Comparative analysis of infected cassava root transcriptomics reveals candidate genes for root rot disease resistance.

Cassava root-rot incited by soil-borne pathogens is one of the major diseases that reduces root yield. Although the use of resistant cultivars is the most effective method of management, the genetic basis for root-rot resistance remains poorly understood. Therefore, our work analyzed the transcriptome of two contrasting genotypes (BRS Kiriris/resistant and BGM-1345/susceptible) using RNA-Seq to understand the molecular response and identify candidate genes for resistance. Cassava seedlings (resistant and susceptible to root-rot) were both planted in infested and sterilized soil and samples from Initial-time and Final-time periods, pooled. Two controls were used: (i) seedlings collected before planting in infested soil (absolute control) and, (ii) plants grown in sterilized soil (mock treatments). For the differentially expressed genes (DEGs) analysis 23.912 were expressed in the resistant genotype, where 10.307 were differentially expressed in the control treatment, 15 DEGs in the Initial Time-period and 366 DEGs in the Final Time-period. Eighteen candidate genes from the resistant genotype were related to plant defense, such as the MLP-like protein 31 and the peroxidase A2-like gene. This is the first model of resistance at the transcriptional level proposed for the cassava × root-rot pathosystem. Gene validation will contribute to screening for resistance of germplasm, segregating populations and/or use in gene editing in the pursuit to develop most promising cassava clones with resistance to root-rot.

LESION SIMULATING DISEASE 3 regulates disease resistance via fine-tuning histone acetylation in cassava.

Bacterial blight seriously affects the growth and production of cassava (Manihot esculenta Crantz), but disease resistance genes and the underlying molecular mechanism remain unknown. In this study, we found that LESION SIMULATING DISEASE 3 (MeLSD3) is essential for disease resistance in cassava. MeLSD3 physically interacts with SIRTUIN 1 (MeSRT1), inhibiting MeSRT1-mediated deacetylation modification at the acetylation of histone 3 at K9 (H3K9Ac). This leads to increased H3K9Ac levels and transcriptional activation of SUPPRESSOR OF BIR1 (SOBIR1) and FLAGELLIN-SENSITIVE2 (FLS2) in pattern-triggered immunity, resulting in immune responses in cassava. When MeLSD3 was silenced, the release of MeSRT1 directly decreased H3K9Ac levels and inhibited the transcription of SOBIR1 and FLS2, leading to decreased disease resistance. Notably, DELLA protein GIBBERELLIC ACID INSENSITIVE 1 (MeGAI1) also interacted with MeLSD3, which enhanced the interaction between MeLSD3 and MeSRT1 and further strengthened the inhibition of MeSRT1-mediated deacetylation modification at H3K9Ac of defense genes. In summary, this study illustrates the mechanism by which MeLSD3 interacts with MeSRT1 and MeGAI1, thereby mediating the level of H3K9Ac and the transcription of defense genes and immune responses in cassava.

Identification of two cassava receptor-like cytoplasmic kinase genes related to disease resistance via genome-wide and functional analysis.

Receptor-like cytoplasmic kinases (RLCKs) play important roles in various developmental processes and stress responses in plants. Whereas, the detailed information of this family in cassava has not clear yet. In this study, A total of 322 MeRLCK genes were identified in the cassava genome, and they could be divided into twelve clades (Clades I-XII) according to their phylogenetic relationships. Most RLCK members in the same clade have similar characteristics and motif compositions. Over half of the RLCKs possess cis-elements in their promoters that respond to ABA, MeJA, defense reactions, and stress. Under Xpm11 infection, the expression levels of four genes show significant changes, suggesting their involvement in Xpm11 resistance. Two RLCK (MeRLCK11 and MeRLCK84) genes potentially involved in resistance to cassava bacterial blight were identified through VIGS experiments. This work laid the foundation for studying the function of the cassava RLCK genes, especially the genes related to pathogen resistance.

Aspergillus section Flavi and aflatoxins in Brazilian cassava (Manihot esculenta Crantz) and products.

Aflatoxins are carcinogenic compounds produced by some species of Aspergillus, especially those belonging to Aspergillus section Flavi. Their occurrence in food may start in the field, in the post-harvest, or during storage due to inadequate handling and storage. Because cassava is a staple food for a high percentage of the Brazilian population, we evaluated the presence of aflatoxin-producing species in cassava tubers, cassava products (cassava flour, cassava starch, sour starch, and tapioca flour), and in soil samples collected from cassava fields. In addition, the levels of aflatoxin contamination in cassava products were quantified. A total of 101 samples were analyzed, and 45 strains of Aspergillus section Flavi were isolated. Among the identified species, Aspergillus flavus, Aspergillus arachidicola, Aspergillus novoparasiticus, and Aspergillus parasiticus were found. The majority of strains (73.3%) tested for their aflatoxin-producing ability in synthetic media was positive. Despite that, cassava and cassava products were essentially free of aflatoxins, and only one sample of cassava flour contained traces of AFB1 (0.35 µg/kg).

Autophagy-related genes serve as heat shock protein 90 co-chaperones in disease resistance against cassava bacterial blight.

Heat shock protein 90 (HSP90) is involved in plant growth and various stress responses via regulating protein homeostasis. Autophagy keeps cellular homeostasis by recycling the components of cellular cytoplasmic constituents. Although they have similar effects on cellular protein homeostasis, the direct association between HSP90 and autophagy signaling remains unclear in plants, especially in tropical crops. In this study, the correlation between HSP90 and autophagy signaling was systematically analyzed by protein-protein interaction in cassava, one of the most important economy fruit in tropic. In addition, their effects on plant disease response and underlying mechanisms in cassava were investigated by functional genomics and genetic phenotype assay. The potential MeHSP90.9-MeSGT1-MeRAR1 chaperone complex interacts with MeATGs and subsequently triggers autophagy signaling, conferring improved disease resistance to cassava bacterial blight (CBB). On the contrary, HSP90 inhibitor and autophagy inhibitor decreased disease resistance against CBB in cassava, and autophagy may be involved in the potential MeHSP90.9-MeSGT1-MeRAR1 chaperone complex-mediated multiple immune responses. This study highlights the precise modulation of autophagy signaling by potential MeHSP90.9-MeSGT1-MeRAR1 chaperone complex in autophagy-mediated disease resistance to CBB.

Enterotoxin Gene Distribution and Genotypes of Bacillus cereussensu lato Isolated from Cassava Starch.

Bacillus cereus is a human pathogenic bacterium found in foods with the potential to cause emesis and diarrhea. This study estimated the presence, toxigenic and genomic diversity of B. cereus s.l. obtained from cassava starch samples collected in bakeries and powdered food companies in Medellín (Colombia). Bacillus cereuss.l. was found in 43 of 75 (57%) cassava starch samples and 98 isolates were obtained. The nheABC, hblCDAB, cytK2, entFM and cesB toxin genes were detected by multiplex PCR and the most frequent operon was nheABC, whereas cesB gene was not found. Twelve toxigenic profiles were determined by the detection of toxin genes, and the most frequent profiles harbored all enterotoxin genes. A broad genomic diversity was detected according to GTG5-PCR fingerprinting results with 76 B. cereus s.l. grouped in sixteen clusters and the 22 isolates clustering separately. No relationship was observed between genomic background and toxigenic profiles. In general, the results showed a high genomic and enterotoxigenic diversity in B. cereus s.l. found in cassava starch. These results should incentive future studies to understand the distribution of B. cereus s.l. isolated on raw materials in comparison with finished products.

Efficient biorefinery of whole cassava for citrate production using Aspergillus niger mutated by atmospheric and room temperature plasma and enhanced co-saccharification strategy.

BACKGROUND: The non-grain crop cassava has attracted intense attention in the biorefinery process. However, efficient biorefinery of whole cassava is faced with some challenges due to the existence of strain inhibition and refractory cellulose during the citrate production process. RESULTS: Here, a novel breeding method - atmospheric and room temperature plasma (ARTP) - was applied for strain improvement of citrate-producing strain Aspergillus niger from whole cassava. The citrate yield of the mutant obtained using ARTP mutagenesis increased by 36.5% in comparison with the original strain. Moreover, citric acid fermentation was further improved on the basis of an enhanced co-saccharification strategy by supplementing glucoamylase and cellulase. The fermentation efficiency increased by 35.8% with a 17.0 g L-1 reduction in residual sugar on a pilot scale. CONCLUSIONS: All these results confirmed that a combination of the novel breeding method and enhanced co-saccharification strategy could be used to efficiently refine whole cassava. The results also provide inspiration for the production of value-added products and waste disposal in agro-based industries. © 2021 Society of Chemical Industry.

Brewing rich 2-phenylethanol beer from cassava and its producing metabolisms in yeast.

BACKGROUND: Cassava is rich in nutrition and has high edible value, but the development of the cassava industry is limited by the traditional low added value processing and utilization mode. In this study, cassava tuber was used as beer adjunct to develop a complete set of fermentation technology for manufacturing cassava beer. RESULTS: The activities of transaminase, phenylpyruvate decarboxylase and dehydrogenase in 2-phenylethanol Ehrlich biosynthesis pathway of Saccharomyces cerevisiae were higher in cassava beer than that of malt beer. Aminotransferase ARO9 gene and phenylpyruvate decarboxylase ARO10 gene were up-regulated in the late stage of fermentation, which indicated that they were the main regulated genes of 2-phenylethanol Ehrlich pathway with phenylalanine as substrate in cassava beer preparation. CONCLUSIONS: Compared with traditional wheat beer, cassava beer was similar in the content of nutrition elements, diacetyl, total acid, alcohol and carbon dioxide, but has the characteristics of fresh fragrance and better taste. The hydrocyanic acid contained in cassava root tubes was catabolized during fermentation and compliant with the safety standard of beverage. Further study found that the content of 2-phenylethanol in cassava beer increased significantly, which gave cassava beer a unique elegant and delicate rose flavor. © 2020 Society of Chemical Industry.

In vitro propagation of three mosaic disease resistant cassava cultivars.

BACKGROUND: Cassava is a staple food for over 800 million people globally providing a cheap source of carbohydrate. However, the cultivation of cassava in the country is facing to viral diseases, particularly cassava mosaic disease (CMD) which can cause up to 95% yield losses. With aim to supply farmers demand for clean planting materials, there is need to accelerate the production of the elite cultivars by use of tissue culture in order to cope with the demand. METHODS: Nodal explants harvested from the greenhouse grown plants were sterilised using different concentrations of a commercial bleach JIK (3.85% NaOCl) and varying time intervals. Microshoots induction was evaluated using thidiazuron (TDZ), benzyl amino purine (BAP), and kinetin. Rooting was evaluated using different auxins (Naphthalene acetic acid NAA and Indole-3-butyricacid IBA). PCR-based SSR and SCAR markers were used to verify the presence of CMD2 gene in the regenerated plantlets. RESULTS: The highest level of sterility in explants (90%) was obtained when 20% Jik was used for 15 min. The best cytokinin for microshoots regeneration was found to be kinetin with optimum concentrations of 5, 10 and 20 µM for Agric-rouge, Atinwewe, and Agblehoundo respectively. Medium without growth regulators was the best for rooting the three cultivars. A survival rate of 100, 98, and 98% was recorded in the greenhouse for Agric-rouge, Atinwewe, and Agblehoundo respectively and the plantlets appeared to be morphologically normal. The SSR and SCAR analysis of micropropagated plants showed a profile similar to that of the mother plants indicating that the regenerated plantlets retained the CMD2 gene after passing through in vitro culture, as expected with micropropagation. CONCLUSION: The nodal explants was established to be 20% of Jik (3.85% NaOCl) with an exposure time of 15 min. Kinetin was proved to be the best cytokinins for microshoot formation with the optimum concentration of 5, 10 and 20 µM for Agric-rouge, Atinwewe, and Agblehoundo respectively. The protocol developed during this study will be useful for mass propagation of the elite cassava cultivars.

A phylogeny for the plant pathogen Piptoporellus baudonii using a multigene data set.

Piptoporellus baudonii is proposed as a new combination for Laetiporus baudonii in the Polyporales (Basidiomycota) based on morphological and molecular features. This parasitic macrofungus attacks cashew trees, Eucalyptus, cassava, Tectona, and some indigenous trees in southern regions of Tanzania and poses a serious threat to agroforestry and livelihood conditions in the area. Phylogenetic trees were produced from partial sequences of three rDNA gene regions and a portion of translation elongation factor 1-alpha (TEF1) gene of Laetiporus baudonii for comparisons with samples from the antrodia clade. Our results reveal a strongly supported group of L. baudonii with Piptoporellus in Fomitopsidaceae. Piptoporellus baudonii shares many morphological features with other members of Piptoporellus but differs from them in having broadly ellipsoid or rarely ovoid basidiospores. Both morphological and phylogenetic evidence justify the placement of L. baudonii in Piptoporellus together with the three other known species in the genus.

Enhancing of anthracnose disease resistance indicates a potential role of antimicrobial peptide genes in cassava.

Cassava (Manihot esculenta Crantz.) is an important economic crop in tropical countries. Demands for using cassava in food, feed and biofuel industries have been increasing worldwide. Cassava anthracnose disease, caused by Colletotrichum gloeosporioides f.sp. manihotis (CAD), is considered a major problem in cassava production. To minimize the effects of such disease, this study investigated the response of cassava to attack by CAD and how the plants defend themselves against this threat. Genome-wide identification of antimicrobial peptide genes (AMPs) and their expression in response to fungal infection was performed in the resistant cassava cultivar (Huay Bong 60; HB60) in comparison with the highly susceptible cultivar (Hanatee; HN). A total of 114 gene members of AMP were identified in the cassava genome database. Fifty-six gene members were selected for phylogenetic tree construction and analysis of putative cis-acting elements in their promoter regions. Differential expression profiles of six candidate genes were observed in response to CAD infection of both cassava cultivars. Upregulation of snakins, MeSN1 and MeSN2 was found in HB60, whereas MeHEL, Me-AMP-D2 and MeLTP2 were highly induced in HN. The MeLTP1 gene was not expressed in either cultivar. HB60 showed a reduced severity rating in comparison to HN after CAD infection. The biomembrane permeability test of fungal CAD was strongly affected after treatment with protein extract derived from CAD-infected HB60. Altogether, these findings suggest that snakins have a potential function in the CAD defense response in cassava. These results could be useful for cassava improvement programs to fight fungal pathogen.

Endophytic bacterial and fungal microbiota in different cultivars of cassava (Manihot esculenta Crantz).

Endophytes colonize tissues of healthy host plants and play a crucial role in plant growth and development. However, little attention has been paid to the endophytes of tuber crops such as cassava, which is used as a staple food by approximately 800 million people worldwide. This study aimed to elucidate the diversity and composition of endophytic bacterial and fungal communities in different cassava cultivars using high-throughput sequencing. Although no significant differences in richness or diversity were observed among the different cassava cultivars, the community compositions were diverse. Two cultivars (SC124 and SC205) tolerant to root rot exhibited similar community compositions, while two other cultivars (SC10 and SC5), which are moderately and highly susceptible to root rot, respectively, harboured similar community compositions. Proteobacteria, Firmicutes, and Ascomycota dominated the endophyte assemblages, with Weissella, Serratia, Lasiodiplodia, Fusarium, and Diaporthe being the predominant genera. The differentially abundant taxonomic clades between the tolerant and susceptible cultivars were mainly rare taxa, such as Lachnoclostridium_5, Rhizobium, Lampropedia, and Stenotrophomonas. These seemed to be key genera that affected the susceptibility of cassava to root rot. Moreover, the comparison of KEGG functional profiles revealed that 'Environmental adaptation' category was significantly enriched in the tolerant cultivars, while 'Infectious diseases: Parasitic' category was significantly enriched in the susceptible cultivars. The present findings open opportunities for further studies on the roles of endophytes in the susceptibility of plants to diseases.

Lactobacillus garii sp. nov., isolated from a fermented cassava product.

A novel Gram-positive, catalase negative, rod-shaped strain, FI11369T, was isolated from gari, a traditional West African fermented food derived from cassava. Based on 16S rRNA gene sequence similarity, the closest type strains were Lactobacillus xiangfangensis LMG 26013T (99.4 % similarity), Lactobacillus plajomi NBRC 107333T (99.1 %), Lactobacillus paraplantarum DSM 10667T (99.1 %), Lactobacillus pentosus DSM 20314T (99.0 %), Lactobacillus plantarum subsp. plantarum ATCC 14917T (99.0 %), Lactobacillus modestisalitolerans NBRC 107235T (98.9 %), Lactobacillus plantarum subsp. argentoratensis DSM 16365T (98.9 %) and Lactobacillus daowaiensis NCIMB 15183T (98.8 %). The genome of strain FI11369T was sequenced and the average nucleotide identity (ANI) was compared with its closest relatives. ANI analysis showed that the closest relative, L. xiangfangensis DSM 27103T, had only a 82.4 % similarity. The main fatty acids of FI11369T were saturated C16 : 0 (18.2 %), unsaturated C18 : 1 ω9c (43.8 %) and cyclopropane C19 : 0 cyclo (ω10c and/or ω6; 22.5 %). Based on the genotypic and phenotypic data obtained in this study, a novel Lactobacillus species, Lactobacillus garii sp. nov., with the type strain FI11369T (=NCIMB 15148=DSM 108249), is proposed.

Responses of soil enzyme activities and plant growth in a eucalyptus seedling plantation amended with bacterial fertilizers.

Plant growth-promoting rhizobacteria (PGPR) are widely used to improve plant nutrient uptake and assimilation and soil physicochemical properties. We investigated the effects of bacterial (Bacillus megaterium strain DU07) fertilizer applications in a eucalyptus (clone DH32-29) plantation in Guangxi, China in February 2011. We used two types of organic matter, i.e., fermented tapioca residue ("FTR") and filtered sludge from a sugar factory ("FS"). The following treatments were evaluated: (1) no PGPR and no organic matter applied (control), (2) 3 × 109 CFU/g (colony forming unit per gram) PGPR plus FS (bacterial fertilizer 1, hereafter referred to as BF1), (3) 4 × 109 CFU/g plus FS (BF2), (4) 9 × 109 CFU/g plus FS (BF3), (5) 9 × 109 CFU/g broth plus FTR (BF4). Soil and plant samples were collected 3 months (M3) and 6 months (M6) after the seedlings were planted. In general, bacterial fertilizer amendments significantly increased plant foliar total nitrogen (TN) and soil catalase activity in the short term (month 3, M3); whereas, it significantly increased foliar TN, chlorophyll concentration (Chl-ab), proline; plant height, diameter, and volume of timber; and soil urease activity, STN, and available N (Avail N) concentrations in the long term (month 6, M6). Redundancy analysis showed that soil available phosphorus was significantly positively correlated with plant growth in M3, and soil Avail N was negatively correlated with plant growth in M6. In M3, soil catalase was more closely correlated with plant parameters than other enzyme activities and soil nutrients, and in M6, soil urease, polyphenol oxidase, and peroxidase were more closely correlated with plant parameters than other environmental factors and soil enzyme activities. PCA results showed that soil enzyme activities were significantly improved under all treatments relative to the control. Hence, photosynthesis, plant growth, and soil N retention were positively affected by bacterial fertilizer in M6, and bacterial fertilizer applications had positive and significant influence on soil enzyme activities during the trial period. Thus, bacterial fertilizer is attractive for use as an environmentally friendly fertilizer in Eucalyptus plantations following proper field evaluation.

Genetic variation and evolutionary history of a mycorrhizal fungus regulate the currency of exchange in symbiosis with the food security crop cassava.

Most land plants form symbioses with arbuscular mycorrhizal fungi (AMF). Diversity of AMF increases plant community productivity and plant diversity. For decades, it was known that plants trade carbohydrates for phosphate with their fungal symbionts. However, recent studies show that plant-derived lipids probably represent the most essential currency of exchange. Understanding the regulation of plant genes involved in the currency of exchange is crucial to understanding stability of this mutualism. Plants encounter many different AMF genotypes that vary greatly in the benefit they confer to plants. Yet the role that fungal genetic variation plays in the regulation of this currency has not received much attention. We used a high-resolution phylogeny of one AMF species (Rhizophagus irregularis) to show that fungal genetic variation drives the regulation of the plant fatty acid pathway in cassava (Manihot esculenta); a pathway regulating one of the essential currencies of trade in the symbiosis. The regulation of this pathway was explained by clearly defined patterns of fungal genome-wide variation representing the precise fungal evolutionary history. This represents the first demonstrated link between the genetics of AMF and reprogramming of an essential plant pathway regulating the currency of exchange in the symbiosis. The transcription factor RAM1 was also revealed as the dominant gene in the fatty acid plant gene co-expression network. Our study highlights the crucial role of variation in fungal genomes in the trade of resources in this important symbiosis and also opens the door to discovering characteristics of AMF genomes responsible for interactions between AMF and cassava that will lead to optimal cassava growth.

Identification of hazards and critical control points during attiéké (a fermented cassava product) process in Côte d'Ivoire.

Attiéké is the major fermented plant food in Côte d'Ivoire. The aim of this study was to identify hazards and critical control points (CCP) in order to implement a HACCP system for the production of attiéké. Physico-chemical and microbiological analyses were carried out. pH of the cossettes used as raw material for attieke process was slightly acidic (6·5 ± 0·23). But attiéké produced had an acid pH (4·55 ± 0·67). The very high amount of hydrocyanic acid in cassava roots (116 ± 9·42 mg kg-1 ) was reduced to a lower value (3·4 ± 0·14 mg kg-1 ) in attiéké. It was less than the Codex Alimentarus recommended dose (10 mg kg-1 ). Microbiological analysis of the samples revealed the presence of coliforms, bacillus, Staphylococcus aureus and moulds in the intermediate products, the packaged attieke, the utensils, environment and ingredients. During the fermentation and pressing stage, the coliforms disappeared and the loads of Bacillus cereus, S. aureus and moulds were reduced. Cooking eliminated all micro-organisms except B. cereus (spores) whose load was reduced to a value of (1·1 ± 0·4)102  CFU per gram. All these micro-organisms reappeared in attiéké just after packaging. The load of micro-organisms in the packaged attiéké was lower than the Codinorm standard, CCP were cassava roots, the crushing, fermentation, and drying, cooking and packaging stage. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates the great need to carry out microbiological tests frequently on attieke and even more the need to apply correct HACCP system during the production. This study will make it possible to minimize the problems encountered by women producers of attiéké, ensure consumer safety, face competition from imported starch products (wheat, rice, etc.), contribute to the opening of a small and medium-scale industrialization path for the production of attiéké and strengthen standardization on attiéké to facilitate its export.

Expansion of the cassava brown streak pandemic in Uganda revealed by annual field survey data for 2004 to 2017.

Cassava brown streak disease (CBSD) is currently the most devastating cassava disease in eastern, central and southern Africa affecting a staple crop for over 700 million people on the continent. A major outbreak of CBSD in 2004 near Kampala rapidly spread across Uganda. In the following years, similar CBSD outbreaks were noted in countries across eastern and central Africa, and now the disease poses a threat to West Africa including Nigeria - the biggest cassava producer in the world. A comprehensive dataset with 7,627 locations, annually and consistently sampled between 2004 and 2017 was collated from historic paper and electronic records stored in Uganda. The survey comprises multiple variables including data for incidence and symptom severity of CBSD and abundance of the whitefly vector (Bemisia tabaci). This dataset provides a unique basis to characterize the epidemiology and dynamics of CBSD spread in order to inform disease surveillance and management. We also describe methods used to integrate and verify extensive field records for surveys typical of emerging epidemics in subsistence crops.

Assessing the Degeneration of Cassava Under High-Virus Inoculum Conditions in Coastal Tanzania.

Cassava brown streak disease (CBSD), caused by cassava brown streak ipomoviruses (CBSIs), has become the most debilitating biotic stress to cassava production in East and Central Africa. Lack of CBSD-resistant varieties has necessitated the search for alternative control measures. Most smallholder farmers reuse stems from previous crops for planting in the new season. Recycling planting material in this way can lead to "degeneration" owing to the compounding effects of disease. In this study, degeneration was defined as the increase in CBSD incidence and reduction in marketable root yield over time. An experiment was established to study the rates of degeneration in selected cassava varieties Chereko, KBH2002_135, Kipusa, Kizimbani, and Mkuranga1 and cultivars Kiroba and Kikombe under high-CBSD inoculum conditions in Bagamoyo, Tanzania from 2013 to 2017. The experiment was replicated across two seasons: the first planted during the long rains (Masika) between March and June and the second planted during the short rains (Vuli) between October and December. Mean abundance of the whitefly vector (Bemisia tabaci) was much greater during the Vuli season (>19 insects per plant) than the Masika season (<2 insects per plant). CBSD shoot symptoms occurred naturally and were observed only on Kikombe, Kiroba, and Kipusa. New materials had overall lower CBSD shoot incidences (1.5%) compared with recycled materials (6.9%) in Masika, although no significant differences were obvious in Vuli. However, Masika (8.7%) had an overall lower CBSD shoot incidence than Vuli (16.5%) in the varieties that had shoot symptoms. CBSD root incidences were higher in Vuli (10.3%) than Masika (4.4%), and root yields in Masika (29.4 t/ha) were significantly greater than those in Vuli (22.5 t/ha). The highest percentage of roots rendered unusable owing to CBSD was observed in Vuli. There was significantly higher unusable root incidence in recycled materials (3.7%) than in new materials (1.4%) in Masika but not in Vuli. Overall root yield was similar between recycled and new materials in either season. Significant reductions in root yield over the course of the experiment were observed both in Masika and Vuli, whereas changes in marketable yield were significant only in Masika. Differences in the response of varieties to degeneration led to the identification of four degeneration patterns, namely "strong," "moderate," "mild," and "delayed" degeneration. The strongest effects of degeneration were most obvious in the susceptible cultivar (Kikombe), which also had the lowest marketable yield in either season. Seasonal differences were a key driver of degeneration, because its effects were much greater in Vuli than Masika. To the best of our knowledge, this work reports the first study of degeneration caused by cassava viruses.[Formula: see text] Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Effect of co-application of phosphorus fertilizer and in vitro-produced mycorrhizal fungal inoculants on yield and leaf nutrient concentration of cassava.

The adaptability of cassava to low fertile and marginal soils facilitates its production in subsistent agriculture. As a result, smallholder farmers rarely apply fertilizers. The current yield gap is therefore very large, calling for application of fertilizers and soil amendments to improve its productivity. Field experiments were carried out to assess the potential of partially substituting Phosphorus (P) fertilizers by in vitro-produced arbuscular mycorrhizal fungal (AMF) inoculants in cassava production in two agro-ecologies of Nigeria: Northern Guinea Savanna (Samaru) and Sudan Savanna (Minjibir). The experiments were laid out in a split plot design with P levels (0, 17.5, 35 and 52.5 kg P2O5 ha-1) as main plot and AMF inoculants (Control, Glomygel, Glomygel carrier, Mycodrip, Mycodrip carrier) as subplots. The results in Samaru showed that there was significant interaction between AMF and P in root fresh weight, total biomass and root to shoot ratio. The root fresh weights of the inoculated cassava increased proportionally with application of P. However, highest root fresh weight of cassava inoculated with Glomygel was observed at 35 kg P2O5 ha-1 recording 25% yield increase compared to 52.5 kg P2O5 ha-1 application. Interestingly, Cassava inoculated with Glomygel at 17.5 kg P2O5 ha-1 gave root fresh yield statistically similar to where 35 kg P2O5 ha-1 was applied. This represented a 50% reduction in P fertilizer use. Also, cassava inoculated with Glomygel increased leaf nutrient concentrations, which strongly correlated with the root fresh yield. However, no effects of inoculant carriers were observed in yield and nutrient concentrations. Contrarily, there was no significant treatment effect in Minjibir for nearly all the measured parameters. Cassava yield was however, higher in Minjibir than Samaru probably due to soil fertility and structural differences, which resulted in few observable effects of AMF and P treatments at Minjibir. We conclude that under low P conditions inoculation with in vitro produced AMF inoculants could be employed to reduce P fertilizer requirements for cassava and improve yields, but the variability of the responses as a result of soil heterogeneity and the identity of the fungal strain in the inoculant require further investigations before recommending the practice.

Engineering Disease-Resistant Cassava.

Manihot esculenta Crantz (cassava) is a food crop originating from South America grown primarily for its starchy storage roots. Today, cassava is grown in the tropics of South America, Africa, and Asia with an estimated 800 million people relying on it as a staple source of calories. In parts of sub-Saharan Africa, cassava is particularly crucial for food security. Cassava root starch also has use in the pharmaceutical, textile, paper, and biofuel industries. Cassava has seen strong demand since 2000 and production has increased consistently year-over-year, but potential yields are hampered by susceptibility to biotic and abiotic stresses. In particular, bacterial and viral diseases can cause severe yield losses. Of note are cassava bacterial blight (CBB), cassava mosaic disease (CMD), and cassava brown streak disease (CBSD), all of which can cause catastrophic losses for growers. In this article, we provide an overview of the major microbial diseases of cassava, discuss current and potential future efforts to engineer new sources of resistance, and conclude with a discussion of the regulatory hurdles that face biotechnology.