Breeding and evaluation of cassava for high storage root yield and early bulking in Uganda.

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.Cassava (Manihot esculenta Crantz), is the world’s most widely grown starch storage root crop. It is a principal food staple in sub-Saharan Africa where it accounts for approximately one-third of the total production of staple food crops. It plays a key role as a food security and an income-generating crop for millions of smallholder farmers. In Uganda, cassava ranks second to bananas (Musa spp.) in terms of area occupied, total production and per capita consumption; however, nearly 5% of the total population experiences hunger with the prevalence of food energy deficiency at the country level standing at 48%. Cassava is a crop with high potential to alleviate food shortages and energy deficiencies, owing to its unique advantages of producing acceptable yields and starch on infertile soils amidst erratic rainfall, when most other crops would fail. Hoewever, its yield potential has not been fully realised since most of the cassava cultivars grown are susceptible to pests and diseases, low yielding and late bulking. The main objective of the research was to develop high yielding, early bulking cassava genotypes that combine resistance to cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) with farmer preferred traits for cultivation in Uganda. The specific objectives were to: (i) evaluate farmers’ attitudes to and/or perceptions of cassava early bulking, production constraints and cultivar preferences; (ii) determine the extent of genetic variability in storage root bulking and other important traits of selected cassava genotypes; (iii) assess the effects of genotype x environment interaction on early bulking and related traits of selected cassava genotypes; (iv) develop and evaluate cassava F1 families for early bulking in terms of the attainment of early, high fresh storage root yield (FSRY) and resistance to CBSD and CMD; and (v) determine the combining ability and gene action controlling early bulking and yield-related traits, as well as resistance to CBSD and CMD. Through the farmer participatory survey, a number of cassava production constraints were identified, key of which were: diseases, especially CBSD and CMD; lack of early bulking cultivars; rodents and insect pests. Farmers rated early bulking as the second most important preferred trait after FSRY, but suggested that early bulking should be complemented with high dry mass content (DMC), sweetness, high FSRY and resistance to pests and diseases. The analysis of variance of 12 cassava genotypes selected for evaluation in three diverse locations and at five different harvest times indicated significant variation among genotypes, harvest times, locations and their interactions for FSRY and most of the other traits evaluated. Fresh storage root yield and the other traits evaluated were predominantly under the control of genetic variation, indicating that genetic advance would be achieved through hybridisation of the test genotypes. Additive main effects and multiplicative interaction (AMMI) analysis of the data collected at nine months after planting (MAP) indicated a non-significant GEI for early FSRY, but significant GEI for other traits assessed. Eight of the 12 genotypes analysed had relatively low interaction with locations for early FSRY, signifying that these genotypes were relatively stable for early FSRY. Thirty-six F1 families were generated from a 9 x 9 diallel and exhibited a high degree of variation between and within families for all the traits assessed at the seedling evaluation stage. Diallel analysis at the seedling evaluation stage at 10 MAP indicated that additive gene effects were predominant in the expression of early FSRY and most of the other traits analysed. At the clonal evaluation stage, the 36 families were assessed for early FSRY at 8 MAP and this trait together with most of the other traits assessed were found to be predominantly under the control of non-additive gene effects. High mid- and better-parent heterosis for early FSRY was recorded in most families at the clonal evaluation stage with NASE3 x Nyara, Nyara x B11 and NASE3 x B11 recording the highest. Selection from the 36 families at the clonal evaluation stage based on farmers’ top two preferred traits, viz. early bulking for FSRY and DMC, plus resistance to CBSD and CMD identified 50 genotypes that had early FSRY of ≥25 t ha-1 at 8 MAP compared to the best parent, CT1 that had 15.9 t ha-1 at 8 MAP. The selected genotypes also had high DMC and dual resistance to CMD and CBSD. Advancement of the selected genotypes should go a long way towards increasing cassava yield per unit time, reducing food shortages and increasing the income of smallholder farmers in Uganda

Analysis of genetic diversity of banana weevils (Cosmopolites sordidus) (Coleoptera: Curculionidae) using tanscriptome-derived simple sequence repeat markers

The banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae) is an economically important insect pest of bananas. It causes up to 100% yield losses and substantial lifespan reduction in bananas. Advances in genomics, proteomics, and sequencing technologies have provided powerful pathways to genotyping disastrous pests such as C. sordidus. However, such technologies are often not available to the majority of rural subtropical African banana growers and pest control managers. This study was therefore motivated by the need to create cheap and easily accessible C. sordidus genotyping methods that could be deployed by banana pest control managers to the benefit of C. sordidus control programs in the tropics where such advanced technologies are not readily accessible. We used an in-house C. sordidus transcriptome from the an-ongoing study from which we mined an array of simple sequence repeat (SSR) markers. Of these, six highly polymorphic transcriptome-derived SSR markers were used to successfully genotype within and among banana weevil population genetic diversity of 12 C. sordidus populations collected from four banana-growing agro-ecological zones (AEZs) in Uganda. The developed transcriptome-derived SSR markers can be used by researchers in population genetics for characterization of the C. sordidus and identification of new genes that are linked to traits of particular interest. The significant genetic diversity revealed in C. sordidus provides pertinent information for integrated pest management strategies

The East African highland cooking bananas 'Matooke' preferences of farmers and traders: Implications for variety development

'Matooke' is a staple food made from Highland cooking bananas in the Great Lakes region of East Africa. Genetic improvement of these bananas for resistance to pests and diseases has been a priority breeding objective. However, there is insufficient information on fruit quality characteristics that different users prefer, resulting in sub‐optimal adoption of new varieties. This study identified matooke characteristics preferred by farmers and traders, using survey data from 123 farmers, 14 focus group discussions and 40 traders. Gender differences were considered. The main characteristics that were found to drive variety preferences were agronomic (big bunch, big fruits) and quality (soft texture, good taste, good aroma, yellow food). There were minimal geographical and gender differences for trait preferences. Quality characteristics need to be defined in terms of physical–chemical underpinnings so that breeding programmes can apply accurate high‐throughput systems, thereby improving adoption and impact of new banana varieties

Assessing new banana genotypes for relevant traits: Implication for variety selection

Understanding the performance of new crop genotypes for traits of relevance is important in selecting potential cultivars to satisfy end-users. The objective of this study was to determine the performance of new banana genotypes for bunch mass (BMS) and BMS-related traits, resistance to black Sigatoka and sensory attributes. Eight cooking banana genotypes consisting of six new hybrid genotypes selected from advanced breeding trials and two control cultivars were evaluated in a randomized complete block design for three crop cycles at three locations in Uganda. Genotype, location, crop cycle and their interaction effects were significantly different for most traits assessed. The overall top two genotypes (“9058K-2” and “8099K-16”) combining high BMS, resistance to black Sigatoka and acceptable sensory attributes were identified. These genotypes are suggested as potential commercial cultivars for release to farmers in Uganda and/or other East African countries with similar environmental conditions to those where the genotypes were tested. It should be noted that high BMS/yield and resistance to diseases are not the only factors to consider when selecting banana genotypes that meet end-user needs. A combination of high BMS/yield, acceptable sensory attributes and resistance to diseases essentially influence the selection process of banana cultivars

Gender and trait preferences for banana cultivation and use in Sub-Saharan Africa: A literature review

Understanding trait preferences of different actors in the banana value chain may facilitate the selection and adoption of new cultivars. We systematically reviewed the scholarly and gray literature on banana trait preferences, with specific attention to studies that document gender-differentiated traits. Of 44 publications reviewed, only four reported gender-specific trait preferences, indicating a significant gap in the literature. The review found that banana farmers, irrespective of gender, value similar characteristics that are related to production constraints, income enhancement, consumption, and cultural or ritual uses. Farmers (as producers, processors, and consumers) often prefer traditional cultivars because of their superior consumption attributes, even if new cultivars have better agronomic and host plant resistance characteristics. Potential differences between trait preferences of farmers and other actors in the value chain should be accounted for to enhance marketing potential. Gender-specific research along the banana value chain and engaging users at the initial stages of breeding can ensure that new cultivars are acceptable to users and may improve adoption. Interdisciplinary teamwork is essential for an efficient and effective breeding program

Molecular markers and their application in Fusarium wilt studies in Musa spp.

Bananas and plantains (Musa spp.) are an important socio-economic fruit crop grown worldwide. Their production across the regions where they are grown is largely hampered by pests and diseases. Fusarium wilt is a disastrous diseases of bananas caused by the fungal pathogen Fusarium oxysporum f.sp. cubense (Foc). Managing it with chemicals, biological control agents and cultural methods is ineffective. Host plant resistance is the most effective and durable approach of managing most pest and disease epidemics in most plant species and could equally be effective in managing Fusarium wilt in bananas. Crossbreeding as one of the ways to introgress disease resistance genes and phenotyping for biotic and abiotic stresses currently used in banana breeding is apparently difficult to apply because of banana’s low fertility, gigantic size, and long-life cycle which prolongs its breeding cycle. There is, therefore, a need to apply molecular markers in banana genetic improvement for Fusarium wilt resistance because of their accuracy, speed, robustness and effectiveness of operation. The objective of this article was to review and discuss molecular markers that have been successfully used in studying Fusarium wilt in bananas and some other important crops. Molecular markers discussed in this article include Random Amplified Polymorphic DNA, Sequence Characterized Amplified Region, Simple Sequence Repeat, Inter-Simple Sequence Repeat, and Single Nucleotide Polymorphism. The information discussed in this article informs future decisions to identify suitable marker systems for fine mapping of target regions and accelerated identification of quantitative trait loci for Foc resistance in bananas

Crossbreeding East African Highland Bananas: Lessons Learnt Relevant to the Botany of the Crop After 21 Years of Genetic Enhancement

East African highland bananas (EAHB) were regarded as sterile. Their screening forfemale fertility with “Calcutta 4” as male parent revealed that 37 EAHB were fertile. Thiswas the foundation for the establishment of the EAHB crossbreeding programs by theInternational Institute of Tropical Agriculture (IITA) and the National Agricultural ResearchOrganization (NARO) in Uganda in the mid-1990s. The aim of this study was to assessthe progress and efficiency of the EAHB breeding program at IITA, Sendusu in Uganda.Data on pollinations, seeds generated and germinated, plus hybrids selected between1995 and 2015 were analyzed. Pollination success and seed germination percentagesfor different cross combinations were calculated. The month of pollination did notresult in significantly different (P= 0.501) pollination success.Musa acuminatasubsp.malaccensisaccession 250 had the highest pollination success (66.8%), followed by thecultivar “Rose” (66.6%) among the diploid males. Twenty-five EAHB out of 41 studiedfor female fertility produced up to 305 seeds per pollinated bunch, and were thereforedeemed fertile. The percentage of seed germination varied among crosses: 26% for2x×4x, 23% for 2x×2x, 11% for 3x×2x,and 7% for 4x×2x. Twenty-seven NARITAhybrids (mostly secondary triploids ensuing from the 4x×2x) were selected for furtherevaluation in the East African region. One so far –“NARITA 7”– was officially released tofarmers in Uganda. Although pollination of EAHB can be conducted throughout the year,the seed set and germination is low. Thus, further research on pollination conditions andoptimization of embryo culture protocols should be done to boost seed set and embryogermination, respectively. More research in floral biology and seed germination as wellas other breeding strategies are required to increase the efficiency of the EAHB breedingprogram

Crossbreeding East African Highland Bananas: Lessons Learnt Relevant to the Botany of the Crop After 21 Years of Genetic Enhancement

East African highland bananas (EAHB) were regarded as sterile. Their screening for female fertility with “Calcutta 4” as male parent revealed that 37 EAHB were fertile. This was the foundation for the establishment of the EAHB crossbreeding programs by the International Institute of Tropical Agriculture (IITA) and the National Agricultural Research Organization (NARO) in Uganda in the mid-1990s. The aim of this study was to assess the progress and efficiency of the EAHB breeding program at IITA, Sendusu in Uganda. Data on pollinations, seeds generated and germinated, plus hybrids selected between 1995 and 2015 were analyzed. Pollination success and seed germination percentages for different cross combinations were calculated. The month of pollination did not result in significantly different (P = 0.501) pollination success. Musa acuminata subsp. malaccensis accession 250 had the highest pollination success (66.8%), followed by the cultivar “Rose” (66.6%) among the diploid males. Twenty-five EAHB out of 41 studied for female fertility produced up to 305 seeds per pollinated bunch, and were therefore deemed fertile. The percentage of seed germination varied among crosses: 26% for 2x × 4x, 23% for 2x × 2x, 11% for 3x × 2x, and 7% for 4x × 2x. Twenty-seven NARITA hybrids (mostly secondary triploids ensuing from the 4x × 2x) were selected for further evaluation in the East African region. One so far –“NARITA 7”– was officially released to farmers in Uganda. Although pollination of EAHB can be conducted throughout the year, the seed set and germination is low. Thus, further research on pollination conditions and optimization of embryo culture protocols should be done to boost seed set and embryo germination, respectively. More research in floral biology and seed germination as well as other breeding strategies are required to increase the efficiency of the EAHB breeding program

Yield stability of East African highland cooking banana ‘Matooke’ hybrids

East African banana (Musa sp.) breeding efforts have focused mainly on enhancing ‘Matooke’ productivity through the development of high-yielding, pathogen-resistant cultivars with adequate stability to contribute to regional food security. Before a breeding program can recommend promising cultivars for release, they must pass the sensory screens; be evaluated in the target population environments; and the data analyzed for yield, adaptability, and stability. Twenty-four primary and secondary triploid hybrids [NARITA (N)] derived from ‘Matooke’ bananas, six triploid local ‘Matooke’ cultivars, and one exotic cultivar were evaluated for their yield, adaptability, and stability across the East African region at three highland sites in Uganda’s western and central regions, as well as at three sites in Tanzania’s northeastern and southern highlands regions, from 2016–19. A randomized complete block design with four replicates was used for multisite trials. The mixed-model restricted maximum likelihood/best linear unbiased prediction approach, along with additive main effect multiplicative interaction model biplots, were used to dissect and visualize genotype-byenvironment patterns. Following the likelihood ratio test, both genotype and interaction effects were highly significant, confirming the influence of genotype and site heterogeneity for selecting specific and broadly adapted cultivars. N23 had the greatest yield across all sites associated with adaptability and stability, outperforming the overall mean yield of all genotypes by 34.2%. In Tanzania, N27 (second), N7 (third), N18 (fourth), N4 (fifth), N12 (sixth), and N13 (seventh); and in Uganda, N17 (second), N18 (third), N2 (fourth), N8 (fifth), N13 (sixth), N12 (seventh), N4 (eighth), and N24 (ninth) demonstrated good adaptability and stability, as well as high yield. Furthermore, the fungal pathogen Pseudocercospora fijiensis had no significant effect (P > 0.05) on yield, stability, and adaptability of the hybrids. As a result, they can be introduced into areas where black leaf streak constrains banana production significantly and threatens farmers’ livelihoods. The average site yield potential ranged from 9.7 to 24.3 t⋅ha–1 per year. The best discriminating sites for testing breeding clones were Lyamungo in Tanzania and Sendusu in Uganda. Hence, these testing sites are recommended as ideal examples of locations for selecting superior genotypes

Farmers' preferences for East African highland cooking banana 'Matooke' hybrids and local cultivars

BackgroundAn understanding of farmers' preferences of new banana cultivars and their characteristics is critical for developing and selecting cultivars that meet consumer needs. Therefore, phenotypic selection in a genetically variable population remains an important aspect of plant breeding.MethodsThe participatory varietal selection approach for preference ranking was used on 31 'Matooke' secondary and primary triploid hybrids and local banana cultivars evaluated between 2016 and 2019 in Uganda and Tanzania to investigate how farmers' preference attributes could help breeders identify superior cultivars. The quantitative data were analyzed using the Statistical Package for Social Sciences (SPSS). The qualitative data from farmers' focus group discussions (FGDs) were described using content analysis. The Mann–Whitney U test and Wilcoxon's signed-rank test were used to confirm the difference in farmers' preferences between groups.ResultsFarmers' approaches for defining characteristics were multivariate, and their preferences varied by site and country. Large fruit, a large bunch, market acceptability of the banana bunch, a sturdy stem, and an attractive appearance of the banana plant were the characteristics most preferred by farmers in Tanzania and Uganda. Tanzanian farmers preferred large bunches over other characteristics like bunch marketability and robust stem. Large fruit, drought tolerance, a strong stem, and phenotypic similarity to local cultivars were prioritized by Ugandan farmers. Both men and women farmers were more concerned with production-related characteristics, but the former valued marketing-related characteristics more, while the latter preferred use-related characteristics. Their preferences did not differ statistically, but the relative importance assigned by each group to the selected attributes was different.ConclusionFarmers' varietal preferences are frequently based on some assumed requirements, resulting in cultivar rejection or non-adoption. Therefore, determining the value attributed to each characteristic by various farmer groups is crucial in developing 'Matooke' banana cultivars with desired attributes that will boost the rate of adoption on-farms. Breeding initiatives that establish a system of integrated approaches and rely on thorough diagnosis of both production and consumption characteristics will best serve farmers' diverse preferences. To accomplish this, planning for varietal improvement initiatives at various levels—including internationally, regionally, nationally, and locally—would require a strong participatory structure that is gender inclusive