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Maize lethal necrosis (MLN) is a new disease in Sub-Saharan Africa (SSA) caused by double infection by maize chlorotic mottle virus (MCMV) with any of the many viral agents in the Potyviridae family. It has become one of the key constraints to maize production in the region due to the significant crop losses caused since its emergence in 2011. Sustainable management of MLN is achievable through genetic improvement and replacement of old susceptible varieties with farmer-preferred varieties that combine MLN resistance with tolerance to other prevailing biotic and abiotic stresses. To effectively breed for MLN resistance, it is important to identify sources of resistance, determine the genetic nature of resistance and employ efficient breeding techniques that will result in high genetic gains from selection. This study aimed to dissect the genetic nature of MLN using elite and introduced inbred lines from tropical and temperate maize genetic pools, new biparental populations and potential hybrids. The genetic analysis was conducted in five studies representing the major stages of maize breeding, from pre-breeding to variety development. In the pre-breeding study, the breeding potential for MLN resistance among 18 tropical and temperate inbred and doubled haploid (DH) lines was conducted to identify the best parents for population development. The second study on the genetic potential and usefulness of new pedigree populations was conducted using nine segregating biparental populations derived by crossing susceptible elite and recycled DH lines to two introduced MLN resistant lines from the KS23 pool. The third study, using a section of these populations, selected three sizable populations, which were phenotyped, genotyped and used to validate quantitative trait loci (QTL) linked to MLN resistance in the KS23 genetic background. The fourth study, moving towards product development, entailed determining the potential of new lines and single crosses for use as MLN resist

In 2016 sub-Saharan Africa (SSA) was invaded by the transboundary maize-eating pest, fall armyworm [Spodoptera frugiperda (J.E. Smith); FAW]. The pest has threatened food security and livelihoods of the majority of smallholder farmers in the region. The main aim of this study was to investigate the potential of breeding maize with resistance to FAW in southern Africa. The first study aimed to assess the breeding potential of introduced exotic FAW resistant trait donor maize lines with southern Africa germplasm. Thirteen mid-altitude adapted inbred lines were crossed with seven FAW-resistant exotic donor lines, in a line x tester mating scheme that produced 84 F1s which were evaluated together with checks at four locations under natural FAW infestation. The best exotic donor lines with low and negative general combining ability (GCA) effects for foliar FAW damage (FFAWD) resistance scores and good grain yield (GYD) per se performance were CML139, CML67, CML121 and CML345. Local lines that showed similar good attributes were CimExp1, CimExp4, CimExp5, CimExp8 and CimExp10. The best crosses were CimExp1/CML331, CimExp1/CML345, CimExp10/CML331 CimExp5/CML331 and CimExp5/CML345. In the second study, two sets of germplasm (hybrids/OPVs and inbred lines) were evaluated for FAW resistance under managed and natural FAW infestation. The objective was to evaluate commercial and experimental maize hybrids and parental lines cultivated in southern Africa for resistance to FAW. Commercial cultivars were significantly more affected by FAW infestation than experimental hybrids. The introduced FAW-resistant donor lines (CML338, CML67, CML121 and CML334) showed better resistance to FAW damage, individually and in hybrid combinations. Local inbreds, SV1P, CML491 and CML539, also showed good FAW resistance. Husk cover, ear rot, anthesis date and plant height were correlated with FAW resistance. The third study aimed to investigate the stability of grain yield performance and resistance

The aim of this study was to identify farmers’ adoption challenges, perceptions and preferences of yellow-flesh cassava. Combining ability and stability of these genotypes were also determined. Total carotenoid content (TCC), proximate values and hydrogen cyanide (HCN) of the yellow-flesh cassava were measured and the retention of carotenoids in boiled biofortified cassava was determined. This information will help breeders to identify genotypes with the best nutritional quality across the tested locations for planting and promotion in Ghana also could provide a basis for implementing a recurrent selection scheme for developing cassava varieties with high levels of carotenoids and dry matter. In all the locations visited, farmers’ knowledge on the improved cassava varieties (white flesh) and the yellow-flesh cassava were generally poor among the men and women interviewed, due to their inability to access planting materials, which could be improved by strengthening the cassava seed system for awareness, and increased availability of the varieties to farmers. Very few men and women cultivated improved varieties and yellow-flesh cassava. The young adults, who are the future of the agricultural sector, lacked access to improved varieties and they must be given extra attention to understand the activities of cassava breeding programmes, to empower them to make use of these materials. The general combining ability (GCA) was larger than specific combining ability (SCA) for cassava mosaic disease (CMD), harvest index (HI) and TCC, with predictability ratios (0.98, 0.88 and 0.92 respectively) close to one. Hence, there is a possibility for improvement of the characteristics by selection. Positive significant correlation between pulp colour and TCC (r=0.59) and pulp colour and cortex colour (r=0.58) were observed. Negative significant correlation were seen between CGM and HI (r=-0.50), CMD and RTN (r=-0.45), and HI and RTN (r=-0.51). It implies that these key traits could be

Water-limited stress (WLS) is associated with adverse changes at morphological, physiological, biochemical and molecular levels among genotypes, which consequently affects crop growth and productivity. These changes are useful indicators in breeding of drought tolerant genotypes. This study was, therefore, carried out to identify genotypes that are good performing under WLS conditions and to determine traits’ response to WLS using a combination of morphological traits, physiological traits, water use efficiency and grain yield. In addition, interrelationships among morphological traits, physiological traits and water use efficiency were determined in order to identify traits that contribute to grain yield under WLS conditions. The study also elucidated the association between drought tolerance indices and grain yield under WLS conditions in separating tolerant genotypes from sensitive genotypes. It further looked at the impact of drought on grain yield of soybean with change in environment and season. The study also tried to understand the mode of gene action considering that the majority of the characteristics of importance in a crop are inherited quantitatively. Genotypes showed significant variability in tolerance levels to WLS. Genotypes with a high drought tolerance level generally exhibited a higher grain yield, 100-seed weight, plant height, number of pods per plant, minimal grain yield reduction, maintained a higher relative chlorophyll content, quantum yield of efficiency for photosystem II and water use efficiency under severe WLS compared to genotypes with a low drought tolerance level. Among the physiological traits, relative chlorophyll content was most significantly associated with genotype, while quantum yield of efficiency for photosystem II, photoprotective nonphotochemical quenching and non-photochemical quenching basal dissipation of light energy for other unregulated process were more frequently and significantly associated with WLS. Plant height

The development of high yielding and stable quality protein maize (QPM) hybrids is important for increasing grain yield output per unit area, to support the fight against hunger and malnutrition in sub-Saharan Africa (SSA), as well as for feed supplement formulation for the animal and poultry industries. Despite the development of QPM genotypes with increased lysine and tryptophan content, important information is lacking on the yield potential of QPM genotypes compared to non-QPM (normal) genotypes. The main objective of this study was to quantify grain yield reduction (if any) due to the QPM trait. The specific objectives were to: (i) compare QPM and non-QPM inbred lines for yield and yield related traits, as well as quality traits, and determine stability for grain yield, (ii) compare QPM and non-QPM hybrids for yield and yield stability, (iii) estimate the combining ability for grain yield and quality traits of QPM and non-QPM inbred lines (iv) estimate the heritability, variance components, principal components, correlation coefficients, and do path analysis of grain yield, and agronomic and quality traits. In this study, 130 single cross hybrids were developed from 33 QPM and non-QPM inbred lines and four testers (two QPM and two non-QPM). Five hybrid checks (two QPM and three non-QPM, all single cross hybrids) were included, obtained from the International Maize and Wheat Improvement Center, Zimbabwe. The 135 hybrids together with the 40 inbred lines were evaluated in South Africa and Zimbabwe during the 2017/2018 and 2018/2019 cropping seasons. The inbred lines were evaluated at seven locations using a 5 x 16 alpha lattice design, while the hybrids were evaluated at 13 locations using a 5 x 27 alpha lattice design with two replications. In the field experiments, two plants per plot were selfpollinated for the determination of zein, tryptophan, amylose and starch, protein, oil, moisture and fibre contents. In the inbred line trials, the top six performing lin

Nitrogen (N) is one of the most yield limiting nutrients in maize. However, farmers in sub-Saharan Africa (SSA) use very little N due to low income. Nitrogen Use Efficient (NUE) varieties can provide a partial solution to the problem through efficient N uptake and utilisation. Designing an effective breeding strategy for improving any trait of interest requires knowledge of quantitative genetic parameters, genomic regions associated with the traits and the use of efficient selection methods. The objectives of this study were to 1) assess the efficiency of indirect selection for grain yield under low N stress conditions through grain yield under optimum N conditions and through secondary traits under low N conditions, 2) identify single nucleotide polymorphism (SNP) marker loci significantly associated with grain yield and secondary traits under low N and optimumconditions, 3) map and characterize the quantitative trait loci (QTL) for grain yield and some secondary traits under optimum and low N stressed conditions, and 4) evaluate the accuracy of genomic selection for improvement of grain yield and other secondary traits under optimum and low N stressed environments. Results showed that genetic variance for grain yield was highly affected by low N stress, more than secondary traits, and low correlation was observed between optimum and low N environments for grain yield. This lead to low relative efficiency of indirect selection for grain yield under low N using grain yield under optimum conditions. The efficiency of indirect selection for grain yield under low N through secondary traits under low N conditions was also low. The efficiency of selection could be enhanced through identification of genomic regions and associated markers linked with grain yield under low N. A total of 158 putative protein coding genes associated with significant SNPs, of which seven linked with four known genes, were identified through a genome-wide association study. Markers associated w, Borlaug LEAP

English: Cassava (Manihot esculanta Crantz) is a perennial woody plant which is cultivated in Africa, Asia and Latin America. It is tolerant to drought and grows in poor soils. It is a source of carbohydrates, vitamins and small quantities of proteins. In Malawi, it is the most important root crop and it is grown across the country. It is consumed as a staple food by 30% of the people living along the central and northern part of Lake Malawi. Its production is constrained by among others, diseases CMD and CBSD. These two diseases are known to spread through white flies. The magnitude of attack by the two diseases depends on the genotype and the environment. No released genotypes in Malawi have ever been evaluated in seed transmission of viruses’ studies. The experiment on the quantification of F1 cassava progenies from open pollinated F1 progeny crosses revealed that genotypes which show high severity of CMD are likely to allow rapid multiplication of EACMMV and SACMV. However, it has been proven that this might not always be the case as some genotypes may have higher virus quantities while showing slightly less severe symptoms. Genotypes which succumb to high disease symptom severity are likely to have high incidence of the disease. CMD symptom severity and incidence were positively correlated. The experiment on determination of virus quantities in different tissues has provided information that virus quantities in particular tissues depend on the cultivar used. The viruses can spread to all the tissues analysed in this research. It was shown that root parenchyma and leaf tissues accommodated most of CBSV and UCBSV in the cultivars used. When there was co-infection, CBSV and UCBSV were positively correlated. EACMMV and SACMV quantity can vary in cassava tissues depending on the cultivar. Leaves have shown to contain a relatively high quantity of the viruses. CBSV, UCBSV, EACMMV and SACMV symptoms were not observed in seedlings grown from seeds which were obtained f, Afrikaans: Cassava (Manihot esculanta Crantz) is ‘n meerjarige houtagtige plant wat verbou word in Afrika, Asië en Latyns Amerika. Dit is droogte tolerant en kan groei in swak grond. Dit is ‘n bron van koolhidrate, vitamines en klein hoeveelhede proteïene. Dit is die belangrikste wortelgewas in Malawi, en dit groei oral in die land. Dit word as stapelvoedsel gebruik deur 30% van die mense wat woon langs die sentrale en noordelike dele van die Malawi meer. Cassava produksie word beperk deur, onder andere, die siektes CMD en CBSD. Hierdie twee siektes word versprei deur witvlieë. Die erns van die infeksie deur hierdie twee siektes hang af van die genotipe en die omgewing. Inligting oor die reaksie van verskillende Malawi genotipes en hulle nageslag aangaande akkumulasie van virusse, is baie beperk. Geen vrygestelde genotipes in Malawi is nog ooit geëvalueer vir saadoordrag van virusse nie. Die eksperiment oor die kwantifikasie van cassava F1 nageslag van oop en spesifieke kruisings het getoon dat genotipes met ‘n hoë vlak van CMD ‘n vinnige vermeerdering van SACMV toelaat. Dit is egter bewys dat dit nie altyd die geval is nie, omdat sekere genotipes groter hoeveelhede virus gehad het terwyl hulle steeds minder simptome getoon het; daar was dus geen korrelasie tussen min simptome van SACMV en CMD en virus insidensie nie. Genotipes wat baie siektesimptome gehad het egter hoë virus insidensie getoon; dus was die graad van die siekte met die insidensie gekorreleer. Die eksperiment vir die bepaling van virus hoeveelhede in verskillende weefseltipes het getoon dat virus hoeveelhede in spesifieke weefsel afhang van die cultivar wat gebruik is. Virusse het versprei na alle weefsel wat in die studie geanaliseer is. Wortel parenkiem weefsel het meeste van die CBSV en UCBSV in die cultivars gehuisves. Waar daar ko-infeksie was, was CBSV en UCBSV positief gekorreleer. SACMV hoeveelheid het gewissel tussen die wortel parenkiem, wortel korteks en stam korteks (5 cm van bo), afhange

English: In Malawi maize is grown even in marginal lands, on steep slopes, wet lands, rocky areas and low pH soils due to the high human population which excert pressure on the land. The objectives of this study were to investigate genetically diverse maize genotypes for tolerance to low pH soil conditions. In the hydroponic experiment genotypes IWDC3SYNF2-B, VPO52, and LPHpop 4 had relatively higher nett seminal root length and were considered tolerant, and DT-YSTR SYNTHETIC-B, TZE-WPOPDTC2STR-B, TZE-YDTSTRC4-B, LPHpop3, LPHpop13, and LPHpop14 were sensitive or susceptible to Al toxicity. Under field conditions, genotypes LPHpop16, LPHpop3, VPO739, VPO5173 and LOW N POOL C3-B were identified to be relatively tolerant to low pH soil conditions. SYNDTE–STY-W-B ranked first in terms of root tolerant index (RTi) with a good NSRL in the glasshouse hydroponic experiment and this was followed by VPO717 which also had a relatively a better root tolerance index and nett seminal root length. Phenotypic traits associated with grain yield, such as plant vigour, seed size (100 seed weight), shelling percentage, number of ears per plant, ear height and plant height can be used alongside grain yield when selecting germplasm for tolerance to low pH stress. In general, the effects of low pH soil conditions contributed to reduction in grain yields and yield components. The combined mean yield reduction due to low pH soil in this study was 69.9%. From AMMI and GGE analysis, genotypes LPHpop21, VPO52, VPO72, VPO744 and VPO96 were identified as the most stable. VPO097 was identified as an unstable genotype. Chitala low-land optimal site was identified as the most discriminating environment in terms of genotypes while Chitedze mid-altitude optimal environment was identified as a stable environment. The diallel study revealed that additive and non-additive gene actions were at play in the expression of some of the traits like grain yield, number ears per plant, shelling percentage, 100 s, Afrikaans: In Malawi word mielies selfs in marginale grond, op steil hellings, vleilande, klipperige gebiede en in lae pH grond verbou, weens die hoë bevolking wat druk op die land plaas. Die doelwitte van hierdie studie was om geneties diverse mielie genotipes vir verdraagsaamheid vir lae pH grondtoestande te ondersoek. In die hidroponiese eksperiment het genotipes IWDC3SYNF2-B, VPO52 en LPHpop4 relatiewe hoër netto seminale wortel lengtes gehad en word as verdraagsaam beskou en DT-YSTR SYNTHETIC-B, TZEWPOPDTC2STR-B, TZE-YDTSTRC4-B, LPHpop 3, LPHpop13, en LPHpop14 was sensitief of vatbaar vir Al toksisiteit. Onder veldtoestande, is genotipes LPHpop16, LPHpop3, VPO739, VPO5173 en LOW N POOL C3-B as relatief verdraagsaam vir lae pH grondtoestande geïdentifiseer. In die glashuis hidroponiese eksperiment was SYNDTESTY-W-B eerste in terme van wortel tolerante indeks met 'n netto seminale wortel lengte van 2.5 cm en is gevolg deur VPO717 met ʼn wortel tolerante indeks van 1.0 en netto seminale wortel lengte van 1.7 cm. Fenotipiese eienskappe wat geassosieer word met graanopbrengs, soos groeikrag, saadgrootte (100 saad gewig), saad persentasie, die aantal koppe per plant, kop hoogte en plant hoogte kan gebruik word saam met graanopbrengs wanneer kiemplasma geselekteer word vir verdraagsaamheid vir lae pH stres. In die algemeen dra die effek van lae pH grondtoestande by tot die verlaging in graanopbrengste en opbrengs komponente. Die gekombineerde gemiddelde opbrengs verlaging as gevolg van lae pH grond in hierdie studie was 69.9%. Deur die AMMI en GGE analise is LPHpop21, VPO52, VPO72 is VPO744 en VPO96 geïdentifiseer as die mees stabiele genotipes. VPO097 is geïdentifiseer as 'n onstabiele genotipe. Chitala lae-ligging optimale omgewing is geïdentifiseer as die mees onstabiele omgewing in terme van genotipes terwyl Chitedze middel-ligging optimale omgewing geïdentifiseer is as 'n stabiele omgewing. Die dialleel studie het getoon dat beide additiewe en nie-additiewe geenak, Ministry of Agriculture

English: Rice is an important food crop with two domesticated species namely Oryza glaberrima Steud. also known as African rice and O. sativa L. also known as Asian rice. Rice is a self-pollinating plant that shows some level of outcrossing under field conditions. Understanding the levels of gene flow is important for managing the conservation and maintenance of germplasm for gene banks and plant breeding programmes. It is equally important for the production of quality rice seed. There is also the concern of gene flow between genetically modified rice and other rice species; wild relatives and weedy (red) rice. This study used agro-morphological and microsatellite markers to evaluate the diversity in a collection of 36 accessions consisting of intraspecific (O. sativa and O. glaberrima) and interspecific (O. sativa x O. glaberrima) hybrid genotypes. The Shannon-Weaver diversity index was low measured by agro-morphological markers. The highest level of diversity was detected in the Indica accessions and the lowest diversity in the O. glaberrima accessions. Japonica accessions had brown or green apiculus and were awnless. O. glaberrima and landrace accessions had purple apiculus and some were awned. The Japonica group comprised mostly of improved varieties with a white pericarp whilst O. glaberrima accessions and landraces had a red pericarp. Selected interspecific hybrids combined traits of O. sativa and O. glaberrima to varying degrees. Microsatellite markers showed a total of 321 alleles with an average of 11.9 alleles per locus and an average major allele frequency of 0.29 per locus. The average gene diversity value was 0.81 and polymorphism information content was 0.80 per locus. Diversity indices for interspecific hybrids were intermediate between O. sativa and O. glaberrima, but closer to the O. sativa Japonica group. Two populations were revealed which corresponded to the O. sativa Indica group and O. sativa Japonica group. Interspecific hybrid accessions wer, Afrikaans: Rys is ‘n belangrike voedselgewas met twee aangeplante spesies naamlik Oryza glaberrima Steud., ook bekend as Afrika rys en O. sativa L., ook bekend as Asiese rys. Rys is ‘n selfbestuiwende gewas met ‘n persentasie kruisbestuiwing onder veldtoestande. ‘n Begrip van die hoeveelheid geenvloei is belangrik vir die bestuur en onderhoud van kiemplasma vir geenbanke en planteteelt programme. Dit is net so belangrik vir die produksie van kwaliteit ryssaad. Daar is ook kommer oor geenvloei tussen GM rys en ander rys spesies; wilde verwantes en onkruidagtige (rooi) rys. Hierdie studie het agro-morfologiese en mikrosatelliet merkers gebruik om diversiteit in ‘n versameling van 36 inskrywings bestaande uit intraspesifieke (O. sativa L. en O. glaberrima Steud.) en interspesifieke (O. sativa x O. glaberrima) rys genotipes te bepaal. Resultate van kwalitatiewe en kwantitatiewe eienskappe het verskille in diversiteit tussen die inskrywings getoon. Die waargenome diversiteit in O. glaberrima was laer as in O. sativa. Interspesifieke rys het intermediêre vlakke van diversiteit getoon. Die Shannon-Weaver diversiteitsindeks was laag gemeet aan agro-morfologiese merkers. Die hoogste diversiteitsvlak is gesien in die Indica inskrywings en die laagste diversiteit in die O. glaberrima inskrywings. Japonica inskrywings het bruin of groen aarpunte gehad en was baardloos. O. glaberrima en landrasinskrywings het pers aarpunte gehad, en sommige het baarde gehad. Die Japonica groep het meestal bestaan uit verbeterde variëteite met ‘n wit perikarp terwyl O. glaberrima inskrywings en landrasse ‘n rooi perikarp gehad het. Die interspesifieke basters het eienskappe van O. sativa en O. glaberrima gekombineer in verskillende grade. Mikrosatelliet merkers het ‘n total van 321 allele getoon met ‘n gemiddeld van 11.9 allele per lokus en ‘n gemiddelde major alleel frekwensie van 0.29 per lokus. Die gemiddelde geendiversiteitswaarde was 0.81 en die polimorfisme informasie inhoud was 0.80 per lo, Africa Rice Center (AfricaRice)