were established for MAS and conventional screening. The objectives of the study were five-fold; 1) to assess the status of MSD in Uganda and understand farmers' preferences and varietal selection criteria for maize using a participatory rural appraisal (PRA), 2) to screen for MSD resistance in early generations of segregating maize populations using conventional method, 3) to screen for resistance to MSD using SSR marker assisted selection , 4) to compare the effectiveness of marker assisted selection and conventional methods for selection for resistance to MSD, and 5) to compare costs associated with MAS and conventional selection methods. Results of PRA showed that unreliable rainfall and insect pests were the dominant constraints to maize productivity in Uganda. Diseases were ranked fifth among the production constraints . Maize streak virus disease was considered the most important disease constraint. Farmers showed common preference for high yielding and early maturing cultivars. However, farmers had other special preferences which were diverse and included large, white and high test density kernels for marketing, and sweet taste, particularly for home consumption. Farmers' research priorities included tolerance to drought, resistance to insect pests and diseases, sweetness, prolificacy, resistance to lodging, and drooping leaves because theyt cover the soil fast and prevent weed growth. Conventional screening for resistance to MSD showed that backcross and selfing populations segregated in 1:1 and 3:1 Mendelian ratios confirming the presence of one major gene with simple inheritance . Severity and incidence of disease were positively correlated suggesting a non-reference by the insects. In the selfing populations, the presence of complete esistance against MSD was suggested because frequency distribution patterns were highly skewed in favour of resistance. There was a decrease in disease severities with selection from BC1F1 to BC2F1 and from F2 to F3 generations indicating that high response to selection was achieved. On the other hand, one marker, umc1917, consistently polymorphic and eo-dominant was selected and used in MAS protocol. Results showed that the observed outcomes fitted the expected ratio of 1:2:1 for a F2 population and 1:1 for a BC1F1 population (X2 not significant). Evaluation of F3 and BC2F1 progeny selected using markers showed low disease severity suggesting that marker assisted selection was effective. However, the study showed that the presence of the O'Tl, was not consistent with symptom expression in the field. Evaluation of lines in three-way crosses identified ten potential lines that were high yielding, highly resistant to MSD and stable across three locations. Both MAS and conventional selection were equally effective in identifying high yielding lines although resistance was higher under MAS. Costs of MAS and conventional method varied depending on the units for comparison. The total costs of conventional method were higher than that of MAS in both first and second selection cycles. Comparing costs per row for conventional and costs per plant or data point for MAS showed that conventional selection was 2.4 times more expensive than costs per sample for MAS. However, costs per plant for MAS were 6.6 times higher than for conventional selection. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006

In Southern Africa and Mozambique, tropical lowland accounts for 22% and 65%, respectively, of area under maize production, but grain yield is compromised by downy mildew disease (DM, which is caused by Peronosclerospora sorghi (Weston and Uppal) Shaw), and lack of appropriate varieties, especially hybrids. Among other factors, productivity can be enhanced by deploying DM resistant hybrids, which are higher yielding than open pollinated varieties. Development of a viable hybrid-breeding programme requires knowledge of genetic effects governing yield and DM resistance in inbreds, and effective germplasm management requires heterotic groups and heterotic patterns to be established. In addition, knowledge of farmer-preferred traits is required. Currently, such information is not available to the hybrid-breeding programme in Mozambique. The objectives of this study were, therefore; i) to identify farmers’ preferred variety traits and major production constraints, ii) to determine combining ability effects of inbred maize S4 lines for grain yield and DM resistance, iii) to determine heterotic groups and heterotic patterns among the elite inbred maize lines, and iv) to investigate gene effects governing resistance to DM in breeding source inbred maize lines from the breeding programme in Mozambique. During 2007/08, 142 households were involved in a survey conducted in three districts representing two maize agro-ecological zones in Mozambique. Formal surveys and informal farmer-participatory methods were employed and data subjected to analysis in the SPSS computer programme. Results indicated that there was a low utilization of improved varieties, especially hybrids, with grain yield estimated at 0.7 t ha-1. Farmers were aware of the major production constraints and could discriminate constraints according to their importance for their respective communities. For the lowland environment, farmers identified downy mildew, drought, and cutworm and stem borer damage as the main constraints. In contrast, for the high altitude environments, they ranked ear rot, seed and fertilizer availability, turcicum leaf blight, grey leaf spot diseases and low soil fertility among the major constraints limiting productivity. The most important variety selection criteria were grain yield, short growth cycle, white and flint grain with stress tolerance to drought, low soil fertility, diseases, and grain weevils. These afore mentioned traits, would be priority for the breeding programmes for the lowland and mid altitude environments in Mozambique. To determine combining ability for downy mildew resistance, heterotic groups and heterotic patterns, two testers (open-pollinated varieties) ZM523 (Z) and Suwan-1 (S), were crossed with 18 lines to generate 36 top crosses for evaluation. Crosses were evaluated at two sites under DM. Preponderance of GCA effects indicated that additive gene effects were more important than non-additive gene effects in governing both grain yield and downy mildew resistance in the new maize lines. Based on specific combining ability (SCA) data, lines for yield were classified into two heterotic groups, S and Z; whereas based on heterosis data, lines were fitted into three heterotic groups (S, Z and SZ). Further heterotic patterns and gene action for yield were determined by subjecting nine inbred lines and the two testers, S and Z, to an 11 x 11 diallel-mating scheme. The diallel crosses, three hybrid checks and the two testers were evaluated in six environments in Mozambique. Results revealed that non-additive gene effects were predominant for yield components. In addition, high levels of heterosis for yield was observed and three heterotic groups identified (Z, S and S/Z), and five exceptional heterotic patterns among the inbred elite maize lines were observed. Topcrosses with yield levels comparable to single cross hybrids were also identified, and these would be advanced in the testing programme with potential for deployment as alternative cheaper and sustainable technology to conventional hybrids for the poor farming communities in Mozambique. To determine gene effects for downy mildew resistance in potential breeding lines, two maize populations were derived from crosses between downy mildew susceptible line LP67, and resistant lines DRAC and Suwan-L1. To generate F2 and backcross progenies (BCP1 and BCP2), F1 progenies were self-pollinated and simultaneously crossed to both inbred parents (P1 and P2). All the six generations (P1, P2, F1, F2, BCP1, and BCP2) of the populations were evaluated at two sites under downy mildew infection. A generation mean analysis was performed in SAS. It was revealed that downy mildew resistance was influenced by genes with additive and dominance effects, plus different types of epistatic effects such as additive x additive, and dominance x dominance. Overall results indicated that genes with predominantly non-additive effects controlled resistance in DRAC, whereas resistance in Suwan-L1 was largely influenced by additive gene effects. These findings have serious implications on the effective use of these downy mildew resistance sources in breeding programmes that aim to generate varieties with downy mildew resistance. Overall, results suggested that inbreeding and selection within heterotic groups, followed by hybridization between inbreds within and across heterotic groups would be effective to generate new hybrids. The breeding programme will consider development of conventional hybrids, such as single crosses and three way crosses, and top crosses. Implications of the findings of the study and recommendations are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

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.

Maize ear rots are among the most important impediments to increased maize production in Africa. Besides yield loss, they produce mycotoxins in their host whose contamination has been linked to several human and animal mycoses. The main objectives of the studies reported on in this thesis were (i) to investigate farmer perceptions of maize ear rot disease and prospects for breeding for host plant resistance in Zambia; and (ii) to establish the levels of incidence and extent of maize ear rot infection as well as the level of mycotoxins in the maize crops of smallholder farms in central and southern Zambia; (iii) to appraise the field inoculation techniques and assess them for their suitability for the Zambian environmental conditions, (iv) to determine the combining ability of Zambian maize populations for resistance to ear rot and investigate the genetic basis of this resistance; and (v) to investigate both direct and indirect responses to full-sib selection for ear rot resistance in Zambian maize populations. A participatory rural appraisal (PRA) was conducted in four communities, involving a total of 90 farmers. Participatory methods were used, such as focused group discussions, group interviews, participant scoring and ranking. Farmers ranked and scored the various constraints affecting their maize production in general and the maize ear rots in particular. Ear rots were ranked as the third most important biotic stress and it was evident that although farmers were aware of the disease, they were not aware of mycotoxins. This was reflected in the way they disposed of rotten maize: either by feeding livestock or eating it in periods of hunger. The survey of ear rots and mycotoxins was carried out in the Southern and Central Provinces of Zambia. A total of 114 farms were covered in the survey: maize samples were collected and both ear rot fungi and mycotoxins were isolated. Fusarium and Stenocarpella were the most frequently isolated fungi from smallholder farms. The levels of fumonisins on these farms ranged from 0.05 to 192 ppm, while those of aflatoxins were between 1.5 and 10.6 ppb. In 50% of the farmsteads surveyed, the mycotoxins, i.e. fumonisins and aflatoxins, exceeded the recommended FAO/WHO 1limits of 2 ppm and 2 ppb, respectively. Five field inoculation techniques namely, colonised toothpick, leaf whorl placement, ear top placement, spore suspension spray, and silk channel injection, were evaluated over three seasons in a series of experiments. It was found that the leaf whorl placement of inoculums, followed by colonized toothpick method, gave a constant ranking of genotypes across locations and years compared to the other three methods. In addition, the use of a mixture of ear rots as inoculum was as effective as its principal single species constituents. In the population diallel analysis, five broad-based maize populations were crossed in a diallel and evaluated under artificial ear rot inoculation using an inoculum mixture of three ear rot fungi, Aspergillus flavus, Fusarium verticilloides and Stenocarpella maydis at four locations in Zambia. The purpose was to estimate general (GCA) and specific combining ability (SCA) and investigate genotype x environment interaction. GCA effects were found not to be significant for disease severity but were significant for grain yield across environments. Populations with a strong GCA effect for disease severity across sites included PRA783244c3, Pop25, MMV600, and ZUCASRc2. Across sites, the F1 combinations, MMV600 x Pop25, ZUCASRc2 X Pop25, and Pop25 x PRA783244c2 had strong SCA effects for root lodging, ear drooping, husk cover and ear insect damage. In a related diallel analysis of 10 full-sib families derived from these populations, it was observed that resistant x susceptible families and their reciprocal crosses performed better than their resistant parents, suggesting an over dominant expression of resistance. Both maternal and non maternal effects were observed to be influencing resistance to ear rots. There was a preponderance influence of non-additive gene action. A response to full-sib recurrent selection was conducted in four locations in Central Zambia. Out of the 343 families created in 2005/6 season, 10% were selected from each population and recombined to create five new populations. These, with the original populations, were evaluated in four sites during the 2007/8 season. There was a net reduction in ear rot incidence and rot severity in the new synthetic population. Pop10 had the largest reduction in disease severity. The predicted gain per cycle was -4.1% and realized gain was -2.5% for disease incidence, and 0.19% and 19.4% for grain yield. Genetic variability was maintained though with low heritability estimates. Negative but at times strong association between grain yield and ear rot disease severity was detected suggesting that in general selecting for ear rot resistance would enhance grain yield in the five populations. Overall the importance of the ear rots and mycotoxins in compromising yield and health of the communities in Zambia, respectively, were confirmed and support the call to improve maize varieties for resistance to ear rots. The results indicate that the five populations could be enhanced for ear rot resistance through population improvement procedures such reciprocal recurrent selection that exploit both additive and non-additive variation. Selection might be compromised by the large genotype x environment interaction effects, and large reciprocal effects and their interaction with the environments. To enhance repeatability genotypes should be artificially inoculated, by placing the inoculum in the leaf whorl followed by colonized toothpick inoculation, and screened in many environments to identify genotypes with stable resistance to ear rots. / Thesis (Ph.D) - University of KwaZulu-Natal, Pietermaritzburg, 2009.

Maize (Zea mays L.) is the principal crop of Southern Africa but production is threatened by gray leaf spot (Cercospora zea-maydis L.) and phaeosphaeria leaf spot (Phaeosphaeria maydis L.) diseases, drought and the use of unadapted cultivars, among other constraints. There are few studies of gray leaf spot (GLS) and Phaeosphaeria leaf spot (PLS) resistance, drought tolerance, yield stability and maize cultivar preferences in Southern Africa. The objective of this study was to: a) determine farmers’ preferences for cultivars; b) investigate the gene action and heritability for resistance to GLS and PLS, and drought tolerance; and c) evaluate yield stability and its relationship with high yield potential in Southern African maize germplasm. The study was conducted in South Africa and Zimbabwe during 2003 to 2004. A participatory rural appraisal (PRA) established that farmers preferred old hybrids of the 1970s because they had better tolerance to drought stress. Farmers also preferred their local landrace because of its flintier grain and better taste than the hybrids. The major prevailing constraints that influenced farmers’ preferences were lack of appropriate cultivars that fit into the ultra short seasons, drought and low soil fertility. Thus they preferred cultivars that combine high yield potential, early maturity, and drought tolerance in all areas. However, those in relatively wet areas preferred cultivars with tolerance to low soil fertility, and weevil resistance, among other traits. A genetic analysis of 72 hybrids from a North Carolina Design II mating revealed significant differences for GLS and PLS resistance, and drought tolerance. General combining ability (GCA) effects accounted for 86% of genetic variation for GLS and 90% for PLS resistance indicating that additive effects were more important than non-additive gene action in controlling these traits. Some crosses between susceptible and resistant inbreds had high resistance to GLS suggesting the importance of dominance gene action in controlling GLS resistance. Resistance to GLS and PLS was highly heritable (62 to 73%) indicating that resistance could be improved by selection. Also large GCA effects for yield (72%), number of ears per plant (77%), and anthesis-silking interval (ASI) (77%) under drought stress indicated that predominantly additive effects controlled hybrid performance under drought conditions. Although heritability for yield declined from 60% under optimum to 19% under drought conditions, heritability for ASI ranged from 32 to 49% under moisture stress. High heritability for ASI suggested that yield could be improved through selection for short ASI, which is positively correlated with high yield potential under drought stress. The stability analyses of the hybrids over 10 environments indicated that 86% had average stability; 8% had below average stability and were adapted to favourable environments; and 6% displayed above average stability and were specifically adapted to drought stress environments. Grain yield potential and yield stability were positively correlated. In sum, the study indicated that farmers’ preferences would be greatly influenced by the major prevailing constraints. It also identified adequate genetic variation for stress tolerance, yield potential and yield stability in Southern African maize base germplasm, without negative associations among them, suggesting that cultivars combining high yield potential, high stress tolerance and yield stability would be obtainable. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

Maize (Zea mays L.) production is constrained by a number of stresses, amongst the most important are gray leaf spot (GLS) caused by a fungus Cercospora zeaemaydis Tehon and E.Y. Daniels and Phaeosphaeria leaf spot (PLS) caused by Phaeosphaeria maydis (Henn.). The diverse germplasm comprising farmer collections and exotic material used in the medium and highland altitudes maize breeding programmes in western Kenya has not been improved for resistance to the two diseases. Heterotic patterns of germplasm from this region have also not been studied. Therefore, the objectives of this study were to (i) assess the prevalence, importance, and farmers’ perceptions of GLS and PLS, (ii) characterize maize germplasm collections into their heterotic groups and (iii) improve four maize populations for GLS and PLS resistance through recurrent selection. The participatory rural appraisal (PRA) was conducted at three sites in western Kenya during the 2005/2006 cropping season. Data was generated using a checklist in group discussions with 109 male and 123 female farmers as well as key informants. Constraints were identified and prioritised. The five most limiting, in order of importance, were low soil fertility, poor varieties and seed, drought, Striga, pests and diseases (GLS and PLS). Gray leaf spot and PLS were reported in all sites but farmers did not know the causes of these diseases. Farmers preferred local varieties Tiriki, Anzika and Kipindi due to their greater resistance to diseases than commercial hybrids. Farmer criteria for variety selection were low fertilizer, Striga and disease resistance, drought tolerance, closed tips, and high yield potential. Due to the high cost of hybrid seed farmers selected and planted their own seed from advanced generations from previous seasons. Across all the sites, yield gap between on-farm and expected yield potential was estimated as ranging from 4.73t ha-1 to 5.3t ha-1 mainly due to the identified constraints. Therefore maize breeding should focus on addressing important maize production constraints and farmers’ preferences identified in this study in developing varieties that will increase maize yields on-farm. During 2005/2006, seventy 77 testcrosses were developed through crossing 47 germplasm collections with four population testers, Kitale synthetic II (KSII), Ecuador 573 (EC 573), Pool A and Pool B. Crosses and testers were evaluated at Kakamega during 2006/2007 in a 9 x 9 triple lattice design. Significant (p < 0.05) differences in grain yield, ear height, days to 50% anthesis, GLS and PLS resistance were observed. Both general and specific combining ability effects (GCA and SCA, respectively) were significant (p < 0.01), with SCA accounting for more than 50% of the variation for GLS, PLS and yield and less than 50% for ear height, days to 50% anthesis and silk. This indicated that both additive and non-additive gene effects were important but non-additive gene effects were more important in conditioning these traits. High SCA effects indicated high heterosis between collections and populations. Both yield heterosis and SCA were used to study heterotic patterns, but percentage yield heterosis data was used to classify these materials into heterotic groups. Based on significance (p < 0.05) of percentage yield heterosis as a primary factor for classification, seven collections were classified to Pool A, 17 to Pool B, 12 to KSII and 6 to EC 573 heterotic groups. The study indicated that germplasm collections belong to distinct heterotic groups therefore they can be infused into these populations (Pool A, Pool B, KSII and EC 573). Four populations, KSII, EC 573, Pool A and Pool B were subjected to one cycle of reciprocal recurrent selection (RRS) and two cycles of simple recurrent selection (SRS) during the 2004-2006 cropping seasons at Kakamega. Response to selection was assessed by evaluating C0, C1 and C2 and four commercial checks in a randomised complete block design in three replications at Kakamega and Kitale during 2007. All cycles except C0 of Pool A were more resistant to GLS than the three checks, H623, KSTP94 and PHB3253. Response to selection for GLS was significant (p < 0.01) in the desired direction. Gains ranged from -32.2% to 6.4% cycle-1 for RRS and 0.0% to -61.3% cycle-1 for SRS. Heritability estimates of between 59% and 76.3% for GLS and 39% and 80% for PLS were observed indicating that both GLS and PLS can be improved through selection. Significant negative correlations between GLS and yield were observed in Pool A C0 (r = -0.947, p < 0.01) and between yield and PLS in Pool A C0 (r = -0.926, p < 0.01). These indicated gain in yield as GLS and PLS were selected against. Generally, SRS out performed RRS method both in genetic gain and time, as indicated by gain of -61% for SRS and -32.2% for RRS, respectively. Two cycles of selection were achieved in two years with SRS as compared to only one with RRS. These results clearly demonstrated that it is possible to improve for GLS resistance using simple and reciprocal recurrent selection methods. The main constraints to maize production in Western Kenya were low soil fertility, Striga, drought, lack of seed and diseases. Farmers preferred varieties that can do well under the constraints mentioned. Local collections belonged to distinct heterotic groups with good resistance to GLS and PLS and were highly heterotic to four maize population testers with both SCA and GCA effects being important in conditioning GLS and PLS resistance. Recurrent selection methods were found to improve maize resistance to GLS and PLS. Breeding should therefore, focus in development of hybrids and improvement of populations using these local collections by employing SRS and RRS selection methods with identified constraints and farmer preferences in mind. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2007.

Maize (Zea mays L.) yields in the smallholder (SH) farming sector in Southern Africa have remained low. despite the availability of many improved varieties. Among the major constraints contributing to tow yields and threatening food security in the region are diseases which include grey leaf spot (GLS). common rust, northern corn leaf blight (NLB) and Phaeosphaeria leaf spot (PLS). These diseases are highly unpredictable in their occurrence every season, making them difficult to control. In addition, the majority of SH farmers cannot afford to control the diseases due to limited access to chemicals. Therefore, maize cultivars with high levels of disease resistance and tolerance to abiotic stresses would provide a long-term solution to addressing the problem of low yields, especially in the smallholder-farming sector. The objectives of this study were therefore to: i) establish farmers' perceptions on diseases, key limiting production constraints and preferred traits of maize cultivars. ii) screen germplasm adapted to tropical environments for resistance to PLS, iii) determine gene action for resistance to PLS and GLS, iv) estimate combining ability effects for resistance to PLS, GLS, NLB and common rust diseases, and v) determine grain yield stability of F, hybrids derived from crosses among selected tropical advanced maize inbred lines. These studies were conducted from 2006/7 to 2008/9 seasons at various sites in South Africa, Zimbabwe, Zambia and Uganda. Structured surveys and participatory rural appraisal (PRA) conducted in Obonjaneni. Busingatha and Okhombe villages of Amazizi district in the Northern Drakensberg established maize as the principal crop grown in the area. All the farmers who participated grew the local variety (landrace) they called Natal-8- row or Is/Zulu. The adoption of hybrids and improved open pollinated varieties (OPVs) was tow. Farmers preferred the local variety ahead of hybrids and improved OPVs mainly for its taste, tolerance to abiotic stresses and yield stability. Characteristics of maize varieties preferred by the farmers included: inexpensive seed, high yield, early maturity and tow input costs. Pests/d is eases and drought were not ranked highly, as farmers planted early to escape diseases and drought. Abiotic stresses were amongst the top four constraints faced by the farmers. The local varieties exhibited high yield potential and genetic variability fordisease resistance. Evaluation of maize germplasm adapted to tropical and subtropical environments of Africa for PLS resistance indicated significant (PS0.05) variation among the inbreds. populations and hybrids. In general, 63% of the inbreds/populations were resistant to PLS. Regionally important inbred lines; SC and N3 and CIMMYT's most successful lines such as CML395. CML444. CML202. CML312. and CML488 were resistant to PLS. Fifty- four percent of the single-cross experimental hybrids were also resistant to PLS. Correlation coefficients for area under disease progress curve (AUDPC) values for disease severity with PLS final disease severity scores were significant (P<0.001) and positive, implying that ranking of the genotypes for AUDPC and final PLS disease severity score was by and large similar. Forty five F, hybrids generated by crossing ten advanced maize inbred lines in a half diallel mating scheme were evaluated in two to six environments to determine combining ability, gene action and heterosis estimates for grain yield and resistance to PLS. GLS. NLB and common rust diseases. Highly significant (PS0.001) general combining ability (GCA) and specific combining ability (SCA) effects were observed for PLS. GLS. NLB. common rust, grain yield and other agronomic traits. The GCA effects were more important than SCA effects, indicating the predominance of additive over non-additive gene action for all the traits studied in these inbred lines. The inbred lines with good GCA for PLS resistance were: A12204, N3. A16. MP18 and CML488. and for GLS resistance were A1220-4. CZL00009. CZL00001. CML205 and CML443. Lines A16 and CML443 had good GCA for NLB and common rust resistance, lines A1220-4, N3, CML205, A16, and CML443 contributed towards high yield. Lines A1220-4 and A16 were late maturing, whereas CZL00009 displayed eariy maturity. High mid-parent and better-parent heterosis for high grain yield and resistance to all the diseases were observed. Generation mean analysis was used to deteimine the inheritance of PLS and GLS resistance in populations involving six tropical advanced maize inbred lines. Reciprocal crosses and backcross progenies were generated among inbreds A1220-4, A15, B17 (resistant. R), CML445 (moderately resistant. MR). CML441 and CZL00001 (susceptible. S) for PLS inheritance, and among inbreds A1220-4. A15, CML441 (resistant. R). and N3 and B17 (susceptible. S), for GLS inheritance. Results indicated highly significant additive effects (P<0.001) for PLS and GLS resistance, with dominance effects accounting forSH%of the variation in all the crosses for PLS and only A15 x B17 cross for GLS. Epistasis and cytoplasmic gene effects in favour of PLS resistance in F, crosses when the more susceptible parent was used as female were significant. For GLS resistance, epistasis was observed only in CML441 x N3 and A1220-4 x B17 crosses, while no cytoplasmic gene effects were detected. Resistance for PLS was medium to highly heritable and conditioned by less than four genes which exhibited incomplete dominance. In general resistance to GLS was controlled by two to three genes exhibiting zero to partial dominance and was moderate to highly heritable. Stability analysis of the hybrids was done over 11 environments using the additive main effects and multiplicative interaction (AMMI) and the genotype and genotype by environment (GGE) biplot analyses. Both AMMI and GGE biplot analyses selected hybrids H21 (CZL00009 x A16). H14 (A1220-4 x A16). S63 (SeedCo hybrid check). N72 (MP72/N3) and H26 (CZL00001 x A16) as stable and high yielding. Hybrids H1 (CML445 x A1220-4), H44 (CZL00009 x CML443) and H18 (CZL00009 x CZL00001) were identified by both methods as unstable but high yielding. AMMI and GGE biplot analyses identified ZAM08, C108, RAO9 and C09 as the most representative environments which were high yielding and relatively stable. In general, the study has revealed that based on the farmers ranking of the constraints in their area, breeding opportunities do exist for incorporating tolerance to both biotic and abiotic stresses in their varieties. It also identified maize lines resistant to the main foliar diseases, with good combining ability and heterosis for resistance and high grain yield. Hybrids with wide adaptation and high yields across environments were also observed. The experimental hybrids that exhibited high levels of resistance can be recommended for further testing and release. On the whole, highly significant additive effects and moderate to high heritability estimates observed for all the diseases and grain yield implied progress would be made through selection, although significant epistasis and dominance could slow progress. Dominance effects towards resistance and high yield could be exploited in developing single cross maize hybrids among these inbreds when only one parent is resistant. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

The majority of farmers in Tanzania have not yet adopted modern maize varieties and still cultivate landraces and open pollinated varieties (OPVs) with low production potential and susceptible to diseases like maize streak virus (MSV), grey leaf spot (GLS) and northern corn leaf blight (NLB). The NLB disease is among the major causes of low yield and has been reported in all 21 maize growing regions in Tanzania. Breeding for host plant resistance with high yielding potential and involving the community in the breeding process is expected to address the problem of low yield, NLB disease susceptibility and low rate of F1 hybrid adoption. Therefore, the study was conducted to obtain additional sources of resistance to NLB disease, high yielding cultivars with community acceptable traits adapted to Tanzanian conditions. The main objective was to contribute to increased maize productivity in the western zone of Tanzania. The specific objectives of this study were therefore to : 1) investigate maize production limiting factors for smallholder farmers in western Tanzania, 2) identify farmers and stockist perceptions, opinions and maize variety selection criteria in western Tanzania, 3) establish NLB disease status in farmers’ fields of western Tanzania, 4) determine the genetic relationships among landraces and assess maize landraces as sources of breeding materials, 5) determine the combining ability and heterosis for NLB disease resistance of eleven maize inbred lines adapted to Tanzanian conditions, and 6) determine the gene action and inheritance of resistance to NLB disease in five maize inbred lines adapted to Tanzanian conditions. The study was conducted from 2008-2011 in three diverse environments which represent all the maize growing regions in the country The participatory rural appraisal (PRA) was conducted in three districts to investigate farmers’ and stockists preferred traits for maize selection in western Tanzania, determine maize production constraints facing farmers and assess NLB disease prevalence in the same area. A focus group of 30 farmers was selected in each of the three villages. Transect walks, wealth ranking and historical profiles were used in an informal survey. One hundred and fifty questionnaires were used in a formal survey. The recorded yield was only 1 t haˉ¹. Thirteen major maize production constraints, 13 insect pests and vermin and, 11 diseases were recorded. The NLB disease was reported to be increasing in severity in all farmers’ fields. Farmers’ preferred traits included resistance to abiotic and biotic stresses, early maturity, preferred milling qualities, high storage qualities and high yielding potential. Stockists mentioned 12 preferred maize variety traits which included high yielding, disease and insect pest resistance, heavy grain, large cob size and large grain sizes. Similarity between farmers and stockist variety preference ranking were found to exist. The occurrence and distribution of northern leaf blight (NLB) disease study was conducted to assess the incidence and severity of NLB disease in farmers’ fields in seven districts. The study was conducted for two seasons. In each season, 175 fields with 5600 plants were sampled. There were sixteen varieties grown with wide NLB disease reaction variation. Gembe, a landrace, was among the three observed resistant varieties. The NLB disease has changed its distribution pattern affecting all districts of the western zone. The disease incidence in season two (2009/2010) significantly increased from season one (2008/2009) t= -3.25 (348), P= 0.001. About 30% of both means of blight incidence and severity were recorded in the area. Characterization and screening of maize landraces for northern leaf blight disease resistance was conducted to determine the genetic relationships among landraces, assess maize landraces as sources of NLB disease resistance and assess important agronomic traits for future maize improvement. Ninety breeding materials consisting of 71 landraces and 19 commercial varieties were evaluated. The average yield of landraces under research management was 2.3 t haˉ¹. Landrace TZA 3075 was identified as NLB disease resistant. Yield potential, dent grain texture, white endosperm and husk cover were important agronomic traits observed among landraces. There were high variations in terms of morphology and NLB disease resistance among the landraces. Five principal components contributed to 71.98 % of total variation. Clusters analysis revealed five distinct groups of landraces. Leaves/plant, infested leaves/plant, lesion number, lesion length, lesion width and NLB disease incidence traits highly contributed to variation and grouping of landraces. Combining ability analysis for northern leaf blight disease resistance was conducted to estimate the combining ability for NLB disease resistance of 11 maize inbred lines adapted to Tanzanian conditions, determine maternal effects which are involved in NLB disease resistance in maize germplasm, and determine the heterosis in the F1 hybrids. A full 11 x 11 diallel cross was performed. All top ten experimental hybrids in each of the three sites had negative midparent heterosis for NLB disease severity. The overall mid-parent heterosis means for yield across sites was 152%. The mean sum of squares for GCA was highly significant (P< 0.001) on disease severity indicating additive gene action effects. Mean sum of squares for SCA were highly significant for disease severity and yield implying non-additive gene action effects. The mean squares for reciprocal effects were highly significant on yield and non-maternal sum of squares had significant effect (P<0.05) on yield. The GCA contribution was high for disease severity (91%) and lesion number (85%). Almost, all GCA effects for NLB disease resistance were negative implying contribution to disease resistance. Due to preponderance of the additive gene action, recurrent selection could be used to improve the resistance of inbred lines while the non-additive gene action could be exploited in breeding for disease resistant hybrids. Generation mean analysis of northern leaf blight disease resistance was conducted to determine the mode of gene action involved in the inheritance of resistance to NLB disease in five inbred lines adapted to Tanzania at contrasting environments, estimate heterosis and heritability in five tropical inbred lines. Generation mean analysis was conducted using a six parameter model comprising P1, P2, F1, F2, BCP1 and BCP2 generation progenies. The mean sum of squares for environment, replication with the nested environment, generations, generations x environment interactions were highly significant (P<0.001). The full model of additive, dominance, additive x additive and additive x dominance epistatic effects was highly significant (P<0.001). Nonetheless, the additive gene effects were predominant ranging between 57% and 89% which was matched by large heritability (54%-85%). The average degree of dominance ranged between -0.52 and 0.88 supporting observations of partial dominance. The NLB disease severity showed a continuous distribution in all three sets for F2, BCP1 and BCP2 populations which is an indication of quantitative nature of inheritance and additive gene effects. The mid parent heterosis ranged from -19 to 1%. Therefore, resistance to NLB disease could be improved through selection by exploiting the additive gene effects. The epistatic gene effects would cause less complications because they were negligible (<25%). The client oriented breeding for maize northern leaf blight disease resistance was carried out to perform farmers and stockists assessment on the 110 F1 experimental maize hybrids and compare them with breeders selection criteria. Breeders selection criteria ranked 10 top high yielding experimental hybrids. Farmers developed 14 while stockists developed 13 selection criteria. The most preferred hybrids by farmers were VL 05616 x CML 159, CML 159 x KS03- 0B15-47 and EB04-0A01-304 x CML 442 while stockists preferred VL 05616 x CML 395, EB04-0A01-304 x CML 442 and VL 05616 x CML 159. Two F1 experimental hybrids EB04- 0A01-304 x CML 442 and CML 159 x CML 442 appeared in all top five ranked hybrids by breeders, farmers and stockists. Generally, findings showed that, farmers, stockists and breeders coincide in some selection criteria but also differ in other cases. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.