Cassava Genotypes Research Articles

Variability of amylose content and its correlation with the paste properties of cassava starch.

The amylose content can significantly impact the diverse industrial applications of cassava starch. This study aimed to assess the variability of cassava germplasm concerning amylose content and other attributes pertinent to root quality, alongside its correlation with paste properties. Starch extracted from 281 genotypes, obtained in germplasm evaluation trials, was evaluated for amylose content, with additional analysis of parameters such as pasting temperature, time to peak viscosity (TPV), viscosity breakdown (BrD), retrogradation tendency, and maximum, minimum, and final viscosities. The genotypes exhibited considerable variation in dry matter content (ranging from 27.06% to 41.02%), starch content (from 14.61% to 25.67%), cyanogenic compounds (1.77 to 7.81), and amylose content (0.05% to 33.23%). High phenotypic variability in paste properties was observed, alongside a low residual effect for most traits, resulting in high broad-sense heritabilities (>0.95). Strong correlations of significant magnitude (>0.80) were found between parameters such as peak viscosity × viscosity breakdown, minimum viscosity × final viscosity, and final viscosity × retrogradation tendency. Moderate correlations were also identified, such as between dry matter content × starch content (0.56). While positive, correlations between amylose content and paste properties were of low magnitude (ranging from 0.13 to 0.35), except for TPV and BrD. Principal component discriminant analysis clustered the germplasm into six distinct groups based on root quality and paste properties, with most improved genotypes falling into two clusters characterized by high starch and dry matter contents. This study underscores the necessity of simultaneous evaluation of amylose content and paste properties in the breeding pipeline. Additionally, clustering cassava genotypes proves beneficial in identifying those that fulfill specific requirements in industrial and breeding applications.

Comparative transcriptome analysis, identification and expression analysis of sucrose phosphate synthase genes in high and low starch cassava (Manihot esculenta Crantz) genotypes

Comparative transcriptome analysis, identification and expression analysis of sucrose phosphate synthase genes in high and low starch cassava (Manihot esculenta Crantz) genotypes

Effect of gamma irradiation on proliferation and growth of friable embryogenic callus and in vitro nodal cuttings of ugandan cassava genotypes.

Cassava (Manihot esculenta Crantz) production and productivity in Africa is affected by two viral diseases; cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). Induced mutagenesis of totipotent/embryogenic tissues or in vitro plant material can lead to the generation of CMD and/or CBSD tolerant mutants. To massively produce non-chimeric plants timely and with less labor, totipotent cells or tissues are a pre-requisite. This study aimed to determine the effect of gamma radiation on the proliferation and growth of friable embryogenic callus (FEC) and in vitro nodal cuttings respectively. To obtain FEC, 2-6 mm sized leaf lobes of nine cassava genotypes were plated on Murashige and Skoog (MS) basal media supplemented with varying levels (37, 50, 70, 100) μM of picloram for production of organized embryogenic structures (OES). The OES of five cassava genotypes (Alado, CV-60444, NASE 3, NASE 13 and TME 204) were crushed and plated in Gresshoff and Doy (GD) basal media in combination with the amino acid tyrosine in varying concentrations for FEC production. FEC from five cassava genotypes and in vitro nodal cuttings of nine genotypes were irradiated using five different gamma doses (0, 5, 10, 15, 20 and 25 Gy) at a dose rate of 81Gy/hr. The lethal dose (LD)50 was determined using the number of roots produced and flow cytometry was done to determine the ploidy status of plants. The highest production of OES was noted in Alado across varying picloram concentrations, while TME 204 obtained the highest amount of FEC. The irradiated FEC gradually died and by 28 days post irradiation, FEC from all five cassava genotypes were lost. Conversely, the irradiated in vitro nodal cuttings survived and some produced roots, while others produced callus. The LD50 based on number of roots varied from genotype to genotype, but plants remained diploid post-irradiation. Accordingly, the effect of gamma irradiation on Ugandan cassava genotypes (UCGs) was genotype-dependent. This information is foundational for the use of in vitro tissues as target material for cassava mutation breeding.

Genotype by environment interaction effect and fresh root yield stability of cassava genotypes under contrasting nitrogen regimes

Nitrogen (N) is an important nutrient element needed by cassava for optimum yield and it is a vital component of nucleotides (nucleic acids), enzymes, amino acids (proteins), chlorophyll molecules and hormones, among other essential compounds required for growth and development of cassava. Nitrogen stress is a major cassava production constraint, the study aimed to examine genotype by environment interaction (GEI) effects and fresh root yield stability of 203 diverse cassava clones to identify genotypes with stable performance under low and optimum nitrogen regimes across environments using AMMI and GGE biplot analysis. Experiments were conducted using an augmented block design with three replications for two years in three locations in Nigeria. There were significant differences (p < 0.001) in the genotype’s mean performances as well as significant differences (p < 0.001) in the environment’s mean performances for all the traits measured in both nitrogen regimes. The AMMI analysis of variance showed significant effects (p < 0.001) for genotypes, environments and the interactions for fresh root yield in both nitrogen regimes. The biplot analysis showed that for fresh root yield in the optimum nitrogen regime, the principal component accounted for 81.54% of the G + GE (Genotype plus and Genotype by Environment) variation. The G + GE for fresh root yield in the low nitrogen regime accounted for a total of 71.64% of the variation. Ten genotypes were identified as the best genotypes under the optimum nitrogen regime, while eleven genotypes were the best under the low nitrogen regime. Three genotypes under optimum nitrogen regimes were high-yielding. Still, they were unstable in their fresh root yield performance across the environments and can be recommended as specifically adapted to the environments they performed best. Three other genotypes were high-yielding genotypes under low nitrogen but were highly unstable in their fresh root yield mean performance across the environments. The environments Otobi_YR1, Igbariam_YR2, and Umudike_YR1 were identified as the most discriminatory among the test environments. The environments Umudike_YR2 and Igbariam_YR1 were identified as the most representative of the test environments and can represent a mega-environment. The best 21 genotypes that performed above the grand mean for fresh root yield in both nitrogen regimes can be further evaluated on the farmer’s field for possible advancement.

Development of a Robust In vitro Regeneration Protocol in Cassava (Manihot esculenta C.) Using Axillary Bud Explants for Cryopreservation

Cassava is an important crop as it is the source of energy in the diet for the most of the tropical countries. Field gene bank is the only viable option for the maintenance of cassava germplasm. Cryopreservation offers the long-term conservation of vegetatively propagates crops without losing its viability through an effective in vitro regeneration system. In vitro regeneration response in YTP-1 and Sree Athulya genotypes of cassava was standardized through optimization of various factors influencing organogenesis. Among the different media tested, highest shoot induction frequencies of 81.4% and 77.8% were recorded in medium supplemented with 0.5 mg/l BAP + 0.2 mg/l NAA (CMSI 2) for YTP 1 and Sree Athulya respectively in the present study. 3 to 5 multiple shoots from a single shoot apex obtained from 70-80% of explants within 50-60 days. Highest regeneration frequencies of 56.6%and 46.6% were recorded in medium supplemented with 1 mg/l IAA (CRM 2) for YTP1 and Sree Athulya. As a result, an easy in vitro regeneration method that is genotype independent was created and may be effectively used to preserve cassava germplasm in the cryogen bank.

Development of standard operating protocol for measurement of cassava root mealiness

One of the major attributes of boiled cassava roots is its ability to soften within a short period, otherwise known as mealiness. This study aimed to establish and validate standard operating procedures for assessing the mealiness of boiled cassava roots. Twenty cassava genotypes, including landrace and improved varieties, were selected for the protocol development, with an additional ten genotypes used for validation. Following cooking, the cassava roots were evaluated for hardness and work done in extrusion using a texturometer equipped with a five-blade Ottawa cell probe. The same samples were assessed for sensory texture analysis using trained panelists for parameters such as softness and chewiness. Pearson's correlation analysis revealed significant positive correlations (p < 0.01) between sensory softness and instrumental texture measurements, as well as between softness and cooking time (p < 0.01, r = 0.94), and between chewiness and cooking time (p < 0.05, r = 0.81). Validation results confirmed significant correlations (p < 0.01) between cooking time, sensory softness, and chewiness. These findings suggest that cooking time can serve as a reliable indicator, closely associated with sensory attributes, in determining the mealiness of boiled cassava roots. This approach offers a practical, mid-throughput method for assessing cassava root mealiness, with implications for breeding improved varieties, farmers adoption, and consumer acceptance.

Photosynthetic Performance, Carbohydrate Partitioning, Growth, and Yield among Cassava Genotypes under Full Irrigation and Early Drought Treatment in a Tropical Savanna Climate.

In a tropical savanna climate like Thailand, cassava can be planted all year round and harvested at 8 to 12 months after planting (MAP). However, it is not clear how water limitation during the dry season without rain affects carbon assimilation, partitioning, and yield. In this field investigation, six cassava genotypes were planted in the rainy season (August 2021) under continuous irrigation (control) or subjected to drought for 60 days from 3MAP to 5MAP during the dry season (November 2021 to January 2022) with no irrigation and rainfall. After that, the plants were rewatered and continued growing until harvest at 12MAP. After 60 days of stress, there were significant reductions in the mean net photosynthesis rate (Pn), petiole, and root dry weight (DW), and slight reductions in leaf, stem, and tuber DW. The mean starch concentrations were reduced by 42% and 16% in leaves and tubers, respectively, but increased by 12% in stems. At 6MAP after 30 days of rewatering, Pn fully recovered, and stem starch was remobilized resulting in a dramatic increase in the DW of all the organs. Although the mean tuber DW of the drought plants at 6MAP was significantly lower than that of the control, it was significantly higher at 12MAP. Moreover, the mean tuber starch concentration at 12MAP of the drought plants (18.81%) was also significantly higher than that of the controls (16.46%). In the drought treatment, the high-yielding varieties, RY9, RY72, KU50, and CMR38-125-77 were similarly productive in terms of tuber DW and starch concentration while the breeding line CM523-7 produced the lowest tuber biomass and significantly lower starch content. Therefore, for cassava planted in the rainy season in the tropical savanna climate, the exposure to drought during the early growth stage was more beneficial than the continuous irrigation.

Assessment of Cassava Pollen Viability and Ovule Fertilizability under Red-Light, 6-Benzyl Adenine, and Silver Thiosulphate Treatments.

Understanding pollen and ovule fertility as factors influencing fruit and seed set is important in cassava breeding. Extended daylength with red light (RL) and plant growth regulators (PGRs) have been used to induce flowering and fruit set in cassava without any reference to effects on pollen viability or ovule fertilizability. This study investigated the effects of field-applied RL and PGR on pollen viability and ovule fertilizability. Panels of cassava genotypes with early or moderate flowering responses were used. RL was administered from dusk to dawn. Two PGRs, 6-benzyl adenine (BA), a cytokinin and silver thiosulphate (STS), an anti-ethylene, were applied. Pollen viability was assessed based on pollen grain diameter, in vitro stainability, in vivo germinability, ovule fertilizability, and ploidy level. Treating flowers with RL increased the pollen diameter from 145.6 in control to 148.5 µm in RL, 78.5 to 93.0% in stainability, and 52.0 to 56.9% in ovule fertilizability in treated female flowers. The fruit set also increased from 51.5 in control to 71.8% in RL-treated female flowers. The seed set followed a similar trend. The ploidy level of pollen from RL-treated flowers increased slightly and was positively correlated with pollen diameter (R2 = 0.09 *), ovule fertilization (R2 = 0.20 *), fruit set (R2 = 0.59 *), and seed set (R2 = 0.60 *). Treating flowers with PGR did not affect pollen diameter but increased stainability from 78.5% in control to 82.1%, ovule fertilizability from 42.9 to 64.9%, and fruit set from 23.2 to 51.9% in PGR-treated female flowers. Combined BA + STS application caused the highest ovule fertilizability, fruit, and seed set efficiency. These results show that RL and PGR treatments increase pollen viability and ovule fertilizability. This is important for planning pollination strategies in cassava breeding programmes.

Stability and genetic parameters for cassava yield attributes in the tropical humid region of Brazil

The performance differences in cassava genotypes arising from genotype vs. environment interactions (G × E) often lead to responses that are significantly lower than expected for selection. The objective of this study was to evaluate different stability methods, both parametric and non-parametric, such as additive main-effects and multiplicative interaction (AMMI), main effect of genotypes plus G × E (GGE), and weighted average of absolute scores (WAASB), in order to quantify the G × E in multi-environmental trials. A total of 12 genotypes were assessed across 12 environments using a completely randomized block design, with three replicates for traits such as fresh root yield (FRY) and dry matter content in the roots (DMC). The data were subjected to analysis of variance and the Scott Knott test (p < 0.05). The sum of squares (SQ) of genotypes, environment, and G × E effects were equally distributed for FRY, whereas for DMC, these effects accounted for 64.1%, 21.9%, and 13.8% of the SQ, respectively, indicating a lower environmental effect on this characteristic. Using the AMMI, GGE, and WAASB methods, genotypes with high agronomic performance and stability for FRY (BR11-34–41 and BR11-34–69) (> 32 t ha−1) and DMC (BRS Novo Horizonte, BR12-107–002, and BR11-24–156) (> 37%) were identified. The broad-sense heritability (h2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${h}^{2}$$\\end{document}) for FRY and DMC was estimated to be 0.45 and 0.75, respectively. Approximately 72% of the methods identified BRS Novo Horizonte as the genotype with the highest stability and performance for DMC, while 47% identified genotypes BR11-34–41 and BR11-34–69 for FRY and intermediate DMC. Genotype BR11-24–156 exhibited high static stability according to 50% of the methods. Significant correlations were observed between stability and agronomic performance across the different methods, enabling the formation of groups based on stability concepts. Additionally, it was found that two mega-environments existed for FRY, whereas DMC displayed a single mega-environment with similar patterns, indicating an absence of G × E. We identified superior genotypes that could be promoted to national performance trials to develop stable cultivars with better yield attributes in cassava.

Genetic diversity and population structure of Uganda cassava germplasm.

Cassava (Manihot esculenta Crantz) holds significant economic importance globally. Evaluating a diverse range of germplasm based on molecular characteristics not only enhances its preservation but also supports its utilization in breeding programs. In this study, we assessed genetic diversity and population structure among 155 cassava genotypes from Uganda using 5247 single nucleotide polymorphism (SNP) markers. Genotyping by sequencing (GBS) was employed for SNP discovery and to evaluate genetic diversity and population structure using the ADMIXTURE software. The cassava accessions comprised two populations: 49 accessions from Ugandan lines and 106 accessions resulting from crosses between South American and Ugandan lines. The average call rate of 96% was utilized to assess marker polymorphism. Polymorphic information content values of the markers ranged from 0.1 to 0.5 with an average of 0.4 which was moderately high. The principal component analysis (PCA) showed that the first two components captured ~ 24.2% of the genetic variation. The average genetic diversity was 0.3. The analysis of molecular variance (AMOVA) indicated that 66.02% and 33.98% of the total genetic variation occurred within accessions and between sub-populations, respectively. Five sub-populations were identified based on ADMIXTURE structure analysis (K = 5). Neighbor-joining tree and hierarchical clustering tree revealed the presence of three different groups which were primarily based on the source of the genotypes. The results suggested that there was considerable genetic variation among the cassava genotypes which is useful in cassava improvement and conservation efforts.

Carbon usage in yellow-fleshed Manihot esculenta storage roots shifts from starch biosynthesis to cell wall and raffinose biosynthesis via the myo-inositol pathway.

Cassava is a crucial staple crop for smallholder farmers in tropical Asia and Sub-Saharan Africa. Although high yield remains the top priority for farmers, the significance of nutritional values has increased in cassava breeding programs. A notable negative correlation between provitamin A and starch accumulation poses a significant challenge for breeding efforts. The negative correlation between starch and carotenoid levels in conventional and genetically modified cassava plants implies the absence of a direct genomic connection between the two traits. The competition among various carbon pathways seems to account for this relationship. In this study, we conducted a thorough analysis of 49 African cassava genotypes with varying levels of starch and provitamin A. Our goal was to identify factors contributing to differential starch accumulation. Considering carotenoid levels as a confounding factor in starch production, we found that yellow- and white-fleshed storage roots did not differ significantly in most measured components of starch or de novo fatty acid biosynthesis. However, genes and metabolites associated with myo-inositol synthesis and cell wall polymer production were substantially enriched in high provitamin A genotypes. These results indicate that yellow-fleshed cultivars, in comparison to their white-fleshed counterparts, direct more carbon toward the synthesis of raffinose and cell wall components. This finding is underlined by a significant rise in cell wall components measured within the 20 most contrasting genotypes for carotenoid levels. Our findings enhance the comprehension of the biosynthesis of starch and carotenoids in the storage roots of cassava.

Identifying Cassava Genotypes Resistant to the African Cassava Whitefly, Bemisia tabaci (Gennadius)

Identifying Cassava Genotypes Resistant to the African Cassava Whitefly, Bemisia tabaci (Gennadius)

Determination of genomic regions associated with early storage root formation and bulking in cassava.

Early cassava storage root formation and bulking is a medium of escape that farmers and processors tend to adopt in cases of abiotic and biotic stresses like drought, flood, and destruction by domestic animals. In this study, 220 cassava genotypes from the International Institute of Tropical Agriculture (IITA), National Root Crops Research Institute (NRCRI), International Center for Tropical Agriculture (CIAT), local farmers (from farmer's field), and NextGen project were evaluated in three locations (Umudike, Benue, and Ikenne). The trials were laid out using a split plot in a randomized incomplete block design (alpha lattice) with two replications in 2 years. The storage roots for each plant genotype were sampled or harvested at 3, 6, 9, and 12 month after planting (MAP). All data collected were analyzed using the R-statistical package. The result showed moderate to high heritability among the traits, and there were significant differences (p< 0.05) among the performances of the genotypes. The genome-wide association mapping using the BLINK model detected 45 single-nucleotide polymorphism (SNP) markers significantly associated with the four early storage root bulking and formation traits on Chromosomes 1, 2, 3, 4, 5, 6, 8, 9, 10, 13, 14, 17, and 18.A total of 199 putative candidate genes were found to be directly linked to early storage root bulking and formation. The functions of these candidate genes were further characterized to regulate i) phytohormone biosynthesis, ii) cellular growth and development, and iii) biosynthesis of secondary metabolites for accumulation of starch and defense. Genome-wide association study (GWAS) also revealed the presence of four pleiotropic SNPs, which control starch content, dry matter content, dry yield, and bulking and formation index. The information on the GWAS could be used to develop improved cassava cultivars by breeders. Five genotypes (W940006, NR090146, TMS982123, TMS13F1060P0014, and NR010161) were selected as the best early storage root bulking and formation genotypes across the plant age. These selected cultivars should be used as sources of early storage root bulking and formation in future breeding programs.

Variation among cassava (Manihot esculenta Crantz) genotypes for storage root yield, yield components and response to cassava mosaic disease at the advanced breeding stage

Variation among cassava (Manihot esculenta Crantz) genotypes for storage root yield, yield components and response to cassava mosaic disease at the advanced breeding stage

Variability in Starch Content, Starch Granule Morphology and Size Distribution of Three Cassava (Manihot esculenta) Genotypes in Relation to Yield, at Different Planting Seasons

Variability in Starch Content, Starch Granule Morphology and Size Distribution of Three Cassava (Manihot esculenta) Genotypes in Relation to Yield, at Different Planting Seasons

The Effect of Drying Method on The Quality of MOCAF (Modified Cassava Flour) from Raw Material Beta-Carotene-Rich Bokor Genotype Cassava

The high dependence on flour imports is a significant challenge to overcome by processing local food ingredients through diversification. To address this challenge, the use of MOCAF (Modified Cassava Flour) as a substitute for wheat flour has been carried out in the manufacture of wet and dry noodles, along with analog rice, and bread. The optimization of MOCAF production from beta-carotene-rich cassava depends on the selection of appropriate equipment technology and drying process. Therefore, this study aimed to analyze the effect of drying method on MOCAF characteristics of beta-carotene-rich cassava genotype. The analysis was carried out using two methods, namely sun drying for 3-4 days and oven drying at 60 o C for 24 hours. Parameters analyzed included viscosity, solubility, syneresis, Near Infra-Red analysis, proximate analysis, and Scanning Electron Microscope (SEM). The results showed that drying affected the physicochemical properties of MOCAF, including viscosity, solubility, and syneresis. NIR (Near-infrared) and proximate analysis showed that drying process affected the decrease in moisture, ash, protein, and fat content, along with an increase in crude fiber, and dry fiber matter content. Furthermore, SEM microstructural analysis resulted in the reformation of starch granules, characterized by changes in morphology and structure, such as the separation of irregular spherical shapes, and hollowness.

Evaluation of potential increase in photosynthetic efficiency of cassava (Manihot esculenta Crantz) plants exposed to elevated carbon dioxide.

Cassava (Manihot esculenta Crantz), an important tropical crop, is affected by extreme climatic events, including rising CO2 levels. We evaluated the short-term effect of elevated CO2 concentration (ECO2 ) (600, 800 and 1000ppm) on the photosynthetic efficiency of 14 cassava genotypes. ECO2 significantly altered gaseous exchange parameters (net photosynthetic rate (P n ), stomatal conductance (g s ), intercellular CO2 (C i ) and transpiration (E )) in cassava leaves. There were significant but varying interactive effects between ECO2 and varieties on these physiological characteristics. ECO2 at 600 and 800ppm increased the P n rate in the range of 13-24% in comparison to 400ppm (ambient CO2 ), followed by acclimation at the highest concentration of 1000ppm. A similar trend was observed in g s and E . Conversely, C i increased significantly and linearly across increasing CO2 concentration. Along with C i , a steady increase in water use efficiency [WUEintrinsic (P n /g s ) and WUEinstantaneous (P n /E )] across various CO2 concentrations corresponded with the central role of restricted stomatal activity, a common response under ECO2 . Furthermore, P n had a significant quadratic relationship with the ECO2 (R 2 =0.489) and a significant and linear relationship with C i (R 2 =0.227). Relative humidity and vapour pressure deficit during the time of measurements remained at 70-85% and ~0.9-1.31kPa, respectively, at 26±2°C leaf temperature. Notably, not a single variety exhibited constant performance for any of the parameters across CO2 concentrations. Our results indicate that the potential photosynthesis can be increased up to 800ppm cassava varieties with high sink capacity can be cultivated under protected cultivation to attain higher productivity.

Phenotypic Variability in Resistance to Anthracnose, White, Brown, and Blight Leaf Spot in Cassava Germplasm.

Despite fungal diseases affecting the aerial parts of cassava (Manihot esculenta Crantz) and causing significant yield losses, there is a lack of comprehensive studies assessing resistance in the species' germplasm. This study aimed to evaluate the phenotypic diversity for resistance to anthracnose disease (CAD), blight leaf spot (BliLS), brown leaf spot (BLS), and white leaf spot (WLS) in cassava germplasm and to identify genotypes suitable for breeding purposes. A total of 837 genotypes were evaluated under field conditions across two production cycles (2021 and 2022). Artificial inoculations were carried out in the field, and data on yield and disease severity were collected using a standardized rating scale. The top 25 cassava genotypes were selected based on a selection index for disease resistance and agronomic traits. High environmental variability resulted in low heritabilities (h2) for CAD, WLS, and BLS (h2 = 0.42, 0.34, 0.29, respectively) and moderate heritability for BliLS (h2 = 0.51). While the range of data for disease resistance was narrow, it was considerably wider for yield traits. Cluster analysis revealed that increased yield traits and disease severity were associated with higher scores of the first and second discriminant functions, respectively. Thus, most clusters comprised genotypes with hybrid characteristics for both traits. Overall, there was a strong correlation among aerial diseases, particularly between BLS and BliLS (r = 0.96), while the correlation between CAD and other diseases ranged from r = 0.53 to 0.58. Yield traits showed no significant correlations with disease resistance. Although the mean selection differential for disease resistance was modest (between -2.31% and -3.61%), selection based on yield traits showed promising results, particularly for fresh root yield (82%), dry root yield (39%), shoot yield (49%), and plant vigor (26%). This study contributes to enhancing genetic gains for resistance to major aerial part diseases and improving yield traits in cassava breeding programs.

Resistance to Cassava Whitefly (Bemisia tabaci) among Eastern and Southern African Elite Cassava Genotypes.

Cassava whitefly, Bemisia tabaci, directly damages cassava leaves by feeding on phloem, causing chlorosis and abscission, leading to a yield loss of up to 50%. The pest also causes indirect damage through sooty mold formation. Most Ugandan cassava varieties resist cassava mosaic disease (CMD) and tolerate cassava brown streak disease (CBSD), but little is known about their response to whitefly infestation. The main objective of this study was to identify cassava genotypes with putative resistance to whitefly in Uganda. This was conducted on 24 improved cassava varieties in three agro-ecological zones during the second rains of 2016. Monthly data were taken for adult and nymph counts, whitefly and sooty mold damage, and CMD and CBSD severities from 2 to 9 months after planting (MAPs). The results show that the whitefly population is highly significantly (p < 0.000) amongst varieties across the three agro-ecological zones. Mkumba consistently supported the low adult numbers and nymphs. The findings demonstrate the potential of the improved cassava varieties as sources of whitefly resistance for sustainable management.

EVALUATION OF RESISTANCE LEVELS TO Fusarium solani IN CASSAVA GENOTYPES

The search for cassava varieties resistant to fungi of the genus Fusarium has proven to be a good option for producers. To achieve this, it is essential to identify sources of resistance that allow genetic parameters to be estimated, providing useful information for breeders. The genus Fusarium is recognized as one of the main responsible for causing significant damage and economic impacts on cassava plantations globally. The present study aimed to identify, in cassava genotypes, resistance levels to F. solani using the detached root inoculation methodology. The experiment was conducted in the laboratory, and evaluations were conducted every two days after inoculation. The experimental design adopted was completely randomized with three replications consisting of a cassava root disc with or without inoculation of pathogen spore suspension. We obtained genotypes grouped as moderately susceptible and extremely susceptible, using an easy-to-execute methodology in a controlled environment in this study.