An integrated model to study varietal diversity in traditional agroecosystems.

Agricultural diversity is one of the bases of traditional agroecosystems, having great environmental and cultural importance. The current loss of agricultural diversity is causing serious concern, mainly because of its essential role in supporting global and local food security. Stopping this loss requires a better understanding of how diversity is managed locally and what mechanisms sustain agricultural diversity. Here we propose a generalist agent-based model that couples biological, cultural, and social dynamics to obtain varietal diversity as an emergent phenomenon at the community level. With a mechanistic approach, we explore how four of the model dynamics can shape systems diversity. To validate the model, we performed a bibliographic review on Manihot esculenta and Zea mays case studies. The model yielded compatible results for manioc and maize varietal richness at both community and household levels.

Genetic diversity of local and introduced cassava germplasm in Burundi using DArTseq molecular analyses.

In Burundi most small-scale farmers still grow traditional cassava landraces that are adapted to local conditions and have been selected for consumer preferred attributes. They tend to be susceptible, in varying degrees, to devastating cassava viral diseases such as Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD) with annual production losses of US$1 billion. For long term resistance to the disease, several breeding strategies have been proposed. A sound basis for a breeding program is to understand the genetic diversity of both landraces and elite introduced breeding cultivars. This will also assist in efforts to conserve landraces ahead of the broad distribution of improved varieties which have the possibility of replacing landraces. Our study aimed at determining the genetic diversity and relationships within and between local landraces and introduced elite germplasm using morphological and single nucleotide polymorphism (SNP) markers. A total of 118 cultivars were characterized for morphological trait variation based on leaf, stem and root traits, and genetic variation using SNP markers. Results of morphological characterization based on Ward's Method revealed three main clusters and five accessions sharing similar characteristics. Molecular characterization identified over 18,000 SNPs and six main clusters and three pairs of duplicates which should be pooled together as one cultivar to avoid redundancy. Results of population genetic analysis showed low genetic distance between populations and between local landraces and elite germplasm. Accessions that shared similar morphological traits were divergent at the molecular level indicating that clustering using morphological traits was inconsistent. Despite the variabilities found within the collection, it was observed that cassava germplasm in Burundi have a narrow genetic base.

Genome-wide association mapping and genomic prediction of yield-related traits and starch pasting properties in cassava.

KEY MESSAGE: GWAS identified eight yield-related, peak starch type of waxy and wild-type starch and 21 starch pasting property-related traits (QTLs). Prediction ability of eight GS models resulted in low to high predictability, depending on trait, heritability, and genetic architecture. Cassava is both a food and an industrial crop in Africa, South America, and Asia, but knowledge of the genes that control yield and starch pasting properties remains limited. We carried out a genome-wide association study to clarify the molecular mechanisms underlying these traits and to explore marker-based breeding approaches. We estimated the predictive ability of genomic selection (GS) using parametric, semi-parametric, and nonparametric GS models with a panel of 276 cassava genotypes from Thai Tapioca Development Institute, International Center for Tropical Agriculture, International Institute of Tropical Agriculture, and other breeding programs. The cassava panel was genotyped via genotyping-by-sequencing, and 89,934 single-nucleotide polymorphism (SNP) markers were identified. A total of 31 SNPs associated with yield, starch type, and starch properties traits were detected by the fixed and random model circulating probability unification (FarmCPU), Bayesian-information and linkage-disequilibrium iteratively nested keyway and compressed mixed linear model, respectively. GS models were developed, and forward predictabilities using all the prediction methods resulted in values of - 0.001-0.71 for the four yield-related traits and 0.33-0.82 for the seven starch pasting property traits. This study provides additional insight into the genetic architecture of these important traits for the development of markers that could be used in cassava breeding programs.

Phosphorylation of RAV1/2 by KIN10 is essential for transcriptional activation of CAT6/7, which underlies oxidative stress response in cassava.

Related to ABI3/VP1 (RAV) transcription factors have important roles in plant stress responses; however, it is unclear whether RAVs regulates oxidative stress response in cassava (Manihot esculenta). In this study, we report that MeRAV1/2 positively regulate oxidative stress resistance and catalase (CAT) activity in cassava. Consistently, RNA sequencing (RNA-seq) identifies three MeCATs that are differentially expressed in MeRAV1/2-silenced cassava leaves. Interestingly, MeCAT6 and MeCAT7 are identified as direct transcriptional targets of MeRAV1/2 via binding to their promoters. In addition, protein kinase MeKIN10 directly interacts with MeRAV1/2 to phosphorylate them at Ser45 and Ser44 residues, respectively, to promote their direct transcriptional activation on MeCAT6 and MeCAT7. Site mutation of MeRAV1S45A or MeRAV2S44A has no significant effect on the activities of MeCAT6 and MeCAT7 promoters or on oxidative stress resistance. In summary, this study demonstrates that the phosphorylation of MeRAV1/2 by MeKIN10 is essential for its direct transcriptional activation of MeCAT6/7 in response to oxidative stress.

Collection, genotyping and virus elimination of cassava landraces from Tanzania and documentation of farmer knowledge.

Cassava (Manihot esculenta Crantz.) has been a vital staple and food security crop in Tanzania for several centuries, and it is likely that its resilience will play a key role in mitigating livelihood insecurities arising from climate change. The sector is dominated by smallholder farmers growing traditional landrace varieties. A recent surge in virus diseases and awareness in the commercial potential of cassava has prompted a drive to disseminate improved varieties in the country. These factors however also threaten the existence of landraces and associated farmer knowledge. It is important that the landraces are conserved and utilized as the adaptive gene complexes they harbor can drive breeding for improved varieties that meet agro-ecological adaptation as well as farmer and consumer needs, thereby improving adoption rates. Here we report on cassava germplasm collection missions and documentation of farmer knowledge in seven zones of Tanzania. A total of 277 unique landraces are identified through high-density genotyping. The large number of landraces is attributable to a mixed clonal/sexual reproductive system in which the soil seed bank and incorporation of seedlings plays an important role. A striking divergence in genetic relationships between the coastal regions and western regions is evident and explained by (i) independent introductions of cassava into the country, (ii) adaptation to prevailing agro-ecological conditions and (iii) farmer selections according to the intended use or market demands. The main uses of cassava with different product profiles are evident, including fresh consumption, flour production, dual purpose incorporating both these uses and longer-term food security. Each of these products have different trait requirements. Individual landraces were not widely distributed across the country with limited farmer-to-farmer diffusion with implications for seed systems.

Population diversity of cassava mosaic begomoviruses increases over the course of serial vegetative propagation.

Cassava mosaic disease (CMD) represents a serious threat to cassava, a major root crop for more than 300 million Africans. CMD is caused by single-stranded DNA begomoviruses that evolve rapidly, making it challenging to develop durable disease resistance. In addition to the evolutionary forces of mutation, recombination and reassortment, factors such as climate, agriculture practices and the presence of DNA satellites may impact viral diversity. To gain insight into the factors that alter and shape viral diversity in planta, we used high-throughput sequencing to characterize the accumulation of nucleotide diversity after inoculation of infectious clones corresponding to African cassava mosaic virus (ACMV) and East African cassava mosaic Cameroon virus (EACMCV) in the susceptible cassava landrace Kibandameno. We found that vegetative propagation had a significant effect on viral nucleotide diversity, while temperature and a satellite DNA did not have measurable impacts in our study. EACMCV diversity increased linearly with the number of vegetative propagation passages, while ACMV diversity increased for a time and then decreased in later passages. We observed a substitution bias toward C→T and G→A for mutations in the viral genomes consistent with field isolates. Non-coding regions excluding the promoter regions of genes showed the highest levels of nucleotide diversity for each genome component. Changes in the 5' intergenic region of DNA-A resembled the sequence of the cognate DNA-B sequence. The majority of nucleotide changes in coding regions were non-synonymous, most with predicted deleterious effects on protein structure, indicative of relaxed selection pressure over six vegetative passages. Overall, these results underscore the importance of knowing how cropping practices affect viral evolution and disease progression.

Unmodified cassava starches with high phosphorus content.

Our study was based on the fact that physiological changes in the plant resulting from the growth conditions alter the properties of the starch. An experimental trial was installed with cassava plants in poor phosphorus soil. A part of plants received phosphate fertilization at a level three times higher than the recommended dose, in order to provide high availability of phosphorus in the soil. The plants grew for two years and the starches were isolated at three times in the second vegetative cycle. The starches had A-type X-ray pattern. Starches isolated from cassava plants grown in soils with high phosphorus had increases of more than 100% in the content of bound phosphorus, which caused changes in the size of the granules, amylose, swelling power, solubility, pasting and thermal properties. These results indicate possibilities of increasing the commercial value of native cassava starch due to the expansion of use, considering the range of uses of phosphate starches for food and non-food purposes.

Environmental responsiveness of flowering time in cassava genotypes and associated transcriptome changes.

Cassava is an important food security crop in tropical regions of the world. Cassava improvement by breeding is limited by its delayed and poor production of flowers, such that cassava flowering under field conditions indirectly lengthens the breeding cycle. By studying genotype and environment interaction under two Nigerian field conditions (Ubiaja and Ibadan) and three controlled temperature conditions (22°C/18°C, 28/24°C and 34/30°C (day/night)), we found that while early flowering genotypes flowered at similar times and rates under all growing conditions (unfavorable and favorable field and controlled-temperature environments), late flowering genotypes were environmentally sensitive such that they were substantially delayed in unfavorable environments. On the basis of nodes-to-flower, flowering of late genotypes approached the flowering time of early flowering genotypes under relatively cool Ubiaja field conditions and in growth chambers at 22°C, whereas warmer temperatures elicited a delaying effect. Analysis of transcriptomes from leaves of field and controlled-temperature environments revealed that conditions which promote early flowering in cassava have low expression of the flowering repressor gene TEMPRANILLO 1 (TEM1), before and after flowering. Expression data of field plants showed that the balance between flower stimulatory and inhibitory signaling appeared to correlate with flowering time across the environments and genotypes.

Differential Tropism in Roots and Shoots of Resistant and Susceptible Cassava (Manihot esculenta Crantz) Infected by Cassava Brown Streak Viruses.

Cassava brown streak disease (CBSD) is a destructive disease of cassava in Eastern and Central Africa. Because there was no source of resistance in African varieties to provide complete protection against the viruses causing the disease, we searched in South American germplasm and identified cassava lines that did not become infected with the cassava brown streak viruses. These findings motivated further investigations into the mechanism of virus resistance. We used RNAscope® in situ hybridization to localize cassava brown streak virus in cassava germplasm lines that were highly resistant (DSC 167, immune) or that restricted virus infections to stems and roots only (DSC 260). We show that the resistance in those lines is not a restriction of long-distance movement but due to preventing virus unloading from the phloem into parenchyma cells for replication, thus restricting the virus to the phloem cells only. When DSC 167 and DSC 260 were compared for virus invasion, only a low CBSV signal was found in phloem tissue of DSC 167, indicating that there is no replication in this host, while the presence of intense hybridization signals in the phloem of DSC 260 provided evidence for virus replication in companion cells. In neither of the two lines studied was there evidence of virus replication outside the phloem tissues. Thus, we conclude that in resistant cassava lines, CBSV is confined to the phloem tissues only, in which virus replication can still take place or is arrested.

Fifty years of a public cassava breeding program: evolution of breeding objectives, methods, and decision-making processes.

This paper reviews and analyzes key features from cassava breeding at the International Center for Tropical Agriculture (CIAT) over 50 years and draws lessons for public breeding efforts broadly. The breeding team, jointly with national program partners and the private processing sector, defined breeding objectives and guiding business plans. These have evolved through the decades and currently focus on four global product profiles. The recurrent selection method also evolved and included innovations such as estimation of phenotypic breeding values, increasing the number of locations in the first stage of agronomic evaluations, gradual reduction of the duration of breeding cycles (including rapid cycling for high-heritability traits), the development of protocols for the induction of flowering, and the introduction of genome-wide predictions. The impact of cassava breeding depends significantly on the type of target markets. When roots are used for large processing facilities for starch, animal feeding or ethanol production (such as in SE Asia), the adoption of improved varieties is nearly universal and productivity at the regional scale increases significantly. When markets and relevant infrastructure are weak or considerable proportion of the production goes for local artisanal processing and on-farm consumption, the impact has been lower. The potential of novel breeding tools needs to be properly assessed for the most effective allocation of resources. Finally, a brief summary of challenges and opportunities for the future of cassava breeding is presented. The paper describes multiple ways that public and private sector breeding programs can learn from each other to optimize success.

KASPar SNP genetic map of cassava for QTL discovery of productivity traits in moderate drought stress environment in Africa.

Cassava is an important staple in Sub-Sahara Africa. While its production has rapidly expanded to the dry savannahs of the continent, productivity is low in this ecology due to drought by farmers, extending the growth cycle from 12 months to 18, and sometimes 24 months to ensure better harvests. Yield is a complex trait and often difficult to manipulate for genetic gain in conventional breeding. Unfortunately, the dearth of molecular tools for decades has hampered molecular breeding (MB) to improve cassava productivity. This study was conducted to explore KASpar SNPs to generate more molecular tools to enhance genetic dissection of elite African germplasm for improved cassava productivity in dry environments of Africa where molecular resources are highly limited for crop improvement. To aid molecular genetic analysis of traits, a linkage map covering 1582.8 cM with an average resolution of 3.69 cM was constructed using 505 polymorphic SNP markers distributed over 21 linkage groups. Composite interval mapping using 267 F1 progeny in initial QTL mapping identified 27 QTLs for productivity traits in the dry savannah of Nigeria. The availability of KASPar SNPs are anticipated to improve the implementation of MB for the development of high performing drought-tolerant cassava varieties in Africa.

Field-transcriptome analyses reveal developmental transitions during flowering in cassava (Manihot esculenta Crantz).

KEY MESSAGE: We characterized genes that function in the photoperiodic flowering pathway in cassava. Transcriptome analysis of field-grown plants revealed characteristic expression patterns of these genes, demonstrating that field-grown cassava experiences two distinct developmental transitions. Cassava is an important crop for both edible and industrial purposes. Cassava develops storage roots that accumulate starch, providing an important source of staple food in tropical regions. To facilitate cassava breeding, it is important to elucidate how flowering is controlled. Several important genes that control flowering time have been identified in model plants; however, comprehensive characterization of these genes in cassava is still lacking. In this study, we identified genes encoding central flowering time regulators and examined these sequences for the presence or absence of conserved motifs. We found that cassava shares conserved genes for the photoperiodic flowering pathway, including florigen, anti-florigen and its associated transcription factor (GIGANTEA, CONSTANS, FLOWERING LOCUS T, CENTRORADIALIS/TERMINAL FLOWER1 and FD) and florigen downstream genes (SUPRESSOR OF OVEREXPRESSION OF CONSTANS1 and APETALA1/FRUITFUL). We conducted RNA-seq analysis of field-grown cassava plants and characterized the expression of flowering control genes. Finally, from the transcriptome analysis we identified two distinct developmental transitions that occur in field-grown cassava.

Character changes and Transcriptomic analysis of a cassava sexual Tetraploid.

BACKGROUND: Cassava (Manihot esculenta Crantz) is an important food crop known for its high starch content. Polyploid breeding is effective in its genetic improvement, and use of 2n gametes in sexual polyploid breeding is one of the potential methods for cassava breeding and improvement. In our study, the cassava sexual tetraploid (ST), which carries numerous valuable traits, was successfully generated by hybridizing 2n female gametes SC5 (♀) and 2n male gametes SC10 (♂). However, the molecular mechanisms remain unclear. To understand these underlying molecular mechanisms behind the phenotypic alterations and heterosis in ST plants, we investigated the differences in gene expression between polyploids and diploids by determining the transcriptomes of the ST plant and its parents during the tuber root enlargement period. We also compared the characters and transcriptomes of the ST plant with its parents. RESULTS: The ST plant was superior in plant height, stem diameter, leaf area, petiole length, plant weight, and root weight than the parent plants, except the leaf number, which was lower. The number of starch granules was higher in the roots of ST plants than those in the parent plants after five months (tuber root enlargement period), which could be due to a higher leaf net photosynthetic rate leading to early filling of starch granules. Based on transcriptome analysis, we identified 2934 and 3171 differentially expressed genes (DEGs) in the ST plant as compared to its female and male parents, respectively. Pathway enrichment analyses revealed that flavonoid biosynthesis and glycolysis/gluconeogenesis were significantly enriched in the ST plants, which might contribute to the colors of petiole (purple-red), root epidermis (dark brown), and tuber starch accumulation, respectively. CONCLUSIONS: After sexual polyploidization, the phenotype of ST has changed significantly in comparison to their diploid parents, mainly manifest as enlarged biomass, yield, early starch filling, deep colored petiole and root epidermis. The tetraploid plants were also mature early due to early starch grain filling. Owing to enriched flavonoid biosynthesis and glycolysis/gluconeogenesis, they are possibly resistant to adversity stresses and provide better yield, respectively.

Comprehensive genotyping of a Brazilian cassava (Manihot esculenta Crantz) germplasm bank: insights into diversification and domestication.

KEY MESSAGE: Brazilian cassava diversity was characterized through population genetics and clustering approaches, highlighting contrasted genetic groups and spatial genetic differentiation. Cassava (Manihot esculenta Crantz) is a major staple root crop of the tropics, originating from the Amazonian region. In this study, 3354 cassava landraces and modern breeding lines from the Embrapa Cassava Germplasm Bank (CGB) were characterized. All individuals were subjected to genotyping-by-sequencing (GBS), identifying 27,045 single-nucleotide polymorphisms (SNPs). Identity-by-state and population structure analyses revealed a unique set of 1536 individuals and 10 distinct genetic groups with heterogeneous linkage disequilibrium (LD). On this basis, a density of 1300-4700 SNP markers were selected for large-effect quantitative trait loci (QTL) detection. Identified genetic groups were further characterized for population genetics parameters including minor allele frequency (MAF), observed heterozygosity [Formula: see text], effective population size estimate [Formula: see text]) and polymorphism information content (PIC). Selection footprints and introgressions of M. glaziovii were detected. Spatial population structure analysis revealed five ancestral populations related to distinct Brazilian ecoregions. Estimation of historical relationships among identified populations suggests an early population split from Amazonian to Atlantic forest and Caatinga ecoregions and active gene flows. This study provides a thorough genetic characterization of ex situ germplasm resources from cassava's center of origin, South America, with results shedding light on Brazilian cassava characteristics and its biogeographical landscape. These findings support and facilitate the use of genetic resources in modern breeding programs including implementation of association mapping and genomic selection strategies.

Genome-wide identification and analysis of the sucrose synthase gene family in cassava (Manihot esculenta Crantz).

Sucrose synthase (SUS), a key enzyme of the sucrose metabolism pathway, is encoded by a multi-gene family in plants. To date, dozens of SUS gene families have been characterized in various plant genomes. However, only a few studies have performed comprehensive analyses in tropical crops like cassava (Manihot esculenta Crantz). In the present study, seven non-redundant members of the SUS gene family (MeSUS1-7) were identified and characterized from the cassava genome. The MeSUS genes were distributed on five chromosomes (Chr1, Chr2, Chr3, Chr14, and Chr16) and the encoded proteins could be classified into three major groups with other SUS proteins from both dicot and monocot species (SUS I, SUS II, and SUS III). The spatio-temporal expression profiles of MeSUS genes showed a developmental stage-dependent, partially overlapping pattern, mainly expressed in the source and sink tissues. Cold and drought treatments significantly induced the expressions of MeSUS2, MeSUS4, MeSUS6, and MeSUS7 and the activities of the encoded enzymes, indicating that these genes may play crucial roles in resistance against abiotic stresses. These results provide new insights into the multifaceted role of the SUS gene family members in various physiological processes, especially sucrose transport and starch accumulation in cassava roots.

Phenotypic and molecular screenings for determination of cassava mosaic disease (CMD) status in farmers' fields in Ebonyi State, Nigeria.

African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) are among the major constraints to cassava productivity within tropical and sub-tropical regions, including Ebonyi State, Nigeria. Thus, virus indexing has become imperative to determine the status of cassava mosaic disease (CMD) in Ebonyi State, to implement appropriate preventive and control strategies. Seventy-eight cassava accessions obtained from different locations of Ebonyi State were phenotypically scored, using scales 1-5 depending on CMD symptomatic expressions, followed by multiplex-PCR and sequencing for validation. 11% of cassava accessions cultivated in Afikpo were resistant (RE) to ACMV compared to 8% of moderately-resistant (MR) accessions in Izzi and 55% of tolerant (TO) ACMV accessions in Ebonyi. 100% of cassava accessions in Onicha and 66% in Afikpo South were susceptible (SU) and highly susceptible (HS) to ACMV, respectively. With multiplex-PCR, 97.4% (ACMV) and 2.6% (EACMV) were positive. Dunn's multiple comparison tests of CMD mean incidence demonstrated differences (P < 0.05), except between RE and MR, and TO and MR. More transitions (A/G, C/T) compared to transversions (A/T, G/T), were detected, with nonsynonymous mutations (Leucine/Isoleucine; Valine/Isoleucine; Arginine/Lysine; Methionine/Isoleucine), and good bit-scores (91.13-99.07% identites; e-values of 7.00e-148-0.00e+00). Phylogeny resolved the sequences into five major groups. DNA sequencing validated the detected ACMV and EACMV species. This study revealed variants of ACMV and low adoption of RE and MR cassava accessions in the farmers' fields. The findings will guide in getting disease-free and resistant varieties as planting materials to significantly mitigate the CMD spread in Ebonyi State, Nigeria.

In vitro multiplication of wild Manihot species with different naphthaleneacetic acid and benzylaminopurine concentrations

In vitro multiplication is an important tissue culture technique that is capable of efficiently producing seedlings at any scale. It is a propagation method based on the aseptic culture of small propagules in a suitable culture medium to enable plant regeneration. Multiplication experiments conducted in vitro to set protocols adapted to wild Manihot species have used modified mineral salts and MS vitamins as basic culture medium. Here, 25 treatments based on combinations of the regulators benzylaminopurine (BAP) and naphthaleneacetic acid (NAA) at 0, 0.025, 0.05, 0.075, and 0.1 mg L-1 were used for in vitro multiplication of three genotypes of wild Manihot species (M. violaceae Pohl Müll. Arg., M. pseudoglaziovii Pax & Hoff., and M. flabellifolia Pohl). Plant height and the number of 1 cm minicuttings, number of roots, shoots, green leaves and senescent leaves were recorded 120 days after explant inoculation. M. violaceae Pohl. Müll. Arg. and M. flabellifolia Pohl. presented favorable results with 0.05 and 0.025 mg L-1 NAA, respectively. Culture medium lacking NAA and BAP favored the in vitro growth of M. pseudoglaziovii Pax & Hoff.

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.

Crop Calendar Shift as a Climate Change Adaptation Solution for Cassava Cultivation Area of Binh Thuan Province, Vietnam.

BACKGROUND AND OBJECTIVE: Binh Thuan Province is one of the large cassava cultivation areas in Vietnam. However, in recent years the cassava crops are facing the increased risks of irrigation water shortage due to drought and abnormal change of rainfall under the impacts of climate variability (ICV), leading to reduce crop yield. The study was, therefore, conducted to define a suitable period for planting cassava crops in Binh Thuan Province, Vietnam to reduce the negative impacts of weather factors. MATERIALS AND METHODS: The study was conducted using the AquaCrop model to predict the cassava yield corresponding to different crop calendars to define the suitable planting period. The model performance was appraised through the calibration and validation process with the index of agreement (d), correlation coefficient (r) up to 0.80 and RMSE lower than 0.40. RESULTS: The results carry out that the cassava yield can be reached 48.18 t ha-1 if the crop calendar (CC) is early shifted from 14-21 days compared with the current crop calendar (CCC) for spring crop while an increase of approximately 5.16% can be achieved if the CC is delayed from 7-14 days for summer crop season. The results stated that the proposed model is suitable for defining the CC based on its simulated biomass and cassava yield. CONCLUSION: The study indicated that rainfall plays an important role in the planting calendar of cassava crops. Through, it is also confirmed that planting calendars of cassava crops is not appropriate for current weather conditions.

The Cassava Source-Sink project: opportunities and challenges for crop improvement by metabolic engineering.

Cassava (Manihot esculenta Crantz) is one of the important staple foods in Sub-Saharan Africa. It produces starchy storage roots that provide food and income for several hundred million people, mainly in tropical agriculture zones. Increasing cassava storage root and starch yield is one of the major breeding targets with respect to securing the future food supply for the growing population of Sub-Saharan Africa. The Cassava Source-Sink (CASS) project aims to increase cassava storage root and starch yield by strategically integrating approaches from different disciplines. We present our perspective and progress on cassava as an applied research organism and provide insight into the CASS strategy, which can serve as a blueprint for the improvement of other root and tuber crops. Extensive profiling of different field-grown cassava genotypes generates information for leaf, phloem, and root metabolic and physiological processes that are relevant for biotechnological improvements. A multi-national pipeline for genetic engineering of cassava plants covers all steps from gene discovery, cloning, transformation, molecular and biochemical characterization, confined field trials, and phenotyping of the seasonal dynamics of shoot traits under field conditions. Together, the CASS project generates comprehensive data to facilitate conventional breeding strategies for high-yielding cassava genotypes. It also builds the foundation for genome-scale metabolic modelling aiming to predict targets and bottlenecks in metabolic pathways. This information is used to engineer cassava genotypes with improved source-sink relations and increased yield potential.