Isozyme Diversity in Cassava Cultivars (Manihot esculenta Crantz)

Isoenzyme electrophoresis was used as a method to determine genetic diversity in various M. esculenta cultivars collected in the Southwestern (SW) and Northwestern (NW) regions of the State of Parana, in the South region of Brazil, and in cultivars produced at the Agronomic Institute of Campinas (IAC), S~ao Paulo State, Southeastern region of Brazil. The cultivars have been maintained by vegetative propagation for 5 years and are useful in production programs. A total of 28 loci in the acid phosphatase (ACP; EC 3.1.3.2), esterases (EST; EC 3.1.1.1), malate dehydrogenase (MDH; EC 1.1.1.37), and shikimate dehydrogenase (SKDH; EC 1.1.1.15) isozymes was analyzed. The proportion of polymorphic loci for NW, SW, and IAC cultivars was 57.14, 50.0, and 53.6%, respectively. Genetic diversity calculated by Nei's genetic identity (I) showed high I values for the three M. esculenta subpopulations. The high degree of polymorphism expressed by cassava cultivars is highly relevant to stimulate breeding programs with M. esculenta species.     

Antholysis in Cassava (Manihot esculenta Crantz) Possibly Caused by Mycoplasma-Like Organisms

Phyllody and apostasis of cassava plants were frequently observed during recent disease surveys in the Cauca Valley of Colombia. Many valuable cassava clones have been affected rendering them unsuitable for hybridization. Light and electron microscopic observations have revealed the presence of mycoplasma-like organisms in the diseased phloem tissues. The causal agent is sensitive to tetracycline and streptomycin at 1000 ppm a. i., but not to penicillin.     

Scopoletin Involvement in Post-Harvest Physiological Deterioration of Cassava Root (Manihot esculenta Crantz)

A study of the mechanism of the rapid deterioration of cassavaroots has shown that this requires the presence of oxygen andscopoletin, the latter acting, apparently, in some autocatalyticfashion. Roots from plants whose tops were pruned off some daysprior to harvest were less liable to spontaneous deterioration,but responded vigorously to the applied scopoletin, whereasroots stored for some time in the absence of O₂, so-called ‘cured’roots were no longer susceptible to exogenously-applied scopoletin.Clearly, metabolically, the two methods for prevention of deteriorationdiffer pruning may be effective due to internally-reduced scopoletinsupply or absence of some factor involved in the primary oxidation;‘curing’ may involve loss of a scopoletin precursoror inactivation of an enzyme system. Key words: Scopoletin, Manihot esculenta, Cassava, Post-harvest deterioration     

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.     

Mining EST-Derived SSR Markers to Assess Genetic Diversity in Cassava (Manihot esculenta Crantz)

Cassava (Manihot esculenta Crantz) is a very important staple and industrial crop in tropical and subtropical regions of the world. The paucity of markers is a serious limitation in marker-assisted breeding. A total of 35,992 expressed sequence tags (ESTs) from cassava, which were clustered in 13,173 unigenes, were used in this study. A total of 1,889 microsatellites were identified, with an average density of one simple sequence repeats (SSRs) every 4.40 kb. Of the 1,058 designed EST-SSRs from cultivars SC06, TMS60444, and W14, 431 were polymorphic. Then, 31 randomly selected EST-SSRs from the 431 polymorphic EST-SSRs were used to evaluate the genetic diversity of 76 cassava accessions. A total of 93 alleles were identified, and the number detected for each EST-SSR ranged from one to four. Based on the 93 alleles, the 76 cassava accessions could be classified into six groups, and the genetic similarity coefficient ranged from 0.55 to 0.94. This study demonstrated the potential of EST-derived SSRs in cassava. The resources developed in this study enriched the available molecular markers for cassava.     

A molecular genetic map of cassava (Manihot esculenta Crantz)

 A genetic linkage map of cassava has been constructed with 132 RFLPs, 30 RAPDs, 3 microsatellites, and 3 isoenzyme markers segregating from the heterozygous female parent of an intraspecific cross. The F₁ cross was made between ‘TMS 30572’ and ‘CM 2177-2’, elite cassava cultivars from Nigeria and Colombia, respectively. The map consists of 20 linkage groups spanning 931.6 cM or an estimated 60% of the cassava genome. Average marker density is 1 per 7.9 cM. Since the mapping population is an F₁ cross between heterozygous parents, with unique alleles segregating from either parent, a second map was constructed from the segregation of 107 RFLPs, 50 RAPDs, 1 microsatellite, and 1 isoenzyme marker from the male parent. Comparison of intervals in the male-and female-derived maps, bounded by markers heterozygous in both parents, revealed significantly less meiotic recombination in the gametes of the female than in the male parent. Six pairs of duplicated loci were detected by low-copy genomic and cDNA sequences used as probes. Efforts are underway to saturate the cassava map with additional markers, to join the male- and female-derived maps, and to elucidate genome organization in cassava. Received: 5 July 1996/Accepted: 22 November 1996     

影响根癌农杆菌介导的木薯遗传转化因素分析

采用根癌农杆菌介导的叶盘转化法,以我国南方地区主栽木薯品种—华南8号的胚状体子叶为受体,对影响木薯遗传转化效率的主要因素进行了分析。研究结果表明,在木薯的遗传转化中,选用GV3101作为浸染外植体的农杆菌菌株,将感染时间和共培养时间分别控制在30~45 min和3~4 d、菌液浓度（OD₆₀₀）采用0.45、并添加200 μmol·L^-1的乙酰丁香酮（AS）均可明显提高其转化效率,但若对外植体进行预培养反而会降低其转化效率。利用该体系从453块外植体中共转化获得10株抗性再生植株,经PCR和Southern杂交检测,有8株木薯的基因组中已整合进了外源基因glgC336,转化率为1.77%。     

In vitro flowering in cassava (Manihot esculenta Crantz)

Meristem-derived plantlets of cassava (Manihot esculenta Crantz) were induced to flower in vitro. Five genotypes out of 13 consistently responded to our culture conditions giving rise to male or female flowers. Male flowers contained anthers in which meiosis occurred and apparently normal pollen grains were formed.     

Comparison of Leaf Proteomes of Cassava (Manihot esculenta Crantz) Cultivar NZ199 Diploid and Autotetraploid Genotypes

Cassava polyploid breeding has drastically improved our knowledge on increasing root yield and its significant tolerance to stresses. In polyploid cassava plants, increases in DNA content highly affect cell volumes and anatomical structures. However, the mechanism of this effect is poorly understood. The purpose of the present study was to compare and validate the changes between cassava cultivar NZ199 diploid and autotetraploid at proteomic levels. The results showed that leaf proteome of cassava cultivar NZ199 diploid was clearly differentiated from its autotetraploid genotype using 2-DE combined MS technique. Sixty-five differential protein spots were seen in 2-DE image of autotetraploid genotype in comparison with that of diploid. Fifty-two proteins were identified by MALDI-TOF-MS/MS, of which 47 were up-regulated and 5 were down-regulated in autotetraploid genotype compared with diploid genotype. The classified functions of 32 up-regulated proteins were associated with photosynthesis, defense system, hydrocyanic acid (HCN) metabolism, protein biosynthesis, chaperones, amino acid metabolism and signal transduction. The remarkable variation in photosynthetic activity, HCN content and resistance to salt stress between diploid and autotetraploid genotypes is closely linked with expression levels of proteomic profiles. The analysis of protein interaction networks indicated there are direct interactions between the 15 up-regulation proteins involved in the pathways described above. This work provides an insight into understanding the protein regulation mechanism of cassava polyploid genotype, and gives a clue to improve cassava polyploidy breeding in increasing photosynthesis and resistance efficiencies.     

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     

Production of Microconidia by Cercospora henningsii Allesch, Cause of Brown Leaf Spot of Cassava (Manihot esculenta Crantz) and Tree Cassava (Manihot glaziovii Muell.-Arg.)

Sporulation ofCercospora henningsii Allesch has been examinedunder various relative humidities, and in the presence of freewater in lesions on leaves of cassava and tree cassava. Matureconidia of the fungus on both cassava and tree cassava do notgerminate in lesions but accumulate, and under the optimum conditionsof 25–32 °C and in the presence of free water, theybud and fragment into numerous microconidia. Microconidia arecylindrical, mostly one-celled, and measure 7.5–17.5x3.7–7.5µm. Production of microconidia significantly decreasesas relative humidity decreases. Microconidia readily germinateby means of a germ tube at 100% relative humidity on both surfacesof host leaf and on glass slides. Some germ tubes form appressoriaand symptoms appear on cassava leaves inoculated with microconidia.The results are discussed in relation to possible modes of dispersalof the spores and control of the disease. Free water; sporulation; budding; microconidia     

Genetic diversity of traditional South American Landraces of Cassava (Manihot esculenta Crantz): an analysis using microsatellites

The extent and structure of the genetic variability of traditional varieties of cassava (Manihot esculenta Crantz) have been little documented, despite considerable evidence for this crop? great varietal diversity in traditional agroecosystems. We used microsatellite markers to assess the genetic structure of traditional landraces of sweet and bitter cassava collected from five South American sites. As reference, we used a sample of 38 accessions from a world collection of cultivated cassava. For a total of 10 loci examined, we found 15 alleles that were not represented in this sample. Ten of these had been previously detected in wild Manihot species. The geographical structure of genetic variability was weak, but the genetic differentiation between bitter and sweet landraces was significant, suggesting that each form had evolved separately after domestication. Our results showed that traditional landraces form an important source of genetic diversity and merit more attention from managers of crop genetic resources.     

Cassava (Manihot esculenta Crantz), Cyanogenic Potential, and Predation in Northwestern Amazonia: The Tukanoan Perspective

The Tukanoans of northwestern Amazonia cultivate high-cyanogenic potential cassava, which provides 80% of their dietary energy. In an effort to understand why the Tukanoans cultivate primarily high-rather than low-cyanogenic potential cassava, which requires far less processing before consumption, this paper seeks to determine whether the Tukanoans discern a difference in levels of predation on high-and low-cyanogenic potential cassava. Given the potential protection afforded by high-cyanogenic potential, it was hypothesized that the Tukanoans would report higher predation upon low-cyanogenic potential cassava in comparison to high-cyanogenic potential cassava. Both unstructured interviews and pile-sort exercises were conducted to address this question. The unstructured interviews provide some support for the hypothesis, while the pile-sort interviews did not support the hypothesis. These data demonstrate that while the Tukanoans are cognizant of differences in predation on different cassava cultivars, resistance to predation may not be a characteristic of paramount concern in cultivar selection.     

Cassava (Manihot esculenta) leaf and tuber concentrate in diets for broiler chickens

Experiment 1 was conducted to determine the nutritive quality of cassava tuber leaf concentrate prepared either by mixing cassava tubers and leaves together before grinding or grinding them separately before mixing. Three mixing proportions of 50:50, 60:40 and 80:20 were used. Samples were subjected to either sundrying or oven drying. Physical examination of samples, proximate analysis and cyanide content of each of the samples were determined. In experiment 2 the sample of highest nutritive value was selected for inclusion in four diets at levels of 0%, 10%, 20% and 30% respectively. A total of 120 day-old broilers were divided into four groups and each group further into three subgroups. The four experimental diets were fed to each of the groups for a period of 9 weeks. Growth parameters, carcass characteristics and haematological parameters were also determined. Results showed that in experiment 1 the grinding together of cassava tubers and leaves in the proportion of 50:50 before sun-drying gave the best texture, highest CP content with low HCN content. Inclusion of 10% cassava concentrate gave good performance in terms of growth and feed conversion, with no detrimental effects on haematological parameters and carcass characteristics.     

Response of cassava (Manihot esculenta Crantz) to water stress and fertilization

Experiments done in Santander de Quilichao (Cauca, Colombia) on two cassava cultivars indicated that cassava had at least three defence mechanisms against water deficit, enabling it to assimilate and store photosynthates in roots, even during prolonged droughts. These mechanisms include partial stomatal closure, ability of leaves to maintain reasonable net photosynthetic rate for long periods of water stress, reduced leaf area, and exploration of water from deep soil layers. While cassava responded positively to fertilization, no significant statistical differences were found between treatments of stress and non-stress, confirming cassava's ability to tolerate soil water deficit. This revised version was published online in June 2006 with corrections to the Cover Date.     

Beta-carotene from cassava (Manihot esculenta Crantz) leaves improves vitamin A status in rats

The bioavailability of beta-carotene from cassava (Manihot esculenta Crantz) leaves was assayed in vitamin A deficient Wistar rats (Rattus norvegicus). Rats were separated into three groups and fed with a modified AIN-93G--vitamin A deficient--diet. Deficient rat received this diet without any additional vitamin A source. Controls received the diet with 7200 microg of synthetic beta-carotene (control), while experimentals (test) received 19.5 g of cassava leaves powder per kg of diet. The cassava leaves with beta-carotene promotes similar growth and tissue weight in rats to the synthetic beta-carotene. The relative bioavailability, estimated as the Retinol Accumulation Factor (RAF), was 16.5 and 27.5 for control and test groups, respectively, indicating that control and test rats should have an intake of 16.5 microg or 27.5 microg of beta-carotene from synthetic form or cassava leaves powder for each 1 microg of hepatic retinol stored, respectively. The cassava leaves beta-carotene bioavailability was lower than the synthetic beta-carotene probably because the beta-carotene from the leaf matrix may be bounded to protein complex or inside organelles, which impair carotenoid absorption. Our findings showed that beside the hepatic retinol recovery, cassava leaf beta-carotene could maintain rat growth and avoid vitamin A deficient symptoms.     

Response of cassava (Manihot esculenta Crantz) to water stress and fertilization

Experiments done in Santander de Quilichao (Cauca, Colombia) on two cassava cultivars indicated that cassava had at least three defence mechanisms against water deficit, enabling it to assimilate and store photosynthates in roots, even during prolonged droughts. These mechanisms include partial stomatal closure, ability of leaves to maintain reasonable net photosynthetic rate for long periods of water stress, reduced leaf area, and exploration of water from deep soil layers. While cassava responded positively to fertilization, no significant statistical differences were found between treatments of stress and non-stress, confirming cassava's ability to tolerate soil water deficit.