Cassava Cultivars Research Articles

Thermal, Pasting, and Hydration Properties of Flour from Novel Cassava Cultivars for Potential Applications in the Food Industry

Abstract Cassava root flours from five different cultivars (C-MSAF2, C-P4/10, C-P98/0505, C-P98/0002, and C-UKF8) were studied for their potential application in the food industry. Proximate composition, functional, thermal, and pasting properties were investigated. Cassava flours were high in carbohydrates (85-86%) and their amino acid profiles varied. Cultivars C-MSAF2, C-P98/0002, and C-UKF8 showed high protein content (5.06%), mineral content (2.36%), and the largest particle size (72.33 µm), respectively. Solubility of cassava flours decreased as temperatures increased, however, swelling power and water absorption capacity increased. C-MSAF2 showed the highest peak viscosity, breakdown viscosity, and shortest peak time. C-P98/0505 showed the highest final viscosity, the highest pasting temperature, and the longest peak time. Cassava flours studied are promising candidates for utilization in the baking industry, however, their incorporation into baked product formulations needs further investigation.

Chemical composition and morphophysiological responses of Manihot plants

Cassava (Manihot esculenta Crantz) is an important forage source for livestock, while wild cassavas (maniçoba and pornunça – Manihot sp.), native from Brazilian semi-arid have the potential to feed ruminants in drylands. We hypothesized that maniçoba and pornunça have a chemical composition and morphophysiological responses similar to cassava cultivars. Nine Manihot plants were evaluated, six wild cassava accessions (BGMS 20, BGMS 21, BGMS 22, BGMS 26, BGMS 79, and BGMS 102), pornunça (BGMS 24) and two cassava cultivars (gema-de-ovo [GO] and engana-ladrão [EL]). We evaluated two 6-month crop cycles under a completely randomized design with four replicates. The genotype BGMS 20 had higher shoot biomass than BGMS 24, BGMS 79, EL, and GO, as well as higher leaf mass than EL and GO. Photosynthesis, leaf temperature, stomatal conductance, and transpiration were similar among the genotypes (13.83 µmol.m-2.s-1, 29.90 ºC, 0.12 mol.m-2.s-1 and 2.75 mmol.m-2.s-1, respectively). EL had a shoot crude protein content higher than the others, except for BGMS 21 and BGMS 24. Genotypes did not differ concerning in situ and in vitro (dry matter (DM)) degradability and mineral composition. BGMS 24 had a higher number of leaves than the others, and BGMS 20 had taller plants than the other genotypes, except for BGMS 21 and BGMS 22. In vitro gas production was similar among the genotypes considering total carbohydrates. Wild cassava accessions showed shoot biomass, leaf mass physiological responses, and chemical composition compatible with cassava cultivars; therefore, they show potential as alternative forages for livestock.

Phenotypic diversity and selection in biofortified cassava germplasm for yield and quality root traits

Increasing carotenoid content and improving other root quality traits has been the focus of cassava biofortification. This study aimed to (i) evaluate the genetic variability for total carotenoid content (TCC), as well as for root yield and root quality attributes; (ii) estimate potentially useful correlations for selection; and (iii) select parents for breeding and estimate the genetic gain. Data from 2011 to 2020 of 265 cassava genotypes with cream and yellow roots were analyzed for dry matter content (DMC), shoot yield, fresh root yield (FRY), dry root yield (DRY), harvest index, average number of roots per plant, starch content, root pulp color, cyanogenic compounds, and TCC. The best linear unbiased predictions showed great phenotypic variation for all traits. Six distinct groups were formed for productive characteristics of root quality, mainly TCC, DMC and FRY. Only TCC showed high broad-sense heritability ({h}^{2}= 0.72), while the other traits had low to medium magnitude (0.21 ≤ {h}^{2} ≤ 0.60). TCC was strongly correlated with pulp color (r = 0.70), but null significance for DMC. The network analysis identified a clear separation between the agronomic and quality attributes of cassava roots. The selection of the 30 genotypes for recombination in the breeding program has the potential to raise TCC by 27.05% and reduce the cyanogenic compounds content by 23.03%, in addition to increasing FRY and DRY by 22.72% and 22.95%, respectively. This is the first consolidated study on the potential of germplasm for the development biofortified cassava cultivars in Brazil.

Evaluation of the effects of elevated CO2 concentrations on the growth of cassava storage roots by destructive harvests and ground penetrating radar scanning approaches.

Cassava (Manihot esculenta Crantz) production will need to be improved to meet future food demands in Sub-Saharan Africa. The selection of high-yielding cassava cultivars requires a better understanding of storage root development. Additionally, since future production will happen under increasing atmospheric CO2 concentrations ([CO2 ]), cultivar selection should include responsiveness to elevated [CO2 ]. Five farmer-preferred African cassava cultivars were grown for three and a half months in a Free Air CO2 Enrichment experiment in central Illinois. Compared to ambient [CO2 ] (~400 ppm), cassava storage roots grown under elevated [CO2 ] (~600 ppm) had a higher biomass with some cultivars having lower storage root water content. The elevated [CO2 ] stimulation in storage root biomass ranged from 33% to 86% across the five cultivars tested documenting the importance of this trait in developing new cultivars. In addition to the destructive harvests to obtain storage root parameters, we explored ground penetrating radar as a nondestructive method to determine storage root growth across the growing season.

Targeted mutagenesis of the CYP79D1 gene via CRISPR/Cas9-mediated genome editing results in lower levels of cyanide in cassava.

Cassava is the world's most essential food root crop, generating calories to millions of Sub-Saharan African subsistence farmers. Cassava leaves and roots contain toxic quantities of the cyanogenic glycoside linamarin. Consumption of residual cyanogens results in cyanide poisoning due to conversion of the cyanogens to cyanide in the body. There is a need for acyanogenic cassava cultivars in order for it to become a consistently safe and acceptable food, and commercial crop. In recent years, the CRISPR/Cas system, has proven to be the most effective and successful genome editing tool for gene function studies and crop improvement. In this study, we performed targeted mutagenesis of the MeCYP79D1 gene in exon 3, using CRISPR/Cas9, via Agrobacterium-mediated transformation. The vector design resulted in knockout in cotyledon-stage somatic embryos regenerated under hygromycin selection. Eight plants were recovered and genotyped. DNA sequencing analysis revealed that the tested putative transgenic plants carried mutations within the MeCYP79D1 locus, with deletions and substitutions being reported upstream and downstream of the PAM sequence, respectively. The levels of linamarin and evolved cyanide present in the leaves of mecyp79d1 lines were reduced up to seven-fold. Nevertheless, the cassava linamarin and cyanide were not completely eliminated by the MeCYP79D1 knockout. Our results indicate that CRISPR/Cas9-mediated mutagenesis is as an alternative approach for development of cassava plants with lowered cyanide content.

Epidemic Pressure of Cassava Mosaic and Brown Streak Diseases on Ten Exotic Cassava (Manihot esculenta Crantz) Cultivars in Kisangani, DRC

The crucial obstacle to cassava production in most of African countries is the diseases and pests. The present study assessed in field the epidemic pressure of Cassava mosaic disease (CMD) and Cassava brown streak disease (CBSD) on 10 exotic cassava genotypes in Kisangani. To assess the disease impact, trials were established in two sites in Kisangani, Tshopo Province in DRC. The experiment was laid out in randomized completed block design and thrice replicated. Sixty stem cuttings per variety were planted in a plot of 7 rows each measuring 25 m long. Results showed a relatively important CBSD pressure on all the ten exotic cassava genotypes tested (incidence close 60%, severity score 2 and 3.5 whiteflies/plant) and low CMD pressure (incidence 3.3%, severity score 2 and 3.5 whiteflies/plant). CMD remained relatively negligible depending on low symptom manifestation of the tested genotypes. Whitefly population varied according to the genotype and the crop age. The most abundant population was recorded on cultivar ‘Mayombe’ (17 whiteflies/plant). A negative relationship was statistically established between the abundance of whiteflies and the incidence and severity as well as for CBSD and for CMD. The production in terms of percentage of marketable tubers was (74.9%) for cultivar ‘Mayombe’, (70.3%) for ‘Obama 1’, (69.9%) for ‘Obama 2’ and (65.3%) for ‘Ngandajika’. CBSD resulted in variable yield loss on all cultivars tested. The cultivar ‘Butamu’ (85%) recorded the highest loss rate, followed by the cultivar ‘Mvuama’ (70.8%) and ‘Muzuri’ (64.3%). The yield in cassava tubers was destroyed (˂ 5 t/ha) by large necrotic spots of the brown streak in the pulp. This loss is due to the depressive of viral pandemia pressure on the output of ten exotic cassava cultivars studied in Kisangani. Our study highlighted that the best moment of harvesting cassava in Kisangani is 9 MAP, this moment would be ideal to minimize harvesting losses due to CBSD root necrosis.

Evolution of the Stock of Total Organic Carbon of Soil under the Culture of Cassava (Manihot Crantz esculenta) Installed in no Incineration in a Forest Fallow of the Yakonde Set (Y2) in Relation to the One of the Old Surrounding Secondary Forest of the Re

The objective pursued in this work is to try to put in evidence the ecological role of the cassava culture installed by no burning of the biomass on the management of the stock of total organic carbon of soil. Thus, an extent of 0,48 ha has been delimited and has been subdivided in 24 parcels in which were installed 24 pedological pits and where 48 samples of soil that means 24 samples no - unsettled and 24 unsettled others, were appropriated in the slices of 0-20 and 20-40 cm of depth these samples served for the determination of the total organic matter, the total organic carbon, the obvious density and of the stock in carbon of soil to seven months of age of the culture of five varieties of cassava. Five cultivars of cassava to know Disanka, Obama, Zizila, Me vuazi and Nsansi have been installed in a fallow forest enhancement by no - incineration of the biomass and an old secondary forest taken like reference, situated in the Yakonde set (Y2) in the Tray Isalowe in Yangambi, RD Congo. The results gotten during our experimentation reveals a relative an impact in the management of the stock of soil carbon by the different cultivars of cassava, with the exception of the Zizila varieties (T3) and Nsansi (T5) in relation to the old secondary forest taken like witness even though that, the analyses statistical attest non meaningful differences between the worth of carbon stock observed so much in soil under the different varieties of cassava that under the old secondary forest. Nevertheless, the no - incineration decorated the most suitable fashion of enhancement of soil in general in the optics of the lasting management of the stock of organic carbon of soil in the agrosystèmes of the tropics and of the region of Yangambi in particular.

CC-type glutaredoxin, MeGRXC3, associates with catalases and negatively regulates drought tolerance in cassava (Manihot esculenta Crantz).

Glutaredoxins (GRXs) are essential for reactive oxygen species (ROS) homeostasis in responses of plants to environment changes. We previously identified several drought-responsive CC-type GRXs in cassava, an important tropical crop. However, how CC-type GRX regulates ROS homeostasis of cassava under drought stress remained largely unknown. Here, we report that a drought-responsive CC-type GRX, namely MeGRXC3, was associated with activity of catalase in the leaves of 100 cultivars (or unique unnamed genotypes) of cassava under drought stress. MeGRXC3 negatively regulated drought tolerance by modulating drought- and abscisic acid-induced stomatal closure in transgenic cassava. It antagonistically regulated hydrogen peroxide (H2 O2 ) accumulation in epidermal cells and guard cells. Moreover, MeGRXC3 interacted with two catalases of cassava, MeCAT1 and MeCAT2, and regulated their activity in vivo. Additionally, MeGRXC3 interacts with a cassava TGA transcription factor, MeTGA2, in the nucleus, and regulates the expression of MeCAT7 through a MeTGA2-MeMYB63 pathway. Overall, we demonstrated the roles of MeGRXC3 in regulating activity of catalase at both transcriptional and post-translational levels, therefore involving in ROS homeostasis and stomatal movement in responses of cassava to drought stress. Our study provides the first insights into how MeGRXC3 may be used in molecular breeding of cassava crops.

A Transformation and Genome Editing System for Cassava Cultivar SC8.

Cassava starch is a widely used raw material for industrial production. South Chinese cassava cultivar 8 (Manihot esculenta Crantz cv. SC8) is one of the main locally planted cultivars. In this study, an efficient transformation system for cassava SC8 mediated with Agrobacterium strain LBA4404 was presented for the first time. Cassava friable embryogenic calli (FECs) were transformed through the binary vector pCAMBIA1304 harboring GUS- and GFP-fused genes driven by the CaMV35S promoter. The transformation efficiency was increased in the conditions of Agrobacterium strain cell infection density (OD600 = 0.65), 250 µM acetosyringone induction, and agro-cultivation with wet FECs for 3 days in dark. Based on the optimized transformation protocol, approximately 120–140 independent transgenic lines per mL settled cell volume (SCV) of FECs were created by gene transformation in approximately 5 months, and 45.83% homozygous mono-allelic mutations of the MePDS gene with a YAO promoter-driven CRISPR/Cas9 system were generated. This study will open a more functional avenue for the genetic improvement of cassava SC8.

Screening of cultivars against cassava brown streak disease and molecular identification of the phytopathogenic infection-associated viruses

Cassava brown streak disease (CBSD) has been reported as a serious and significant constraint on the cassava crop in Democratic Republic of the Congo (DRC), especially in its eastern part, South Kivu, where cassava has exceedingly high socio-economic value in small-holder farming systems. The recent rapid spread and damage of CBSD are alarming. Compared to cassava mosaic disease (CMD) which causes yield losses of up to 70% in very susceptible cassava cultivars, CBSD destroys whole the field causing 100% crop loss, including immediate and direct losses of tuberous roots, planting material, and quality of leaves. The study gathered information on the circulation of viral species present in the region, and screening of cassava cultivars against CBSD. Here we evaluated the disease incidence (DI) and severity (DS), whitefly vector Bemisia tabaci parameters including number of nymphs and adults. Thereat, the work consisted of quantifying the pressure of the disease to find performing cassava cultivars, which may still be recommendable for farmers. Thirty-one improved and local Congolese cassava cultivars were selected. Disease assessment focused more specifically on morphological, epidemiologic studies, and advanced molecular diagnostic techniques for virus detection. The mean extreme values of disease incidence and severity ranged respectively from 0.0 to 59.44%, and 1 to 2.86, root infection up to 100%, whiteflies up to 2 adults, and 68 nymphs per plant. Accordingly, the viral species identified in circulation are Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) (picornalike (+) ssRNA viruses, Ipomovirus, Potyviridae). Varieties like Cibongoyoka, Dorothea, Kamegere, Korengo, Liyayi, M’Bailo, Nabana, Rav, and Siri showed no symptoms of necrosis on the roots. Some cultivars are even less susceptible or not to the disease and may be recommended in this time of the lack of planting material for farmers.

Physiological and Proteomic Responses of Cassava to Short-Term Extreme Cool and Hot Temperature.

Temperature is one of the most critical factors affecting cassava metabolism and growth. This research was conducted to investigate the effects of short-term exposure to extreme cool (15 °C) and hot (45 °C) temperature on photosynthesis, biochemical and proteomics changes in potted plants of two cassava cultivars, namely Rayong 9 and Kasetsart 50. One-month-old plants were exposed to 15, 30, and 45 °C for 60 min in a temperature chamber under light intensity of 700 μmol m−2 s−1. Compared to the optimum temperature (30 °C), exposure to 15 °C resulted in 28% reduction in stomatal conductance (gs) and 62% reduction in net photosynthesis rate (Pn). In contrast, gs under 45 °C increased 2.61 folds, while Pn was reduced by 50%. The lower Pn but higher electron transport rate (ETR) of the cold-stressed plants indicated that a greater proportion of electrons was transported via alternative pathways to protect chloroplast from being damaged by reactive oxygen species (ROS). Moreover, malondialdehyde (MDA) contents, a marker related to the amount of ROS, were significantly higher at low temperature. Proteomics analysis revealed some interesting differentially expressed proteins (DEPs) including annexin, a multi-functional protein functioning in early events of heat stress signaling. In response to low-temperature stress, AP2/ERF domain-containing protein (a cold-related transcription factor) and glutaredoxin domain-containing protein (a component of redox signaling network under cold stress) were detected. Taken together, both cultivars were more sensitive to low than high temperature. Moreover, Rayong 9 displayed higher Pn under both temperature stresses, and was more efficient in controlling ROS under cold stress than Kasetsart 50.

Resistant cassava cultivars inhibit the papaya mealybug Paracoccus marginatus population based on their interaction: from physiological and biochemical perspectives

Paracoccus marginatus papaya mealybugs cause considerable threats and challenges to cassava production and processing. The deployment of resistant cultivars offers effective, economical and eco-friendly management strategies for pest management. We measured P. marginatus mortality, development and reproduction to evaluate the resistance of fifteen cassava cultivars and conducted physiological and biochemical analyses when P. marginatus was fed on two resistant cultivars (Myanmar and C1115) and three susceptible cultivars (BRA900, Bread, SC205). Significantly lower digestive (amylase, sucrase, lipase), detoxification (glutathione-S-transferase and carboxylesterase) and antioxidant activity, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO), enzyme activities were observed in P. marginatus feeding on resistant cultivars compared to susceptible cultivars. For resistant cultivars, a significant reduction was found in nutritional components containing free amino acids, nitrogen, soluble sugars and the secondary metabolite malondialdehyde. Additionally, significantly higher enzymatic activity (SOD, CAT, POD and PPO) levels and secondary metabolite quantities (total phenol and tannins) were found in resistant cultivars induced by P. marginatus compared with susceptible ones. Additionally, RT-qPCR tests showed that the transcripts of ten genes involved in nutrition, secondary metabolites and antioxidant activities were consistent with physiology changes. Thus, the resistant cultivars suffered lower P. marginatus damage by elevating secondary metabolite contents and antioxidant activities, reducing plant nutrition levels and decreasing insect enzymatic activities. This study will be beneficial in developing indices for standard regulation to evaluate P. marginatus-resistant cassavas and effectively manage this pest.

Overexpression of leucoanthocyanidin reductase or anthocyanidin reductase elevates tannins content and confers cassava resistance to two-spotted spider mite.

The two-spotted spider mite (TSSM) is a destructive cassava pest. Intensive demonstration of resistance mechanism greatly facilitates the creation of TSSM-resistant cassava germplasm. Gene to metabolite network plays a crucial role in modulating plant resistance, but little is known about the genes and related metabolites which are responsible for cassava resistance to TSSM. Here, a highly resistant (HR) and a highly susceptible (HS) cassava cultivar were used, integrative and comparative transcriptomic and metabolomic analyses between these two cultivars after TSSM infestation revealed that several genes and metabolites were closely related and significantly different in abundance. In particular, the expression of leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) genes showed a high positive correlation with most of the metabolites in the tannin biosynthesis pathway. Furthermore, transgenic cassava lines overexpressing either of the genes elevated tannin concentrations and conferred cassava resistance to TSSM. Additionally, different forms of tannins possessed distinct bioactivity on TSSM, of which total condensed tannins (LC50 = 375.68 mg/l) showed maximum lethal effects followed by procyanidin B1 (LC50 = 3537.10 mg/l). This study accurately targets LAR, ANR and specific tannin compounds as critical genes and metabolites in shaping cassava resistance to TSSM, which could be considered as biomarkers for evaluation and creation of pest-resistant cassava germplasm.

Values of Cassava Tuber Peels Produced in the Farms and Home-Scale Snack Food Industries as Feed Based on Yield Rate, Crude Nutrient, and Mineral Composition

The Payakumbuh region is an important tourist destination in West Sumatra. They produce various snack food made from cassava tubers, producing a large cassava peel as a by-product. The research aimed to study the meal yield rate, crude nutrient, fiber fraction, and mineral composition of cassava peels as by-products of cassava farm and snack food industries. Twenty cassava farms and ten snack food industries were visited, and the owners were interviewed for data on the type of cassava used, products, and handling of cassava peel. The quantity of cassava peel produced and potentially used as feed was recorded. Samples of fresh peels from three different varieties and tuber sizes were collected, weighed, dried, and ground in meal form to determine the meal yield rates and analyze for dry matter (DM) content, crude nutrient, fiber fraction, and mineral composition. Results found three cassava cultivars used to produce snack foods, i.e., black, bread, and sticky cassava. The percentage of fresh peel and meal yield rates ranged from 16.4-16.7% and 21.9-26.9%, respectively. DM and crude protein content varied between 23.8 to 27.0% and 9.3 to 11.2%, respectively. Bread cassava peels showed the highest DM, ash, and ADF content. Cassava peel contained considerably high Fe and was a good source of K, Mg, P, Na, Mn, and Zn.

Photochemical, Anatomical, and Growth Changes in Cassava Cultivars after Application of Post-Emergent Herbicides

Plants develop a series of adaptive mechanisms capable of tolerating the action of herbicides; however, little is known about the physiological mechanisms developed by cassava. The purpose of this research was to evaluate the influence of post-emergence herbicides on the physiological and anatomical characteristics of two cassava cultivars subjected to six herbicide treatments. The evaluations occurred at 0, 24, 48, 72, and 168 h after herbicide application. Herbicide application induced changes in the physiological and anatomical leaf profile. These changes were observed through the thickening of the leaf blade midrib caused by the herbicides fomesafen and fenoxaprop-p-ethyl in the Campinas cultivar. On the other hand, the leaves of the Sergipana cultivar showed a reduction in the thickness of the midrib tissues. Minor effects on cassava plants were observed with the herbicide fluazifop-p-butyl.

The differential impact of four tropical species of root-knot nematodes (Meloidogyne spp.) on biofortified cassava

Summary Cassava plays an important food security role in Africa. Although a hardy crop in general, average yields are low, while traditional cultivars tend to be low in nutrients and vitamins. Substantial efforts have therefore been made to improve the nutritional quality of cassava through the development of biofortified cultivars. Although root-knot nematodes (RKN) are among the various important constraints affecting production, details on the impact of different species of RKN on cassava productivity are scarce. In this study, six popular cultivars of biofortified cassava were evaluated for their response to M. arenaria, M. enterolobii, M. incognita, M. javanica and a combination of all four species, in pots. All tested cultivars were susceptible to the four Meloidogyne species, but some cultivars showed a tolerance to M. arenaria infection. Galling damage was observed on feeder roots of inoculated plants, with nematode reproduction factors ranging between 2.3 and 9.5. Plant height, stem girth and fresh plant mass were significantly lower for most cultivars by as much as 70% following RKN infection. The highest root galling and damage were observed in plants following inoculation with a combination of the four species. As individual species inoculations, M. incognita and M. javanica were the most damaging, with the least damage observed in plants inoculated with M. arenaria only. These results confirm the pathogenicity of M. arenaria, M. incognita and M. javanica and further illustrate the potential of M. enterolobii to impact cassava production, while combined species infections demonstrate the greater levels of damage that these may cause.

African cassava whitefly and viral disease management through timed application of imidacloprid

Cassava whitefly are a group of cryptic species within the Bemisia tabaci sensu lato complex that causes significant damage to cassava in Africa. B. tabaci Sub-Saharan Africa 1 (SSA1) is the major species in the study region which transmits plant-virus diseases to cassava and causes direct feeding damage. Benefits from management of cassava viral diseases through deployment of resistant varieties are being undermined by their susceptibility to B. tabaci SSA1 and the problem is exacerbated by high populations of B. tabaci in cassava fields. To develop a clean seed system that is disease-free, the judicious use of insecticides is required to manage this pest and vector. This study evaluated the effect of timing of insecticide application on controlling B. tabaci SSA1 population abundance and damage to cassava. Field trials were carried out between 2017 and 2018 in Kamuli and Wakiso districts of Uganda using the widely available insecticide Imidacloprid. Three cassava cultivars (NAROCASS1, SAUTI, KBH/2002/026) were planted in a randomized complete block trial design replicated three times. The insecticide was applied in split-plots designated as: (i) no protection (NP), no insecticide applied (control), (ii) early protection (EP), insecticide applied 2 times between 0 and 4 months after planting, (iii) long protection (LP), insecticide applied 3 times between 0 and 8 months after planting, and (iv) total protection (TP), insecticide applied 4 times between 0 and 12 months after planting. Except for control plots, stem cuttings were first dipped into a diluted solution of Imidacloprid prior to planting. Bi-monthly data were collected on the B. tabaci population, feeding damage, cassava mosaic disease and cassava brown streak disease. Stem cuttings and root yields were determined at harvest. The marginal rate of return for each treatment was calculated to determine cost effectiveness. Insecticide application effectively reduced B. tabaci populations, feeding damage and disease spread. Cassava yield differed significantly with insecticide treatment and amongst cultivars. Root and stem yield losses of >60% was recorded in unprotected control plots. The marginal rate of return of the early protection (0–4 MAP) program was 163%. We discuss these findings and the implication for judicious use of insecticides as part of a cassava clean seed system.

Genetic contributions to productivity and nutritional aspects in cassava crops

This study aimed to highlight the behavior of cassava cultivars when subjected to different densities and biostimulants at planting and to select superior cultivars based on nutritional and productive attributes using the multivariate approach. The experiment design used randomized blocks in a three-factor scheme, with three cassava cultivars (FEPAGRO-RS 13 Vassourinha, BRS CS01, Iapar - 19 Pioneira) × two planting densities (10 and 20 buds per linear meter) × two biostimulator forms (with and without) in three replications, totaling 36 experiment units. Cultivar BRS CS01 had the highest yield and concentration of mineral material, genotype FEPAGRO - RS 13 Vassourinha had the highest lipid content, and Iapar 19 - Pioneira had the highest protein concentrations. The starch content was tested with a comparison of means and MGIDI index. Cultivar FEPAGRO - RS 13 Vassourinha had the highest content and, according to the index, was the ideal cultivar based on multi-characteristics. Density 10 with the biostimulator was favorable for productivity and lipids, whereas density 10 without the biostimulator was favorable for starch, lipids, proteins and productivity. Density 20 with the biostimulator was favorable for lipids.

Effects of growth media on growth and commercialisable percentage of disease-free cassava cultivar KM140 (Manihot esculenta Crantz “KM140”)

Cassava mosaic disease (CMD) is one of the most serious diseases that has caused heavy losses in starch yield. In vitro propagation from CMD disease-free cassava is the optimal method to produce healthy seedlings. Identification of a suitable growth medium for the development of ex vitro plantlets during the acclimation stage is an important step in order to obtain healthy plant. In this study, common substrates such as coir, rice husk ash, and vermicompost were mixed in different proportions to create formulations for the autotrophic stage of disease-free KM140 cassava plants. The parameters measured including plant height, number of leaves, stem diameter, number of branches, root length, dry matter ratio of leaves, roots, survival rate, and percentage of nurse stage cassava plantlets were evaluated. The results showed that cassava plants were transferred from in vitro to ex vitro environments gained a survival rate of 84.5% in coir substrate after 1 week. The growth medium contained a mix of 85% coir + 10% rice husk ash + 5% vermicompost was suitable for the growth and development of KM140 cassava plantlets. In this condition, the plantlets reached height of 38.8 cm with 22.0 leaves and the percentage of commercialisable plantlets reached 85.3%.

The haplotype-resolved chromosome pairs of a heterozygous diploid African cassava cultivar reveal novel pan-genome and allele-specific transcriptome features.

BackgroundCassava (Manihot esculenta) is an important clonally propagated food crop in tropical and subtropical regions worldwide. Genetic gain by molecular breeding has been limited, partially because cassava is a highly heterozygous crop with a repetitive and difficult-to-assemble genome.FindingsHere we demonstrate that Pacific Biosciences high-fidelity (HiFi) sequencing reads, in combination with the assembler hifiasm, produced genome assemblies at near complete haplotype resolution with higher continuity and accuracy compared to conventional long sequencing reads. We present 2 chromosome-scale haploid genomes phased with Hi-C technology for the diploid African cassava variety TME204. With consensus accuracy >QV46, contig N50 >18 Mb, BUSCO completeness of 99%, and 35k phased gene loci, it is the most accurate, continuous, complete, and haplotype-resolved cassava genome assembly so far. Ab initio gene prediction with RNA-seq data and Iso-Seq transcripts identified abundant novel gene loci, with enriched functionality related to chromatin organization, meristem development, and cell responses. During tissue development, differentially expressed transcripts of different haplotype origins were enriched for different functionality. In each tissue, 20–30% of transcripts showed allele-specific expression (ASE) differences. ASE bias was often tissue specific and inconsistent across different tissues. Direction-shifting was observed in <2% of the ASE transcripts. Despite high gene synteny, the HiFi genome assembly revealed extensive chromosome rearrangements and abundant intra-genomic and inter-genomic divergent sequences, with large structural variations mostly related to LTR retrotransposons. We use the reference-quality assemblies to build a cassava pan-genome and demonstrate its importance in representing the genetic diversity of cassava for downstream reference-guided omics analysis and breeding.ConclusionsThe phased and annotated chromosome pairs allow a systematic view of the heterozygous diploid genome organization in cassava with improved accuracy, completeness, and haplotype resolution. They will be a valuable resource for cassava breeding and research. Our study may also provide insights into developing cost-effective and efficient strategies for resolving complex genomes with high resolution, accuracy, and continuity.