Quantitative Growth Relationships of Cassava (Manihot esculenta Crantz): Crop Development in a Savanna Wet Season

Growth characteristics of Manihot esculenta Crantz cv. Cubanawere determined for a crop, cultivated in savanna soil withfive different levels of fertilizer. A population of 25000 plantsha^–1 was studied using conventional growth analysis techniques. The storage root does not act as a sink for large amouns ofassimilates and differences in growth response were mainly aresult of the morphology development and function of leavesin the cassava canopy (source activity). Thus, during tuberization,the cultivar Cubana produces a progressively higher proportionof new leaves, maintaining throughout the season a relativelyhigh net assimilation rate and leaf area index. Manihot esculenta Crantz, Cassava, source-sink relationship, net assimilation rate, leaf area index, growth analysis     

Accumulation of Hydroxycoumarins During Post-harvest Deterioration of Tuberous Roots of Cassava (Manihot esculenta Crantz)

The use of the root crop Cassava (Manihot esculenta Crantz)is constrained by its rapid deterioration after harvest. Chemicaland spectroscopic examination revealed the accumulation of fourhydroxycoumarins (esculin, esculetin, scopolin and scopoletin),compounds derived from the phenylpropanoid pathway, during thetime course of post-harvest deterioration. Fluorescence-microscopyrevealed their localization in the apoplast of the parenchyma.Scopoletin and scopolin showed the most dramatic increases inconcentration, peaking by day 2 after harvesting. A smallersecondary peak of scopoletin tended to be more pronounced incultivars showing lower susceptibility to deterioration. Evidencefor the metabolism of scopoletin to an insoluble coloured productby means of a peroxidase is presented. This product may be thecause of the discolouration of the vascular tissue during storage.Copyright 2000 Annals of Botany Company Cassava, hydroxycoumarins, Manihot esculenta, peroxidases, post-harvest physiological deterioration, wound response     

Effects of the Temperature of the Rooting Zone on the Growth and Development of Roots of Potato (Solanum tuberosum)

In solution culture the effect of optimal (20 °C) and supra-optimal(30 °C) root-zone temperatures on root growth and root morphologyof six potato clones (Solanum tuberosum L spp) was studied Growthwas compared with sweet potato (Ipomoea batatas L) and cassava(Manihot esculenta Crantz) Significant genotypical differencesin the responses of potato roots to supra-optimal temperatureswere observed, indicating the potential for selecting heat tolerantpotato clones In both heat tolerant and heat sensitive clones,the size of the root system was reduced by supra-optimal root-zonetemperature This was principally a result of decreased numberand length of lateral roots The first symptom of heat damagewas a reduction in the rate of cell division, followed by cessationof root elongation Bending of the apical root-zone togetherwith the formation of root hairs on the inner (concave) andlateral roots on the outer (convex) side were other symptoms,these coincided with the loss of starch granules in the root-cap Potato, genotypical differences, root morphology, root growth, temperature, Solanum tuberosum L     

Isoelectric focusing of cassava protoplasts

Cassava (Manihot esculenta Crantz) protoplast was analyzed by using isoelectric focusing techniques. Two populations, representing 68 and 32% of the total sample, with mean isoelectric points of 4.48 and 4.60, were obtained using mesophyll protoplasts. The use of this technique allows demonstration of a discontinuous distribution of protoplast isoelectric point from one species according to their surface potential.     

Gene-based microsatellites for cassava (Manihot esculenta Crantz): prevalence, polymorphisms, and cross-taxa utility

Background  

Cassava (Manihot esculenta Crantz), a starchy root crop grown in tropical and subtropical climates, is the sixth most important crop in the world after wheat, rice, maize, potato and barley. The repertoire of simple sequence repeat (SSR) markers for cassava is limited and warrants a need for a larger number of polymorphic SSRs for germplasm characterization and breeding applications.     

Pathological and Molecular Characterization of Xanthomonas campestris Strains Causing Diseases of Cassava (Manihot esculenta)

Fifty-one strains representing Xanthomonas campestris pv. manihotis and cassavae and different pathovars occurring on plants of the family Euphorbiaceae were characterized by ribotyping with a 16S+23S rRNA probe of Escherichia coli and by restriction fragment length polymorphism analysis with a plasmid probe from X. campestris pv. manihotis. Pathogenicity tests were performed on cassava (Manihot esculenta). Histological comparative studies were conducted on strains of two pathovars of X. campestris (vascular and mesophyllic) that attack cassava. Our results indicated that X. campestris pv. manihotis and cassavae have different modes of action in the host and supplemented the taxonomic data on restriction fragment length polymorphism that clearly separate the two pathovars. The plasmid probe could detect multiple restriction fragment length polymorphisms among strains of the pathovar studied. Ribotyping provides a useful tool for rapid identification of X. campestris pathovars on cassava.     

A Comparison of Two Approaches for Modelling Cassava (Manihot esculenta Crantz.) Crop Growth

Two approaches for modelling the growth and development of cassava,Manihot esculenta Crantz, are described and evaluated. The twomodels differ only in the hypotheses accounting for storageroot growth. In model 1, assimilate allocation to storage rootsis governed by the combined Chanter's (1976: Mathematical modelsin mushroom research and production. PhD Thesis, Universityof Sussex, UK) growth equation; and in model 2 the spill-overhypothesis for assimilate allocation to storage root governsstorage root growth. In both models, canopy photosynthesis generatesthe carbon substrate required for all growth processes. Thegrowth rates of leaves, stems and storage roots are definedby growth equations subject to substrate saturation kinetics.A key feature of both models is that the growth demands of thestem, fibrous roots and storage roots are related to leaf demandrates. Allocation to stems and branches was modelled by meansof a modified logistic growth equation which includes all theparameters and variables (number of nodes, internode lengths,stem density, stem modulus of elasticity and branch tensilestrength) that define the limits of the load bearing capacityof the shoot's supportive structures. The correlation coefficientsfor determination of yield prediction for the models werer =0.898,P =0.0385 (model 1) and r =0.954, P =0.0117 (model 2). For agrowth season of 290 d (after which leaf area index equals zeroand crop growth ceases), both models simulate the sigmoidaltransition from the lag to exponential phase of crop growth.Both models are equally well corroborated by observed data;however, model 1 has greater explanatory power. Copyright 2000Annals of Botany Company Allocation, simulation, model, crop growth, cassava, Manihot esculenta Crantz.     

Genetic mapping of a dominant gene conferring resistance to cassava mosaic disease

Cassava mosaic disease (CMD) is the most-important disease of cassava (Manihot esculenta) in Africa, and is a potential threat to Latin American (LA) cassava production. Although this viral disease is still unknown in LA, its vector - the whitefly - has recently been found. The disease is best controlled through host-plant resistance, which was first found in third backcross derivatives of an interspecific cross between cassava and Manihot glaziovii, and is thought to be polygenic. Recently, high levels of resistance were also found in several Nigerian cassava landraces. Classical genetic analysis and molecular genetic-mapping of the landraces showed that a major dominant gene confers this resistance. Bulk segregant analysis (BSA) was used to quickly identify a simple sequence repeat (SSR) marker linked to the CMD-resistance gene. The marker, SSRY28, is located on linkage group R of the male-parent-derived molecular genetic map. The gene, designated as CMD2, is flanked by the SSR and RFLP marker GY1 at 9 and 8 cM, respectively. To our knowledge, this is the first report of qualitative virus resistance in cassava, and of molecular markers that tag CMD resistance in cassava. We discuss the use of markers linked to CMD2 for marker-assisted breeding of CMD resistance in Latin America and for increasing the cost-effectiveness of resistance breeding in Africa.     

A comparative anatomical study in cassava diploid and tetraploid hybrids

Cassava, Manihot esculenta Crantz, is the most important crop for poor people in the tropics and subtropics. It is a woody plant scarcely studied from the anatomical viewpoint. Information on its anatomy is needed for use in plant breeding programs. An interspecific hybrid between cassava and M. oligantha Pax was obtained and artificially polyploidized by the second author. Hand cross sections were applied to the stem, colored by safranin and alcian blue, and mounted in synthetic resin. Tetraploid type showed a larger portion of medulla and absence of a growth ring. Vascular tissues in tetraploid were larger too. Both of these types had similar structure of vessel elements and articulated laticifers. Distribution of different tissues in the two types refers to more resistance to drought in the tetraploid type than in the diploid one.     

Risk assessment of gene flow from genetically engineered virus resistant cassava to wild relatives in Africa: an expert panel report

The probability and consequences of gene flow to wild relatives is typically considered in the environmental risk assessment of genetically engineered crops. This is a report from a discussion by a group of experts who used a problem formulation approach to consider existing information for risk assessment of gene flow from cassava (Manihot esculenta) genetically engineered for virus resistance to the ‘wild’ (naturalized) relative M. glaziovii in East Africa. Two environmental harms were considered in this case: (1) loss of genetic diversity in the germplasm pool, and (2) loss of valued species, ecosystem resources, or crop yield and quality due to weediness or invasiveness of wild relatives. Based on existing information, it was concluded that gene flow will occur, but it is not likely that this will reduce the genetic diversity in the germplasm pool. There is little existing information about the impact of the virus in natural populations that could be used to inform a prediction about whether virus resistance would lead to an increase in reproduction or survival, hence abundance of M. glaziovii. However, an increase in the abundance of M. glaziovii should be manageable, and would not necessarily lead to the identified environmental harms.     

AFLP analysis of relationships among cassava and other Manihot species

 Despite the worldwide importance of cultivated cassava (M. esculenta Crantz) its origin and taxonomic relationships with other species in the genus have not been clearly established. We evaluated a representative sample of the crop’s diversity and six wild taxa with AFLPs to estimate genetic relationships within the genus. Groupings of accessions of each species by data analysis corresponded largely with their previous taxonomic classifications. A mixed group, consisting of Manihot esculenta subsp. flabellifolia and M. esculenta subsp. peruviana, was most similar to cassava, while M. aesculifolia, M. brachyloba, and M. carthaginensis were more distant. Species-specific markers, which may be useful in germ-plasm classification or introgression studies, were suggested by the unique presence of AFLP products in samples of each of the three wild species. Heterogeneity of similarities among individuals of certain species suggested the existence of intraspecific gene pools, a hypothesis that was supported by morphological or ecogeographic evidence with varying degrees of success. Quantitative assessment of genetic diversity revealed greater homogeneity among cassava accessions than among itsclosest wild relatives. The demonstration of unique genetic diversity in the two M. esculenta subspecies and their genetic similarity to the crop supports the hypothesis that these materials may be the ancestors of cassava. Received: 4 November 1996 / Accepted: 20 December 1996     

Response of cassava to water stress

Summary Cassava (Manihot esculenta Crantz) is a staple food for a large sector of human population in the tropics. It is widely produced for its starchy roots by small farmers over a range of environments on poor infertile soils with virtually no inputs. It is highly productive under favorable conditions and produces reasonably well under adverse conditions where other crops fail. The crop, once established, cansurvive for several months without rain. There is a wide variation within the cassava germplasm for tolerance to prolonged drought and the possibility to breed and select for stable and relative high yields under favorable and adverse conditions does indeed exist. Research with several cassava clones at CIAT has shown that high root yield under mid—term stress is not incompatible with high yield under nonstress conditions. Plant types with high yield potential under both conditions (e.g. the hybrid CM 507-37) are characterized by having slightly higher than optimum leaf area index under nonstress conditions, higher leaf area ratio and more intensive and extensive fine root system.     

Cytogenetics of the F1 hybrid between cassava and ceara rubber,and its backcross

Cytogenetical studies of the F₁ hybrid between the commercially cultivated tuber crop, cassava (Manihot esculenta Crantz.) and the closely related wild speciesManihot glaziovii Muell. (Ceara rubber) used as donor specles for Cassava mosaic discase and drought-resistant genes and back crosses (to cassava parent) were made. The contrasting parental characters showed partial to total dominance in the F₁ hybrid, while the back cross plants were similar to cassava in most of their characters. Eleven of the twelve backeross plants exhibited resistance to Cassava mosaic under field conditions. Karyological similarities and differences as resolved on the basis of a comparative study of the karyotypes of the cassava parent and coara rubber were corroborated by the study of chromosomal pairing in the F₁ at pachytene. Major chromosomal differentiation in the two species involved three chromosomes of their haploid complement which were represented by three heteromorphic bivalent associations in F₁ each consisting of a probably basic chromosomal type and a derived type. Pachytene analyses of three back cross plants provided direct proof for random transmission of marker chromosomes of both the parents through male gametes of the F₁ hybrid. An increase in the chiasma frequency in the back cross plants over the F₁ hybrid at metaphase I stage was also observed. Pollen fertility of the backeross plants showed considerable variation.     

Cryopreservation of Somatic Embryos of Four Species With and Without Cryoprotectant Pre-treatment

The development of cryostorage procedures for somatic embryosproduced from the tissues of plants that normally propagateby means of desiccation- and (often) chilling-sensitive seeds,and that are unstorable by conventional means, offers a viablealternative to the conservation of this otherwise recalcitrantgermplasm. A cryopreservation procedure utilizing cryoprotectantsand partial dehydration was previously developed for hydratedand germinating Pisum sativum embryonic axes. The present contributionapplies that technology to the somatic embryos of a range ofspecies, viz., Coffea arabica (coffee), Manihot esculenta (cassava),Phoenix dactylifera (date palm) and Pisum sativum (pea) andcompares it with results for material that was partially dehydrated,then very rapidly frozen. Cassava, coffee and date palm showedsimilar recovery from cryopreservation irrespective of the procedure.Pea somatic embryos, on the other hand, recovered best fromcryopreservation when pre-treated with the cryoprotectants,glycerol and sucrose, and then subjected to partial dehydration.Copyright1995, 1999 Academic Press Coffea arabica, Manihot esculenta, Phoenix dactylifera, Pisum sativum, cryopreservation, somatic embryos     

Species diversity within the Morchella esculenta group (Ascomycota: Morchellaceae) in Germany and France

The distribution of the Morchella esculenta group in Germany and France is examined based on 22 samples, a sample from Montenegro is studied as well. In the recent literature the group was often treated as a single species, M. esculenta sensu lato. Our study, based on the polymorphism of the internal transcribed spacer (ITS) region within the nuclear ribosomal DNA (nrDNA), indicates the presence of three distinct species: M. esculenta (L.) Pers., M. crassipes (Vent.) Pers. : Fr., and M. spongiola Boud. They can be identified easily by restriction fragment length polymorphisms (RFLP) of the ITS region.     

Germination of Stored Cassava Seed at Constant and Alternating Temperatures

Cassava seed is only capable of germinating over a restrictedrange of constant temperatures. During storage the optimum constanttemperature for germination decreases from about 35 to 30 °Cor possibly less. The rate at which the optimum temperaturechanges during dry storage increases with increase in storagetemperature over the range 0 to 40 °C. Some alternating-temperatureregimes (16 h at the lower temperature; 8 h at the higher temperature)can provide conditions as favourable for germination as theoptimum constant temperatures. Furthermore, it has been shownthat temperature alternation itself is stimulatory because whenthe range of the alternation does not include the optimum constanttemperature value, percentage germination is often higher thancould be obtained at any constant temperature within the range,though this stimulatory response declines during storage. Forthese reasons it is provisionally recommended that cassava seedshould be germinated at 25/35 °C which is as stimulatorya treatment as any which has so far been investigated and hasthe advantage of encompassing the range over which the optimumconstant temperature changes during storage. Manihot esculenta Crantz, cassava, germination, dormancy, seed viability, storage of seeds, after-ripening     

Mapping EST-derived SSRs and ESTs involved in resistance to bacterial blight in Manihot esculenta.

Cassava (Manihot esculenta Crantz) is a major root crop widely grown in the tropics. Cassava bacterial blight, caused by Xanthomonas axonopodis pv. manihotis (Xam), is an important disease in Latin America and Africa resulting in significant losses. The preferred control method is the use of resistant genotypes. Mapping expressed sequence tags (ESTs) and determining their co-localization with quantitative trait loci (QTLs) may give additional evidence of the role of the corresponding genes in resistance or defense. Twenty-one EST-derived simple sequence repeats (SSRs) were mapped in 16 linkage groups. ESTs showing similarities with candidate resistance genes or defense genes were also mapped using strategies such as restriction fragment length polymorphisms, cleaved amplified polymorphic sequences, and allele-specific primers. In total, 10 defense-related genes and 2 bacterial artificial chromosomes (BACs) containing resistance gene candidates (RGCs) were mapped in 11 linkage groups. Two new QTLs associated with resistance to Xam strains CIO121 and CIO151 were detected in linkage groups A and U, respectively. The QTL in linkage group U explained 61.6% of the phenotypic variance and was associated with an RGC-containing BAC. No correlation was found between the new EST-derived SSRs or other mapped ESTs and the new or previously reported QTLs.     

Characterization of Rhodanese from Cassava Leaves and Tubers

Rhodanese activity has been established in the leaves, in thepeel, and in the flesh of the tuberous part of Manihot esculentaCrantz. The pattern of distribution of enzyme activity is shownto follow that of the concentration of the cyanogenic glucosideestimated on the basis of HCN released. For the first time,the presence of rhodanese is reported in higher plant tissuesother than the leaves. Identity has been established betweenrhodanese from peel, leaves, and flesh of the cassava plant.The enzyme is inhibited by cyanide in the absence of thiosuiphateor cysteine. Rhodanese is suggested to play a role in the detoxificationof cyanide in cassava.     

Somatic Embryogenesis in Cassava: The Anatomy and Morphology of the Regeneration Process

Anatomical and morphological studies demonstrated that somaticembryos developed similarly on mature seed and clonal leaf explantsof cassava (Manihot esculenta Crantz) cultured for 20–24d on Murashige and Skoog (MS2) basal medium supplemented with4.0 mg l^–1 2,4-D (Stage 1) before transfer to MS2 basalmedium supplemented with 0–01 mg l^–1 2,4-D and 0–1mg l^–1 6-benzylaminopurine (Stage II medium). Within 7d of inoculation onto Stage I medium, cell divisions occurredin the adaxial tissues of cotyledon-piece and leaf-lobe explants,and associated with this was the development of embryogeneticprotusions and ridges on the adaxial surface. Foliose structuresand somatic embryo initials developed from these tissues oncotyledon, embryonic axis and leaf-lobe explants and, when cultureswere transferred to Stage II medium, further somatic embryodevelopment occurred. Somatic embryos apparently originatedfrom groups of cells and were identified by the presence ofa closed root axis, a shoot axis and cotyledons of similar shapeand venation to those of zygotic embryos. Somatic embryos hadno vascular connection with parental cultures. Manihot esculenta, cassava, somatic embryogenesis, tissue culture, anatomy, morphology, morphogenesis